Co-reporter:Pengfei Cheng, Tao Wu, Jiangwei Zhang, Yajuan Li, Junxue Liu, Lei Jiang, Xin Mao, Rui-Feng Lu, Wei-Qiao Deng, and Keli Han
The Journal of Physical Chemistry Letters September 21, 2017 Volume 8(Issue 18) pp:4402-4402
Publication Date(Web):August 31, 2017
DOI:10.1021/acs.jpclett.7b01985
Recently, two-dimensional organic–inorganic perovskites have attracted increasing attention due to their unique photophysical properties and high stability. Here we report a lead-free, two-dimensional perovskite, (PEA)2GeI4 (PEA = C6H5(CH2)2NH3+). Structural characterization demonstrated that this 2D perovskite structure is formed with inorganic germanium iodide planes separated by organic PEAI layers. (PEA)2GeI4 has a direct band gap of 2.12 eV, in agreement with 2.17 eV obtained by density functional theory (DFT) calculations, implying that it is suitable for a tandem solar cell. (PEA)2GeI4 luminesces at room-temperature with a moderate lifetime, exhibiting good potential for photovoltaic applications. In addition, 2D (PEA)2GeI4 is more stable than 3D CH3NH3GeI3 in air, owing to the presence of a hydrophobic organic long chain. This work provides a direction for the development of 2D Ge-based perovskites with potential for photovoltaic applications.
Co-reporter:Cui-Lian Liu, Rui-Ling Zhang, Chen-Sheng Lin, Li-Peng Zhou, Li-Xuan Cai, Jin-Tao Kong, Song-Qiu Yang, Ke-Li Han, and Qing-Fu Sun
Journal of the American Chemical Society September 13, 2017 Volume 139(Issue 36) pp:12474-12474
Publication Date(Web):August 24, 2017
DOI:10.1021/jacs.7b05157
Luminescent supramolecular lanthanide edifices have many potential applications in biology, environments, and materials science. However, it is still a big challenge to improve the luminescent performance of multinuclear lanthanide assemblies in contrast to their mononuclear counterparts. Herein, we demonstrate that combination of intraligand charge transfer (ILCT) sensitization and coordination-driven self-assembly gives birth to bright EuIII tetrahedral cages with a record emission quantum yield of 23.1%. The ILCT sensitization mechanism has been unambiguously confirmed by both time-dependent density functional theory calculation and femtosecond transient absorption studies. Meanwhile, dual-responsive sensing toward both anions and cations has been demonstrated making use of the ILCT transition on the ligand. Without introduction of additional recognition units, high sensitivity and selectivity are revealed for the cage in both turn-off luminescent sensing toward I– and turn-on sensing toward Cu2+. This study offers important design principles for the future development of luminescent lanthanide molecular materials.
The Journal of Physical Chemistry C October 22, 2009 Volume 113(Issue 42) pp:18436-18440
Publication Date(Web):Publication Date (Web): September 24, 2009
DOI:10.1021/jp906807t
One of the important issues in the development of new Li-ion battery technologies is to seek novel electrode materials with higher energy densities and a faster charge−discharge process. Using the first-principles calculations based on density functional theory, we systematically study the lithium interaction with the recently reported inorganic Mo12S9I9 nanowires. Eleven initial Li positions are optimized to identify the rich energetically preferable sites for Li adsorption in the nanowire at the sulfur bridge planes and on the nanowire between dressing S and I atoms. The charge density and the electronic band structure are calculated to investigate the Li−host physics. Using the climbing image nudged elastic band method, we obtain that the diffusion barrier for Li migration into the Mo12S9I9 nanowire is 0.86 eV, which is far lower than that of Li diffusion into the carbon nanotube through the sidewall (about 10 eV [Meunier et al. Phys. Rev. Lett. 2002, 88, 075506.]). These results indicate that the Mo12S9I9 nanowire will be a promising candidate material for anodes in Li-ion battery application.
Co-reporter:Mohan Singh Mehata, Yang Yang, and Keli Han
ACS Omega October 2017? Volume 2(Issue 10) pp:6782-6782
Publication Date(Web):October 17, 2017
DOI:10.1021/acsomega.7b00921
We report the existence of a short-lived triplet electronic state of 2,6-ANS (2-anilinonaphthalene-6-sulfonic acid), which, together with nonplanar (NP) and planar [charge-transfer (CT)] states, is produced following photoexcitation; these results are based on nanosecond transient absorption and time-resolved decays. The short-lived triplet state has a lifetime of ∼126 ns and is observed via triplet–triplet (T–T) transitions after exciting 2,6-ANS with a pump laser pulse of 355 nm (probe wavelength range of 360–500 nm). Moreover, the CT state, which is very close to the NP state produced from the locally excited state/NP state, emits active fluorescence with a lifetime of ∼11 ns. The solvent plays a major role in the rotation of the phenylamino group during the conversion of the NP state to the CT state, and vice versa. Intersystem crossing occurs from the CT state. Thus, investigating the triplet state together with the CT/NP states of 2,6-ANS, a commonly used probe for sensing proteins and other biomolecules, is highly relevant and helps reveal its photoexcitation dynamics.Topics: Electron transfer; Electronic structure; Fluorescence; Magnetic processes; Quantum transition;
The long carrier lifetimes in perovskite single crystals have drawn significant attention recently on account of their irreplaceable contribution to high-performance photovoltaic (PV) devices. Herein, the optical and optoelectronic properties of CH3NH3PbI3 and CH3NH3PbI3–xBrx (with five different contents of Br doped) single crystals were investigated. Notably, a superior carrier lifetime of up to 262 μs was observed in the CH3NH3PbI3–xBrx (I/Br = 10:1 in the precursor) single-crystal PV device under 1 sun illumination, which is two times longer than that in the CH3NH3PbI3 single crystal. Further study confirmed that the ultralong carrier lifetime was ascribed to the integrated superiority derived from both the low trap-state density and high charge-injection efficiency of the device interface. On this basis, appropriate incorporation of Br is useful in the design of better PV devices.Keywords: carrier lifetime; charge-injection efficiency; photovoltaic device; single crystal; trap-state density;
Co-reporter:Junsheng Chen, Karel Žídek, Pavel Chábera, Dongzhou Liu, Pengfei Cheng, Lauri Nuuttila, Mohammed J. Al-Marri, Heli Lehtivuori, Maria E. Messing, Keli Han, Kaibo Zheng, and Tõnu Pullerits
The Journal of Physical Chemistry Letters May 18, 2017 Volume 8(Issue 10) pp:2316-2316
Publication Date(Web):May 8, 2017
DOI:10.1021/acs.jpclett.7b00613
All-inorganic colloidal perovskite quantum dots (QDs) based on cesium, lead, and halide have recently emerged as promising light emitting materials. CsPbBr3 QDs have also been demonstrated as stable two-photon-pumped lasing medium. However, the reported two photon absorption (TPA) cross sections for these QDs differ by an order of magnitude. Here we present an in-depth study of the TPA properties of CsPbBr3 QDs with mean size ranging from 4.6 to 11.4 nm. By using femtosecond transient absorption (TA) spectroscopy we found that TPA cross section is proportional to the linear one photon absorption. The TPA cross section follows a power law dependence on QDs size with exponent 3.3 ± 0.2. The empirically obtained power-law dependence suggests that the TPA process through a virtual state populates exciton band states. The revealed power-law dependence and the understanding of TPA process are important for developing high performance nonlinear optical devices based on CsPbBr3 nanocrystals.
Co-reporter:Rui-Ling Zhang, Yang Yang, Song-Qiu Yang, VenKata S. Pavan K. Neti, Hajar Sepehrpour, Peter J. Stang, and Ke-Li Han
The Journal of Physical Chemistry C July 13, 2017 Volume 121(Issue 27) pp:14975-14975
Publication Date(Web):June 14, 2017
DOI:10.1021/acs.jpcc.7b05025
An interesting triplet
excited-state absorption-emission conversion
of a fullerene-functionalized Pt(II) metallacycle (C 60 –Pt) caused by a concentration
effect was directly observed by nanosecond transient absorption (ns
TA) spectroscopy. In dilute solution, the triplet excited-state absorption
(TESA) band was observed at about 750 nm with a lifetime of ca. 10.7
μs. However, with increasing the concentration, the absorption
band converted to a triplet excited-state emission (TESE) band with
a longer lifetime of ca. 15.4 μs. Femtosecond transient absorption
experiments and quantum chemistry calculations were performed to reveal
the excited-state decay pathways of C 60 –Pt in concentrated solution. This conversion
was ascribed to the formation of a triplet excimer, which forms at
localized 3C60 * states. This work demonstrates that radiative excimers with
longer-lived triplet excited states can exist in concentrated solution,
and this finding will provide useful information for applications
of fullerene complexes, especially as photosensitizers.
Co-reporter:Pengfei Cheng;Tao Wu;Yajuan Li;Lei Jiang;Weiqiao Deng
New Journal of Chemistry (1998-Present) 2017 vol. 41(Issue 18) pp:9598-9601
Publication Date(Web):2017/09/11
DOI:10.1039/C7NJ02365K
Under the guidance of our theoretical calculations, we synthesized a lead-free double perovskite ((CH3NH3)2AgBiI6) and explored its electronic structure and optical properties using a combination of experiment and density functional theory. (CH3NH3)2AgBiI6 has an indirect bandgap of 1.96 eV, and exhibits high-stability in air.
Co-reporter:Pengfei Cheng;Tao Wu;Yajuan Li;Lei Jiang;Weiqiao Deng
New Journal of Chemistry (1998-Present) 2017 vol. 41(Issue 18) pp:9598-9601
Publication Date(Web):2017/09/11
DOI:10.1039/C7NJ02365K
Under the guidance of our theoretical calculations, we synthesized a lead-free double perovskite ((CH3NH3)2AgBiI6) and explored its electronic structure and optical properties using a combination of experiment and density functional theory. (CH3NH3)2AgBiI6 has an indirect bandgap of 1.96 eV, and exhibits high-stability in air.
Co-reporter:Bin Yang;Junsheng Chen;Feng Hong;Xin Mao;Kaibo Zheng;Songqiu Yang;Yajuan Li; Dr. Tõnu Pullerits; Dr. Weiqiao Deng; Dr. Keli Han
Angewandte Chemie International Edition 2017 Volume 56(Issue 41) pp:12471-12475
Publication Date(Web):2017/10/02
DOI:10.1002/anie.201704739
AbstractLead-based perovskite nanocrystals (NCs) have outstanding optical properties and cheap synthesis conferring them a tremendous potential in the field of optoelectronic devices. However, two critical problems are still unresolved and hindering their commercial applications: one is the fact of being lead-based and the other is the poor stability. Lead-free all-inorganic perovskite Cs3Bi2X9 (X=Cl, Br, I) NCs are synthesized with emission wavelength ranging from 400 to 560 nm synthesized by a facile room temperature reaction. The ligand-free Cs3Bi2Br9 NCs exhibit blue emission with photoluminescence quantum efficiency (PLQE) about 0.2 %. The PLQE can be increased to 4.5 % when extra surfactant (oleic acid) is added during the synthesis processes. This improvement stems from passivation of the fast trapping process (2–20 ps). Notably, the trap states can also be passivated under humid conditions, and the NCs exhibited high stability towards air exposure exceeding 30 days.
Co-reporter:Jian Luo, Yan Liu, Songqiu Yang, Amandine L. Flourat, Florent AllaisKeli Han
The Journal of Physical Chemistry Letters 2017 Volume 8(Issue 5) pp:
Publication Date(Web):February 8, 2017
DOI:10.1021/acs.jpclett.7b00083
Sunscreens are aimed at protecting skin from solar ultraviolet (UV) irradiation. By utilizing femtosecond transient absorption spectroscopy and time-dependent density functional theory, we explain nature’s selection of sinapoyl malate rather than sinapic acid as the plant sunscreen molecule. In physiological pH conditions, the two molecules are deprotonated, and their excited ππ* states are found to relax to the ground states in a few tens of picoseconds via a barrierless trans–cis photoisomerization. After the cis-photoproduct is formed, the efficacy of sinapic acid is greatly reduced. In contrast, the efficacy of sinapoyl malate is affected only slightly because the cis-product still absorbs UV light strongly. In addition, protonated sinapic acid is found to be a good potential sunscreen molecule.
Co-reporter:Po-Yu Ho, Chi-Ho Siu, Wai-Hong Yu, Panwang Zhou, Tao Chen, Cheuk-Lam Ho, Lawrence Tien Lin Lee, Ying-Hsuan Feng, Jianyong Liu, Keli Han, Yih Hsing Lo and Wai-Yeung Wong
Journal of Materials Chemistry A 2016 vol. 4(Issue 4) pp:713-726
Publication Date(Web):23 Dec 2015
DOI:10.1039/C5TC03308J
A series of new D–π–A organic photosensitizers 7a–7d featuring a novel starburst electron donor unit and uncommon selenophene containing π-linker were synthesized, characterized, and applied for fabrication of dye-sensitized solar cells (DSSCs). Dyes 11d–13d with thiophene or phenyl ring as the π-linker also were synthesized for comparison. The best power conversion efficiency (PCE) of 6.67% was attained for 11d with a relatively high open-circuit voltage (Voc) of 0.825 V using conventional I−/I3− redox electrolyte in DSSCs, and this value reaches about 84% of the device based on standard dye N719 (7.91%) under the same device fabrication conditions. Electrochemical impedance spectroscopy (EIS) and open-circuit voltage decay (OCVD) were applied to verify the findings. All the results suggest that starburst electron donor design strategy can be used to minimize dye aggregation on TiO2 and to slow down the charge recombination kinetics in DSSCs to improve the photovoltaic performance. Effects of using selenophene as the π-linker building block on the photovoltaic parameters also were explored and evaluated.
Co-reporter:Zongjin Qu, Peng Li, Xuexiang Zhang and Keli Han
Journal of Materials Chemistry A 2016 vol. 4(Issue 5) pp:887-892
Publication Date(Web):21 Dec 2015
DOI:10.1039/C5TB02090E
A turn-on fluorescent probe for the detection of Fe2+ is facilely synthesized via a nucleophile substitution reaction. The fluorescent probe, N-butyl-4-phenyltellanyl-1,8-naphthalimide (Naph-Te), shows excellent selectivity to Fe2+ in a mixed solution of acetonitrile and phosphate buffer under aerobic conditions. The coexistence of biological abundant metal ions such as Na+, K+, Ca2+ and Mg2+ has little effect on the fluorescence signal. This turn-on response is achieved via a redox-involved reaction triggered by Fe2+ at neutral pH and room temperature, which removes the heavy-atom effect of the tellurium atom on the naphthalimide fluorophore to afford a fluorescent product (N-butyl-4-hydroxyl-1,8-naphthalimide). The probe has excellent cell membrane permeability and is further applied successfully to monitor supplementary Fe2+ in live HL-7702 cells using a laser confocal fluorescence microscope.
Co-reporter:Xue-Xiang Zhang, Hao Wu, Peng Li, Zong-Jin Qu, Ming-Qian Tan and Ke-Li Han
Chemical Communications 2016 vol. 52(Issue 53) pp:8283-8286
Publication Date(Web):06 Jun 2016
DOI:10.1039/C6CC04373A
We have described the design, synthesis, spectroscopy and biological applications of NI–βGal, a versatile fluorescent probe to detect E. coli β-galactosidase in live cells and mice sensitively and directly, which holds great promise for its application in biomedical research such as gene therapy for cancer in the future.
Co-reporter:Xue-Xiang Zhang, Hao Wu, Peng Li, Zong-Jin Qu, Ming-Qian Tan and Ke-Li Han
Chemical Communications 2016 vol. 52(Issue 60) pp:9470-9470
Publication Date(Web):08 Jul 2016
DOI:10.1039/C6CC90284G
Correction for ‘A versatile two-photon fluorescent probe for ratiometric imaging E. coli β-galactosidase in live cells and in vivo’ by Xue-Xiang Zhang et al., Chem. Commun., 2016, 52, 8283–8286.
Two-photon-pumped amplified spontaneous emission (ASE) of CH3NH3PbBr3 microdisks (MDs) were investigated by using femtosecond laser system. Low threshold at 2.2 mJ cm–2 was obtained. Also, emission spectral tunability from 500 to 570 nm was demonstrated by synthesis the mixed halide perovskite MDs. The spatial effect of photoluminescence (PL) properties under one-photon and two-photon excitation were also studied by means of two-photon laser scanning microscope (TPLSM) and time-resolved PL spectroscopy. It was found that the band to band emission of near-surface regions and photocarriers’ diffusion from near-surface regions to interior regions is significant for one-photon excitation. By contrast, reabsorption of emission under two-photon excitation plays a major role in the emission properties of the MDs. These results will give a more comprehensive understanding of the nonlinear effect of CH3NH3PbBr3 single crystals.
S-Adenosylhomocysteine hydrolase (SAHase) is a cellular enzyme that plays a key role in the methylation process, and a potential drug target in the discovery of antiviral and anticancer agents. There is increasing interest in determining its activity in the biological and clinical fields with chemosensors but with limited success so far. Herein, we designed and developed for the first time an off/on-type of fluorogenic substrate (NADE) that is directly responsive to SAHase activity. NADE used 1,8-naphthalimide as the signal reporter and adenosine (Ade) as the reaction center; removal of the Ade moiety enhanced the fluorescence by >10-fold. Kinetic study showed that NADE followed a non-Michaelis–Menten pattern that corresponded to the allosteric behavior of SAHase. NADE showed excellent selectivity and functioned efficiently in cells, allowing the microscopic imaging of SAHase activity. NADE can also be used to identify and measure the effectiveness of inhibitors in a markedly superior way. In a word, NADE would be broadly useful in clinical applications and academic studies.Keywords: bioimaging; fluorogenic substrate; inhibitor screening; kinetic study; S-adenosylhomocysteine hydrolase
Co-reporter:Yan Zhang, Peng Xie, Xiaohu He, and Keli Han
Journal of Chemical Theory and Computation 2016 Volume 12(Issue 9) pp:4632-4643
Publication Date(Web):August 9, 2016
DOI:10.1021/acs.jctc.6b00547
We present here a double-optimizations-of-buffer-region (DOBR) microiterative scheme for high-efficiency energy minimizations of large, flexible systems in combined quantum-mechanical/molecular-mechanical (QM/MM) calculations. In the DOBR scheme, an entire system is divided into three regions: the core, buffer, and outer regions. The core region includes QM atoms and the MM atoms within a cutoff distance R1 to the QM atoms (denoted by MM1 atoms), and the buffer region consists of MM atoms within another cutoff distance R2 to MM1 atoms. Each DOBR microcycle involves two steps: First, QM atoms are assigned electrostatic-potential (ESP) charges, and the buffer and outer regions are optimized at the MM level with the core region kept frozen. Second, the core and buffer regions are optimized at the QM/MM level using the electrostatic embedding with the outer region kept frozen. The two steps are repeated until two optimizations converge at one structure. The DOBR scheme was tested in the optimizations of nucleobases solvated in water spheres of 30 Å radius, where the initial geometries were extracted from the trajectories of classical molecular dynamics simulations, and the cutoff distances R1 and R2 were set to 5.0 and 4.0 Å, respectively. For comparisons, the optimizations were also carried out by a “standard” scheme without microiteration and by the two-region microiterative (TRM) method. We found that the averaged number of QM calculations for the DOBR scheme is only ∼1% of that of the standard scheme and ∼6% of the TRM approach. The promising results indicate that the DOBR scheme could significantly increase the efficiency of geometry optimizations for large, flexible systems in QM/MM calculations.
The Journal of Physical Chemistry A 2016 Volume 120(Issue 27) pp:4961-4965
Publication Date(Web):February 17, 2016
DOI:10.1021/acs.jpca.5b12612
The understanding of the interplay between microenvironment and molecular rotors is helpful for designing and developing of molecular sensors of local physical properties. We present a study on the two rotational relaxation paths of excited 9-(dicyanovinyl) julolidine in several solvents. One rotational path (C–C single-bond rotation, τb) quickly leads to the formation of a twisted state. The other path (C═C double-bond rotation, τc) shows that the populations go back to the ground state directly via a conical intersection between the S1 and ground state. The increase in the solvent dielectric constant shows little effect on the τb lifetime for its small energy barrier (<0.01 eV), but τc lifetime is increased in larger dielectric constant solvents due to the larger energy gap at conical intersection. Both τb and τc are increased greatly with the increased solvent viscosity. τb is more sensitive to viscosity than τc may be due to its larger rotational moiety.
Accounts of Chemical Research 2015 Volume 48(Issue 5) pp:1358
Publication Date(Web):April 22, 2015
DOI:10.1021/acs.accounts.5b00009
In an aerobic organism, reactive oxygen species (ROS) are an inevitable metabolic byproduct. Endogenously produced ROS have a significant role in physiological processes, but excess ROS can cause oxidative stress and can damage tissue. Cells possess elaborate mechanisms to regulate their internal redox status. The intracellular redox homeostasis plays an essential role in maintaining cellular function. However, moderate alterations in redox balance can accompany major transitions in a cell’s life cycle. Because of the role of ROS in physiology and in pathology, researchers need new tools to study redox chemistry in biological systems.In recent years, researchers have made remarkable progress in developing new, highly sensitive and selective fluorescent probes that respond to redox changes, and in this Account we highlight related research, primarily from our own group. We present an overview of the design, photophysical properties, and fluorescence transduction mechanisms of reported molecules that probe redox changes. We have designed and synthesized a series of fluorescent probes for redox cycles in biological systems relying on the active center of glutathione peroxidase (GPx). We have also constructed probes based on the oxidation and reduction of hydroquinone and of 2,2,6,6-tetramethylpiperidinooxy (TEMPO). Most of these probes exhibit high sensitivity and good selectivity, absorb in the near-infrared, and respond rapidly. Such probes are useful for confocal fluorescence microscopy, a dynamic imaging technique that could allow researchers to observe biologically important ROS and antioxidants in real time. This technique and these probes provide potentially useful tools for exploring the generation, transport, physiological function, and pathogenic mechanisms of ROS and antioxidants.We also describe features that could improve the properties of redox-responsive fluorescent probes: greater photostability; rapid, dynamic, cyclic and ratiometric responses; and broader absorption in the near-IR region. In addition, fluorescent probes that include organochalcogens such as selenium and tellurium show promise for a new class of fluorescent redox probes that are both chemically stable and robustly reversible. However, further investigations of the chemical and fluorescence transduction mechanisms of selenium-based probes in response to ROS are needed.
Co-reporter:Mohan Singh Mehata, Yang Yang, Zong-Jin Qu, Jun-Sheng Chen, Feng-Jiao Zhao and Ke-Li Han
RSC Advances 2015 vol. 5(Issue 92) pp:75210-75210
Publication Date(Web):04 Sep 2015
DOI:10.1039/C5RA90082D
Correction for ‘Spin mixed charge transfer states of iridium complex Ir(ppy)3: transient absorption and time-resolved photoluminescence’ by Mohan Singh Mehata et al., RSC Adv., 2015, 5, 34094–34099.
Co-reporter:Mohan Singh Mehata, Yang Yang, Zong-Jing Qu, Jun-Sheng Chen, Feng-Jiao Zhao and Ke-Li Han
RSC Advances 2015 vol. 5(Issue 43) pp:34094-34099
Publication Date(Web):13 Apr 2015
DOI:10.1039/C5RA01404B
Nanosecond transient absorption and time-resolved spectroscopic techniques were applied to study an organometallic phosphorescent emitter Ir(ppy)3 complex, tris[2-phenylpyridinato-C2,N] iridium(III) dissolved in tetrahydrofuran (THF) under degassed conditions at ambient temperature. Transient absorption curves obtained at a pump pulse of 355 nm and at a probe wavelength of 430–600 nm show positive and negative signals, indicating triplet–triplet (T–T) absorption and triplet–singlet (T–S) emission. Tri-exponential global fitted transient absorption curves and time-resolved photoluminescence (PL) decays demonstrated the presence of four close low lying triplet states, of which, two emit green PL with a lifetime of 210 ns and 1.71 μs. The emitting states are spin mixed metal-to-ligand charge transfer (3MLCT) states produced from a non-equilibrium 1MLCT state following fast intersystem crossing (ISC), whereas the 1MLCT state is produced directly and indirectly depending on the excitation wavelength. Moreover, the electronic structures for the ground state and low-lying excited states of Ir(ppy)3 were studied using quantum chemistry calculations.
Chemistry – An Asian Journal 2015 Volume 10( Issue 11) pp:2444-2451
Publication Date(Web):
DOI:10.1002/asia.201500280
Abstract
Current probes for alkaline phosphatase (ALP) detection had been developed mainly by adding a phosphate group to a dye, which would lead to indistinct performance when implemented in a living system as several phosphatases exist together. In this study, the nucleotides adenosine monophosphate (AMP) and guanosine monophosphate (GMP) were introduced into 2′-(2′-hydroxyphenyl)-benzothiazole-based probes, and highly fluorescent turn-on probes with good selectivity towards ALP over several phosphatases, as well as high affinity and low toxicity were obtained. In the presence of l-phenylalanine, an ALP inhibitor, a strong decrease in fluorescence recovery was observed. These probes allowed for real-time imaging of endogenous ALP activity in living cells as well as in a zebrafish model.
Co-reporter:Xiaoneng Cui, Jianzhang Zhao, Zhangrong Lou, Shujing Li, Huijian Wu, and Ke-li Han
The Journal of Organic Chemistry 2015 Volume 80(Issue 1) pp:568-581
Publication Date(Web):December 1, 2014
DOI:10.1021/jo502554y
Rhodamine–bromonaphthaleneimide (RB–NI) and rhodamine–bromonaphthalenediimide (RB–NDI) dyads were prepared for switching of the triplet excited states. Bromo-NI or bromo-NDI parts in the dyads are the spin converters, i.e., the triplet state producing modules, whereas the RB unit is the acid-activatable electron donor/energy acceptor. NI and NDI absorb at 359 and 541 nm, and the T1 state energy levels are 2.25 and 1.64 eV, respectively. RB undertakes the reversible spirolactam (RB-c) ↔ opened amide (RB-o) transformation. RB-c shows no visible light absorption, and the triplet-state energy level is ET1 = 3.36 eV. Conversely RB-o shows strong absorption at 557 nm, and ET1 is 1.73 eV. Thus, the acid-activated fluorescence-resonance-energy-transfer (FRET) competes with the ISC of NI or NDI. No triplet state was observed for the dyads with nanosecond time-resolved transient absorption spectroscopy. Upon addition of acid, strong fluorescence and long-living triplet excited states were observed. Thus, the producing of triplet state is acid-activatable. The triplet state of RB–NI is localized on RB-o part, whereas in RB–NDI the triplet state is delocalized on both the NDI and RB-o units. The ISC of spin converter was not outcompeted by RET. These studies are useful for switching of triplet excited state.
Co-reporter:Feng-jiao Zhao, Lei Liu, Yang Yang, Rui-ling Zhang, Guang-hua Ren, Da-li Xu, Pan-wang Zhou, and Ke-li Han
The Journal of Physical Chemistry A 2015 Volume 119(Issue 50) pp:12579-12585
Publication Date(Web):November 12, 2015
DOI:10.1021/acs.jpca.5b09949
The effect of a hydrogen bond on the photochemical synthesis of silver nanoparticles has been investigated via experimental and theoretical methods. In a benzophenone system, the photochemical synthesis process includes two steps, which are that hydrogen abstraction reaction and the following reduction reaction. We found that for the first step, an intermolecular hydrogen bond enhances the proton transfer. The efficiency of hydrogen abstraction increases with the hydrogen bond strength. For the second step, the hydrogen-bonded ketyl radical complex shows higher reducibility than the ketyl radical. The inductively coupled plasma-optical emission spectroscopy (ICP-OES) measurement exhibits a 2.49 times higher yield of silver nanoparticles in the hydrogen bond ketyl radical complex system than that for the ketyl radical system. Theoretical calculations show that the hydrogen bond accelerates electron transfer from the ketyl radical to the silver ion by raising the SOMO energy of the ketyl radical; thus, the SOMO–LUMO interaction is more favorable.
Co-reporter:Yang Yang; Jun-Sheng Chen; Jian-Yong Liu; Guang-Jiu Zhao; Lei Liu; Ke-Li Han; Timothy R. Cook;Peter J. Stang
The Journal of Physical Chemistry Letters 2015 Volume 6(Issue 10) pp:1942-1947
Publication Date(Web):May 7, 2015
DOI:10.1021/acs.jpclett.5b00783
Supramolecular systems are capable of unique photophysical properties due to possible interactions between subcomponents, such as between an encapsulated molecule and its cage in a host/guest environment. Here, we report that the encapsulation of a chromophore by a metallacage dramatically enhances its photophysical properties. In the visible region, the encapsulated photosensitizer achieves a 6.5-fold enhancement to its absorptivity. The triplet lifetime of the encapsulated photosensitizer is three times longer than that of its free analogue. These enhancements are attributed to two key factors: (i) encapsulation-induced core-to-cage charge transfer (CCCT) generates new visible-light absorbing states, accounting for the enhanced absorption, and (ii) the microenvironment inside the metallacage inhibits nonradiative decay processes, resulting in prolonged triplet lifetime. The CCCT arises from the electrostatic interaction between the delocalized electrons of the guest coronene and the positive charge associated with the metallacage host. The work herein provides insight into the CCCT phenomenon.
Co-reporter:Panwang Zhou, Mark R. Hoffmann, Keli Han, and Guozhong He
The Journal of Physical Chemistry B 2015 Volume 119(Issue 6) pp:2125-2131
Publication Date(Web):March 28, 2014
DOI:10.1021/jp501881j
In this paper, we propose a new and complete mechanism for dual fluorescence of methyl salicylate (MS) under different conditions using a combined experimental (i.e., steady-state absorption and emission spectra and time-resolved fluorescence spectra) and theoretical (i.e., time-dependent density function theory) study. First, our theoretical study indicates that the barrier height for excited state intramolecular proton transfer (ESIPT) reaction of ketoB depends on the solvent polarity. In nonpolar solvents, the ESIPT reaction of ketoB is barrierless; the barrier height will increase with increasing solvent polarity. Second, we found that, in alcoholic solvents, intermolecular hydrogen bonding plays a more important role. The ketoB form of MS can form two hydrogen bonds with alcoholic solvents; one will facilitate ESIPT and produce the emission band in the blue region; the other one precludes ESIPT and produces the emission band in the near-UV region. Our proposed new mechanism can well explain previous results as well as our new experimental results.
In this paper, we have investigated the tandem reaction mechanism for the N-aziridinyl imine compounds forming triquinanes via trimethylenemethane (TMM) diyls in detail. Based on the calculated results, the reaction is initiated by the cleavage of the N-aziridinyl in the substrate, followed by an intramolecular 1,3-dipolar (3 + 2) cycloaddition preferentially leading to a linearly-fused tetrahydrocyclopentapyrazole intermediate. Next, the intermediate loses N2 to form the singlet TMM diyl M3S, which can then undergo another concerted (3 + 2) cycloaddition to generate the linearly-fused cis–trans or cis–syn triquinane products. In addition, M3S can also undergo intersystem crossing to the triplet TMM diyl M3T, and the six possible reaction pathways associated with M3T have also been identified. The calculated results reveal that the cis–trans fused pathway associated with M3S is energetically preferred with the highest free energy barrier of 25.0 kcal mol−1. In comparison, the cyclization of M3T requires much higher activation free energies (ΔG≠ = 34.4–57.8 kcal mol−1). At the experimental temperature 110 °C, only the linearly-fused cis–trans and cis–syn pathways associated with M3T (ΔG≠ = 34.4 and 35.5 kcal mol−1 respectively) are possible. The calculated results also indicate that for both M3S and M3T, the linearly-fused cis–trans triquinane should be the main product, which is consistent with the experimental observation. At last, conformational and NBO analyses on key transition states identified the cis–trans stereocontrol factors. Further calculations indicate that the methyl substituent on the allene group of the reactant substrate improves the stereoselectivity of the reaction but does not affect the rate-determining step.
Co-reporter:Yang Yang, Lei Liu, Junsheng Chen and Keli Han
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 33) pp:17828-17834
Publication Date(Web):16 Jun 2014
DOI:10.1039/C4CP01371A
The spontaneous and collision-assisted hydrogen-atom abstracting reaction (HA) dynamics of triplet benzil are investigated through the combination of transient absorption spectroscopy with TD-DFT calculations. HA dynamics exhibit a remarkable dependence on the hydrogen donor properties. The effects of the triplet-state hydrogen bonding on the reaction dynamics are illustrated. In particular, it is experimentally observed that strengthened triplet-state hydrogen bonding could accelerate the HA, whereas weakened triplet-state hydrogen bonding would postpone the HA. The triplet-state hydrogen bonding has great influences on the early stage of the HA reaction, while the bond dissociation energy of the hydrogen donors determines the subsequent reaction pathways. Protic solvents could sustain longer lifetimes of the excited-state intermediate formed after HA than non-protic solvents by 10 μs. This investigation provides insights into the HA dynamics and guidance to improve the product efficiency of photochemical reactions.
Co-reporter:Zhangrong Lou, Songqiu Yang, Peng Li, Panwang Zhou and Keli Han
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 8) pp:3749-3756
Publication Date(Web):26 Nov 2013
DOI:10.1039/C3CP54093F
In this article, the sensing mechanism of a fluorescence probe for hypochloric acid, NI–Se, has been investigated using experimental and theoretical methods. Based on the results of the steady-state and time-resolved emission spectra of NI–Se and its oxidized form NI–SeO, we suggested that there was twist internal charge transfer (TICT) state with faint fluorescence in NI–Se. Subsequently, the ground and excited state minimum geometries of NI–Se and NI–SeO were optimized with DFT/TD-DFT methods. The results demonstrated there was a twisting process in the excited state of NI–Se and that this twist process was induced by the nonbonding interaction between the Se and N atoms. In addition, the calculated spectra and molecular orbitals confirmed the charge transfer character of the TICT state in NI–Se. To further investigate the driving force behind the twist in NI–Se, we synthesized NI–O, which has no Se⋯N nonbonding interaction, as a control sample. Herein, we also present the characterization, fluorescence properties and the optimized geometries of NI–O. Moreover, the results showed that Se⋯N nonbonding interaction plays a significant role in the twisting process of NI–Se.
The Journal of Physical Chemistry A 2014 Volume 118(Issue 39) pp:8929-8935
Publication Date(Web):June 18, 2014
DOI:10.1021/jp5009779
A parallel code for state-to-state quantum dynamics with propagation of time-dependent wavepacket in reactant coordinates has been developed on graphical processing units (GPUs). The propagation of wavepacket and the transformation of wavepacket from reactant to product Jacobi coordinates are entirely calculated on GPUs. A new interpolation procedure is introduced for coordinate transformation to decrease the five-loop computation to two four-loop computations. This procedure has a negligible consumption of extra GPU memory in comparison with that of the wavepacket and produces a considerable acceleration of the computational speed of the transformation. The code is tested to get differential cross sections of H+HD reaction and state-resolved reaction probabilities of O+HD for total angular momenta J = 0, 10, 20, and 30. The average speedups are 57.0 and 83.5 for the parallel computations on two C2070 and K20m GPUs relative to serial computation on Intel E5620 CPU, respectively.
Co-reporter:Jun-Sheng Chen ; Guang-Jiu Zhao ; Timothy R. Cook ; Ke-Li Han ;Peter J. Stang
Journal of the American Chemical Society 2013 Volume 135(Issue 17) pp:6694-6702
Publication Date(Web):April 7, 2013
DOI:10.1021/ja402421w
In this work, spectroscopic techniques and quantum chemistry calculations were used to investigate the photophysical properties of various multinuclear platinum complexes with different conformational geometries. This suite of complexes includes a Pt–pyridyl square, a Pt–carboxylate triangle, and a mixed Pt–pyridyl–carboxylate rectangle, as well as two mononuclear Pt model complexes. Studying the individual molecular precursors in the context of larger assemblies is important to provide a complete understanding of the factors governing the observed photophysical properties of a given system. The absorption and emission bands of the parent linear dipyridyl donor (ligand 1) are largely preserved in the [4 + 4] square and the multicomponent [4 + 2 + 2] rectangle (3 and 4, respectively), with significant red shifts. The [3 + 3] Pt–carboxylate triangle containing p-phthalic acid is nonemissive. Phosphorescence and nanosecond transient spectroscopy on 3 and 4 reveal that the introduction of platinum atoms enhances spin–orbital coupling, thereby increasing the rate of intersystem crossing. This phenomenon is consistent with the low fluorescence quantum yields and short fluorescence lifetimes of 3 and 4. Moreover, the electronic structures for the ground state and low-lying excited states of these compounds were studied using quantum chemistry calculations. The fluorescent states of the platinum complexes are local excited states of ligand-centered π–π* transition features, whereas the nonfluorescent states are intramolecular charge-transfer states. These low-lying intramolecular charge-transfer states are responsible for the nonemissive nature of small molecules 1 and 2 and triangle 5. As the interactions between these components determine the properties of their corresponding assemblies, we establish novel excited-state decay mechanisms which dictate the observed spectra.
Journal of the American Chemical Society 2013 Volume 135(Issue 20) pp:7674-7680
Publication Date(Web):April 27, 2013
DOI:10.1021/ja401360a
The redox homeostasis between peroxynitrite and glutathione is closely associated with the physiological and pathological processes, e.g. vascular tissue prolonged relaxation and smooth muscle preparations, attenuation hepatic necrosis, and activation matrix metalloproteinase-2. We report a near-infrared fluorescent probe based on heptamethine cyanine, which integrates with telluroenzyme mimics for monitoring the changes of ONOO–/GSH levels in cells and in vivo. The probe can reversibly respond to ONOO– and GSH and exhibits high selectivity, sensitivity, and mitochondrial target. It is successfully applied to visualize the changes of redox cycles during the outbreak of ONOO– and the antioxidant GSH repair in cells and animal. The probe would provide a significant advance on the redox events involved in the cellular redox regulation.
Co-reporter:Bingshuai Wang, Peng Li, Fabiao Yu, Junsheng Chen, Zongjin Qu and Keli Han
Chemical Communications 2013 vol. 49(Issue 51) pp:5790-5792
Publication Date(Web):01 May 2013
DOI:10.1039/C3CC42313A
We have developed a near-infrared (NIR) reversible and ratiometric fluorescence sensor based on Se-BODIPY for the redox cycle between hypobromous acid oxidative stress and hydrogen sulfide repair. Real-time imaging shows that the probe is able to monitor intracellular HBrO/H2S redox cycle replacement.
Co-reporter:Zhangrong Lou, Peng Li, Qiang Pan and Keli Han
Chemical Communications 2013 vol. 49(Issue 24) pp:2445-2447
Publication Date(Web):06 Feb 2013
DOI:10.1039/C3CC39269D
Based on a novel strategy for modulating the fluorescence of selenide and selenoxide, we have designed and developed a reversible fluorescent probe for hypochloric acid. And the synthesis, characterization, fluorescence properties, as well as the biological applications in living cells and animals, have all been described.
Co-reporter:Bingshuai Wang, Peng Li, Fabiao Yu, Ping Song, Xiaofei Sun, Songqiu Yang, Zhangrong Lou and Keli Han
Chemical Communications 2013 vol. 49(Issue 10) pp:1014-1016
Publication Date(Web):12 Dec 2012
DOI:10.1039/C2CC37803E
We have developed a new reversible fluorescence probe MPhSe–BOD for the redox cycle process between hypochlorous acid and hydrogen sulfide in solution and in living cells. Confocal microscopy imaging using RAW264.7 cell lines shows that the probe has good cell membrane permeability, and can monitor intracellular HClO/H2S redox cycles continuously.
Co-reporter:Zhangrong Lou, Peng Li, Xiaofei Sun, Songqiu Yang, Bingshuai Wang and Keli Han
Chemical Communications 2013 vol. 49(Issue 4) pp:391-393
Publication Date(Web):31 Oct 2012
DOI:10.1039/C2CC36839K
A diselenide containing fluorescent probe based on a fluorescein scaffold for thiols was developed. The fluorescent probe exhibited rapid response, high selectivity and reversibility. Confocal fluorescence microscopy was used to visualize the redox changes mediated by thiols and reactive oxygen species in living HeLa cells.
Co-reporter:Bingshuai Wang, Fabiao Yu, Peng Li, Xiaofei Sun, Keli Han
Dyes and Pigments 2013 Volume 96(Issue 2) pp:383-390
Publication Date(Web):February 2013
DOI:10.1016/j.dyepig.2012.09.006
We present the synthesis, spectroscopic properties, and live-cell application of a new BODIPY (boron dipyrromethene) fluorescence probe BOD-Se based on selenoxide spirocyclization reaction for peroxynitrite detection. The probe employs BODIPY dye as fluorophore, and is integrated with a chemical peroxynitrite responsive organoselenium functional group. By using reactive diaryl selenide and modulating by intramolecular charge-transfer (ICT) process, the probe is employed for evaluating intracellular peroxynitrite level changes. Different intracellular peroxynitrite levels can be detected with BOD-Se by confocal microscopy experiments using mouse macrophage cell line RAW264.7.Highlights► A new fluorescence probe BOD-Se was synthesized. ► The probe could detect peroxynitrite based on selenoxide spirocyclization reaction. ► The detection mechanism was modulated via intramolecular charge transfer (ICT) process. ► Confocal microscopy imaging confirm the probe can evaluate intracellular ONOO− level changes.
Co-reporter:Zhangrong Lou, Peng Li, Peng Song and Keli Han
Analyst 2013 vol. 138(Issue 21) pp:6291-6295
Publication Date(Web):09 Aug 2013
DOI:10.1039/C3AN00198A
A series of ratiometric probes based on heptamethine cyanine dyes for detecting hypochlorous acid have been developed. Here we present the synthesis, characterization and fluorescence properties of these probes. And it turns out that the probes are highly sensitive and selective toward hypochlorous acid. More importantly, the application in living cells for ratiometric imaging of hypochlorous acid has been achieved successfully.
Co-reporter:Junxia Ding, Liang Zhang, Yan Zhang, and Ke-Li Han
The Journal of Physical Chemistry A 2013 Volume 117(Issue 16) pp:3266-3278
Publication Date(Web):April 1, 2013
DOI:10.1021/jp311498u
n-Heptane is the most important straight chain paraffin in the fossil-fuel industry. In this work, pyrolysis of n-heptane at high temperature is investigated by a series of ReaxFF based reactive molecular dynamic simulations. The pyrolysis correlated intermediate reactions, important product/intermediate distributions, and corresponding kinetics behaviors are systematically analyzed at atomistic level. The results indicate that the entire pyrolysis process is radical-dominated. The unimolecular dissociation is the main pathway of n-heptane decomposition. Initiation of the decomposition is mainly through C–C bond fission. Central C–C bonds would dissociate prior to the terminal ones. Besides, the Rice–Kossiakoff theory is proved for the pyrolysis of n-heptane at the atomistic level. To give a better description of the pyrolysis behavior, some alkane related intermolecular reactions should be considered in the mechanism. The apparent activation energy extracted from the present simulations is 43.02–54.49 kcal/mol in the temperature range 2400–3000 K, which is reasonably consistent with the experimental results.
The Journal of Physical Chemistry A 2013 Volume 117(Issue 36) pp:8512-8518
Publication Date(Web):February 7, 2013
DOI:10.1021/jp400102r
An efficient graphics processing units (GPUs) version of time-dependent wavepacket code is developed for the atom–diatom state-to-state reactive scattering processes. The propagation of the wavepacket is entirely calculated on GPUs employing the split-operator method after preparation of the initial wavepacket on the central processing unit (CPU). An additional split-operator method is introduced in the rotational part of the Hamiltonian to decrease communication of GPUs without losing accuracy of state-to-state information. The code is tested to calculate the differential cross sections of H + H2 reaction and state-resolved reaction probabilities of nonadiabatic triplet–singlet transitions of O(3P,1D) + H2 for the total angular momentum J = 0. The global speedups of 22.11, 38.80, and 44.80 are found comparing the parallel computation of one GPU, two GPUs by exact rotational operator, and two GPU versions by an approximate rotational operator with serial computation of the CPU, respectively.
Accounts of Chemical Research 2012 Volume 45(Issue 3) pp:404
Publication Date(Web):November 9, 2011
DOI:10.1021/ar200135h
Because of its fundamental importance in many branches of science, hydrogen bonding is a subject of intense contemporary research interest. The physical and chemical properties of hydrogen bonds in the ground state have been widely studied both experimentally and theoretically by chemists, physicists, and biologists. However, hydrogen bonding in the electronic excited state, which plays an important role in many photophysical processes and photochemical reactions, has scarcely been investigated.Upon electronic excitation of hydrogen-bonded systems by light, the hydrogen donor and acceptor molecules must reorganize in the electronic excited state because of the significant charge distribution difference between the different electronic states. The electronic excited-state hydrogen-bonding dynamics, which are predominantly determined by the vibrational motions of the hydrogen donor and acceptor groups, generally occur on ultrafast time scales of hundreds of femtoseconds. As a result, state-of-the-art femtosecond time-resolved vibrational spectroscopy is used to directly monitor the ultrafast dynamical behavior of hydrogen bonds in the electronic excited state. It is important to note that the excited-state hydrogen-bonding dynamics are coupled to the electronic excitation. Fortunately, the combination of femtosecond time-resolved spectroscopy and accurate quantum chemistry calculations of excited states resolves this issue in laser experiments. Through a comparison of the hydrogen-bonded complex to the separated hydrogen donor or acceptor in ground and electronic excited states, the excited-state hydrogen-bonding structure and dynamics have been obtained. Moreover, we have also demonstrated the importance of hydrogen bonding in many photophysical processes and photochemical reactions.In this Account, we review our recent advances in electronic excited-state hydrogen-bonding dynamics and the significant role of electronic excited-state hydrogen bonding on internal conversion (IC), electronic spectral shifts (ESS), photoinduced electron transfer (PET), fluorescence quenching (FQ), intramolecular charge transfer (ICT), and metal-to-ligand charge transfer (MLCT). The combination of various spectroscopic experiments with theoretical calculations has led to tremendous progress in excited-state hydrogen-bonding research. We first demonstrated that the intermolecular hydrogen bond in the electronic excited state is greatly strengthened for coumarin chromophores and weakened for thiocarbonyl chromophores. We have also clarified that the intermolecular hydrogen-bond strengthening and weakening correspond to red-shifts and blue-shifts, respectively, in the electronic spectra. Moreover, radiationless deactivations (via IC, PET, ICT, MLCT, and so on) can be dramatically influenced through the regulation of electronic states by hydrogen-bonding interactions. Consequently, the fluorescence of chromophores in hydrogen-bonded surroundings is quenched or enhanced by hydrogen bonds. Our research expands our understanding of the nature of hydrogen bonding by delineating the interaction between hydrogen bonds and photons, thereby providing a basis for excited-state hydrogen bonding studies in photophysics, photochemistry, and photobiology.
Cytochrome P450 (P450) enzymes are the major catalysts involved in the oxidative metabolism of most drugs, steroids, carcinogens, and other chemicals. They catalyze a variety of reactions and convert chemicals to potentially reactive products as well as make compounds less toxic. More than 75% of drugs in clinical use are metabolized by P450s. Understanding the mechanism of drug metabolism by P450, in particular the chemical process, is indispensable in the early phases of drug discovery process. In this review, we discuss our recent theoretical studies on the mechanism of some specific compounds catalyzed by P450. Density functional theory (DFT) is used as the quantum mechanical (QM) tool to explore the fundamental mechanism of these reactions. These DFT calculations provide structures, energies, and some other properties of transition states and intermediates and thus shed light on the electronic factors that govern the stability and reactivity. These theoretical studies provide a complementary insight to experiment and suggest some new features. DFT serves a powerful tool to explore the chemical mechanism of drug metabolism by P450. The revealed fundamental mechanism concerning how the enzyme catalyzes the drug metabolism, especially the transition state of the rate-determining reaction step, could provide a valuable mechanistic base for rational design of novel drugs.Highlights► We discuss our recent theoretical studies on the mechanism of some specific compounds catalyzed by P450. ► The density functional theory (DFT) is used as the quantum mechanical (QM) tool to explore the fundamental mechanism of these reactions. ► These studies provide a complementary insight to experiment and suggest some new features.
Co-reporter:Fabiao Yu, Ping Song, Peng Li, Bingshuai Wang and Keli Han
Chemical Communications 2012 vol. 48(Issue 62) pp:7735-7737
Publication Date(Web):13 Jun 2012
DOI:10.1039/C2CC33264G
We describe the synthesis, properties, and application of two reversible fluorescent probes, mCy-TemOH and Cy-TemOH, for HOBr sensing and imaging in live cells. The two probes contain a hydroxylamine functional group for the monitoring of HOBr oxidation/ascorbic acid reduction events. Confocal fluorescence microscopy has established the HOBr detection in live-cells.
Co-reporter:Fabiao Yu, Peng Li, Ping Song, Bingshuai Wang, Jianzhang Zhao and Keli Han
Chemical Communications 2012 vol. 48(Issue 41) pp:4980-4982
Publication Date(Web):21 Mar 2012
DOI:10.1039/C2CC30985H
We presented the design, synthesis, spectroscopy, and biological applications of DA–Cy, an on–off–on fluorescent probe to monitor H2O2 oxidative stress and thiols reducing repair in living cells and tissues simply and directly.
Co-reporter:Fabiao Yu, Peng Li, Ping Song, Bingshuai Wang, Jianzhang Zhao and Keli Han
Chemical Communications 2012 vol. 48(Issue 23) pp:2852-2854
Publication Date(Web):12 Jan 2012
DOI:10.1039/C2CC17658K
We present a colorimetric and ratiometric fluorescent probe Cy–N3 that exhibits a selective response to H2S. The probe employs a near-infrared cyanine as a fluorophore, and is equipped with an operating azide unit. It is readily employed for assessing intracellular H2S levels, and confocal ratiometric imaging is achieved successfully.
Co-reporter:Fabiao Yu, Ping Song, Peng Li, Bingshuai Wang and Keli Han
Analyst 2012 vol. 137(Issue 16) pp:3740-3749
Publication Date(Web):30 May 2012
DOI:10.1039/C2AN35246J
We present the design, synthesis, spectroscopy, and biological applications of PyBor, a new type of fluorescent probe for peroxynitrite detection in aqueous solution and living cells. The probe employs pyrene as the fluorophore, and is equipped with a chemically responsive unit boronate. The fluorescent probe can selectively detect peroxynitrite with fluorimetric determination and high-performance liquid chromatography analyses in aqueous solution and RAW264.7 cells intracellular free extracts. We also study our probe to time dependent peroxynitrite release from 3-morpholinylsydnonimine hydrochloride. Confocal microscopy experiments using mouse macrophage cell line RAW264.7 show that PyBor is able to detect the different intracellular peroxynitrite levels. In addition, we have performed quantum chemical calculations with TD-DFT/M06/TZVP level with COSMO solvation model basis sets using a suite of Gaussian 09 programs to provide insights into the structure optical properties of PyBor and PyOH.
The phosphine-catalyzed [4 + 2] annulations between allenoates and electron-poor trifluoromethyl ketones or N-tosylbenzaldimine dipolarophiles have been investigated in continuum solvation using density functional theory (DFT) calculations. The detailed reaction mechanisms as well as the high cis-diastereoselectivities of the reactions have been firstly clarified. Our calculated results reveal that the whole catalytic process is presumably initiated with the nucleophilic attack of phosphine catalyst at the allenoate to produce the zwitterionic intermediate M1, which subsequently undergoes γ-addition to the electron-poor CO (or CN) dipolarophile to form another intermediate M2. The following [1,3] hydrogen shift of M2 is demonstrated to proceed via two consecutive proton transfer steps without the assistance of protic solvent: the anionic O6 (or N6) of M2 first acts as a base catalyst to abstract a proton from C1 to produce the intermediate M3, and then the OH (or NH) group can donate the acidic proton to C3 to complete the [1,3] hydrogen shift and generate the intermediate M4. Finally, the intramolecular Michael-type addition followed by the elimination of catalyst furnishes the final product. High cis-diastereoselectivities are also predicted for both the two reactions, which is in good agreement with the experimental observations. For the reaction of allenoates with trifluoromethyl ketones, the first proton transfer is found to be the diastereoselectivity-determining step. The cumulative effects of the steric repulsion, electrostatic interaction as well as other weak interactions appear to contribute to the relative energies of transition states leading to the diastereomeric products. On the contrary, in the case of N-tosylbenzaldimines, the Michael-type addition is found to be the diastereoselectivity-determining step. Similarly, steric repulsion, as well as electrostatic interaction is also identified to be the dominant factors in controlling the high cis-diastereoselectivity of this reaction.
Co-reporter:Songqiu Yang, Jianyong Liu, Panwang Zhou, Junsheng Chen, Keli Han, Guozhong He
Journal of Luminescence 2012 Volume 132(Issue 9) pp:2275-2280
Publication Date(Web):September 2012
DOI:10.1016/j.jlumin.2012.03.062
Subpicosecond fluorescence depletion spectroscopy (FDS) was used to measure the solvation dynamics of coumarin 153 (C153) in methanol. The FDS mechanisms were discussed. A quasi-continuous model was used to describe the solvational relaxation of excited states. The perturbations of the probe pulse on the excited sample system, including up-conversion and stimulated emission, were sufficiently discussed. For a probe molecule used in the FDS experiment, ensuring that the up-conversion perturbation can be negligible is important. FDS was found to be a good technique for measuring the solvation dynamics of C153 in methanol.Highlights► Mechanisms of subpicosecond fluorescence depletion spectroscopy. ► Quasi-continuous model was used to describe the solvational relaxation. ► The solvation dynamics of coumarin 153 in methanol has been measured.
Co-reporter:Jin-Dou Huang, Jian-Yong Liu, Ke-Li Han
International Journal of Hydrogen Energy 2012 Volume 37(Issue 23) pp:17870-17881
Publication Date(Web):December 2012
DOI:10.1016/j.ijhydene.2012.09.003
The structural and electronic properties of the wurtzite ZnxCd1−xS and (ZnxCd1−x)(SexS1−x) alloys are calculated using density functional theory calculations with HSE06 hybrid exchange-correlation functional. Special quasirandom structures are used to describe the disordered alloys, for x = 0.125, 0.25, 0.375, 0.5, 0.625, 0.75 and 0.875, respectively. Our calculations reveal that ZnxCd1−xS alloy with the appropriate Zn doping concentration not only causes the elevation of the conduction band minimum energy, but also increase the mobility of photogenerated holes and electrons, which well explains the high photocatalytic activity and stability of Zn0.2Cd0.8S alloy under a long-term light irradiation. Compared with ZnxCd1−xS alloy, (ZnxCd1−x)(SexS1−x) alloy holds greater potential to simultaneously meet band gap, band edge, and mobility criteria for water splitting. Theoretical results predict that (ZnxCd1−x)(SexS1−x) alloy with the ZnSe concentration in the range from 0.38 to 0.75 could be a more promising candidate than Zn0.2Cd0.8S alloy for photoelectrochemical hydrogen production through water splitting.Highlights▶ Lattice parameters and band gaps of ZnxCd1−xS and (ZnxCd1−x)(SexS1−x) are nicely reproduced. ▶ Our results rationalize experimental results which showed that Zn0.2Cd0.8S exhibits higher photocatalytic activity than CdS. ▶ (ZnxCd1−x)(SexS1−x) holds great potential to simultaneously satisfy the criteria for water splitting.
Co-reporter:Peng Zhao, Dan Chen, Guoyong Song, Keli Han, and Xingwei Li
The Journal of Organic Chemistry 2012 Volume 77(Issue 3) pp:1579-1584
Publication Date(Web):December 27, 2011
DOI:10.1021/jo202228k
Palladium(II) can catalyze the oxidative coupling of tert-butyl 2-alkynylbenzoates with olefins such as acrylates and styrenes, leading to isocoumarines. The reaction was carried out under simple aerobic conditions, and in most cases, high selectivity has been attained.
Co-reporter:Jin-Dou Huang;Dr. Shu-Hao Wen; Ke-Li Han
Chemistry – An Asian Journal 2012 Volume 7( Issue 5) pp:1032-1040
Publication Date(Web):
DOI:10.1002/asia.201100904
Abstract
Herein, we calculated reorganization energies, vertical ionization energies, electron affinities, and HOMO–LUMO gaps of fused thiophenes and their derivatives, and analyzed the influence of different substituents on their electronic properties. Furthermore, we simulated the angular resolution anisotropic mobility for both electron- and hole-transport, based on quantum-chemical calculations combined with the Marcus–Hush electron-transfer theory. We showed that: 1) styrene-group substitution can effectively elevate the HOMO energy level and lower the LUMO energy level, and therefore lower both the hole- and electron-injection barriers; and 2) chemical oxidation of the thiophene ring can significantly improve the semiconductor properties of the fused oligothiophenes through a decrease of the injection barrier and an increase in the charge-transfer mobility for electrons but without lowering their hole-transfer mobilities, which suggests that it may be a promising way to convert p-type semiconductors into ambipolar or n-type semiconductor materials.
Co-reporter:Fabiao Yu ; Peng Li ; Guangyue Li ; Guangjiu Zhao ; Tianshu Chu
Journal of the American Chemical Society 2011 Volume 133(Issue 29) pp:11030-11033
Publication Date(Web):June 27, 2011
DOI:10.1021/ja202582x
We have developed a near-IR reversible fluorescent probe containing an organoselenium functional group that can be used for the highly sensitive and selective monitoring of peroxynitrite oxidation and reduction events under physiological conditions. The probe effectively avoids the influence of autofluorescence in biological systems and gave positive results when tested in both aqueous solution and living cells. Real-time images of cellular peroxynitrite were successfully acquired.
Co-reporter:Dongmei Li ; Xiaoqin Huang ; Keli Han ;Chang-Guo Zhan
Journal of the American Chemical Society 2011 Volume 133(Issue 19) pp:7416-7427
Publication Date(Web):April 22, 2011
DOI:10.1021/ja111657j
A series of computational methods were used to study how cytochrome P450 2A6 (CYP2A6) interacts with (S)-(−)-nicotine, demonstrating that the dominant molecular species of (S)-(−)-nicotine in CYP2A6 active site exists in the free base state (with two conformations, SRt and SRc), despite the fact that the protonated state is dominant for the free ligand in solution. The computational results reveal that the dominant pathway of nicotine metabolism in CYP2A6 is through nicotine free base oxidation. Further, first-principles quantum mechanical/molecular mechanical free energy (QM/MM-FE) calculations were carried out to uncover the detailed reaction pathways for the CYP2A6-catalyzed nicotine 5′-hydroxylation reaction. In the determined CYP2A6–(S)-(−)-nicotine binding structures, the oxygen of Compound I (Cpd I) can abstract a hydrogen from either the trans-5′- or the cis-5′-position of (S)-(−)-nicotine. CYP2A6-catalyzed (S)-(−)-nicotine 5′-hydroxylation consists of two reaction steps, that is, the hydrogen transfer from the 5′-position of (S)-(−)-nicotine to the oxygen of Cpd I (the H-transfer step), followed by the recombination of the (S)-(−)-nicotine moiety with the iron-bound hydroxyl group to generate the 5′-hydroxynicotine product (the O-rebound step). The H-transfer step is rate-determining. The 5′-hydroxylation proceeds mainly with the stereoselective loss of the trans-5′-hydrogen, that is, the 5′-hydrogen trans to the pyridine ring. The calculated overall stereoselectivity of ∼97% favoring the trans-5′-hydroxylation is close to the observed stereoselectivity of 89–94%. This is the first time it has been demonstrated that a CYP substrate exists dominantly in one protonation state (cationic species) in solution, but uses its less-favorable protonation state (neutral free base) to perform the enzymatic reaction.
A series of n-type perylene bisimide (PBI) derivatives with electron-withdrawing substituents at both bay and imide nitrogen positions were investigated. The effects of these substituents on internal energy relaxation, molecular orbitals, air stability, electronic properties and charge transport behaviors were systematically discussed with density functional theory (DFT) which has been demonstrated reliable for organic semiconductor study. The investigated derivatives with electron-withdrawing substituents show favorable performances in terms of these properties. The LUMO levels are greatly stabilized by at least 0.3 eV and these derivatives show the strong absorption from 400 to 700 nm which match with the solar spectra very well. The charge transport mainly happens between molecules in the same organic molecular layer and electronic couplings between layer-to-layer molecules are very weak, thus the mobility along layer-to-layer direction is less efficient. The variation of molecular packings and intermolecular interactions produce the highly anisotropic mobilities. The derivative with two fluorine atoms at bay positions and –CH2C3F7 at imide group has broad and strong absorption in the UV-Visible region and the electron mobility could get to 0.514 cm2 V−1 s−1 which is greatly encouraging for molecular and material design in organic solar-cell devices. These calculated results are in good agreement with the experimental data. However, not all the functionalization with halogen substituents would induce the increase of the electronic coupling and electron mobility. The derivatives with four halogen substituents at the bay positions could not show advantages in terms of electron mobility which is induced by the distorted conjugated structures. The theoretical understanding of these n-type organic semiconductors figures out the importance of tuning the molecular geometry to get high performance semiconductor materials.Graphical abstractHighlights► Electron-withdrawing substituents are attached to conjugated perylene molecule. ► The charge transport properties of derivatives are improved. ► The mobility shows angular-resolution anisotropic characteristic. ► These substituents enhance the electron mobility and stability.
Co-reporter:Xiao-Fang Chen, Bo-Zhou Wang and Ke-Li Han
RSC Advances 2011 vol. 1(Issue 5) pp:765-767
Publication Date(Web):15 Sep 2011
DOI:10.1039/C1RA00239B
The reaction of HCHO with CH3CN to yield a key RDX precursor (TRAT) was proposed to undergo four sequential stages. More attention was suggested to be paid to the mid and final terms. A parallel product could be controlled by using the concentrated sulfuric acid in almost drying conditions.
Co-reporter:Songqiu Yang, Jianyong Liu, Panwang Zhou, Keli Han, Guozhong He
Chemical Physics Letters 2011 Volume 512(1–3) pp:66-69
Publication Date(Web):16 August 2011
DOI:10.1016/j.cplett.2011.06.088
Abstract
Time-resolved transient absorption spectroscopy in the visible region and density functional theory methods are used to investigate the excited-state dynamics of two metal-free organic sensitizers used in dye-sensitized solar cells (DSSCs). The triphenylamine (TPA) group in TH305 acts as an energy antenna to absorb light at approximately 381 nm. The energy absorbed by TPA can be efficiently used by DSSCs through intramolecular charge transfers from the TPA group to the cyanoacrylic acid group.
Co-reporter:Jin-Dou Huang, Shu-Hao Wen, Wei-Qiao Deng, and Ke-Li Han
The Journal of Physical Chemistry B 2011 Volume 115(Issue 10) pp:2140-2147
Publication Date(Web):February 22, 2011
DOI:10.1021/jp108125q
We investigated oligofuran (nF) (n = 3, 4, 6) heterocyclic oligomers as p-type organic semiconductor materials, based on quantum chemistry calculations combined with the Marcus−Hush electron transfer theory. It was found that 6F single crystal, with a structure similar to that of 6T, possesses high hole-transfer mobility, which is nearly 17 times larger than that of 6T single crystal. In addtion, the ionization potential (IP) value of 6F is about 5.60 eV, that is, slightly smaller than the IP value of 6T (5.74 eV). The relatively small IP values ensure effective hole injection from the source electrode. Considering that 6T and functional oligothiophenes are active p-type semiconducting materials widely used in organic electronic devices, nFs and nF-based molecules have the potential to be developed as potential high efficiency p-type organic semiconducting materials.
Co-reporter:Guang-Jiu Zhao, Fabiao Yu, Ming-Xing Zhang, Brian H. Northrop, Haibo Yang, Ke-Li Han, and Peter J. Stang
The Journal of Physical Chemistry A 2011 Volume 115(Issue 24) pp:6390-6393
Publication Date(Web):May 11, 2011
DOI:10.1021/jp202825q
An investigation of a series of platinum-containing organometallic complexes for the study of fluorescence phenomena in organometallic chromophores controlled by the intramolecular charge transfer (ICT) is presented in this work. We report steady-state and time-resolved spectroscopic experiments as well as quantum chemistry calculations to investigate the substituent effects on the ICT and fluorescence emission. We demonstrate that the fluorescence maximum and lifetimes greatly depend on different substituents and the presence of bimetallic platinum donor. This work paves the way for an understanding of the fluorescence phenomena controlled by molecular ICT characters of these kinds of platinum-containing organometallic complexes.
Co-reporter:Shuhao Wen, Wei-Qiao Deng and Ke-Li Han
Chemical Communications 2010 vol. 46(Issue 28) pp:5133-5135
Publication Date(Web):09 Jun 2010
DOI:10.1039/C0CC00955E
We have investigated the conduction mechanism at the TTF–TCNQ organic hetero-interface by means of quantum mechanical (QM) calculations. The calculated resistances at the TTF–TCNQ interface are 39–64 kΩ per square, which is in good agreement with the experimental values of 1–30 kΩ per square.
Co-reporter:Huan Yang, M. Hankel, Antonio Varandas and Keli Han
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 33) pp:9619-9623
Publication Date(Web):07 Jul 2010
DOI:10.1039/C003930F
Nonadiabatic quantum dynamics calculations on the two coupled potential energy surfaces (PESs) (12A′ and 22A′) and also adiabatic quantum calculations on the lowest adiabatic PES are reported for the title reaction. Reaction probabilities for total angular momenta, J, varying from 0 to 160, are calculated to obtain the integral cross section (ICS) for collision energies ranging from 0.05 to 1.0 eV. Calculations using both the close coupling and the Centrifugal Sudden (CS) approximation are carried out to evaluate the role of Coriolis coupling effects for this reaction. The results of the nonadiabatic calculations show that the nonadiabatic effects in the title reaction for the initial state of NH (v = 0, j = 0) could be neglected, at least in the collision energy range considered in this study.
Co-reporter:Shu-Hao Wen, Wei-Qiao Deng and Ke-Li Han
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 32) pp:9267-9275
Publication Date(Web):07 Jul 2010
DOI:10.1039/B923862J
The intermolecular electronic coupling (transfer integral) and the intramolecular vibronic coupling (reorganization energy) are key parameters determining the transport properties of organic electronic materials. Using quantum mechanism calculations, we revealed the correlation between the reorganization energies and the partial charge difference values on the conjugated acene backbone, which can be used to evaluate the reorganization energies for acene and acene derivative systems with the same conjugated backbone but different substitutional groups. We used rigorous quantitative functions to investigate the electronic coupling oscillation behavior in slipped-cofacial stacking acene and acene derivative molecules, and revealed characteristic parameters in the electronic coupling oscillation. We suggest using a similar strategy to establish the quantitative structure–activity relationship database for different families of organic semiconducting materials.
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 31) pp:8914-8918
Publication Date(Web):16 Jun 2010
DOI:10.1039/B924549A
In this work, a new model compound, the twisted intramolecular charge transfer (TICT) excited state of Milrinone (MIR), has been theoretically presented. MIR exists in different tautomeric and ionic forms in aqueous solution with different pH values. The TICT excited state properties for various forms of MIR are demonstrated to be significantly different and controlled by the pH values of MIR in aqueous solution.
Microporous and Mesoporous Materials 2010 Volume 127(1–2) pp:90-95
Publication Date(Web):January 2010
DOI:10.1016/j.micromeso.2009.06.034
The adsorption and dehydrogenation of methanol on an alkali-cation-exchanged zeolite model, M-zeolite (M = Na+, K+, Rb+, and Cs+), were studied using first-principles calculations based on density functional theory (DFT). The adsorption energies, geometric structures, and vibrational frequencies of the transition states were computed by full-geometry optimization with a 6MR (membered-ring) cluster model. We have calculated the transition states and adsorption complexes of the reactants, transition states, and products, as well as the corresponding activation barriers and adsorption energies of the numerous reactions involved in these processes. The interaction first leads to the formation of a methanol complex, where the methanol via the oxygen atom and the alkali metal cation of the 6MR. Then, a transition state involves the coordination of two hydrogen bonds. Finally, the adsorbed formaldehyde and hydrogen complex is formed. The calculated results are compared with the data obtained from previous experimental studies.
The geometric structures and mechanisms for hydrogen abstraction from cyclohexane for four high-valent complexes, [FeIV(O)(TMC)(NCMe)]2+ (where TMC is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane; 1-NCMe), the inverted isomer [FeIV(NCMe)(TMC)(O)]2+ (2-NCMe), [RuIV(O)(TMC)(NCMe)]2+ (the ruthenium analogue of 1-NCMe; 3-NCMe), and the inverted isomer [RuIV(NCMe)(TMC)(O)]2+ (4-NCMe), were investigated using density functional theory. The axial NCMe ligand was found to be sterically more hindered in 2-NCMe than in 1-NCMe, which is in accord with the calculated results that the Fe–Laxial distance is longer in the former. Both 1-NCMe and 2-NCMe are capable of hydrogen abstraction from cyclohexane via two-state reactivity patterns. In contrast, 3-NCMe and 4-NCMe react with cyclohexane by a single-state mechanism. The reaction pathways computed reveal that 2-NCMe is more reactive than 1-NCMe, in agreement with experimental results, whereas the reactivity of 3-NCMe and 4-NCMe shows little dependence on whether the oxo unit is syn or anti to the four N-methyl groups. Our analysis shows that along the reaction pathway for 2-NCMe in the triplet spin state, the NCMe ligand moves away from the iron center, and therefore the energy of the \( \sigma_{z}^{* 2} \) (α-spin) orbital decreases and an electron is transferred to this orbital. Finally, we calculated the kinetic isotope effect and investigated the relationship between this effect and reaction barriers.
Co-reporter:Yu-Hui Liu, Guang-Jiu Zhao, Guang-Yue Li, Ke-Li Han
Journal of Photochemistry and Photobiology A: Chemistry 2010 Volume 209(2–3) pp:181-185
Publication Date(Web):25 January 2010
DOI:10.1016/j.jphotochem.2009.11.012
Spectroscopic studies on benzo[b]fluorenone (BF) solvatochromism in several aprotic and alcoholic solvents have been performed to investigate the fluorescence quenching by hydrogen bonding and proposed a weaker ability to form intermolecular hydrogen bond of BF than fluorenone (FN). In this work, the time-dependent density functional theory (TD-DFT) method was used to study the excited-state hydrogen bonding of both FN and BF in ethanol (EtOH) solvent. As a result, it is demonstrated by our theoretical calculations that the hydrogen bond of BF–EtOH complex is almost identical with that of FN–EtOH. Moreover, the fluorescence quantum yields of FN and BF in the alcoholic solvent is efficiently dependent on the energy gap between the lowest excited singlet state (fluorescent state) and ground state, which can be used to explain the fluorescence quenching by the excited-state hydrogen bond strengthening.
Co-reporter:Guang-Jiu Zhao, Brian H. Northrop, Peter J. Stang and Ke-Li Han
The Journal of Physical Chemistry A 2010 Volume 114(Issue 10) pp:3418-3422
Publication Date(Web):February 19, 2010
DOI:10.1021/jp911597z
In this work, the photophysical properties of coordination-driven self-assembled metallosupramolecular rhomboids with the donor ligands 1,2-bis(3-pyridyl)ethyne (3a) and 1,4-bis(3-pyridyl)-1,3-butadiyne (3b) are investigated by use of both spectroscopic experiments and quantum chemistry calculations. All the geometric conformations of the chair and boat conformers of 3a and 3b are fully optimized using density functional theory. The time-dependent density functional theory method was also used to study the excited-state properties of these self-assembled metallosupramolecular rhomboids. At the same time, steady-state absorption and fluorescence as well as the time-correlated single photon counting techniques are used to measure their various spectral properties. The fluorescence spectra of these self-assembled metallosupramolecular rhomboids are very wide and show an evident two-peak feature, which can be tuned by different excitation wavelengths. It has been demonstrated that the chair conformers of both 3a and 3b are formed preferentially over their boat conformers due to the close proximity of the chelated bisphosphine platinum groups. Moreover, an additional shoulder observed at 416 nm in the fluorescence spectra of 3b indicates the presence of minor amounts of the boat conformer of 3b. In addition, we have also demonstrated that lengthening the acetylene chain of the donor ligand component of these rhomboids results in a red-shifted and broadened absorption band for these metallosupramolecular rhomboids. Furthermore, the nature of the excited states for these metallosupramolecular rhomboids varies with the acetylene chain length of the donor ligands and with the different conformers.
Co-reporter:Guang-Jiu Zhao, Brian H. Northrop, Ke-Li Han and Peter J. Stang
The Journal of Physical Chemistry A 2010 Volume 114(Issue 34) pp:9007-9013
Publication Date(Web):August 11, 2010
DOI:10.1021/jp105009t
The bimetallic platinum complexes are known as unique building blocks and arewidely utilized in the coordination-driven self-assembly of functionalized supramolecular metallacycles. Hence, photophysical study of the bimetallic platinum complexes will be very helpful for the understanding on the optical properties and further applications of coordination-driven self-assembled supramolecular metallacycles. Herein, we report steady-state and time-resolved spectroscopic experiments as well as quantum chemistry calculations to investigate the significant intermolecular hydrogen bonding effects on the intramolecular charge transfer (ICT) fluorescence of a bimetallic platinum compound 4,4′-bis(trans-Pt(PEt3)2OTf)benzophenone 3 in solution. We demonstrated that the fluorescent state of compound 3 can be assigned as a metal-to-ligand charge transfer (MLCT) state. Moreover, it was observed that the formation of intermolecular hydrogen bonds can effectively lengthen the fluorescence lifetime of 3 in alcoholic solvents compared with that in hexane solvent. At the same time, the electronically excited states of 3 in solution are definitely changed by intermolecular hydrogen bonding interactions. As a consequence, we propose a new fluorescence modulation mechanism by hydrogen bonding to explain different fluorescence emissions of 3 in hydrogen-bonding solvents and nonhydrogen-bonding solvents.
Simple C–NO2 homolysis, 4,6-dinitroanthranil (DNAt) production by dehydration, and the nitro-nitrite rearrangement–homolysis for gas-phase TNT decomposition were recently studied by Cohen et al. (J Phys Chem A 111:11074, 2007), based on DFT calculations. Apart from those three pathways, other possible initiation processes were suggested in this study, i.e., CH3 removal, O elimination, H escape, OH removal, HONO elimination, and nitro oxidizing adjacent backbone carbon atom. The intermediate, 3,5-dinitro-2(or 4)-methyl phenoxy, is more favor to decompose into CO and 3,5-dinitro-2(or 4)-methyl-cyclopentadienyl than to loss NO following nitro-nitrite rearrangement. Below ~1,335 K, TNT condensing to DNAt by dehydration is kinetically the most favor process, and the formations of substituted phenoxy and following cyclopentadienyl include minor contribution. Above ~1,335 K, simple C–NO2 homolysis kinetically dominates TNT decomposition; while the secondary process changes from DNAt production to CH3 removal above ~2,112 K; DNAt condensed from TNT by dehydration yields to that by sequential losses of OH and H above ~1,481 K and to nitro-nitrite rearrangement–fragmentation above ~1,778 K; O elimination replaces DNAt production above ~2,491 K, playing the third role in TNT decomposition; H escaping directly from TNT thrives in higher temperature (above ~2,812 K), as the fourth largest process. The kinetic analysis indicates that CH3 removal, O elimination, and H escape paths are accessible at the suggested TNT detonation time (~100–200 fs), besides C–NO2 homolysis. HONO elimination and nitro oxidizing adjacent backbone carbon atom paths are negligible at all temperatures. The calculations also demonstrated that some important species observed by Rogers and Dacons et al. are thermodynamically the most favor products at all temperatures, possibly stemmed from the intermediates including 4,6-dinitro-2-nitroso-benzyl alcohol, 3,5-dinitroanline, 2,6-dinitroso-4-nitro-phenylaldehyde, 3,5-dinitro-1-nitrosobenzene, 3,5-dinitroso-1-nitrobenzene, and nitrobenzene. All transition states, intermediates, and products have been indentified, the structures, vibrational frequencies, and energies of them were verified at the uB3LYP/6-311++G(d,p) level. Our calculated energies have mean unsigned errors in barrier heights of 3.4–4.2 kcal/mol (Lynch and Truhlar in J Phys Chem A 105:2936, 2001), and frequencies have the recommended scaling factors for the B3-LYP/6-311+G(d,p) method (Andersson and Uvdal in J Phys Chem A 109:2937, 2005; Merrick et al. in J Phys Chem A 111:11683, 2007). All calculations corroborate highly with the previous experimental and theoretical results, clarifying some pertinent questions.
Co-reporter:Pei-Yu Zhang, Rui-Feng Lu, Tian-Shu Chu and Ke-Li Han
The Journal of Physical Chemistry A 2010 Volume 114(Issue 24) pp:6565-6568
Publication Date(Web):May 26, 2010
DOI:10.1021/jp1024069
Nonadiabatic quantum scattering calculations have been carried out for the reactive and nonreactive quenching of OH(A2Σ+) in collisions with molecular H2 on two new potential energy surfaces of the 1A′ and 2A′ states. Integral cross sections of the reactive and nonreactive quenching channels and the quantum state distributions of the nonreactive channel have been obtained. The theory reveals a high degree of rotational excitation of the quenched OH(X2II) products and vibrational excitation of the H2 products. The calculated results are in good agreement with the existing experimental data. The topography of the potential energy surfaces in the conical intersection regions is provided in order to discuss the origin of the internal excitations of nonreactive products and the branching of the reactive and nonreactive channels.
Co-reporter:Xiao-Fang Chen, Chun-Yuan Hou and Ke-Li Han
The Journal of Physical Chemistry A 2010 Volume 114(Issue 2) pp:1169-1177
Publication Date(Web):December 17, 2009
DOI:10.1021/jp909670w
Two novel types of intermolecular hetero cycloadditions in the participation of the nitro group are put forward in the dimerization of TNT, in comparison with Diels−Alder cross-linking of benzene ring skeletons. Possible transition states and products; for example, their geometrical details, vibrational frequencies, and energies are verified at the B3LYP/6-31+G(d,p) level. Contrary to the hetero Diels−Alder reaction, the folding of the benzene ring side endo is slightly selective specific in 1,3-dipolar cycloaddition. The substituent pattern on reactivity indicates that the methyl group at the bridged sites significantly retards the reaction. Two new σ bonds are formed kinetically and thermodynamically through the single state; however, the first σ bond is more easily generated by the triplet state. The shock-wave-produced chemically bound dimer of TNT is most likely to be the oxygen−carbon linkage product. The initial chemical events in TNT under high pressure can be extended to interpret the shock insensitivity of other unsaturated nitro-explosives. The calculated results agree well with some experimental observations.
Co-reporter:Dongmei Li, Yong Wang, Keli Han and Chang-Guo Zhan
The Journal of Physical Chemistry B 2010 Volume 114(Issue 27) pp:9023-9030
Publication Date(Web):June 24, 2010
DOI:10.1021/jp102225e
The reaction pathways for 5′-hydroxylation and N-demethylation of nicotine catalyzed by cytochrome P450 were investigated by performing a series of first-principle electronic structure calculations on a catalytic reaction model system. The computational results indicate that 5′-hydroxylation of nicotine occurs through a two-state stepwise process, that is, an initial hydrogen atom transfer from nicotine to Cpd I (i.e., the HAT step) followed by a recombination of the nicotine moiety with the iron-bound hydroxyl group (i.e., the rebound step) on both the high-spin (HS) quartet and low-spin (LS) doublet states. The HAT step is the rate-determining one. This finding represents the first case that exhibits genuine rebound transition state species on both the HS and the LS states for Cα-H hydroxylation of amines. N-Demethylation of nicotine involves a N-methylhydroxylation to form N-(hydroxymethyl)nornicotine, followed by N-(hydroxymethyl)nornicotine decomposition to nornicotine and formaldehyde. The N-methylhydroxylation step is similar to 5′-hydroxylation, namely, a rate-determining HAT step followed by a rebound step. The decomposition process occurs on the deprotonated state of N-(hydroxymethyl)nornicotine assisted by a water molecule, and the energy barrier is significantly lower than that of the N-methylhydroxylation process. Comparison of the rate-determining free energy barriers for the two reaction pathways predicts a preponderance of 5′-hydroxylation over the N-demethylation by roughly a factor of 18:1, which is in excellent agreement with the factor of 19:1 derived from available experimental data.
Co-reporter:Yong Wang, Dongmei Li, Keli Han and Sason Shaik
The Journal of Physical Chemistry B 2010 Volume 114(Issue 8) pp:2964-2970
Publication Date(Web):February 10, 2010
DOI:10.1021/jp9097974
This paper addresses the experimentally observed mechanistic differences between the cytochrome P450-catalyzed N-demethylation of substituted N,N-dimethylanilines (DMA) and of N,N-dimethylbenzamides (DMBA). The two reactions of these substrates are initiated by C−H activation of the methyl groups on the nitrogen. Thus, the DMA reactions exhibit small deuterium kinetic isotope effects (KIEs), and these KIEs and the corresponding reaction rates exhibit a linear response to the electronic nature of the para substituent. By contrast, the DMBA reactions exhibit large KIEs; the KIEs and reaction rates do not at all respond to the nature of the para substituent. Accordingly, the present paper uses density functional theoretical calculations to address these reactivity patterns in para-substituted DMBA and compare these results to those obtained for the DMA reactions previously (Wang, Y.; Kumar, D.; Yang, C. L.; Han, K. L.; Shaik, S. J. Phys. Chem. B 2007, 111, 7700). The theoretical calculations reproduce the experimental trends of narrow variations in rates and KIEs. It is shown that the above mechanistic differences between the two reaction series of DMA and DMBA are caused by the ability of the para substituent to maintain a conjugation path between the C−H reaction center and the aryl moiety. Furthermore, the computational results show a new feature of reactivity, namely, that the N-demethylation of DMBA proceeds by a spin-selective reaction via the high spin state of the active species of the enzyme. This conclusion is reinforced by the match of the calculated and experimental KIE values.
Co-reporter:Guang-Jiu Zhao, Ke-Li Han and Peter J. Stang
Journal of Chemical Theory and Computation 2009 Volume 5(Issue 8) pp:1955-1958
Publication Date(Web):July 6, 2009
DOI:10.1021/ct900216m
Density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods have been performed to investigate the ground and excited states of aquo palladium(II) complexes cis-[(dppp)Pd(H2O)2]2+, cis-[(dppp)Pd(H2O)(OSO2CF3)]+(OSO2CF3)−, and cis-[(dppp)Pd(H2O)2]2+(OSO2CF3)−2. Insights into the influence of hydrogen bonding on the structural and spectral properties of these three aquo Pd(II) complexes are presented. The structures and the HOMO−LUMO energy gap of the three aquo Pd(II) complexes can be markedly influenced by hydrogen bonding interactions. Hydrogen bonds can also significantly influence their absorption spectra.
Co-reporter:Dongmei Li, Yong Wang, Chuanlu Yang and Keli Han
Dalton Transactions 2009 (Issue 2) pp:291-297
Publication Date(Web):19 Nov 2008
DOI:10.1039/B810767J
The mechanism of N-dealkylation of N-cyclopropyl-N-methylaniline (3) catalyzed by cytochrome P450 (P450) was investigated using density functional theory. This reaction involves two steps. The first one is a Cα–H hydroxylation on the N-substituent to form a carbinolaniline complex, and the second is a decomposition of the carbinolaniline to yield cyclopropanone (or formaldehyde) and N-methylaniline (or N-cyclopropylaniline). Our calculations demonstrate that the first step proceeds in a spin-selective mechanism (SSM), mostly on the low-spin (LS) doublet state. The rate-limiting Cα–H activation is an isotope-sensitive hydrogen atom transfer (HAT) step. The environmental effect switches the regioselectivity of this reaction from a competition between N-decyclopropylation and N-demethylation to a clear preference for N-demethylation. This preference is consistent with former experimental studies. However, it is not in accord with the normal ΔE-BDE correlation since the BDE of Cα–H on the methyl group is higher than that on the cyclopropyl group. Insight into the origin of the preference for N-demethylation reveals that tertiary amine 3 is different from normal hydrocarbons, possessing a unique πPh-πC-N conjugated system. The electron delocalization effect of the πPh-πC-N conjugated system in 3 makes the transition state pose a polar character, and the bulk polarity and hydrogen bonding capability of the protein pocket can exert a remarkable effect on the regioselectivity of N-dealkylation of 3. Decomposition of carbinolaniline is a water-assisted proton-transfer process in the nonenzymatic environment. The ring-intact cyclopropanone formed in the reaction sheds some light on the inability of 3 to inactivate P450 during its N-decyclopropylation.
Co-reporter:Panwang Zhou, Peng Song, Jianyong Liu, Keli Han and Guozhong He
Physical Chemistry Chemical Physics 2009 vol. 11(Issue 41) pp:9440-9449
Publication Date(Web):21 Aug 2009
DOI:10.1039/B910043A
The rotational reorientation dynamics of 7-aminocoumarin derivatives with different alkylation degrees in methanol, dimethylformamide, and dimethyl sulfoxide have been investigated using femtosecond time-resolved stimulated emission pumping fluorescence depletion (FS TR SEP FD) spectroscopy. In addition to a long anisotropy decay time that accounts for the overall rotational relaxation of solutes, a short anisotropy decay time on the order of picoseconds or sub-picoseconds was also observed in hydrogen-bonding systems. Three types of hydrogen bonds involving the nitrogen lone pair, carbonyl group, and amino group of 7-aminocoumarin derivatives were denoted as types A, B, and C, respectively. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were carried out to investigate the geometric structures of isolated coumarins and hydrogen-bonded complexes in the ground and excited states, respectively. According to our results and analysis, the rapid anisotropy decays observed here in hydrogen-bonding systems may be associated with the strengthening of hydrogen bonds B or C, or both in the excited state of hydrogen-bonded coumarin–solvent complexes, and are independent of the breaking of hydrogen bond A. The strengthening of hydrogen bond C in the excited state of 7-aminocoumarin–DMF and 7-aminocoumarin–DMSO complexes has been demonstrated theoretically for the first time. Further experimental studies would be crucial to confirm this observation.
Co-reporter:Shuo Chai, Guang-Jiu Zhao, Peng Song, Song-Qiu Yang, Jian-Yong Liu and Ke-Li Han
Physical Chemistry Chemical Physics 2009 vol. 11(Issue 21) pp:4385-4390
Publication Date(Web):23 Mar 2009
DOI:10.1039/B816589K
In the present work, the excited-state double proton transfer (ESDPT) in 2-aminopyridine (2AP)/acid systems has been reconsidered using the combined experimental and theoretical methods. The steady-state absorption and fluorescence spectra of 2AP in different acids, such as formic acid, acetic acid, propionic acid, etc. have been measured. We demonstrated for the first time that the ESDPT reaction can take place between 2AP and all of these acids due to the formation of the intermolecular double hydrogen bonds. Furthermore, the vitally important role of the intermolecular double hydrogen bonds between 2AP and acids for ESDPT reaction has also been confirmed by the disappearance of ESDPT when we add the polar acetonitrile to the 2AP/acids systems. This may be due to that the respective polar solvation of 2AP and acids by the acetonitrile solvent disrupts the formation of intermolecular double hydrogen bonds between 2AP and acids. Moreover, the intermolecular double hydrogen bonds are demonstrated to be significantly strengthened in the electronic excited state of 2AP/acid systems using the time-dependent density functional theory (TDDFT) method. The ESDPT reaction is facilitated by the electronic excited-state hydrogen bond strengthening. In addition, potential energy curves of the electronic excited state along the proton transfer coordinate are also calculated by the TDDFT method. The stepwise mechanism of the ESDPT reaction in the 2AP/acid systems is theoretically reconfirmed, and the concerted mechanism is theoretically excluded. At the same time, the sequence of the double proton transfers is theoretically clarified for the first time using the potential energy curves calculated by TDDFT method.
Co-reporter:Panwang Zhou, Jianyong Liu, Peng Song, Keli Han, Guozhong He
Journal of Luminescence 2009 Volume 129(Issue 3) pp:283-289
Publication Date(Web):March 2009
DOI:10.1016/j.jlumin.2008.10.002
The rotational reorientation dynamics of rhodamine 700 (LD700) in the first (S1) and the fifth (S5) excited state in three aprotic polar solvents have been investigated using femtosecond time-resolved stimulated emission pumping fluorescence depletion (FS TR SEP TD) spectroscopy. In both excited states, the overall rotational relaxation of LD700 occurs on a time scale of 40–230 ps depending on the solvent, and a quantitative analysis of this time constant has been performed using the Stokes–Einstein–Debye (SED) hydrodynamic theory combined with the extended charge distribution model developed by Alavi and Waldeck. The experimentally measured reorientation times for LD700 in S5 are smaller than those in S1, which is in accord with the predictions by the SED theory. In addition, for LD700 in S5, a rapid initial decrease on the time scale less than 0.5 ps has been found. According to our analysis, this fast component may account for the rapid internal conversion from S5 to S1, and the rate of internal conversion was found to be sensitive to the solvent polarity.
Co-reporter:Tian-Shu Chu, António J.C. Varandas, Ke-Li Han
Chemical Physics Letters 2009 Volume 471(4–6) pp:222-228
Publication Date(Web):26 March 2009
DOI:10.1016/j.cplett.2009.02.049
Abstract
Using time-dependent nonadiabatic and adiabatic wave packet methods, we investigate nonadiabatic effects in collisions of D+(H+) with H2(D2) for collision energies from 1.7 to 2.5 eV. A new accurate diabatic potential energy surface [L.P. Viegas, A. Alijah, A.J.C. Varandas, J. Chem. Phys. 126 (2007) 74309] of the system fitted from full multireference configuration interaction calculations with a cc-pV5Z basis set is incorporated into the quantum calculations of initial state resolved integral cross sections. Comparison with previous calculations and experimental measurements are used to give insight on the nonadiabatic charge transfer process and isotope effect.
The Journal of Physical Chemistry A 2009 Volume 113(Issue 16) pp:4788-4794
Publication Date(Web):December 2, 2008
DOI:10.1021/jp8083666
Time-dependent density functional theory (TDDFT) method was performed to investigate the excited state electronic structures and photochemistry of a variety of heterocyclic annulated perylene (HAP) materials. The calculated electronic structures and photochemical properties of the newly synthesized S-, Se-, and N-heterocyclic annulated perylenes were in good agreement with the experimental results. Moreover, the O-, C-, Si-, and B-heterocyclic annulated perylenes were also theoretically designed and investigated by using the same computational methods in this work. As a result, we found that the electronic structures and photochemical properties of S-, Se-, N-, O-, and C-heterocyclic annulated perylenes are similar to each other. The energy levels of the LUMO orbital for the S-, Se-, N-, O-, and C-heterocyclic annulated perylenes become higher than those of unsubstituted perylene. At the same time, the energy gaps between LUMO and HOMO for these heterocyclic annulated perylenes are also increased in comparison with those of unsubstituted perylene. Hence, both absorption and fluorescence spectra of S-, Se-, N-, O-, and C-heterocyclic annulated perylenes are correspondingly blue-shifted relative to those of unsubstituted perylene. In addition, two bonds formed by heteroatoms with perylene are lengthened in the electronic excited state of S-, Se-, N-, O-, and C-heterocyclic annulated perylenes. On the contrary, these bonds formed by heteroatoms with perylene are shortened in the electronic excited state of Si- and B-heterocyclic annulated perylenes. Furthermore, energy levels of the LUMO orbital for Si- and B-heterocyclic annulated perylenes become significantly lowered in comparison with that of unsubstituted perylene. At the same time, energy gaps between LUMO and HOMO for Si- and B-heterocyclic annulated perylenes become decreased relative to those of unsubstituted perylene. Thus, both absorption and fluorescence spectra of Si- and B-heterocyclic annulated perylenes are significantly red-shifted in comparison with those of unsubstituted perylene. The differences of electronic structures and photochemistry of these heterocyclic annulated perylene materials can be ascribed to the electron delocalization of LUMO orbital from heteroatom into the perylene skeleton for Si- and B-heterocyclic annulated perylenes, because the electron of the LUMO orbital for S-, Se-, N-, O-, and C-heterocyclic annulated perylenes is localized on the heteroatoms.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2009 Volume 74(Issue 3) pp:753-757
Publication Date(Web):15 October 2009
DOI:10.1016/j.saa.2009.08.010
Experimental and theoretical methods have been used to investigate the relaxation dynamics and photophysical properties of the donor–acceptor compound 4′-(4-N,N-diphenylaminophenyl)-2,2′:6′,2″-terpyridine (DPAPT), a compound which is found to exhibit efficient intramolecular charge transfer emission in polar solvents with relatively large Stokes shifts and strong solvatochromism. The difference between the ground and excited state dipole moments (Δμ) is estimated to be 13.7 D on the basis of Lippert–Mataga models. To gain insight into the relaxation dynamics of DPAPT in the excited state, the potential energy curves for conformational relaxation are calculated. From the frontier molecular orbital (MO) pictures at the geometry of the twisted ICT excited state, the intramolecular charger transfer mainly takes place from HOMO (triphenylamine) to LUMO (terpyridine) in this donor–acceptor system.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2009 Volume 71(Issue 5) pp:2016-2022
Publication Date(Web):January 2009
DOI:10.1016/j.saa.2008.07.044
The ground state and lowest triplet-state structures of [Re(4,4′-(COOEt)2-2,2′-bpy)(CO)3py]PF6 photosensitizer (bpy = bipyridine, py = pyridine) have been studied with density functional theory (DFT). Time-dependent density functional theory (TD-DFT) was carried out to predict the photophysical properties of the photosensitizer. The effects of the solvents were evaluated using the conductor-like polarizable continuum (CPCM) method in dichloromethane, chloroform, acetonitrile, acetone, ethanol and dimethylsulfoxide. The electronic transition energies computed with BLYP, MPWPW91, B3LYP and MPW1PW91 functionals are compared with the experimental spectra. Based on the calculated excited energies, the experimental absorption maximum is assigned as metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT) mixed transition, and the luminescence originates from the lowest triplet state that is ascribed as the mixed transition of MLCT/LLCT.
Co-reporter:Shu-Hao Wen, An Li, Junling Song, Wei-Qiao Deng, Ke-Li Han and William A. Goddard III
The Journal of Physical Chemistry B 2009 Volume 113(Issue 26) pp:8813-8819
Publication Date(Web):June 9, 2009
DOI:10.1021/jp900512s
We report a simple first-principles-based simulation model (combining quantum mechanics with Marcus−Hush theory) that provides the quantitative structural relationships between angular resolution anisotropic hole mobility and molecular structures and packing. We validate that this model correctly predicts the anisotropic hole mobilities of ruberene, pentacene, tetracene, 5,11-dichlorotetracene (DCT), and hexathiapentacene (HTP), leading to results in good agreement with experiment.
Co-reporter:Xian-Fang Yue, Ju-Long Sun, Hong-Ming Yin, Qiang Wei and Ke-Li Han
The Journal of Physical Chemistry A 2009 Volume 113(Issue 14) pp:3303-3310
Publication Date(Web):March 13, 2009
DOI:10.1021/jp810731d
Photodissociation of methyl nitrite and n-butyl nitrite at 266 and 355 nm has been investigated in the gas phase at room temperature. OH photoproducts were observed, and their internal state distributions were measured by the one-photon laser-induced fluorescence (LIF) technique. It was found that the nascent OH from the 266 nm photolysis of methyl nitrite was vibrationally cold, and its rotational state distribution conformed to a Boltzmann behavior with a rotational temperature of Trot = 2200 ± 150 K. In contrast, the nascent OH from the 266 nm photolysis of n-butyl nitrite was found to be vibrationally excited, and the measured relative population of v′′ = 0:1 was 0.78:0.22. The rotational state distribution of the OH v′′ = 1 state conformed to Boltzmann behavior, with a rotational temperature of Trot = 1462 ± 120 K. However, a simple Boltzmann distribution was not found for the OH v′′ = 0 state. In the photolysis of n-butyl nitrite at 355 nm, the OH fragment was found to be vibrationally cold and its rotational state distribution showed non-Boltzmann behavior. A photodissociation mechanism involving an intramolecular hydrogen atom transfer process is proposed for the OH product pathway for methyl nitrite, which has been compared with the potential energy surfaces obtained from density functional theory (DFT) calculations. A photodissociation mechanism of n-butyl nitrite is also proposed for the OH product pathway, which differs from that of methyl nitrite due to the effects of the different alkoxy substituents.
Co-reporter:Emilia L. Wu, Kin-Yiu Wong, Xin Zhang, Keli Han and Jiali Gao
The Journal of Physical Chemistry B 2009 Volume 113(Issue 8) pp:2477-2485
Publication Date(Web):February 3, 2009
DOI:10.1021/jp808182y
Acutolysin A, which is isolated from the snake venom of Agkistrodon acutus, is a member of the SVMPs subfamily of the metzincin family, and it is a snake venom zinc metalloproteinase possessing only one catalytic domain. The catalytic zinc ion, in the active site, is coordinated in a tetrahedral manner with three imidazole nitrogen atoms of histidine and one oxygen atom. It is uncertain whether this oxygen atom is a water molecule or a hydroxide ion just from the three-dimensional X-ray crystal structure. The identity of the fourth ligand of zinc is theoretically determined for the first time by performing both combined quantum mechanical and molecular mechanical (QM/MM) simulation and high-level quantum mechanical calculations. All of the results obtained indicate that the fourth ligand in the active site of the reported X-ray crystal structure is a water molecule rather than a hydroxide anion. On the basis of these theoretical results, we note that the experimental observed pH dependence of the proteolytic and hemorrhagic activity of Acutolysin A can be attributed to the deprotonation of the zinc-bound water to yield a better nucleophile, the hydroxide ion. Structural analyses revealed structural details useful for the understanding of acutolysin catalytic mechanism.
The Journal of Physical Chemistry A 2009 Volume 113(Issue 52) pp:14329-14335
Publication Date(Web):May 29, 2009
DOI:10.1021/jp903200x
Time-dependent density functional theory method was performed to investigate the intramolecular and intermolecular hydrogen bonding in both the singlet and triplet electronic excited states of aminofluorenones AF, MAF, and DMAF in alcoholic solutions as well as their important roles on the excited-state photophysical processes of these aminofluorenones, such as internal conversion, intersystem crossing (ISC), twisted intramolecular charge transfer (TICT), and so forth. The intramolecular hydrogen bond C═O···H−N can be formed between the carbonyl group and amino group for the isolated AF and MAF. However, no intramolecular hydrogen bond for DMAF can be formed. At the same time, the most stable conformation of DMAF is out-of-plane structure, where the two dihedral angles formed between dimethyl groups and fluorenone plane are 163.1° and 41.74°, respectively. The formation of intramolecular hydrogen bond for AF and MAF is tightly associated with the intersystem crossing of these aminofluorenones. Furthermore, the ISC process can be dominantly determined by the change of intramolecular hydrogen bond between S1 and T1 states of aminofluorenones. Since the change of hydrogen bond between S1 and T1 states of AF is stronger than that of MAF, the rate of ISC process for AF is faster than that for MAF. Moreover, the rate constant of the ISC process of DMAF is nearly close to zero because of the absence of intramolecular hydrogen bond. On the other hand, the intermolecular hydrogen bond C═O···H−O can be also formed between all aminofluorenones and alcoholic solvents. The internal conversion process from S1 to S0 state of these aminofluorenones is facilitated by the intermolecular hydrogen bond strengthening in the electronic excited state of aminofluorenones because of the decrease of energy gap between S1 and S0 states. At the same time, the change of intermolecular hydrogen bond between S1 and T1 states for AF is much stronger than that for MAF, which may also contribute to the faster ISC process for AF than that for MAF in the same solvents. The TICT process plays an important role in the deactivation of the photoexcited DMAF, since the TICT process along the twisted dihedral angle is nearly barrierless in the S1 state of DMAF. However, the TICT cannot take place for AF and MAF because of the presence of the intramolecular hydrogen bond.
Density functional theory calculations have been carried out to elucidate the mechanism of cyclohexane hydroxylation by three possible isomers of [FeIV(O)(N-R-N,N′,N′-tris(2-pyridylmethyl)ethane-1,2-diamine)]2+ (R is methyl or benzyl) (Klinker et al. in Angew Chem Int Ed 44:3690–3694, 2005). The calculations offer a mechanistic view and reveal the following features: (a) all the three isomers possess triplet ground states and low-lying quintet excited states, (b) the relative stability follows the order isomer A > isomer B > isomer C, in agreement with the conclusions of Klinker et al., (c) the theoretical investigations provide a rationale to explain the interconversion of the three isomers, (d) the reaction pathways of the C–H hydroxylation are initiated by a hydrogen-abstraction step, and (e) the three isomers react with cyclohexane via two-state-reactivity patterns on competing triplet and quintet spin-state surfaces. As such, in the gas phase, the relative reactivity exhibits the trend isomer B > isomer A, while at the highest level, B2//B1 with zero point energy and solvation corrections, the relative reactivity follows the order isomer B > isomer A > isomer C. Thus, the calculated reaction pathway shows that pyridine rings perpendicular to the Fe–O axis result in more reactive species, and a pyridine ring coordinated trans to the oxygen atom leads to the least reactive isomer.
Physical Chemistry Chemical Physics 2008 vol. 10(Issue 18) pp:2431-2441
Publication Date(Web):05 Mar 2008
DOI:10.1039/B715180B
It is essential to evaluate the role of Coriolis coupling effect in molecular reaction dynamics. Here we consider Coriolis coupling effect in quantum reactive scattering calculations in the context of both adiabaticity and nonadiabaticity, with particular emphasis on examining the role of Coriolis coupling effect in reaction dynamics of triatomic molecular systems. We present the results of our own calculations by the time-dependent quantum wave packet approach for H + D2 and F(2P3/2,2P1/2) + H2 as well as for the ion–molecule collisions of He + H2+, D− + H2, H− + D2, and D+ + H2, after reviewing in detail other related research efforts on this issue.
Co-reporter:Lihua Kang, Weiqiao Deng, Tao Zhang, Zhongmin Liu, Ke-Li Han
Microporous and Mesoporous Materials 2008 Volume 115(Issue 3) pp:261-266
Publication Date(Web):1 November 2008
DOI:10.1016/j.micromeso.2008.01.042
We theoretically investigate the properties of the IM-12 to address a catalyst for acidic conversion reaction of larger organic molecules. The acidic characteristics of the IM-12 are investigated by density functional theory (DFT) considering both the local density and generalized gradient approximations, LDA and GGA, respectively. Based on quantum mechanical (QM) calculation results, we find that the zeolite with Al element prefers the tetrahedral (T) sites, T4 and T6, when replacing Si in IM-12 framework. Isomorphously substituted IM-12 on the T4 and T6 sites by B, Al, and Ga is studied, respectively. Both of the sites give the Brönsted acidity order: B–IM-12 < Ga–IM-12 < Al–IM-12, which is the same as other zeolites. The calculated NH3 adsorption energies are compared with the calculated and experimental results of H–[Al]MOR [M. Elanany, D.P. Vercauteren, M. Koyama, M. Kubo, P. Selvam, E. Broclawik, A. Miyamoto, J. Mol. Catal. A 243 (2006) 1; C. Lee, D.J. Parrillo, R.J. Gorte, W.E. Farneth, J. Am. Chem. Soc. 118 (1996) 3262]. Molecular dynamics (MD) results show that IM-12 zeolite allows the large molecules such as diisopropylbenzene (DIPB) and triisopropylbenzene (TIPB) to diffuse faster than those in MOR zeolite and IM-12 may have significant selectivity for TIPB over DIPB. We conclude that the IM-12 with Al impurity would be a good candidate for large organic molecule acidic conversion reaction.
Co-reporter:Lihua Kang, Weiqiao Deng, Keli Han, Tao Zhang, Zhongmin Liu
International Journal of Hydrogen Energy 2008 Volume 33(Issue 1) pp:105-110
Publication Date(Web):January 2008
DOI:10.1016/j.ijhydene.2007.08.027
The coordination of extra-framework Li+Li+ in faujasite (FAU) and the interaction between H2 and Li-FAU were studied by the generalized-gradient approximation (GGA) of density functional theory (DFT) with the Perdew–Burke–Ernzerhof (PBE) exchange-correction functional. Four adsorption sites have been found to be stable for Li+Li+: site SI′SI′, the most stable one, in the sodalite cage; site SII in the six-ring windows of the sodalite unit and sites SIII and SIII′SIII′ in the supercage. Hydrogen interacting with these sites prefers the side-on coordination geometry. Calculated adsorption energies decrease in the sequence of SIII′>SIII>SI′>SIISIII′>SIII>SI′>SII, consistent with the calculated Li–H distance and the charge on H2. The H–H stretching frequencies of adsorbed species at 4286–4346cm-1 are by about 7–67cm-1 lower than in the free hydrogen molecules. The small bathochromic harmonic H2 frequency shift is in agreement with the small H2 bond elongation.
Co-reporter:Ruikui Chen, Guangjiu Zhao, Xichuan Yang, Xiao Jiang, Jifeng Liu, Haining Tian, Yan Gao, Xien Liu, Keli Han, Mengtao Sun, Licheng Sun
Journal of Molecular Structure 2008 Volume 876(1–3) pp:102-109
Publication Date(Web):30 March 2008
DOI:10.1016/j.molstruc.2007.05.045
Novel thiophene-π-conjugated donor–acceptor molecules, 5-[2-(1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinolin-6-yl)-vinyl]-thiophene-2-carbaldehyde (QTC) and (1-cyano-2-{5-[2-(1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinolin-6-yl)-vinyl]-thiophen-2-yl}-vinyl)-phosphonic acid diethyl ester (QTCP), were designed and synthesized. Combined experimental and theoretical methods were performed to investigate the photoinduced intramolecular charge-transfer (ICT) processes of these compounds. Steady-state absorption and fluorescence measurements in different solvents indicate the photoinduced ICT characters of QTC and QTCP. Solvent dependency of the large Stokes shifts and high dipole moment of the excited state also support the charge-transfer character of the excited state. Theoretical calculations based on time-dependent density functional theory (TDDFT) method were performed to investigate ICT states of these compounds. The results reveal that the excited states have adopted a distortion of the CC double bond between the donor moiety and the thiophene-π-bridge.
Chemical Physics Letters 2008 Volume 453(1–3) pp:29-34
Publication Date(Web):20 February 2008
DOI:10.1016/j.cplett.2008.01.015
Detailed dynamic simulation study on the excited-state torsional dynamics of the gas phase 9,9′-bianthryl (BA) following photoexcitation to its S1 state by a femtosecond laser pulse has been reported for the first time. The novel oscillation behavior with the torsional coordinate between the two symmetric potential minima of the S1 state is observed by real-time monitoring dihedral angles formed by the two anthracene moieties. The dihedral angles are twisted between 60° and 120°. At the same time, the central C–C bond is shortened following the conformational torsion. Our simulation results are in good agreement with the previous spectroscopic studies.Dynamic simulation study on the excited-state torsional dynamics of 9,9′-bianthryl following photoexcitation to S1 state by a femtosecond laser pulse.
Co-reporter:Shu-Hao Wen ; Wei-Qiao Deng ;Ke-Li Han
The Journal of Physical Chemistry C 2008 Volume 112(Issue 32) pp:12195-12200
Publication Date(Web):July 17, 2008
DOI:10.1021/jp801893f
By using first-principles calculations within the frame of the density functional theory, we have investigated the encapsulation of metal atoms (Li, Na, Be, Mg, and Ti) in a B36N36 cage and the effects of endohedral metal atoms on hydrogen storage in the B36N36. The calculations showed that the chemisorption energies of the H on the B36N36 cage shell can be modified by the charged endohedral metal atom in the B36N36 cage, due to the electrostatic interaction and polarization of the cage electrons. Endohedral metal atoms also exert influences on H2 molecules residing inside the B36N36 cage. For Ti@B36N36, we predict a high hydrogen content (8 wt %) structure with a full H coverage on the outer cage shell and with the Kubas complex in the inner cavity.
The ultrafast dynamics of oxazine 750 dye was studied in methanol, ethanol, 1-propanol, 1-butanol solvents using the femtosecond time-resolved stimulated emission pumping fluorescence depletion (FS TR SEP FD) technique. The faster decays on the hundreds of femtosecond time scale and the slower decays on the order of picosecond were found. The intramolecular vibrational redistribution (IVR) and the solute-solvent intermolecular photoinduced electron transfer (ET) should account for the faster decay, while the slower decay is attributable to the diffusive solvent relaxation. The results show that the intermolecular hydrogen-bonding network will hinder the rearrangement of the alcoholic molecules in the solvation process and the time constants of the slower diffusive solvent relaxation decays are found to increase with the hydrogen-bonding energy in alcoholic solvents.
Chemistry - A European Journal 2008 Volume 14( Issue 28) pp:8704-8714
Publication Date(Web):
DOI:10.1002/chem.200800277
Abstract
Molecular dynamics (MD) simulations followed by molecular mechanics generalized Born surface area (MM-GBSA) analyses have been carried out to study the selectivity of two neutral and weakly basic P1 group inhibitors (177 and CDA) to thrombin and trypsin. Detailed binding free energies between these inhibitors and individual protein residues are calculated by using a per-residue basis decomposition method. The analysis of the detailed interaction energies provides insight on the protein–inhibitor-binding mechanism and helps to elucidate the basis for achieving selectivity through interpretation of the structural and energetic results from the simulations. The study shows that the dominant factor of selectivity for both inhibitors is van der Waals energy, which suggests better shape complementarity and packing with thrombin. Nonpolar solvation free energy and total entropy contribution are also in favor of selectivity, but the contributions are much smaller. Binding mode and structural analysis show that 177 binds to thrombin and trypsin in a similar binding mode. In contrast, the CDA binds to thrombin and trypsin in very different modes.
Co-reporter:Xiao-Jing Liu, Ke-Li Han, Shu-Tao Sun, Zi-Chao Tang, Zheng-Bo Qin and Zhi-Feng Cui
The Journal of Physical Chemistry A 2008 Volume 112(Issue 30) pp:6850-6858
Publication Date(Web):July 10, 2008
DOI:10.1021/jp711459x
The pyridyl−lead complexes [Pbm−C5H4N]− (m = 1−4), which are produced from the reactions between lead clusters formed by laser ablation and the pyridine molecules seeded in argon carrier gas, are studied by photoelectron (PE) spectra and density functional theory. The adiabatic electron affinity (EA) of [PbmC5H4N]− is obtained from PE spectra at photon energies of 308 and 193 nm. Theoretical calculation is carried out to elucidate their structures and bonding modes. A variety of geometries for the isomers are optimized to search for the lowest-energy geometry. By comparing the theoretical results, including the EA and simulated density of state spectra, with the experimental determination, the lowest-energy structures for each species are obtained. The following analysis of the molecular orbital composition provides the evidence that the pyridyl binds on lead clusters through the Pb−C σ bond. Moreover, there is an apparent spin-state transition from triplet state toward singlet state for the ground-state structure of [PbmC5H4N]− with an increase of lead cluster.
Chemical Physics Letters 2007 Volume 442(1–3) pp:17-20
Publication Date(Web):6 July 2007
DOI:10.1016/j.cplett.2007.05.061
The time-dependent-wave-packet method has been applied to calculate the photoelectron spectra of Br2 molecule with zero time delay. Meanwhile, Br+ ion that mainly resulted from the dissociation of Br2 (C1Πu) can be seen in the photoelectron spectra of Br2 molecule. We presume that more Br atoms will be ionized later, as the dissociation is nearly complete. In addition, it is found that Br2+(X2Σg+) has the largest increasing rate as the increase of the laser intensities.The time-dependent-wave-packet method has been applied to calculate the time-resolved photoelectron spectra of Br2 molecule. The calculated results are in good agreement with experimental ones. Some phenomena have been revealed.
Journal of Photochemistry and Photobiology A: Chemistry 2007 Volume 187(2–3) pp:305-310
Publication Date(Web):15 April 2007
DOI:10.1016/j.jphotochem.2006.10.027
The charge transfer mechanism of a synthesized near-infrared (NIR) heptamethine cyanine dye has been studied with 3D real space analysis method. A new phenomenon about the intramolecular charge transfer (ICT) process is observed: the sulfonate (–SO3−) groups are mainly concerned with the ICT process. The electrons can transfer from the sulfonate (–SO3−) groups to the bridgehead amine and the electron-defect conjugated system. And the absorption and fluorescence spectra of the ICT state in alcoholic and aprotic solvents are analyzed. The spectral regularities are explained by the Kamlet and Taft (π*, α, β) scale and the ICT mechanism. Specific hydrogen-bonding interactions between the solute and solvent are considered to explain the different spectral regularities of the dye in alcoholic and aprotic solvents.
Co-reporter:Yong Wang;Chuanlu Yang ;Hongming Wang Dr. ;Sason Shaik
ChemBioChem 2007 Volume 8(Issue 3) pp:
Publication Date(Web):12 JAN 2007
DOI:10.1002/cbic.200600510
Breaking the habit. A new mechanism, called reversed dual hydrogen abstraction (R-DHA), is presented for ethanol oxidation by cytochrome P450 2E1 (CYP2E1). It is shown that the competition of R-DHA with the consensus mechanism (gem-diol) is modulated by the ethanol population in the enzyme pocket. Thus, as a response to growing blood ethanol level, CYP2E1 adapts its ethanol metabolism by a mechanistic switch from gem-diol to R-DHA.
Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2007 Volume 8(Issue 2) pp:55-66
Publication Date(Web):October 2007
DOI:10.1016/j.jphotochemrev.2007.03.002
In recent years, the photodissociation dynamics of aryl halides has been a subject of intensive studies, which is closely related to the atmospheric chemistry. Here we present a review on the photochemistry of aryl halides, with emphasis on the recent progress in photodissociation dynamics at 266 nm by using photofragment translational spectroscopy. The ab initio calculations have also been employed to investigate those photodissociation processes. It has been found that the photodissociation of aryl halides at 266 nm is attributed to the nonadiabatic process via intersystem crossings from bound singlet excited state to triplet excited state and/or via internal conversion from bound singlet excited state to ground state. Also, the substitution effects in the photodissociation dynamics of aryl halides are discussed.
The mechanism of aldehyde to carboxylic acid conversion catalyzed by P450 enzymes via a series of reactions was studied systematically for the first time with density functional theory calculations. A two-state reactivity mechanism has been proposed, which can be adopted for many aldehyde oxidation reactions catalyzed by P450 enzymes. The mechanism involves initial hydrogen abstraction as the rate-limiting step and this is followed by steps of oxygen rebound without barriers owing to the quick recombination of the resultant radical species. Meanwhile, in an attempt to explore whether there exist some rules for the hydroxylation of aldehyde substrates by P450, the transition state barriers of the rate-limiting step for a series of aldehyde hydroxylation reactions have been compared. A predictive pattern of extended barrier/bond energy correlation for different hydroxylations of aldehyde substrates by P450 has been established, which was further confirmed to be a reliable reactivity scale by experimental results.
Co-reporter:Yamin Li, Julong Sun, Keli Han, Guozhong He, Zhuangjie Li
Chemical Physics Letters 2006 Volume 421(1–3) pp:232-236
Publication Date(Web):3 April 2006
DOI:10.1016/j.cplett.2006.01.055
Abstract
Photodissociation of gaseous nitroethane at 266 nm has been studied by monitoring the NO(X2Π) product using laser-induced fluorescence technique. Rotational state distributions of the NO(X2Π1/2 and X2Π3/2, v″ = 0) photofragment have been measured and characterized by Boltzmann temperature of 810 ± 100 K. Only the NO photoproduct in v″ = 0 state can be observed in the present work. The geometries of the nitroethane, the ethyl nitrite and the transition state connecting the two isomeric structures have been investigated using ab initio method. The photodissociation dynamics of nitroethane is discussed on the basis of experimental observation and calculation results.
Co-reporter:António J.C. Varandas, Tian-Shu Chu, Ke-Li Han, Pedro J.S.B. Caridade
Chemical Physics Letters 2006 Volume 421(4–6) pp:415-420
Publication Date(Web):15 April 2006
DOI:10.1016/j.cplett.2006.01.073
Abstract
We report accurate close coupling quantum wave packet calculations of the rate constant for the reaction N(2D) + H2 → NH + H using a recently reported single-sheeted double many-body expansion potential energy surface for NH2(12A″) that has been calibrated from high level ab initio MRCI energies. Results from quasi-classical trajectories run on the same potential energy surface are also given, and used to rationalize the quantum ones. The calculated rotationally averaged rate constant is found to be in good agreement with experimental data. A comparison with other theoretical results is also presented.
Co-reporter:Xiaofang Chen, Xin Zhang, Keli Han, António J.C. Varandas
Chemical Physics Letters 2006 Volume 421(4–6) pp:453-459
Publication Date(Web):15 April 2006
DOI:10.1016/j.cplett.2005.12.103
Abstract
The mechanism of the H + ClONO2 reaction is examined by performing QCISD calculations at geometries optimized at the MP2 level. Each of the six reaction channels involves stereoisomeric transition states that have identical energy barriers. The lowest energy barrier is 24.2 kcal mol−1 for the indirect metathetical pathway leading to OH + cis-ClONO, being the corresponding rate constant calculated employing TST theory. The NO2-elimination channel and the indirect metathetical pathway leading to OH + trans-ClONO should compete with each other as they have barriers of 24.8 and 25.1 kcal mol−1. For Cl-substitution, Cl-abstraction, and N-attack, the barriers are 27.4, 35.1, and 41.3 kcal mol−1.
Chemical Physics Letters 2006 Volume 424(4–6) pp:243-246
Publication Date(Web):24 June 2006
DOI:10.1016/j.cplett.2006.03.101
First principles quantum dynamics calculation has been carried out to investigate a recently observed resonance feature in the F + CH4 reaction by molecular beam experiment [W.C. Shiu, J.J. Lin, K.P. Liu, Phys. Rev. Lett., 92 (2004) 103201]. The generalized semi-rigid vibrating rotor target (GSVRT) method is employed to perform the quantum dynamics calculation on new ab initio potential energy surfaces (PES) constructed from the extensive high level ab initio calculations. A resonance near the reaction threshold energy is observed in both the calculated microscopic reaction probabilities and integral cross-sections on the ZYH2 PES. The calculated resonance on the ZYH2 PES is in good agreement with the experimental observation. This resonance feature is highly quantum mechanical and sensitive to the accuracy of ab initio energies.The present quantum dynamics calculation is very sensitive to the ab initio calculation level. The dynamics calculation performed on the ZYH2 PES, constructed at QCISD(T)/6-311++G(3df,2p) level, predicted the resonance in close agreement with experimental measurement, while that on the ZYH1 PES at QCISD/6-311++G(3df,2p) level failed to do so.
The product rotational polarization of the reaction Cl + C3H8 → C3H7 + HCl is calculated via the quasiclassical trajectory method based on extended London–Eyring–Polanyi–Sato potential energy surface (PES) at collision energies of 6.0, 7.4, and 8.0 kcal/mol. Compared the dynamics of Cl substituting the primary and secondary hydrogen of C3H8, four polarization dependent generalized differential cross-sections (2π/σ)(dσ00/dωt), (2π/σ)(dσ20/dωt), (2π/σ)(dσ22+/dωt) and (2π/σ)(dσ21−/dωt) have been presented in the center of mass frame, respectively. The distribution of dihedral angle p(ϕr), the distribution of angle between k and j′, p(θr), and the angular distribution of product rotational vectors in the form of polar plots in θr and ϕr are calculated as well. The different character of the abstraction of primary vs. secondary hydrogen atoms from C3H8 may be ascribed to that the different PESs and substituent site. The calculated results are in agreement with the experimental data.
Co-reporter:Jing Li, Yong-Quan Qu, Ke-Li Han, Guo-Zhong He
Surface Science 2005 Volume 586(1–3) pp:45-55
Publication Date(Web):20 July 2005
DOI:10.1016/j.susc.2005.04.050
Density functional theory simulations with cluster model are performed to investigate the reaction mechanism of CH2CH–CH2OH on the bare Si(1 0 0)-2 × 1 and Ge(1 0 0)-2 × 1 surfaces and probe the factors that control the competition and selectivity of organic functionalization on the clean semiconductor surfaces. Our calculations indicate that the reaction pathway via O–H dissociation is favored in kinetic factors on the Si(1 0 0)-2 × 1 and the Ge(1 0 0)-2 × 1 surfaces. The dissociation can occur on a single dimer or across two adjacent dimers along a dimer row. Some candidate rearrangements after the dissociation of O–H bond on the Si(1 0 0)-2 × 1 surface are also described.
Co-reporter:Ju-Long Sun, Haichuan Liu, Hong-Ming Wang, Ke-Li Han, Shihe Yang
Chemical Physics Letters 2004 Volume 392(4–6) pp:285-290
Publication Date(Web):11 July 2004
DOI:10.1016/j.cplett.2004.05.031
Abstract
Complexes of magnesium cation with cytosine were produced by laser ablation of a magnesia and cytosine mixture. Photo-induced reactions in the complexes of Mg+–cytosine have been studied at 230–440 nm. The evaporation product, Mg+, as well as other four and five reactive products were observed in the long and short wavelength regions, respectively. The ground state structures of the complexes composed of magnesium cation and the low-lying tautomers of cytosine were fully optimized at the B3LYP/6-31+G** level. The bond dissociation energies (BDEs) of the complexes for the channels we observed were calculated at the same theoretical level.
Co-reporter:Ting-Xian Xie, Yan Zhang, Mei-Yu Zhao and Ke-Li Han
Physical Chemistry Chemical Physics 2003 vol. 5(Issue 10) pp:2034-2038
Publication Date(Web):17 Apr 2003
DOI:10.1039/B300763D
In this paper, the three-dimensional time-dependent quantum wave packet calculation has been employed to study the non-adiabatic reaction dynamics of F+HD on three, electronically non-adiabatic potential energy surfaces fitted by Alexander, Stark and Werner (J. Chem. Phys., 2000, 113, 11084; named ASW). The integral cross-sections and branching ratio of the reaction as a function of collision energy are calculated. The integral cross-sections are compared with the experimental measurements and other theoretical results. For the reaction of F in its excited state with HD, the calculated function of integral cross sections as collision energy shows that a steplike feature near 0.9 kcal mol−1 probably arises from the collinear FHD geometry.
Co-reporter:Jia-Hai Wang, Ke-Li Han, Guo-Zhong He, Zhuangjie Li
Chemical Physics Letters 2003 Volume 368(1–2) pp:139-146
Publication Date(Web):14 January 2003
DOI:10.1016/S0009-2614(02)01810-9
Abstract
The reaction mechanism of C2+H2S has been investigated using ab initio method. On the basis of calculations using CCSD(T) in conjunction with 6-311++G(d, pd) basis set with the geometry optimized at MP2/6-311++G** level, the H-abstraction reaction on the triplet energy potential surface is an exothermic process with formation of a precomplex as an intermediate, which further dissociate to yield with an energy barrier of . The addition of to on leads to a bound intermediate (3,3-dihydrodicarbonsulfide), which can further isomerize into HSCCH(1A) (thiohydroxyacetylene) in a one-step hydrogen migration process.
Co-reporter:Xi-Bin Gu, Guang-Jun Wang, Jian-Hua Huang, Ke-Li Han, Guo-Zhong He and Nan-Quan Lou
Physical Chemistry Chemical Physics 2002 vol. 4(Issue 24) pp:6027-6033
Publication Date(Web):05 Nov 2002
DOI:10.1039/B205228H
The photodissociation dynamics of m-, o- and p-chlorotoluene at 266 nm was studied using the universal crossed molecular beams machine and photofragment translational spectroscopy (PTS) technique. The time-of-flight (TOF) spectra of Cl and C7H7 photofragments were measured at different angles. By employing both forward convolution method and least-squares fitting method, the TOF spectra of photofragments (Cl and C7H7) and the angular distribution of Cl are fitted, at the same time the translational energy distributions of photofragment and anisotropy parameters (β) have been derived. The geometries of the ground state, the first excited state and the triplet state have been optimized using CASSCF(8,7)/6-311G** method. The transition electronic dipole moments were calculated at the CIS/6-311G* level. The calculation results are in good agreement with the experiment. Plausible photodissociation mechanisms are proposed and the substitution effects of methyl are discussed.
Co-reporter:Ming-Jun Yang, Xue-Qin Pang, Xin Zhang, Ke-Li Han
Journal of Structural Biology (January 2011) Volume 173(Issue 1) pp:57-66
Publication Date(Web):1 January 2011
DOI:10.1016/j.jsb.2010.07.013
Two GTPases in the signal recognition particle (SRP) and SRP receptor (SR) interact with one another to mediate the cotranslational protein targeting pathway. Previous studies have shown that a universally conserved SRP RNA facilitates an efficient SRP–SR interaction in the presence of a signal sequence bound to SRP. However, a remarkable exception has been found in chloroplast SRP (cpSRP) pathway, in which the SRP RNA is missing. Based on biochemical and structural analyses, it is proposed that free cpSRP receptor (cpFtsY) has already been preorganized into a closed state for efficient cpSRP–cpFtsY association. However, no direct evidence has been reported to support this postulation thus far. In this study, we characterized the structural dynamics of cpFtsY and its conformational rearrangements induced by GTP binding using molecular dynamics (MD) simulations. Our results showed that the GTP-binding event triggered substantial conformational changes in free cpFtsY, including the relative orientation of N–G domain and several conserved motifs that are critical in complex formation. These rearrangements enabled the cpFtsY to relax into a preorganized ‘closed’ state that favored the formation of a stable complex with cpSRP54. Interestingly, the intrinsic flexibility of αN1 helix facilitated these rearrangements. In addition, GTP binding in cpFtsY was mediated by conserved residues that have been shown in other SRP GTPases. These findings suggested that GTP-bound cpFtsY could fluctuate into conformations that are favorable to form the stable complex, providing explanation of why SRP–SR interaction bypasses the requirement of the SRP RNA at a molecular level.
Co-reporter:Emilia L. Wu, Ye Mei, KeLi Han, John Z.H. Zhang
Biophysical Journal (15 June 2007) Volume 92(Issue 12) pp:
Publication Date(Web):15 June 2007
DOI:10.1529/biophysj.106.099150
Molecular dynamics simulations followed by quantum mechanical calculation and Molecular Mechanics Poisson-Boltzmann Surface Area (MM-PBSA) analysis have been carried out to study binding of proline- and pyrazinone-based macrocyclic inhibitors (L86 and T76) to human α-thrombin. Detailed binding interaction energies between these inhibitors and individual protein fragments are calculated using DFT method based on a new quantum mechanical approach for computing protein-ligand interaction energy. The analysis of detailed interaction energies provides insight on the protein-ligand binding mechanism. Study shows that T76 and L86 bind to thrombin in a very similar “inhibition mode” except that T76 has relatively weaker binding interaction with Glu217. The analysis from quantum calculation of binding interaction is consistent with the MM-PBSA calculation of binding free energy, and the calculated free energies for L86/T76-thrombin binding agree well with the experimental data.
Biophysical Journal (1 January 2008) Volume 94(Issue 1) pp:
Publication Date(Web):1 January 2008
DOI:10.1529/biophysj.107.113738
The site-specific solvation of the photoexcited protochlorophyllide a (Pchlide a) in methanol solvent was investigated using the time-dependent density functional theory method for the first time to our knowledge. The intermolecular site-specific coordination and hydrogen-bonding interactions between Pchlide a and methanol molecules play a very important role in the steady-state and time-resolved spectra. All the calculated absorption and fluorescence spectra of the isolated Pchlide a and its coordinated and hydrogen-bonded complexes with methanol demonstrate that the novel fluorescence shoulder at ∼690 nm of Pchlide a in methanol should be ascribed to the coordinated and hydrogen-bonded Pchlide a-(MeOH)4 complex. This coordinated and hydrogen-bonded complex can also account for the intermediate state found in the time-resolved spectroscopic studies. Herein, we have theoretically confirmed that the intermolecular coordination and hydrogen bonds between Pchlide a and methanol molecules can be strengthened in the electronically excited state of Pchlide a. Furthermore, the site-specific solvation of the photoexcited Pchlide a can be induced by the intermolecular coordination and hydrogen-bond strengthening upon photoexcitation. Then the hydrogen-bonded intermediate state is formed in 22–27 ps timescales after the site-specific solvation. All the steady-state and time-resolved spectral features of Pchlide a in different solvents can be explained by the formation of this hydrogen-bonded intermediate state after the site-specific solvation, which is induced by the coordination and hydrogen-bond strengthening.
Physical Chemistry Chemical Physics 2008 - vol. 10(Issue 18) pp:NaN2441-2441
Publication Date(Web):2008/03/05
DOI:10.1039/B715180B
It is essential to evaluate the role of Coriolis coupling effect in molecular reaction dynamics. Here we consider Coriolis coupling effect in quantum reactive scattering calculations in the context of both adiabaticity and nonadiabaticity, with particular emphasis on examining the role of Coriolis coupling effect in reaction dynamics of triatomic molecular systems. We present the results of our own calculations by the time-dependent quantum wave packet approach for H + D2 and F(2P3/2,2P1/2) + H2 as well as for the ion–molecule collisions of He + H2+, D− + H2, H− + D2, and D+ + H2, after reviewing in detail other related research efforts on this issue.
Co-reporter:Panwang Zhou, Peng Song, Jianyong Liu, Keli Han and Guozhong He
Physical Chemistry Chemical Physics 2009 - vol. 11(Issue 41) pp:NaN9449-9449
Publication Date(Web):2009/08/21
DOI:10.1039/B910043A
The rotational reorientation dynamics of 7-aminocoumarin derivatives with different alkylation degrees in methanol, dimethylformamide, and dimethyl sulfoxide have been investigated using femtosecond time-resolved stimulated emission pumping fluorescence depletion (FS TR SEP FD) spectroscopy. In addition to a long anisotropy decay time that accounts for the overall rotational relaxation of solutes, a short anisotropy decay time on the order of picoseconds or sub-picoseconds was also observed in hydrogen-bonding systems. Three types of hydrogen bonds involving the nitrogen lone pair, carbonyl group, and amino group of 7-aminocoumarin derivatives were denoted as types A, B, and C, respectively. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were carried out to investigate the geometric structures of isolated coumarins and hydrogen-bonded complexes in the ground and excited states, respectively. According to our results and analysis, the rapid anisotropy decays observed here in hydrogen-bonding systems may be associated with the strengthening of hydrogen bonds B or C, or both in the excited state of hydrogen-bonded coumarin–solvent complexes, and are independent of the breaking of hydrogen bond A. The strengthening of hydrogen bond C in the excited state of 7-aminocoumarin–DMF and 7-aminocoumarin–DMSO complexes has been demonstrated theoretically for the first time. Further experimental studies would be crucial to confirm this observation.
Co-reporter:Shuo Chai, Guang-Jiu Zhao, Peng Song, Song-Qiu Yang, Jian-Yong Liu and Ke-Li Han
Physical Chemistry Chemical Physics 2009 - vol. 11(Issue 21) pp:NaN4390-4390
Publication Date(Web):2009/03/23
DOI:10.1039/B816589K
In the present work, the excited-state double proton transfer (ESDPT) in 2-aminopyridine (2AP)/acid systems has been reconsidered using the combined experimental and theoretical methods. The steady-state absorption and fluorescence spectra of 2AP in different acids, such as formic acid, acetic acid, propionic acid, etc. have been measured. We demonstrated for the first time that the ESDPT reaction can take place between 2AP and all of these acids due to the formation of the intermolecular double hydrogen bonds. Furthermore, the vitally important role of the intermolecular double hydrogen bonds between 2AP and acids for ESDPT reaction has also been confirmed by the disappearance of ESDPT when we add the polar acetonitrile to the 2AP/acids systems. This may be due to that the respective polar solvation of 2AP and acids by the acetonitrile solvent disrupts the formation of intermolecular double hydrogen bonds between 2AP and acids. Moreover, the intermolecular double hydrogen bonds are demonstrated to be significantly strengthened in the electronic excited state of 2AP/acid systems using the time-dependent density functional theory (TDDFT) method. The ESDPT reaction is facilitated by the electronic excited-state hydrogen bond strengthening. In addition, potential energy curves of the electronic excited state along the proton transfer coordinate are also calculated by the TDDFT method. The stepwise mechanism of the ESDPT reaction in the 2AP/acid systems is theoretically reconfirmed, and the concerted mechanism is theoretically excluded. At the same time, the sequence of the double proton transfers is theoretically clarified for the first time using the potential energy curves calculated by TDDFT method.
Co-reporter:Huan Yang, M. Hankel, Antonio Varandas and Keli Han
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 33) pp:NaN9623-9623
Publication Date(Web):2010/07/07
DOI:10.1039/C003930F
Nonadiabatic quantum dynamics calculations on the two coupled potential energy surfaces (PESs) (12A′ and 22A′) and also adiabatic quantum calculations on the lowest adiabatic PES are reported for the title reaction. Reaction probabilities for total angular momenta, J, varying from 0 to 160, are calculated to obtain the integral cross section (ICS) for collision energies ranging from 0.05 to 1.0 eV. Calculations using both the close coupling and the Centrifugal Sudden (CS) approximation are carried out to evaluate the role of Coriolis coupling effects for this reaction. The results of the nonadiabatic calculations show that the nonadiabatic effects in the title reaction for the initial state of NH (v = 0, j = 0) could be neglected, at least in the collision energy range considered in this study.
Co-reporter:Shu-Hao Wen, Wei-Qiao Deng and Ke-Li Han
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 32) pp:NaN9275-9275
Publication Date(Web):2010/07/07
DOI:10.1039/B923862J
The intermolecular electronic coupling (transfer integral) and the intramolecular vibronic coupling (reorganization energy) are key parameters determining the transport properties of organic electronic materials. Using quantum mechanism calculations, we revealed the correlation between the reorganization energies and the partial charge difference values on the conjugated acene backbone, which can be used to evaluate the reorganization energies for acene and acene derivative systems with the same conjugated backbone but different substitutional groups. We used rigorous quantitative functions to investigate the electronic coupling oscillation behavior in slipped-cofacial stacking acene and acene derivative molecules, and revealed characteristic parameters in the electronic coupling oscillation. We suggest using a similar strategy to establish the quantitative structure–activity relationship database for different families of organic semiconducting materials.
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 31) pp:NaN8918-8918
Publication Date(Web):2010/06/16
DOI:10.1039/B924549A
In this work, a new model compound, the twisted intramolecular charge transfer (TICT) excited state of Milrinone (MIR), has been theoretically presented. MIR exists in different tautomeric and ionic forms in aqueous solution with different pH values. The TICT excited state properties for various forms of MIR are demonstrated to be significantly different and controlled by the pH values of MIR in aqueous solution.
Co-reporter:Yang Yang, Lei Liu, Junsheng Chen and Keli Han
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 33) pp:NaN17834-17834
Publication Date(Web):2014/06/16
DOI:10.1039/C4CP01371A
The spontaneous and collision-assisted hydrogen-atom abstracting reaction (HA) dynamics of triplet benzil are investigated through the combination of transient absorption spectroscopy with TD-DFT calculations. HA dynamics exhibit a remarkable dependence on the hydrogen donor properties. The effects of the triplet-state hydrogen bonding on the reaction dynamics are illustrated. In particular, it is experimentally observed that strengthened triplet-state hydrogen bonding could accelerate the HA, whereas weakened triplet-state hydrogen bonding would postpone the HA. The triplet-state hydrogen bonding has great influences on the early stage of the HA reaction, while the bond dissociation energy of the hydrogen donors determines the subsequent reaction pathways. Protic solvents could sustain longer lifetimes of the excited-state intermediate formed after HA than non-protic solvents by 10 μs. This investigation provides insights into the HA dynamics and guidance to improve the product efficiency of photochemical reactions.
Co-reporter:Zhangrong Lou, Songqiu Yang, Peng Li, Panwang Zhou and Keli Han
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 8) pp:NaN3756-3756
Publication Date(Web):2013/11/26
DOI:10.1039/C3CP54093F
In this article, the sensing mechanism of a fluorescence probe for hypochloric acid, NI–Se, has been investigated using experimental and theoretical methods. Based on the results of the steady-state and time-resolved emission spectra of NI–Se and its oxidized form NI–SeO, we suggested that there was twist internal charge transfer (TICT) state with faint fluorescence in NI–Se. Subsequently, the ground and excited state minimum geometries of NI–Se and NI–SeO were optimized with DFT/TD-DFT methods. The results demonstrated there was a twisting process in the excited state of NI–Se and that this twist process was induced by the nonbonding interaction between the Se and N atoms. In addition, the calculated spectra and molecular orbitals confirmed the charge transfer character of the TICT state in NI–Se. To further investigate the driving force behind the twist in NI–Se, we synthesized NI–O, which has no Se⋯N nonbonding interaction, as a control sample. Herein, we also present the characterization, fluorescence properties and the optimized geometries of NI–O. Moreover, the results showed that Se⋯N nonbonding interaction plays a significant role in the twisting process of NI–Se.
Co-reporter:Po-Yu Ho, Chi-Ho Siu, Wai-Hong Yu, Panwang Zhou, Tao Chen, Cheuk-Lam Ho, Lawrence Tien Lin Lee, Ying-Hsuan Feng, Jianyong Liu, Keli Han, Yih Hsing Lo and Wai-Yeung Wong
Journal of Materials Chemistry A 2016 - vol. 4(Issue 4) pp:NaN726-726
Publication Date(Web):2015/12/23
DOI:10.1039/C5TC03308J
A series of new D–π–A organic photosensitizers 7a–7d featuring a novel starburst electron donor unit and uncommon selenophene containing π-linker were synthesized, characterized, and applied for fabrication of dye-sensitized solar cells (DSSCs). Dyes 11d–13d with thiophene or phenyl ring as the π-linker also were synthesized for comparison. The best power conversion efficiency (PCE) of 6.67% was attained for 11d with a relatively high open-circuit voltage (Voc) of 0.825 V using conventional I−/I3− redox electrolyte in DSSCs, and this value reaches about 84% of the device based on standard dye N719 (7.91%) under the same device fabrication conditions. Electrochemical impedance spectroscopy (EIS) and open-circuit voltage decay (OCVD) were applied to verify the findings. All the results suggest that starburst electron donor design strategy can be used to minimize dye aggregation on TiO2 and to slow down the charge recombination kinetics in DSSCs to improve the photovoltaic performance. Effects of using selenophene as the π-linker building block on the photovoltaic parameters also were explored and evaluated.
Co-reporter:Zongjin Qu, Peng Li, Xuexiang Zhang and Keli Han
Journal of Materials Chemistry A 2016 - vol. 4(Issue 5) pp:NaN892-892
Publication Date(Web):2015/12/21
DOI:10.1039/C5TB02090E
A turn-on fluorescent probe for the detection of Fe2+ is facilely synthesized via a nucleophile substitution reaction. The fluorescent probe, N-butyl-4-phenyltellanyl-1,8-naphthalimide (Naph-Te), shows excellent selectivity to Fe2+ in a mixed solution of acetonitrile and phosphate buffer under aerobic conditions. The coexistence of biological abundant metal ions such as Na+, K+, Ca2+ and Mg2+ has little effect on the fluorescence signal. This turn-on response is achieved via a redox-involved reaction triggered by Fe2+ at neutral pH and room temperature, which removes the heavy-atom effect of the tellurium atom on the naphthalimide fluorophore to afford a fluorescent product (N-butyl-4-hydroxyl-1,8-naphthalimide). The probe has excellent cell membrane permeability and is further applied successfully to monitor supplementary Fe2+ in live HL-7702 cells using a laser confocal fluorescence microscope.
Co-reporter:Dongmei Li, Yong Wang, Chuanlu Yang and Keli Han
Dalton Transactions 2009(Issue 2) pp:NaN297-297
Publication Date(Web):2008/11/19
DOI:10.1039/B810767J
The mechanism of N-dealkylation of N-cyclopropyl-N-methylaniline (3) catalyzed by cytochrome P450 (P450) was investigated using density functional theory. This reaction involves two steps. The first one is a Cα–H hydroxylation on the N-substituent to form a carbinolaniline complex, and the second is a decomposition of the carbinolaniline to yield cyclopropanone (or formaldehyde) and N-methylaniline (or N-cyclopropylaniline). Our calculations demonstrate that the first step proceeds in a spin-selective mechanism (SSM), mostly on the low-spin (LS) doublet state. The rate-limiting Cα–H activation is an isotope-sensitive hydrogen atom transfer (HAT) step. The environmental effect switches the regioselectivity of this reaction from a competition between N-decyclopropylation and N-demethylation to a clear preference for N-demethylation. This preference is consistent with former experimental studies. However, it is not in accord with the normal ΔE-BDE correlation since the BDE of Cα–H on the methyl group is higher than that on the cyclopropyl group. Insight into the origin of the preference for N-demethylation reveals that tertiary amine 3 is different from normal hydrocarbons, possessing a unique πPh-πC-N conjugated system. The electron delocalization effect of the πPh-πC-N conjugated system in 3 makes the transition state pose a polar character, and the bulk polarity and hydrogen bonding capability of the protein pocket can exert a remarkable effect on the regioselectivity of N-dealkylation of 3. Decomposition of carbinolaniline is a water-assisted proton-transfer process in the nonenzymatic environment. The ring-intact cyclopropanone formed in the reaction sheds some light on the inability of 3 to inactivate P450 during its N-decyclopropylation.
Co-reporter:Shuhao Wen, Wei-Qiao Deng and Ke-Li Han
Chemical Communications 2010 - vol. 46(Issue 28) pp:NaN5135-5135
Publication Date(Web):2010/06/09
DOI:10.1039/C0CC00955E
We have investigated the conduction mechanism at the TTF–TCNQ organic hetero-interface by means of quantum mechanical (QM) calculations. The calculated resistances at the TTF–TCNQ interface are 39–64 kΩ per square, which is in good agreement with the experimental values of 1–30 kΩ per square.
Co-reporter:Fabiao Yu, Ping Song, Peng Li, Bingshuai Wang and Keli Han
Chemical Communications 2012 - vol. 48(Issue 62) pp:NaN7737-7737
Publication Date(Web):2012/06/13
DOI:10.1039/C2CC33264G
We describe the synthesis, properties, and application of two reversible fluorescent probes, mCy-TemOH and Cy-TemOH, for HOBr sensing and imaging in live cells. The two probes contain a hydroxylamine functional group for the monitoring of HOBr oxidation/ascorbic acid reduction events. Confocal fluorescence microscopy has established the HOBr detection in live-cells.
Co-reporter:Fabiao Yu, Peng Li, Ping Song, Bingshuai Wang, Jianzhang Zhao and Keli Han
Chemical Communications 2012 - vol. 48(Issue 23) pp:NaN2854-2854
Publication Date(Web):2012/01/12
DOI:10.1039/C2CC17658K
We present a colorimetric and ratiometric fluorescent probe Cy–N3 that exhibits a selective response to H2S. The probe employs a near-infrared cyanine as a fluorophore, and is equipped with an operating azide unit. It is readily employed for assessing intracellular H2S levels, and confocal ratiometric imaging is achieved successfully.
Co-reporter:Bingshuai Wang, Peng Li, Fabiao Yu, Junsheng Chen, Zongjin Qu and Keli Han
Chemical Communications 2013 - vol. 49(Issue 51) pp:NaN5792-5792
Publication Date(Web):2013/05/01
DOI:10.1039/C3CC42313A
We have developed a near-infrared (NIR) reversible and ratiometric fluorescence sensor based on Se-BODIPY for the redox cycle between hypobromous acid oxidative stress and hydrogen sulfide repair. Real-time imaging shows that the probe is able to monitor intracellular HBrO/H2S redox cycle replacement.
Co-reporter:Zhangrong Lou, Peng Li, Xiaofei Sun, Songqiu Yang, Bingshuai Wang and Keli Han
Chemical Communications 2013 - vol. 49(Issue 4) pp:NaN393-393
Publication Date(Web):2012/10/31
DOI:10.1039/C2CC36839K
A diselenide containing fluorescent probe based on a fluorescein scaffold for thiols was developed. The fluorescent probe exhibited rapid response, high selectivity and reversibility. Confocal fluorescence microscopy was used to visualize the redox changes mediated by thiols and reactive oxygen species in living HeLa cells.
Co-reporter:Bingshuai Wang, Peng Li, Fabiao Yu, Ping Song, Xiaofei Sun, Songqiu Yang, Zhangrong Lou and Keli Han
Chemical Communications 2013 - vol. 49(Issue 10) pp:NaN1016-1016
Publication Date(Web):2012/12/12
DOI:10.1039/C2CC37803E
We have developed a new reversible fluorescence probe MPhSe–BOD for the redox cycle process between hypochlorous acid and hydrogen sulfide in solution and in living cells. Confocal microscopy imaging using RAW264.7 cell lines shows that the probe has good cell membrane permeability, and can monitor intracellular HClO/H2S redox cycles continuously.
Co-reporter:Fabiao Yu, Peng Li, Ping Song, Bingshuai Wang, Jianzhang Zhao and Keli Han
Chemical Communications 2012 - vol. 48(Issue 41) pp:NaN4982-4982
Publication Date(Web):2012/03/21
DOI:10.1039/C2CC30985H
We presented the design, synthesis, spectroscopy, and biological applications of DA–Cy, an on–off–on fluorescent probe to monitor H2O2 oxidative stress and thiols reducing repair in living cells and tissues simply and directly.
Co-reporter:Xue-Xiang Zhang, Hao Wu, Peng Li, Zong-Jin Qu, Ming-Qian Tan and Ke-Li Han
Chemical Communications 2016 - vol. 52(Issue 60) pp:NaN9470-9470
Publication Date(Web):2016/07/08
DOI:10.1039/C6CC90284G
Correction for ‘A versatile two-photon fluorescent probe for ratiometric imaging E. coli β-galactosidase in live cells and in vivo’ by Xue-Xiang Zhang et al., Chem. Commun., 2016, 52, 8283–8286.
Co-reporter:Xue-Xiang Zhang, Hao Wu, Peng Li, Zong-Jin Qu, Ming-Qian Tan and Ke-Li Han
Chemical Communications 2016 - vol. 52(Issue 53) pp:NaN8286-8286
Publication Date(Web):2016/06/06
DOI:10.1039/C6CC04373A
We have described the design, synthesis, spectroscopy and biological applications of NI–βGal, a versatile fluorescent probe to detect E. coli β-galactosidase in live cells and mice sensitively and directly, which holds great promise for its application in biomedical research such as gene therapy for cancer in the future.
Co-reporter:Zhangrong Lou, Peng Li, Qiang Pan and Keli Han
Chemical Communications 2013 - vol. 49(Issue 24) pp:NaN2447-2447
Publication Date(Web):2013/02/06
DOI:10.1039/C3CC39269D
Based on a novel strategy for modulating the fluorescence of selenide and selenoxide, we have designed and developed a reversible fluorescent probe for hypochloric acid. And the synthesis, characterization, fluorescence properties, as well as the biological applications in living cells and animals, have all been described.
In this paper, we have investigated the tandem reaction mechanism for the N-aziridinyl imine compounds forming triquinanes via trimethylenemethane (TMM) diyls in detail. Based on the calculated results, the reaction is initiated by the cleavage of the N-aziridinyl in the substrate, followed by an intramolecular 1,3-dipolar (3 + 2) cycloaddition preferentially leading to a linearly-fused tetrahydrocyclopentapyrazole intermediate. Next, the intermediate loses N2 to form the singlet TMM diyl M3S, which can then undergo another concerted (3 + 2) cycloaddition to generate the linearly-fused cis–trans or cis–syn triquinane products. In addition, M3S can also undergo intersystem crossing to the triplet TMM diyl M3T, and the six possible reaction pathways associated with M3T have also been identified. The calculated results reveal that the cis–trans fused pathway associated with M3S is energetically preferred with the highest free energy barrier of 25.0 kcal mol−1. In comparison, the cyclization of M3T requires much higher activation free energies (ΔG≠ = 34.4–57.8 kcal mol−1). At the experimental temperature 110 °C, only the linearly-fused cis–trans and cis–syn pathways associated with M3T (ΔG≠ = 34.4 and 35.5 kcal mol−1 respectively) are possible. The calculated results also indicate that for both M3S and M3T, the linearly-fused cis–trans triquinane should be the main product, which is consistent with the experimental observation. At last, conformational and NBO analyses on key transition states identified the cis–trans stereocontrol factors. Further calculations indicate that the methyl substituent on the allene group of the reactant substrate improves the stereoselectivity of the reaction but does not affect the rate-determining step.
The phosphine-catalyzed [4 + 2] annulations between allenoates and electron-poor trifluoromethyl ketones or N-tosylbenzaldimine dipolarophiles have been investigated in continuum solvation using density functional theory (DFT) calculations. The detailed reaction mechanisms as well as the high cis-diastereoselectivities of the reactions have been firstly clarified. Our calculated results reveal that the whole catalytic process is presumably initiated with the nucleophilic attack of phosphine catalyst at the allenoate to produce the zwitterionic intermediate M1, which subsequently undergoes γ-addition to the electron-poor CO (or CN) dipolarophile to form another intermediate M2. The following [1,3] hydrogen shift of M2 is demonstrated to proceed via two consecutive proton transfer steps without the assistance of protic solvent: the anionic O6 (or N6) of M2 first acts as a base catalyst to abstract a proton from C1 to produce the intermediate M3, and then the OH (or NH) group can donate the acidic proton to C3 to complete the [1,3] hydrogen shift and generate the intermediate M4. Finally, the intramolecular Michael-type addition followed by the elimination of catalyst furnishes the final product. High cis-diastereoselectivities are also predicted for both the two reactions, which is in good agreement with the experimental observations. For the reaction of allenoates with trifluoromethyl ketones, the first proton transfer is found to be the diastereoselectivity-determining step. The cumulative effects of the steric repulsion, electrostatic interaction as well as other weak interactions appear to contribute to the relative energies of transition states leading to the diastereomeric products. On the contrary, in the case of N-tosylbenzaldimines, the Michael-type addition is found to be the diastereoselectivity-determining step. Similarly, steric repulsion, as well as electrostatic interaction is also identified to be the dominant factors in controlling the high cis-diastereoselectivity of this reaction.
![Propanedinitrile,2-[(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)methylene]-](http://img.cochemist.com/ccimg/58300/58293-56-4.png)
![Propanedinitrile,2-[(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)methylene]-](http://img.cochemist.com/ccimg/58300/58293-56-4_b.png)
![1H-BENZ[DE]ISOQUINOLINE-1,3(2H)-DIONE, 2-BUTYL-6-HYDROXY-](/data/chemimg/2344700/791-80-0.png)
![1H-BENZ[DE]ISOQUINOLINE-1,3(2H)-DIONE, 2-BUTYL-6-HYDROXY-](/data/chemimg/2344700/791-80-0_b.png)
![Methyl (3s,4r)-3-benzoyloxy-8-methyl-8-azabicyclo[3.2.1]octane-4-carboxylate](http://img.cochemist.com/ccimg/100/50-36-2.png)
![Methyl (3s,4r)-3-benzoyloxy-8-methyl-8-azabicyclo[3.2.1]octane-4-carboxylate](http://img.cochemist.com/ccimg/100/50-36-2_b.png)
