Co-reporter:Xia Li;Yongjun Li;Yi Rao;Marissa R. Solomon;David C. Paik
Journal of Applied Polymer Science 2013 Volume 128( Issue 6) pp:3696-3701
Publication Date(Web):
DOI:10.1002/app.38604
Abstract
β-Nitroalcohols (βNAs) are promising corneoscleral crosslinking agents for the treatment of diseases such as keratoconus and myopia. Although it is believed that formaldehyde is released from the crosslinking reactions of βNAs, the mechanism by which βNAs react with amine-functionalized polymers has yet to be known. In this study, we present the reaction mechanism of the βNA crosslinking. Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) data provide strong evidence that formaldehyde is released during the reaction. Catalytic studies show that sodium bicarbonate (NaHCO3) and salmon testes DNA accelerate the reaction while hydroxynitrile lyase from Arabidopsis thaliana decelerates the crosslinking reaction. These results suggest that βNAs are potential self-administered crosslinking agents for future clinical use. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
Co-reporter:Nicholas J. Turro, Yongjun Li, Steffen Jockusch, Yuji Hagiwara, Masahiro Okazaki, Ryan A. Mesch, David I. Schuster, and C. Grant Willson
The Journal of Organic Chemistry 2013 Volume 78(Issue 5) pp:1735-1741
Publication Date(Web):October 29, 2012
DOI:10.1021/jo302149u
The investigation of the photochemistry of a two-stage photobase generator (PBG) is described. Absorption of a photon by a latent PBG (1) (first step) produces a PBG (2). Irradiation of 2 in the presence of water produces a base (second step). This two-photon sequence (1 + hν → 2 + hν → base) is an important component in the design of photoresists for pitch division technology, a method that doubles the resolution of projection photolithography for the production of microelectronic chips. In the present system, the excitation of 1 results in a Norrish type II intramolecular hydrogen abstraction to generate a 1,4-biradiacal that undergoes cleavage to form 2 and acetophenone (Φ ∼ 0.04). In the second step, excitation of 2 causes cleavage of the oxime ester (Φ = 0.56) followed by base generation after reaction with water.
Co-reporter:Luca Garbuio ; Sabrina Antonello ; Ivan Guryanov ; Yongjun Li ; Marco Ruzzi ; Nicholas J. Turro ;Flavio Maran
Journal of the American Chemical Society 2012 Volume 134(Issue 25) pp:10628-10637
Publication Date(Web):May 31, 2012
DOI:10.1021/ja303696s
We synthesized two series of compounds in which a nitroxide radical and a fullerene C60 moiety were kept separated by a 310-helical peptide bridge containing two intramolecular C═O···H–N hydrogen bonds. The direction of the resulting molecular dipole moment could be reversed by switching the position of fullerene and nitroxide with respect to the peptide nitrogen and carbon termini. The resulting fullerene–peptide–radical systems were compared to the behaviors of otherwise identical peptides but lacking either C60 or the free radical moiety. Electrochemical analysis and chemical nitroxide reduction experiments show that the dipole moment of the helix significantly affects the redox properties of both electroactive groups. Besides providing evidence of a folded helical conformation for the peptide bridge, IR and NMR results highlight a strong effect of peptide orientation on the spectral patterns, pointing to a specific interaction of one of the helical orientations with the C60 moiety. Time-resolved EPR spectra show not only that for both systems triplet quenching by nitroxide induces spin polarization of the radical spin sublevels, but also that the coupling interaction can be either weak or strong depending on the orientation of the peptide dipole. As opposed to the concept of dyads, the molecules investigated are thus better described as fullerene–peptide–radical systems to stress the active role of the bridge as an important ingredient capable of tuning the system’s physicochemical properties.
Co-reporter:Alfonso Zoleo ; Ronald G. Lawler ; Xuegong Lei ; Yongjun Li ; Yasujiro Murata ; Koichi Komatsu ; Marilena Di Valentin ; Marco Ruzzi
Journal of the American Chemical Society 2012 Volume 134(Issue 31) pp:12881-12884
Publication Date(Web):July 19, 2012
DOI:10.1021/ja305704n
An endofulleropyrrolidine, with H2 as a guest, has been reduced to a paramagnetic endofulleride radical anion. The magnetic interaction between the electron delocalized on the fullerene cage and the guest H2 has been probed by pulsed ENDOR. The experimental hyperfine couplings between the electron and the H2 guest were measured, and their values agree very well with DFT calculations. This agreement provides clear evidence of magnetic communication between the electron density of the fullerene host cage and H2 guest. The ortho-H2/para-H2 interconversion is revealed by temperature-dependent ENDOR measurements at low temperature. The conversion of the paramagnetic ortho-H2 to the diamagnetic para-H2 causes the ENDOR signal to decrease as the temperature is lowered due to the spin catalysis by the paramagnetic fullerene cage of the radical anion fulleride.
Co-reporter:Nazmiye B. Yapici, Steffen Jockusch, Alberto Moscatelli, Srinivas Rao Mandalapu, Yasuhiro Itagaki, Dallas K. Bates, Sherri Wiseman, K. Michael Gibson, Nicholas J. Turro, and Lanrong Bi
Organic Letters 2012 Volume 14(Issue 1) pp:50-53
Publication Date(Web):December 16, 2011
DOI:10.1021/ol202816m
The synthesis, characteristics, and biological applications of a series of new rhodamine nitroxide fluorescent probes that enable imaging of hydroxyl radicals (•OH) in living cells are described. These probes are highly selective for •OH in aqueous solution, avoiding interference from other reactive oxygen species (ROS), and they facilitate •OH imaging in biologically active samples. The robust nature of these probes (high specificity and selectivity, and facile synthesis) offer distinct advantages over previous methods for •OH detection.
Co-reporter:Yongjun Li, Xuegong Lei, Ronald G. Lawler, Yasujiro Murata, Koichi Komatsu, and Nicholas J. Turro
Organic Letters 2012 Volume 14(Issue 15) pp:3822-3825
Publication Date(Web):July 17, 2012
DOI:10.1021/ol3013155
H2O@C60 derivatives covalently linked to a nitroxide radical were synthesized. The 1H NMR of the guest H2O revealed the formation of many isomers with broad signals. Reduction to the diamagnetic hydroxylamines sharpened the 1H NMR signals considerably and allowed for an “isomer count” based on the number of observed distinct signals. For H2O@K-8, 17 positional isomeric nitroxides are predicted, not including additional numbers of regioisomers; indeed, 17 signals are observed in the 1H NMR spectrum.
Co-reporter:Ellane J. Park, Tina Wagenaar, Siyan Zhang, A. James Link, Robert K. Prud’homme, Jeffrey T. Koberstein, and Nicholas J. Turro
Langmuir 2012 Volume 28(Issue 29) pp:10934-10941
Publication Date(Web):July 1, 2012
DOI:10.1021/la302113k
There is considerable current interest in developing methods to integrate nanoparticles into optical, electronic, and biological systems due to their unique size-dependent properties and controllable shape. We report herein a versatile new approach for covalent immobilization of nanoparticles onto substrates modified with photoactive, phthalimide-functional, self-assembled monolayers. Upon illumination with UV radiation, the phthalimide group abstracts a hydrogen atom from a neighboring organic molecule, leading to radical-based photografting reactions. The approach is potentially “universal” since virtually any polymeric or organic–inorganic hybrid nanoparticle can be covalently immobilized in this fashion. Because grafting is confined to illuminated regions that undergo photoexcitation, masking provides a simple and direct method for nanoparticle patterning. To illustrate the technique, nanoparticles formed from diblock copolymers of poly(styrene-b-polyethylene oxide) and laden with Hostasol Red dye are photografted and patterned onto glass and silicon substrates modified with photoactive phthalimide-silane self-assembled monolayers. Atomic force microscopy and X-ray photoelectron spectroscopy are applied to characterize the grafted nanoparticle films while confocal fluorescence microscopy is used to image patterned nanoparticle deposition.
Co-reporter:Jia Guo;Jingyue Ju
Analytical and Bioanalytical Chemistry 2012 Volume 402( Issue 10) pp:3115-3125
Publication Date(Web):2012 April
DOI:10.1007/s00216-011-5526-x
Due to their high sensitivity and selectivity, minimum interference with living biological systems, and ease of design and synthesis, fluorescent hybridization probes have been widely used to detect nucleic acids both in vivo and in vitro. Molecular beacons (MBs) and binary probes (BPs) are two very important hybridization probes that are designed based on well-established photophysical principles. These probes have shown particular applicability in a variety of studies, such as mRNA tracking, single nucleotide polymorphism (SNP) detection, polymerase chain reaction (PCR) monitoring, and microorganism identification. Molecular beacons are hairpin oligonucleotide probes that present distinctive fluorescent signatures in the presence and absence of their target. Binary probes consist of two fluorescently labeled oligonucleotide strands that can hybridize to adjacent regions of their target and generate distinctive fluorescence signals. These probes have been extensively studied and modified for different applications by modulating their structures or using various combinations of fluorophores, excimer-forming molecules, and metal complexes. This review describes the applicability and advantages of various hybridization probes that utilize novel and creative design to enhance their target detection sensitivity and specificity.
Co-reporter:Massimo Bietti, Michela Salamone, Gino A. DiLabio, Steffen Jockusch, and Nicholas J. Turro
The Journal of Organic Chemistry 2012 Volume 77(Issue 3) pp:1267-1272
Publication Date(Web):January 4, 2012
DOI:10.1021/jo201454c
A time-resolved kinetic study of the hydrogen atom abstraction reactions from phenol by the cumyloxyl radical (CumO•) was carried out in different solvents. The hydrogen atom abstraction rate constant (kH) was observed to decrease by almost 3 orders of magnitude on going from isooctane to MeOH. In TFE, MeCN/H2O 2:1, and MeOH, the measured kH values were lower than expected on the basis of the Snelgrove–Ingold (SI) equation that correlates log kH to the solvent hydrogen bond acceptor (HBA) ability parameter β2H. As these solvents also act as hydrogen bond donors (HBDs), we explored the notion that a more thorough description of solvent effects could be provided by including a solvent HBD ability term, α2H, into the SI equation via β2H(1 + α2H). The inclusion of such a term greatly improves the fitting for TFE, MeCN/H2O 2:1, and MeOH but at the expense of that for tertiary alkanols. This finding suggests that, for the reaction of CumO• with phenol, the HBA and HBD abilities of both the solvent and the substrate could be responsible for the observed KSEs. but this requires that primary and tertiary alkanols exhibit different solvation behaviors. Possible explanations for this different behavior are explored.
Co-reporter:Qinsi Zheng, Steffen Jockusch, Zhou Zhou, Roger B. Altman, J. David Warren, Nicholas J. Turro, and Scott C. Blanchard
The Journal of Physical Chemistry Letters 2012 Volume 3(Issue 16) pp:2200-2203
Publication Date(Web):July 30, 2012
DOI:10.1021/jz300670p
Cyanine fluorophores exhibit greatly improved photostability when covalently linked to stabilizers, such as cyclooctatetraene (COT), nitrobenzyl alcohol (NBA), or Trolox. However, the mechanism by which photostabilization is mediated has yet to be determined. Here, we present spectroscopic evidence that COT, when covalently linked to Cy5, substantially reduces the lifetime of the Cy5 triplet state and that the degree of triplet-state quenching correlates with enhancements in photostability observed in single-molecule fluorescence measurements. By contrast, NBA and Trolox did not quench the Cy5 triplet state under our conditions, suggesting that their mechanism of photostabilization is different from that of COT and does not target the fluorophore triplet state directly. These findings provide insights into the mechanisms of fluorophore photostabilization that may lead to improved fluorophore designs for biological imaging applications.Keywords: COT; Cy5; laser flash photolysis; single-molecule spectroscopy;
Co-reporter:Yongjun Li, Judy Y.-C. Chen, Xuegong Lei, Ronald G. Lawler, Yasujiro Murata, Koichi Komatsu, and Nicholas J. Turro
The Journal of Physical Chemistry Letters 2012 Volume 3(Issue 9) pp:1165-1168
Publication Date(Web):April 12, 2012
DOI:10.1021/jz3002794
The successful synthesis of H2O@C60 makes possible the study of magnetic interactions of an isolated water molecule in a geometrically well-defined hydrophobic environment. Comparisons are made between the T1 values of H2O@C60 and the previously studied H2@C60 and their nitroxide derivatives. The value of T1 is approximately six times longer for H2O@C60 than for H2@C60 at room temperature, is independent of solvent viscosity or polarity, and increases monotonically with decreasing temperature, implying that T1 is dominated by the spin-rotation interaction. Paramagnetic nitroxides, either attached covalently to the C60 cage or added to the medium, produce strikingly similar T1 enhancements for H2O@C60 and H2@C60 that are consistent with through-space interaction between the internal nuclear spins and the external electron spin. This indicates that it should be possible to apply to the endo-H2O molecule the same methodologies for manipulating the ortho and para spin isomers that have proven successful for H2@C60.Keywords: endofullerene; fullerene derivatives; fullerene nitroxides; H2@C60; H2O@C60; Host@guest; proton relaxation;
Co-reporter:Salvatore Mamone, Judy Y.-C. Chen, Rangeet Bhattacharyya, Malcolm H. Levitt, Ronald G. Lawler, Anthony J. Horsewill, Toomas Rõõm, Zlatko Bačić, Nicholas J. Turro
Coordination Chemistry Reviews 2011 Volume 255(7–8) pp:938-948
Publication Date(Web):April 2011
DOI:10.1016/j.ccr.2010.12.029
The supramolecular complex, H2@C60, represents a model of a quantum rotor in a nearly spherical box. In providing a real example of a quantum particle entrapped in a small space, the system cuts to the heart of many important and fundamental quantum mechanical issues. This review compares the predictions of theory of the quantum behaviour of H2 incarcerated in C60 with the results of infrared spectroscopy, inelastic neutron scattering and nuclear magnetic resonance. For H2@C60, each of these methods supports the quantization of translational motion of H2 and the coupling of the translational motion with rotational motion and provides insights to the factors leading to breaking of the degeneracies of states expected for a purely spherical potential. Infrared spectroscopy and inelastic neutron scattering experiments at cryogenic temperatures provide direct evidence of a profound quantum mechanical feature of H2 predicted by Heisenberg based on the Pauli principle: the existence of two nuclear spin isomers, a nuclear spin singlet (para-H2) and a nuclear triplet (ortho-H2). Nuclear magnetic resonance is capable of probing the local lattice environment of H2@C60 through analysis of the H2 motional effects on the ortho-H2 spin dynamics (para-H2, the nuclear singlet state, is NMR silent). In this review we will show how the information obtained by three different forms of spectroscopy join together with quantum theory to create a complementary and consistent picture which strikingly shows the intrinsically quantum nature of H2@C60.
Co-reporter:Michael Frunzi ; Steffen Jockusch ; Judy Y.-C. Chen ; Rafael M. Krick Calderon ; Xuegong Lei ; Yasujiro Murata ; Koichi Komatsu ; Dirk M. Guldi ; Ronald G. Lawler
Journal of the American Chemical Society 2011 Volume 133(Issue 36) pp:14232-14235
Publication Date(Web):August 16, 2011
DOI:10.1021/ja206383n
The photochemical interconversion of the two allotropes of the hydrogen molecule [para-H2 (pH2) and ortho-H2 (oH2)] incarcerated inside the fullerene C70 (pH2@C70 and oH2@C70, respectively) is reported. Photoexcitation of H2@C70 generates a fullerene triplet state that serves as a spin catalyst for pH2/oH2 conversion. This method provides a means of changing the pH2/oH2 ratio inside C70 by simply irradiating H2@C70 at different temperatures, since the equilibrium ratio is temperature-dependent and the electronic triplet state of the fullerene produced by absorption of the photon serves as an “on–off” spin catalyst. However, under comparable conditions, no photolytic pH2/oH2 interconversion was observed for H2@C60, which was rationalized by the significantly shorter triplet lifetime of H2@C60 relative to H2@C70.
Co-reporter:Yan Xia ; Yongjun Li ; Alan O. Burts ; M. Francesca Ottaviani ; David A. Tirrell ; Jeremiah A. Johnson ; Nicholas J. Turro ;Robert H. Grubbs
Journal of the American Chemical Society 2011 Volume 133(Issue 49) pp:19953-19959
Publication Date(Web):October 24, 2011
DOI:10.1021/ja2085349
Spin-labeled polylactide brush polymers were synthesized via ring-opening metathesis polymerization (ROMP), and nitroxide radicals were incorporated at three different locations of brush polymers: the end and the middle of the backbone, and the end of the side chains (periphery). Electron paramagnetic resonance (EPR) was used to quantitatively probe the macromolecular structure of brush polymers in dilute solutions. The peripheral spin-labels showed significantly higher mobility than the backbone labels, and in dimethylsulfoxide (DMSO), the backbone end labels were shown to be more mobile than the middle labels. Reduction of the nitroxide labels by a polymeric reductant revealed location-dependent reactivity of the nitroxide labels: peripheral nitroxides were much more reactive than the backbone nitroxides. In contrast, almost no difference was observed when a small molecule reductant was used. These results reveal that the dense side chains of brush polymers significantly reduce the interaction of the backbone region with external macromolecules, but allow free diffusion of small molecules.
Co-reporter:Yongjun Li, Xuegong Lei, Xia Li, Ronald G. Lawler, Yasujiro Murata, Koichi Komatsu and Nicholas J. Turro
Chemical Communications 2011 vol. 47(Issue 46) pp:12527-12529
Publication Date(Web):26 Oct 2011
DOI:10.1039/C1CC15149E
1H NMR of two H2@C60 nitroxide derivatives has been characterized indirectly by reducing to their corresponding hydroxylamines. Nuclear spin relaxation of the endohedral H2 and external protons of the H2@C60 nitroxide and its corresponding hydroxylamine were measured and analyzed. The observed spectra are consistent with negligible scalar coupling between the unpaired electron and the endo-H2. An unexpectedly large bimolecular relaxivity induced in the hydroxylamine by the corresponding nitroxide can be explained by rapid hydrogen atom transfer between the two species.
Co-reporter:Yongjun Li, Xuegong Lei, Ronald G. Lawler, Yasujiro Murata, Koichi Komatsu and Nicholas J. Turro
Chemical Communications 2011 vol. 47(Issue 8) pp:2282-2284
Publication Date(Web):20 Dec 2010
DOI:10.1039/C0CC04862C
Bisadduct isomers of a H2@C60 derivative with nitroxide addends have been synthesized, isolated and characterized. The 1H NMRs of endohedral H2 of the major isomers show well-separated chemical shifts, which could be useful for structural assignment and identification of the purity of the C60 bisadduct isomers.
Co-reporter:Gregory T. Carroll;L. Devon Triplett;Alberto Moscatelli;Jeffrey T. Koberstein
Journal of Applied Polymer Science 2011 Volume 122( Issue 1) pp:168-174
Publication Date(Web):
DOI:10.1002/app.34133
Abstract
In this manuscript we report the crosslinking of pre-existing macromolecules in solution through the use of photoactive benzophenone chromophores. We show that a bifunctional crosslinker composed of two benzophenone chromophores as well as a single benzophenone chromophore crosslink poly (butadiene) and poly (ethylene oxide) in solution to form insoluble gels when irradiated with UV light. The molecular weight between crosslinks of the photogenerated gels was compared for the two crosslinkers, for an equivalent amount of benzophenone chromophores in each solution, by measuring the swelling ratio of the gels formed. Gels formed from the bifunctional benzophenone crosslinker were shown to contain more than twice as many crosslinks compared to gels formed from the crosslinker composed of a single benzophenone chromophore. EPR measurements of a nitroxide derivative absorbed into the gels further supported a higher crosslink density for the gels formed from the bifunctional benzophenone crosslinker. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Co-reporter:Arun Kumar Sundaresan, Steffen Jockusch and Nicholas J. Turro
Photochemical & Photobiological Sciences 2011 vol. 10(Issue 9) pp:1450-1454
Publication Date(Web):21 Apr 2011
DOI:10.1039/C1PP05095H
Photolysis of 2-diphenylmethoxyacetophenone (1) in deaerated acetonitrile at room temperature is expected to proceed via Norrish Type II reaction to generate benzophenone (2) and acetophenone (4) as the main isolated photoproducts. Although the acetophenone enol intermediate (3) is generally considered a putative intermediate that is a precursor of acetophenone, there are few reports of the direct spectroscopic detection of 3 when a Type II reaction is conducted in solution at room temperature. Presumably, rapid enol-ketone isomerisation under the reaction conditions causes 3 to have a very short lifetime that lowers its concentration below limits detectable by standard organic spectroscopic methods such as 1H NMR. We report that 3 is readily observed at room temperature by 1H NMR spectroscopy and showed a remarkably long lifetime of almost 1 h under our reaction conditions. It was found that the acetophenone enols from the classic Norrish Type II reactions of valerophenone and butyrophenone could also be readily detected by 1H NMR in acetonitrile at room temperature, but that their lifetimes were similar (tens of minutes) from both precursors, but were considerably shorter than that of 1. The reason for the differences in the lifetime of the acetophenone enol is probably due to small amounts of adventitious catalysts that arise during the photolysis.
Co-reporter:Michael Frunzi, Anne M. Baldwin, Nobuyuki Shibata, Sho-Ichi Iwamatsu, Ronald G. Lawler, and Nicholas J. Turro
The Journal of Physical Chemistry A 2011 Volume 115(Issue 5) pp:735-740
Publication Date(Web):January 10, 2011
DOI:10.1021/jp110832m
Kinetic and thermodynamic properties of water encapsulation from organic solution by an open-cage [60]fullerene derivative have been investigated. 2D exchange NMR spectroscopy (EXSY) measurements were employed to determine the association and dissociation constants at 300−330 K (ka = 4.3 M−1 × s−1 and kd = 0.42 s−1 at 300 K) in 1,1,2,2-tetrachloroethane-d2 as well as the activation energies (Ea,ass = 27 kJ mol−1, Ea,diss = 50 kJ mol−1). The equilibrium constants and thermodynamic parameters in various solvents (benzene-d6, 1,2-dichlorobenzene-d4, and dimethylsulfoxide-d6) were estimated using 1D-1H NMR spectroscopy. The parameters were dependent on the polarity of the solvent; ΔH depended linearly on the solvent polarity, becoming increasingly unfavorable as polarity increased. Mixtures of polar dimethylsulfoxide-d6 in less polar 1,1,2,2-tetrachloroethane-d2 showed a similar trend.
Co-reporter:Yi Rao, Xia Li, Xuegong Lei, Steffen Jockusch, Michael W. George, Nicholas J. Turro, and Kenneth B. Eisenthal
The Journal of Physical Chemistry C 2011 Volume 115(Issue 24) pp:12064-12067
Publication Date(Web):May 26, 2011
DOI:10.1021/jp201799z
The complementary interface-sensitive methods of sum frequency generation (SFG) and surface tension have been used to investigate surfactants at the air/water interface. SFG yields information on the density and orientation of surfactants at the interface, whereas surface tension yields information on the surface excess of surfactants, which, however, is not their interfacial density. The rapid rise in the SFG signal to its maximum value at 1 mM, which remained essentially constant thereafter, was attributed to the formation of large surfactant domains. Above 1 mM, the domains, all of which have the same density, dominated the SFG signal. As a consequence, the SFG signal remained essentially constant. The surface excess had an equally rapid rise to its maximum value at 1 mM, which remained constant until reaching a concentration of 3 mM, where it dropped to a zero value, indicating that a full surfactant monolayer had been formed. This coincides with the formation of bulk micelles, which is commonly referred to as the critical micelle concentration. The orientation of the surfactant carbonyl chromophore was obtained from polarization measurements of the SFG signal and showed a small change at and above a 1 mM concentration. The SFG results and the surface tension results, though inherently different, were found to be consistent with each other.
Co-reporter:Steffen Jockusch, Mintu Porel, V. Ramamurthy, and Nicholas J. Turro
The Journal of Physical Chemistry Letters 2011 Volume 2(Issue 22) pp:2877-2880
Publication Date(Web):October 26, 2011
DOI:10.1021/jz201328f
Thioxanthone and benzil derivatives were incarcerated into an octa acid nanocapsule. Photoexcitation of these ketones generated electronic triplet excited states, which become efficiently quenched by positively charged nitroxides adsorbed outside on the external surface of the negatively charged nanocapsule. Although the triplet excited ketone and quencher are separated by a molecular wall (nanocapsule), quenching occurs on the nanosecond time scale and generates spin-polarized nitroxides, which were observed by time-resolved EPR spectroscopy. Because opposite signs of spin polarization of nitroxides were observed for thioxanthone and benzil derivatives, it is proposed that the electron spin polarization transfer mechanism of spin-polarized triplet states to nitroxides is the major mechanism of generating nitroxide polarization.Keywords: laser flash photolysis; TEMPO; time-resolved EPR;
Co-reporter:Yongjun Li, Xuegong Lei, Ronald G. Lawler, Yasujiro Murata, Koichi Komatsu, and Nicholas J. Turro
The Journal of Physical Chemistry Letters 2011 Volume 2(Issue 7) pp:741-744
Publication Date(Web):March 11, 2011
DOI:10.1021/jz200192s
The ortho-H2→para-H2 conversion in a series of H2@C60 derivatives covalently linked to a nitroxide radical has been investigated. The resulting conversion rates are in good agreement with the Wigner’s theory, modified for intramolecular interaction of H2 with the paramagnet.Keywords: distance-dependent; H2@C60; nitroxide radical; ortho-H2/para-H2 conversion;
Co-reporter:Nicholas J. Turro, Judy Y.-C. Chen, Elena Sartori, Marco Ruzzi, Angel Marti, Ronald Lawler, Steffen Jockusch, Juan López-Gejo, Koichi Komatsu and Yasujiro Murata
Accounts of Chemical Research 2010 Volume 43(Issue 2) pp:335
Publication Date(Web):November 10, 2009
DOI:10.1021/ar900223d
One of the early triumphs of quantum mechanics was Heisenberg’s prediction, based on the Pauli principle and wave function symmetry arguments, that the simplest molecule, H2, should exist as two distinct species—allotropes of elemental hydrogen. One allotrope, termed para-H2 (pH2), was predicted to be a lower energy species that could be visualized as rotating like a sphere and possessing antiparallel (↑↓) nuclear spins; the other allotrope, termed ortho-H2 (oH2), was predicted to be a higher energy state that could be visualized as rotating like a cartwheel and possessing parallel (↑↑) nuclear spins. This remarkable prediction was confirmed by the early 1930s, and pH2 and oH2 were not only separated and characterized but were also found to be stable almost indefinitely in the absence of paramagnetic “spin catalysts”, such as molecular oxygen, or traces of paramagnetic impurities, such as metal ions. The two allotropes of elemental hydrogen, pH2 and oH2, may be quantitatively incarcerated in C60 to form endofullerene guest@host complexes, symbolized as pH2@C60 and oH2@C60, respectively. How does the subtle difference in nuclear spin manifest itself when hydrogen allotropes are incarcerated in a buckyball? Can the incarcerated “guests” communicate with the outside world and vice versa? Can a paramagnetic spin catalyst in the outside world cause the interconversion of the allotropes and thereby effect a chemical transformation inside a buckyball? How close are the measurable properties of H2@C60 to those computed for the “quantum particle in a spherical box”? Are there any potential practical applications of this fascinating marriage of the simplest molecule, H2, with one of the most beautiful of all molecules, C60? How can one address such questions theoretically and experimentally? A goal of our studies is to produce an understanding of how the H2 guest molecules incarcerated in the host C60 can “communicate” with the chemical world surrounding it. This world includes both the “walls” of the incarcerating host (the carbon atom “bricks” that compose the wall) and the “outside” world beyond the atoms of the host walls, namely, the solvent molecules and selected paramagnetic molecules added to the solvent that will have special spin interactions with the H2 inside the complex. In this Account, we describe the temperature dependence of the equilibrium of the interconversion of oH2@C60 and pH2@C60 and show how elemental dioxygen, O2, a ground-state triplet, is an excellent paramagnetic spin catalyst for this interconversion. We then describe an exploration of the spin spectroscopy and spin chemistry of H2@C60. We find that H2@C60 and its isotopic analogs, HD@C60 and D2@C60, provide a rich and fascinating platform on which to investigate spin spectroscopy and spin chemistry. Finally, we consider the potential extension of spin chemistry to another molecule with spin isomers, H2O, and the potential applications of the use of pH2@C60 as a source of latent massive nuclear polarization.
Co-reporter:Jia Guo, Lin Yu, Nicholas J. Turro and Jingyue Ju
Accounts of Chemical Research 2010 Volume 43(Issue 4) pp:551
Publication Date(Web):February 3, 2010
DOI:10.1021/ar900255c
The Human Genome Project has concluded, but its successful completion has increased, rather than decreased, the need for high-throughput DNA sequencing technologies. The possibility of clinically screening a full genome for an individual’s mutations offers tremendous benefits, both for pursuing personalized medicine and for uncovering the genomic contributions to diseases. The Sanger sequencing method, although enormously productive for more than 30 years, requires an electrophoretic separation step that, unfortunately, remains a key technical obstacle for achieving economically acceptable full-genome results. Alternative sequencing approaches thus focus on innovations that can reduce costs. The DNA sequencing by synthesis (SBS) approach has shown great promise as a new sequencing platform, with particular progress reported recently. The general fluorescent SBS approach involves (i) incorporation of nucleotide analogs bearing fluorescent reporters, (ii) identification of the incorporated nucleotide by its fluorescent emissions, and (iii) cleavage of the fluorophore, along with the reinitiation of the polymerase reaction for continuing sequence determination. In this Account, we review the construction of a DNA-immobilized chip and the development of novel nucleotide reporters for the SBS sequencing platform. Click chemistry, with its high selectivity and coupling efficiency, was explored for surface immobilization of DNA. The first generation (G-1) modified nucleotides for SBS feature a small chemical moiety capping the 3′-OH and a fluorophore tethered to the base through a chemically cleavable linker; the design ensures that the nucleotide reporters are good substrates for the polymerase. The 3′-capping moiety and the fluorophore on the DNA extension products, generated by the incorporation of the G-1 modified nucleotides, are cleaved simultaneously to reinitiate the polymerase reaction. The sequence of a DNA template immobilized on a surface via click chemistry is unambiguously identified with this chip−SBS system. The second generation (G-2) SBS system was developed based on the concept that the closer the structures of the added nucleotide and the primer are to their natural counterparts, the more faithfully the polymerase would incorporate the nucleotide. In this approach, the polymerase reaction is performed with the combination of 3′-capped nucleotide reversible terminators (NRTs) and cleavable fluorescent dideoxynucleotides (ddNTPs). By sacrifice of a small amount of the primers permanently terminated by ddNTPs, the majority of the primers extended by the reversible terminators are reverted to the natural ones after each sequencing cycle. We have also developed the 3′-capped nucleotide reversible terminators to solve the problem of deciphering the homopolymeric regions of the template in conventional pyrosequencing. The 3′-capping moiety on the DNA extension product temporarily terminates the polymerase reaction, which allows only one nucleotide to be incorporated during each sequencing cycle. Thus, the number of nucleotides in the homopolymeric regions are unambiguously determined using the 3′-capped NRTs. It has been established that millions of DNA templates can be immobilized on a chip surface through a variety of approaches. Therefore, the integration of these high-density DNA chips with the molecular-level SBS approaches described in this Account is expected to generate a high-throughput and accurate DNA sequencing system with wide applications in biological research and health care.
Co-reporter:Francesco Sebastianelli ; Minzhong Xu ; Zlatko Bačić ; Ronald Lawler
Journal of the American Chemical Society 2010 Volume 132(Issue 28) pp:9826-9832
Publication Date(Web):June 28, 2010
DOI:10.1021/ja103062g
Recent synthesis of the endohedral complexes of C70 and its open-cage derivative with one and two H2 molecules has opened the path for experimental and theoretical investigations of the unique dynamic, spectroscopic, and other properties of systems with multiple hydrogen molecules confined inside a nanoscale cavity. Here we report a rigorous theoretical study of the dynamics of the coupled translational and rotational motions of H2 molecules in C70 and C60, which are highly quantum mechanical. Diffusion Monte Carlo (DMC) calculations were performed for up to three para-H2 (p-H2) molecules encapsulated in C70 and for one and two p-H2 molecules inside C60. These calculations provide a quantitative description of the ground-state properties, energetics, and the translation−rotation (T−R) zero-point energies (ZPEs) of the nanoconfined p-H2 molecules and of the spatial distribution of two p-H2 molecules in the cavity of C70. The energy of the global minimum on the intermolecular potential energy surface (PES) is negative for one and two H2 molecules in C70 but has a high positive value when the third H2 is added, implying that at most two H2 molecules can be stabilized inside C70. By the same criterion, in the case of C60, only the endohedral complex with one H2 molecule is energetically stable. Our results are consistent with the fact that recently both (H2)n@C70 (n = 1, 2) and H2@C60 were prepared, but not (H2)3@C70 or (H2)2@C60. The ZPE of the coupled T−R motions, from the DMC calculations, grows rapidly with the number of caged p-H2 molecules and is a significant fraction of the well depth of the intermolecular PES, 11% in the case of p-H2@C70 and 52% for (p-H2)2@C70. Consequently, the T−R ZPE represents a major component of the energetics of the encapsulated H2 molecules. The inclusion of the ZPE nearly doubles the energy by which (p-H2)3@C70 is destabilized and increases by 66% the energetic destabilization of (p-H2)2@C60. For these reasons, the T−R ZPE has to be calculated accurately and taken into account for reliable theoretical predictions regarding the stability of the endohedral fullerene complexes with hydrogen molecules and their maximum H2 content.
Co-reporter:Olaf Zeika, Yongjun Li, Steffen Jockusch, Gerard Parkin, Aaron Sattler, Wesley Sattler and Nicholas J. Turro
Organic Letters 2010 Volume 12(Issue 16) pp:3696-3699
Publication Date(Web):July 28, 2010
DOI:10.1021/ol101529u
The scope and limitations of the synthesis of polynitroxides by nucleophilic substitution of electron-deficient fluorinated aromatic compounds are described. The method provides a facile route to the formation of polynitroxides exhibiting strong electron exchange between nitroxide groups.
Co-reporter:Marissa R. Solomon, J. Sivaguru, Steffen Jockusch, Waldemar Adam and Nicholas J. Turro
Organic Letters 2010 Volume 12(Issue 9) pp:2142-2145
Publication Date(Web):April 12, 2010
DOI:10.1021/ol100174r
Systematically designed oxazolidinone-derived enecarbamates reveal that solvent and temperature effects on the stereoselectivity during photooxygenation are likely due to the conformational flexibility of the chiral phenethyl side chain (entropy factors); the extent of enantiomeric excess in the photoproduct is dictated by the alkene geometry.
Co-reporter:Marissa R. Solomon;Naphtali A. O'Connor;David C. Paik
Journal of Applied Polymer Science 2010 Volume 117( Issue 2) pp:1193-1196
Publication Date(Web):
DOI:10.1002/app.31944
Abstract
Certain β-nitroalcohols degrade under basic conditions or upon heating to form formaldehyde. This reaction provides an elegant approach to generate formaldehyde within a system at a desired time using the stimulus of pH or temperature. Using β-nitroalcohols as a delivery agent for formaldehyde, polymer crosslinking can be induced via stimulus. Such an approach is akin to those used to prepare “self-healing” polymers, which have received much attention recently. Herein, we describe the use of certain β-nitroalcohols as a masked formaldehyde delivery system and demonstrate its use as a crosslinking agent of amine functionalized polymers to form hydrogels. We examine the temperature and pH dependence of 2-nitro-1,3-propanediol and 2-(hydroxymethyl)-2-nitro-1,2-propanediol on the rate and extent of gelation and characterize the resulting gel by swelling and FTIR experiments. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
Co-reporter:Arun Kumar Sundaresan, Steffen Jockusch, Yongjun Li, Jeffrey R. Lancaster, Steven Banik, Paul Zimmerman, James M. Blackwell, Robert Bristol and Nicholas J. Turro
Photochemical & Photobiological Sciences 2010 vol. 9(Issue 8) pp:1082-1084
Publication Date(Web):05 Jun 2010
DOI:10.1039/C0PP00096E
The cycloadducts of tethered naphthalene and anthracene derivatives undergo photochemical ring opening to an electronically excited product with adiabatic yields up to 90%.
Co-reporter:Judy Y.-C. Chen, Angel A. Martí, Nicholas J. Turro, Koichi Komatsu, Yasujiro Murata, and Ronald G. Lawler
The Journal of Physical Chemistry B 2010 Volume 114(Issue 45) pp:14689-14695
Publication Date(Web):June 24, 2010
DOI:10.1021/jp102860m
Spin−lattice relaxation times, T1, have been measured from 200−340 K for the protons in H2 and HD molecules dissolved in toluene-d8 and incarcerated in C60. It is found that HD relaxes more slowly than H2 in both environments and at all temperatures, as expected from the smaller values of the spin-rotation and dipole−dipole coupling in HD compared to H2. More detailed analysis using models developed to describe relaxation in both condensed media and the gas phase indicates that transitions among the rotational states of H2 occur at a rate similar to those of HD in both toluene-d8 solution and in C60, in contrast to the situation in gas phase collisions between hydrogen and He or Ar, where the lifetimes of rotational states of HD are markedly shorter than those for H2. Measurements of the relative 1H chemical shifts of H2 and HD, the coupling constant JHD, and the widths of the HD peaks at various temperatures revealed only small effects with insufficient accuracy to warrant more detailed interpretation.
Co-reporter:Shufeng Ye, Minzhong Xu, Zlatko Bačić, Ronald Lawler, and Nicholas J. Turro
The Journal of Physical Chemistry A 2010 Volume 114(Issue 36) pp:9936-9947
Publication Date(Web):July 14, 2010
DOI:10.1021/jp104367j
We report rigorous quantum five-dimensional (5D) calculations of the translation-rotation (T-R) energy levels and wave functions of H2 inside aza-thia-open-cage fullerene (ATOCF). Translational and rotational excitations of this endohedral complex have been measured in a recent inelastic neutron scattering (INS) study, enabling direct comparison between theory and experiment. ATOCF has no symmetry, and therefore the intermolecular potential energy surface (PES) governing the T-R dynamics of H2 is strongly anisotropic. A pairwise additive PES is employed in the calculations. Inspection of the wave functions shows three regular quasi-1D translational modes aligned with the Cartesian x, y, and z axes, respectively. These and other translational excitations can be assigned with the Cartesian quantum numbers vx, vy, and vz. The radial anisotropy of the cage environment causes the splitting of the translational fundamental into three excitations whose frequencies differ substantially; the z mode directed toward the ATOCF orifice has the lowest frequency and is the most anharmonic. All three translational modes exhibit negative anharmonicity. The j = 1 rotational level of H2 is also split into a triplet, due to the angular anisotropy of the cage. The complete lifting of the degeneracies of the translational fundamental and the j = 1 triplet of the encapsulated H2 molecule that emerges from the calculations is also observed in the INS spectra of H2@ATOCF. The calculated magnitudes of both splittings, as well as the energies of the individual sublevels, rotational and translational, are in good agreement with the INS data.
Co-reporter:Yusuf Yagci, Steffen Jockusch and Nicholas J. Turro
Macromolecules 2010 Volume 43(Issue 15) pp:6245-6260
Publication Date(Web):June 16, 2010
DOI:10.1021/ma1007545
The use of photoinitiated polymerization is continuously growing in industry as reflected by the large number of applications in not only conventional areas such as coatings, inks, and adhesives but also high-tech domains, optoelectronics, laser imaging, stereolithography, and nanotechnology. In this Perspective, the latest developments in photoinitiating systems for free radical and cationic polymerizations are presented. The potential use of photochemical methods for step-growth polymerization is also highlighted. The goal is, furthermore, to show approaches to overcome problems associated with the efficiency, wavelength flexibility, and environmental and safety issues in all photoinitiating systems for different modes of activation. Much progress has been made in the past 10 years in the preparation of complex and nano-structured macromolecules by using photoinitiated polymerizations. Thus, the new and emerging applications of photoinitiated polymerizations in the field of biomaterials, surface modification, preparation of block and graft copolymers, and nanocomposites have been addressed.
Co-reporter:Yongjun Li, Xuegong Lei, Ronald G. Lawler, Yasujiro Murata, Koichi Komatsu and Nicholas J. Turro
The Journal of Physical Chemistry Letters 2010 Volume 1(Issue 14) pp:2135-2138
Publication Date(Web):June 28, 2010
DOI:10.1021/jz100645w
A series of H2@C60 derivatives covalently linked to a nitroxide radical has been synthesized. We report distance-dependent nuclear spin relaxivity of H2 in these derivatives. The results clearly indicate that the relaxivity of H2 is distance-dependent and in good agreement with the Solomon−Bloembergen equation, which predicts a 1/r6 dependence.Keywords (keywords): distance-dependent; H2@C60; inner sphere relaxivity; nitroxide radical; nuclear spin relaxation;
Co-reporter:Michael Frunzi, Xuegong Lei, Yasujiro Murata, Koichi Komatsu, Sho-Ichi Iwamatsu, Shizuaki Murata, Ronald G. Lawler and Nicholas J. Turro
The Journal of Physical Chemistry Letters 2010 Volume 1(Issue 9) pp:1420-1422
Publication Date(Web):April 15, 2010
DOI:10.1021/jz100336x
The bimolecular contribution, R1 (M−1 s−1), to the T1 of isolated H2 and H2O protons, as well as free H2O in organic solution, by paramagnetic metal complexes was determined. Isolation was achieved by encapsulation in a fullerene: H2 was trapped in pristine C60 or in C60 with a 13-atom opening, and H2O in an open-C60 with a 19-atom opening. The R1 values in the presence of the various M(acac)x complexes [M = Fe(III), Cr(III), Cu(II), Co(III)] scale with μeff2 of the metal complex. The R1 values were significantly smaller for the trapped species than the free H2O. Surprisingly, R1 was nearly identical for the all three endohedral proton pairs, even in different solvents. This suggests that the magnetic isolation effects of the carbon cage are not significantly affected by the solvent, the completeness of the carbon cage, or separation of the hydrogens by an oxygen atom.Keywords (keywords): endohedral fullerene; fullerene; H2@C60; relaxivity; trapped water; water;
Co-reporter:Steffen Jockusch, Olaf Zeika, Nithyanandhan Jayaraj, V. Ramamurthy, and Nicholas J. Turro
The Journal of Physical Chemistry Letters 2010 Volume 1(Issue 18) pp:2628-2632
Publication Date(Web):August 20, 2010
DOI:10.1021/jz101006s
A thioxanthone derivative containing a covalently attached 15N-labeled nitroxide was incarcerated into an octaacid nanocapsule. Photoexcitation of the thioxanthone chromophore generated electron spin polarization of the nitroxide. This spin polarization of the 15N-labeled nitroxide was transferred through the walls of the carcerand to a 14N-labeled nitroxide in external bulk solvent, a process that was directly observed by time-resolved EPR spectroscopy. The efficiency of the communication between the incarcerated guest and molecules in the bulk solvent was shown to be controlled by supramolecular factors such as Coulombic attraction and repulsion between the guest@host complex and charged molecules in the bulk solvent phase.Keywords (keywords): cucurbituril; laser flash photolysis; superexchange; TEMPO; time-resolved EPR;
Co-reporter:Naphtali A. O’Connor, Nathan Stevens, Diana Samaroo, Marissa R. Solomon, Angel A. Martí, Joanne Dyer, Harshad Vishwasrao, Daniel L. Akins, Eric R. Kandel and Nicholas J. Turro
Chemical Communications 2009 (Issue 19) pp:2640-2642
Publication Date(Web):20 Apr 2009
DOI:10.1039/B900290A
A phenanthridine derivative covalently linked to a ruthenium complex yields an imaging probe whose fluorescence intensity and lifetime change substantially in the presence of RNA.
Co-reporter:Marissa R. Solomon, J. Sivaguru, Steffen Jockusch, Waldemar Adam and Nicholas J. Turro
Photochemical & Photobiological Sciences 2009 vol. 8(Issue 7) pp:912-915
Publication Date(Web):24 Mar 2009
DOI:10.1039/B903848E
Physical and chemical quenching rate constants were measured for the reaction of singlet oxygen with oxazolidinone-functionalized enecarbamates to investigate the role of vibrational deactivation in product stereoselectivity.
Co-reporter:Steffen Jockusch;Yoshiro Mitsukami;Makoto Matsumoto;Taku Iwamura;Torsten Lindner;Andreas Flohr;Giuseppe di Massimo
Journal of Applied Polymer Science 2009 Volume 111( Issue 5) pp:2163-2170
Publication Date(Web):
DOI:10.1002/app.29209
Abstract
Superabsorbent polymer particles, consisting of partly neutralized, slightly crosslinked poly(acrylic acid), have been surface-crosslinked photochemically. Surface crosslinking is required for many applications of superabsorbent polymers, such as disposable diapers, to control the flow and absorption of liquids in the gel bed. Photoinduced surface crosslinking has been achieved under UV irradiation (200–300 nm) with (NH4)2S2O8 as a photoactivated crosslinking agent. In comparison with the currently used thermal ester bridging method for surface crosslinking, the new photochemical method generates superabsorbent particles with superior properties, such as an improved flow of liquid through the gel bed, which utilizes the entire gel bed. These improved properties have been shown by water absorption capacity studies, fluid flow dynamics, environmental scanning electron microscopy, and low-energy ion-scattering studies. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Co-reporter:Simone Moser;Thomas Müller;Andreas Holzinger;Cornelius Lütz;Steffen Jockusch;Bernhard Kräutler
PNAS 2009 Volume 106 (Issue 37 ) pp:15538-15543
Publication Date(Web):2009-09-15
DOI:10.1073/pnas.0908060106
Breakdown of chlorophyll is a major contributor to the diagnostic color changes in fall leaves, and in ripening apples and
pears, where it commonly provides colorless, nonfluorescent tetrapyrroles. In contrast, in ripening bananas (Musa acuminata) chlorophylls fade to give unique fluorescent catabolites (FCCs), causing yellow bananas to glow blue, when observed under
UV light. Here, we demonstrate the capacity of the blue fluorescent chlorophyll catabolites to signal symptoms of programmed
cell death in a plant. We report on studies of bright blue luminescent rings on the peel of very ripe bananas, which arise
as halos around necrotic areas in ‘senescence associated’ dark spots. These dark spots appear naturally on the peel of ripe
bananas and occur in the vicinity of stomata. Wavelength, space, and time resolved fluorescence measurements allowed the luminescent
areas to be monitored on whole bananas. Our studies revealed an accumulation of FCCs in luminescent rings, within senescing
cells undergoing the transition to dead tissue, as was observable by morphological textural cellular changes. FCCs typically
are short lived intermediates of chlorophyll breakdown. In some plants, FCCs are uniquely persistent, as is seen in bananas,
and can thus be used as luminescent in vivo markers in tissue undergoing senescence. While FCCs still remain to be tested
for their own hypothetical physiological role in plants, they may help fill the demand for specific endogenous molecular reporters
in noninvasive assays of plant senescence. Thus, they allow for in vivo studies, which provide insights into critical stages
preceding cell death.
Co-reporter:J. Sivaguru, Marissa R. Solomon, Thomas Poon, Steffen Jockusch, Sara G. Bosio, Waldemar Adam and Nicholas J. Turro
Accounts of Chemical Research 2008 Volume 41(Issue 3) pp:387
Publication Date(Web):February 13, 2008
DOI:10.1021/ar7001254
Photochirogenesis, the control of chirality in photoreactions, is one of the most challenging problems in stereocontrolled photochemistry, in which the stereodifferentiation has to be imprinted within the short lifetime of the electronically excited state. Singlet oxygen (1O2), an electronically excited molecule that is known to be sensitive to vibrational deactivation, has been selected as a model case for testing stereoselective control by vibrational deactivation. The stereoselectivity in the reaction of 1O2 with E/Z enecarbamates 1, equipped with the oxazolidinone chiral auxiliary, has been examined for the mode selectivity ([2 + 2]-cycloaddition versus ene-reaction) and the stereoselectivity in the oxidative cleavage of the alkenyl functionality to the methyldesoxybenzoin (MDB) product. Through the appropriate choice of substituents in the enecarbamate, the mode selectivity (ene versus [2 + 2]), which depends on the alkene geometry (E or Z), the steric bulk of the oxazolidinone substituent at the C-4 position, and the C-3′ configuration on the side chain, may be manipulated. Phenethyl substitution gives exclusively the [2 + 2]-cycloaddition product, irrespective of the alkene geometry. The stereoselection in the resulting methyldesoxybenzoin (MDB) product is examined in a variety of solvents as a function of temperature by using chiral GC analysis. The extent (% ee) as well as the sense (R versus S) of the stereoselectivity in the MDB formation for the E isomer depends significantly on solvent and temperature, whereas the corresponding Z isomers are not affected by such variations. The complex temperature and solvent effects are scrutinized in terms of the differential activation parameters (ΔΔS⧧, ΔΔH⧧) for the photooxygenation of E/Z-enecarbamates in various solvents at different temperatures. The enthalpy−entropy compensations provide a mechanistic understanding of the temperature dependence of the ee values for the MDB product and the difference in the behavior between the Z and E enecarbamates. The E enecarbamates show a relatively high contribution from the entropy term and an appreciable contribution from the enthalpy term; both terms possess the same sign. In contrast, the corresponding relative insensitivity of Z enecarbamates to temperature and solvent variation is convincingly explained by the near-zero ΔΔS‡ and ΔΔH‡. Such effects, associated with temperature- and solvent-dependent conformational factors, are most likely dictated by the stereogenic center at the C-3′ phenethyl substituent. The high stereocontrol during the photooxygenation of the chiral enecarbamates is shown to be independent of the steric demand of the oxazolidinone substituent at the C-4 position. In view of the reduced stereocontrol on deuteration of the oxazolidinone substituent at the C-4 position, we propose that the unusual stereoselective vibrational quenching of the attacking singlet oxygen (excited-state reactivity), a novel mechanistic concept, works in concert with the usual steric impositions (ground-state reactivity) exercised by the substituents to afford the high stereoselectivity observed in the dioxetane product during the [2 + 2] cycloaddition. Such synergistic interplay is held responsible for the highly stereoselective photooxidative cleavage of the chiral enecarbamates. The efficacy of stereocontrol in this photooxidation is demonstrated by kinetically resolving the epimers of the enecarbamate cleavage product (MDB) in essentially perfect stereoselectivity, a new methodology that we coin “photo-Pasteur-type kinetic resolution”.
Co-reporter:Jeremiah A. Johnson, Jeremy M. Baskin, Carolyn R. Bertozzi, Jeffrey T. Koberstein and Nicholas J. Turro
Chemical Communications 2008 (Issue 26) pp:3064-3066
Publication Date(Web):24 Apr 2008
DOI:10.1039/B803043J
Bifunctional, fluorinated cyclooctynes were used for the in situ “click” crosslinking of azide-terminated photodegradable star polymers, yielding photodegradable polymeric model networks with well-defined structures and tunable gelation times.
Co-reporter:Jeremiah A. Johnson;M. G. Finn;Jeffrey T. Koberstein
Macromolecular Rapid Communications 2008 Volume 29( Issue 12-13) pp:1052-1072
Publication Date(Web):
DOI:10.1002/marc.200800208
Co-reporter:Jeremiah A. Johnson;M. G. Finn;Jeffrey T. Koberstein
Macromolecular Rapid Communications 2008 Volume 29( Issue 16) pp:
Publication Date(Web):
DOI:10.1002/marc.200800411
No abstract is available for this article.
Co-reporter:Marissa Solomon, J. Sivaguru, Steffen Jockusch, Waldemar Adam and Nicholas J. Turro
Photochemical & Photobiological Sciences 2008 vol. 7(Issue 5) pp:531-533
Publication Date(Web):13 Mar 2008
DOI:10.1039/B719387D
Oxazolidinone-substituted enecarbamates offer a system to explore vibrational quenching and the strategic placement of CH bonds as a method for manipulating the stereoselectivity of photoreactions.
Co-reporter:Patrizia Costi;Luigi Zecca;Alberto Moscatelli;Alberto Albertini;Luigi Casella;Melvin Eisner;Luigi Bergamaschi;Chiara Bellei;Weslyn C. Ward;William D. Bush;Enrico Monzani;John D. Simon;Pier Raimondo Crippa;Mario Gallorini;Fabio A. Zucca;Kazumasa Wakamatsu;Shosuke Ito
PNAS 2008 Volume 105 (Issue 45 ) pp:17567-17572
Publication Date(Web):2008-11-11
DOI:10.1073/pnas.0808768105
Neuronal pigments of melanic type were identified in the putamen, cortex, cerebellum, and other major regions of human brain.
These pigments consist of granules 30 nm in size, contained in organelles together with lipid droplets, and they accumulate
in aging, reaching concentrations as high as 1.5–2.6 μg/mg tissue in major brain regions. These pigments, which we term neuromelanins,
contain melanic, lipid, and peptide components. The melanic component is aromatic in structure, contains a stable free radical,
and is synthesized from the precursor molecule cysteinyl-3,4-dihydroxyphenylalanine. This contrasts with neuromelanin of the
substantia nigra, where the melanic precursor is cysteinyl-dopamine. These neuronal pigments have some structural similarities
to the melanin found in skin. The precursors of lipid components of the neuromelanins are the polyunsaturated lipids present
in the surrounding organelles. The synthesis of neuromelanins in the various regions of the human brain is an important protective
process because the melanic component is generated through the removal of reactive/toxic quinones that would otherwise cause
neurotoxicity. Furthermore, the resulting melanic component serves an additional protective role through its ability to chelate
and accumulate metals, including environmentally toxic metals such as mercury and lead.
Co-reporter:Angel A. Martí, Steffen Jockusch, Nathan Stevens, Jingyue Ju and Nicholas J. Turro
Accounts of Chemical Research 2007 Volume 40(Issue 6) pp:402
Publication Date(Web):April 25, 2007
DOI:10.1021/ar600013q
We outline the different approaches taken by our group in the design of fluorescent hybridization sensors. Molecular beacons (MBs) and binary probes (BPs) using two dyes (2d-MB and 2d-BP, respectively) have been synthesized; these sensors serve as switches in emission upon binding to target biomolecules, such as DNA. These sensors allow for ratiometric fluorescence detection of polynucleotides (PNs) by visualization of the probes when bound to a target PN. Additionally, three-dye MBs (3d-MB) and BPs (3d-BP) have been developed, where an energy-transfer cascade is employed to decrease the overlap between the fluorophore emission spectra, resulting in a low direct excitation of the acceptor fluorophore. Pyrene-based MB (Py-MB) and BP (Py-BP), which possess the advantage of long fluorescence lifetimes, have also been synthesized. Time-resolved fluorescence spectra (TRES) can be used to discriminate between short-lived background fluorescence and long-lived fluorescence of the pyrene probes. This technique was demonstrated by time-resolving the signal of a Py-BP from the background fluorescence in Aplysia californica cell extracts.
Co-reporter:Hideaki Saito, J. Sivaguru, Steffen Jockusch, Joanne Dyer, Yoshihisa Inoue, Waldemar Adam and Nicholas J. Turro
Chemical Communications 2007 (Issue 8) pp:819-821
Publication Date(Web):14 Nov 2006
DOI:10.1039/B609177F
Photoisomerization of encapsulated Z-enecarbamates within the hydrophobic chiral cavities of γ-CD showed higher diastereoselectivities in the photoproducts than those obtained in solution. The selective encapsulation of the enecarbamates and the following isomerization process are both diastereoselectively controlled by γ-CD.
Co-reporter:Nathan Stevens, Joanne Dyer, Angel A. Martí, Marissa Solomon and Nicholas J. Turro
Photochemical & Photobiological Sciences 2007 vol. 6(Issue 8) pp:909-911
Publication Date(Web):24 Apr 2007
DOI:10.1039/B702631E
The process of modeling the fluorescence resonance energy transfer (FRET) process for a donor–acceptor pair can be rather challenging, yet few computer programs exist that allow such modeling to be done with relative ease. In order to address this, we have developed a Java-based program, FRETView, which allows numerous FRET parameters to be obtained with just a few mouse clicks. Being a Java-based program, it runs equally well on all the major operating systems such as Windows, Mac OS X, Linux, Solaris. The program allows the user to effortlessly input pertinent information about the donor–acceptor pair, including the absorption and/or emission spectra, and outputs the calculated FRET parameters in table format, as well as graphical plots.
Co-reporter:Chandima Abeywickrama;Hiroko Matsuda;Steffen Jockusch;Jilin Zhou;Young P. Jang;Bi-Xing Chen;Yasuhiro Itagaki;Bernard F. Erlanger;Koji Nakanishi;Janet R. Sparrow
PNAS 2007 Volume 104 (Issue 37 ) pp:14610-14615
Publication Date(Web):2007-09-11
DOI:10.1073/pnas.0706806104
The autofluorescent lipofuscin pigment A2E accumulates in retinal pigment epithelial cells with age and is particularly abundant
in some retinal disorders. To generate a polyclonal antibody that recognizes this pyridinium bisretinoid molecule, we immunized
rabbits with bovine serum albumin (BSA) conjugates in which the protein was linked to the A2E molecule via its pyridinium
ethanolamine moiety. Analysis by matrix-assisted laser desorption ionization/time of flight mass spectrometry (MALDI-TOF MS)
of the A2E–BSA conjugate indicated the presence of five intact A2E molecules covalently linked to BSA, thus deeming it a suitable
antigen for immunization. By immunocytochemical staining, the rabbit polyclonal antibody recognized A2E that had accumulated
in cultured cells, whereas dot-blot analysis revealed binding to both A2E and A2E-rabbit serum albumin (A2E–RSA) conjugate
but no cross-reactivity with various retinoids. Preimmune serum was nonreactive. In fluorescence spectroscopy studies, antibody-A2E
binding was evidenced by a fluorescence increase and by a blue-shift in the emission maximum consistent with a change in A2E
milieu upon antibody binding. The changes in fluorescence emission upon antibody binding could reflect several processes including
restrictions on trans-cis isomerization and intersystem crossing of photo-excited A2E.
Co-reporter:Irina V. Lebedeva;Ilyas Washington;Devanand Sarkar;Jennifer A. Clark;Robert L. Fine;Paul Dent;David T. Curiel;Paul B. Fisher
PNAS 2007 Volume 104 (Issue 9 ) pp:3484-3489
Publication Date(Web):2007-02-27
DOI:10.1073/pnas.0700042104
Effective therapies for most solid cancers, especially those that have progressed to metastasis, remain elusive because of
inherent and acquired resistance of tumor cells to conventional treatments. Additionally, the effective therapeutic window
for many protocols can be very narrow, frequently resulting in toxicity. The present study explores an anticancer strategy
that effectively eliminates resistant cancer cells without exerting deleterious effects on normal cells. This approach employs
melanoma differentiation-induced gene-7/interleukin-24 (mda-7/IL-24), a cancer-specific, apoptosis-inducing cytokine, in combination with nontoxic doses of a chemical compound from
the endoperoxide class that decomposes in water generating singlet oxygen. This combinatorial regimen specifically induced
in vitro apoptosis in prostate carcinoma cells, with innate resistance to chemotherapy or engineered resistance to mda-7/IL-24, as well as pancreatic carcinoma cells inherently resistant to any treatment modality, including mda-7/IL-24. Apoptosis induction correlated with increased cellular reactive oxygen species production and was prevented by general
antioxidants, such as N-acetyl-l-cysteine or Tiron. Induction of apoptosis in combination-treated cancer cells correlated with a reduction in the antiapoptotic
protein BCL-xL. In contrast, both normal prostate and pancreatic epithelial cells were unaffected by the single or combination treatment.
These provocative findings suggest that this combinatorial strategy might provide a platform for developing effective treatments
for therapy-resistant cancers.
Co-reporter:J. Sivaguru;Hideaki Saito;Marissa R. Solomon;Lakshmi S. Kaanumalle;Thomas Poon;Steffen Jockusch;Waldemar Adam;V. Ramamurthy;Yoshihisa Inoue
Photochemistry and Photobiology 2006 Volume 82(Issue 1) pp:123-131
Publication Date(Web):28 JUN 2008
DOI:10.1562/2005-06-15-RA-573
On photooxygenation of the optically active Z/E enecarbamates 1 (X =i-Pr) and 2 (X = Me) equipped with the oxazolidinone chiral auxiliary in methylene-blue (MB)-incorporated, alkali-metal (M = Li, Na, K, Cs, Rb), exchanged Y-type zeolites (MY-MB), oxidative cleavage of the alkenyl functionality releases the enantiomerically enriched methyl-desoxybenzoin (MDB) product. The extent (%ee) and/or the sense (R or S) of the stereoselectivity in the formation of the MDB product depends on the choice of the alkyl substiuent (i-Pr or Me) at the C-4 position of the oxazolidinone chiral auxiliary, the Z/E configuration of the alkene functionality in the enecarhamates, and the type of alkali metal in the zeolite. Most significantly—the highlight of this stuy—is the reversed sense (R or S) in the stereoselection when the photooxygena tion is run in CDCI3 solution versus inside the MY-MB zeolite. As a mechanistic rationale for this novel stereochemical behavior, we propose the combined action of spatial confine ment and metal-ion coordination (assessed by density-functional calculations) of the substrate within the zeolite supercage, both of which greatly reduce the freedom of the substrate and entropically manipulate the stereochemical outcome.
Co-reporter:Alberto Moscatelli;M. Francesca Ottaviani;Waldemar Adam;Anatoly Buchachenko;Steffen Jockusch;Nicholas J. Turro
Helvetica Chimica Acta 2006 Volume 89(Issue 10) pp:2441-2449
Publication Date(Web):25 OCT 2006
DOI:10.1002/hlca.200690224
At high concentrations of oxygen, the EPR spectrum of the nitroxide radical 4-oxo-TEMPO (= 4-oxo-2,2,6,6-tetramethylpiperidin-1-yloxy) is found to broaden significantly. In addition to the expected broadening, double integration of the EPR signals indicates that a significant fraction of the nitroxide spins has ‘disappeared’. In perfluoro(2-butyltetrahydrofuran) at 273 K, the extent of diminution of the EPR signal intensity is ca. 20%. The results are analyzed in terms of collision and supramolecular complexes between oxygen and 4-oxo-TEMPO. It is concluded that a supramolecular complex is responsible for the observed phenomenon.
Co-reporter:Hideaki Saito, J. Sivaguru, Steffen Jockusch, Yoshihisa Inoue, Waldemar Adam and Nicholas J. Turro
Chemical Communications 2005 (Issue 27) pp:3424-3426
Publication Date(Web):01 Jun 2005
DOI:10.1039/B504413H
Oxazolidinone-functionalized enecarbamates undergo diastereoselective E/Z photoisomerization upon direct and triplet sensitized irradiations with chiral/achiral sensitizers, showing that the enhanced product diastereoselectivity depends on the solvent and temperature.
Co-reporter:Steffen Jockusch;Zengmin Li;Jingyue Ju
Photochemistry and Photobiology 2005 Volume 81(Issue 2) pp:238-241
Publication Date(Web):30 APR 2007
DOI:10.1111/j.1751-1097.2005.tb00180.x
Two-photon excitation of a trifluorophore (6-carboxyfluorescein, N, N, N′, N′-tetramethyl-6-carboxyrhodamine and cyamine-5 monofunctional dye) labeled DNA, which has a scaffold of 26 nucleotides, was achieved using focused laser light of a Q-switched Nd-YAG laser (1064 nm). The observed fluorescence signature (emission ratio from the three fluorophores) of the labeled DNA after two-photon excitation is very different from the fluorescence signatures produced by one-photon excitation at different wavelenght. The additional fluorescence signatures produced by two-photon excitation of the fluorescent oligonucleotides will facilitate their use as combinatorial fluorescence energy transfer tags for multiplex genetic analysis.
Co-reporter:Ilyas Washington Dr.;Steffen Jockusch Dr.;Yasuhiro Itagaki Dr. ;Koji Nakanishi
Angewandte Chemie 2005 Volume 117(Issue 43) pp:
Publication Date(Web):12 OCT 2005
DOI:10.1002/ange.200501346
Eng und persönlich: Eng zusammenstehende Retinoidpolyene, wie sie auf dem rechten Sessel abgebildet sind, reagieren leicht mit Sauerstoff (rot) zu polyoxygenierten Verbindungen. Getrennte Polyene dagegen, wie sie auf dem linken Sofa zu sehen sind, werden nur eingeschränkt oxidiert.
Co-reporter:Nicholas J. Turro;
Proceedings of the National Academy of Sciences 2005 102(31) pp:10766-10770
Publication Date(Web):July 26, 2005
DOI:10.1073/pnas.0501376102
Co-reporter:Ilyas Washington, Steffen Jockusch, Yasuhiro Itagaki, Nicholas J. Turro,Koji Nakanishi
Angewandte Chemie International Edition 2005 44(43) pp:7097-7100
Publication Date(Web):
DOI:10.1002/anie.200501346
Co-reporter:Naphtali A. O’Connor, Nathan Stevens, Diana Samaroo, Marissa R. Solomon, Angel A. Martí, Joanne Dyer, Harshad Vishwasrao, Daniel L. Akins, Eric R. Kandel and Nicholas J. Turro
Chemical Communications 2009(Issue 19) pp:NaN2642-2642
Publication Date(Web):2009/04/20
DOI:10.1039/B900290A
A phenanthridine derivative covalently linked to a ruthenium complex yields an imaging probe whose fluorescence intensity and lifetime change substantially in the presence of RNA.
Co-reporter:Yongjun Li, Xuegong Lei, Xia Li, Ronald G. Lawler, Yasujiro Murata, Koichi Komatsu and Nicholas J. Turro
Chemical Communications 2011 - vol. 47(Issue 46) pp:NaN12529-12529
Publication Date(Web):2011/10/26
DOI:10.1039/C1CC15149E
1H NMR of two H2@C60 nitroxide derivatives has been characterized indirectly by reducing to their corresponding hydroxylamines. Nuclear spin relaxation of the endohedral H2 and external protons of the H2@C60 nitroxide and its corresponding hydroxylamine were measured and analyzed. The observed spectra are consistent with negligible scalar coupling between the unpaired electron and the endo-H2. An unexpectedly large bimolecular relaxivity induced in the hydroxylamine by the corresponding nitroxide can be explained by rapid hydrogen atom transfer between the two species.
Co-reporter:Jeremiah A. Johnson, Jeremy M. Baskin, Carolyn R. Bertozzi, Jeffrey T. Koberstein and Nicholas J. Turro
Chemical Communications 2008(Issue 26) pp:NaN3066-3066
Publication Date(Web):2008/04/24
DOI:10.1039/B803043J
Bifunctional, fluorinated cyclooctynes were used for the in situ “click” crosslinking of azide-terminated photodegradable star polymers, yielding photodegradable polymeric model networks with well-defined structures and tunable gelation times.
Co-reporter:Hideaki Saito, J. Sivaguru, Steffen Jockusch, Joanne Dyer, Yoshihisa Inoue, Waldemar Adam and Nicholas J. Turro
Chemical Communications 2007(Issue 8) pp:NaN821-821
Publication Date(Web):2006/11/14
DOI:10.1039/B609177F
Photoisomerization of encapsulated Z-enecarbamates within the hydrophobic chiral cavities of γ-CD showed higher diastereoselectivities in the photoproducts than those obtained in solution. The selective encapsulation of the enecarbamates and the following isomerization process are both diastereoselectively controlled by γ-CD.
Co-reporter:Yongjun Li, Xuegong Lei, Ronald G. Lawler, Yasujiro Murata, Koichi Komatsu and Nicholas J. Turro
Chemical Communications 2011 - vol. 47(Issue 8) pp:NaN2284-2284
Publication Date(Web):2010/12/20
DOI:10.1039/C0CC04862C
Bisadduct isomers of a H2@C60 derivative with nitroxide addends have been synthesized, isolated and characterized. The 1H NMRs of endohedral H2 of the major isomers show well-separated chemical shifts, which could be useful for structural assignment and identification of the purity of the C60 bisadduct isomers.
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