The newly built 177 nm all-solid-state deep ultraviolet (DUV) laser photoionization mass spectrometer finds a unique advantage to identify porphyrins that bear ionization energies close to 7.0 eV. We observed dramatic selectivity of tetraphenylporphyrins (TPPs) pertaining to varied photochemical processes initiated by the DUV laser excitation. Single-photon ionization was found dominant for 2H-TPP resulting in a fragmentation-free mass spectrum; photoinduced dehydrogenation was observed for zinc TPP, but both dehydrogenation and demetalation are noted for copper TPP. Along with first-principle calculations, we demonstrate how the photoinduced reactions vary with residual energies of photoionization, highest occupied molecular orbital–lowest unoccupied molecular orbital gaps, donor–acceptor orbital overlaps, single-step barriers, and whether or not there is a major process of structural rearrangement. It is demonstrated that the rotation of benzene ring under proper laser radiation prompts dehydrogenation process; also, metallo-TPPs do not support direct demetalation, but it is selectively accomplishable along with dehydrogenation and successive hydrogenation processes. These findings not only provide insights into the hydrogen atom transfer in porphyrins initiated by ultraviolet laser but also suggest promising applications of the DUV laser in designed synthesis and chemical modification of porphyrins.

Cluster assembly materials with unique electronic and optical properties are significant for a variety of potential applications but often susceptible to intermolecular interactions which may alter the performance determined by their individual components. For the first time, here we report the assembly of a pyridine-protected tungsten–copper cluster on porous alumina, and find superior optical limiting (OL) properties retainable for multilevel clustering due to unaffected reverse saturable absorption (RSA) and constant photo-excited triplet states. Also clarified is that this transition metal W–Cu cluster bears an interesting framework structure with reasonable stability reinforced by strong donor–acceptor charge-transfer interactions.

We report the synthesis of penicillamine-protected Ag20 nanoclusters (NCs), with properties of high monodispersity, red fluorescence and water solubility. Full characterization of the Ag20 NCs is addressed, along with first-principles optimization calculations, revealing the chemical composition and structure of the as-prepared Ag NCs within a molecular formula [Ag20(DPA)18-H]−. Moreover, natural bond orbital (NBO) analysis demonstrates the charge-transfer interactions between the ligand and Ag atoms, and helps in understanding the origins of fluorescence of Ag20 NCs related to the ligand-to-metal charge transfer (LMCT) mechanism. Further, fluorescence chemosensing of the Ag20 NCs is demonstrated for tracing copper ions with high sensitivity and selectivity in aqueous solution.

The conversion of glycerol to epichlorohydrin (GTE) is of great interest because the product is widely used in plastics, rubbers and adhesives, and also contributes to the disposal of the reactant glycerol, a major by-product in biodiesel production. Here we find effective catalysis by small gold clusters for the GTE reaction in water with an enhanced selectivity towards the desired product. Along with natural bond orbital (NBO) analysis rationalizing the donor–acceptor charge-transfer interactions, we illustrate the mechanism for bond activation in the reactants and intermediates over gold cluster catalysts, and present thermodynamically and kinetically favoured reaction pathways for dehydrochlorination in GTE processes.

•Largely enhanced fluorescence is found for the BSA-Lyz Au/Ag NCs.•The BSA-Lyz Au/Ag NCs exhibited high selectivity for Hg2+ over other metal ions.•The limit of detection of BSA-Lyz Au NCs was as low as 0.7 nM for Hg2+.•The Hg2+ probe (BSA-Lyz Au NCs) is of low cytotoxicity and can be used in living cell imaging.We have synthesized gold/silver nanoclusters (NCs) under the protection of both bovine-serum-albumin (BSA) and lysozyme (Lyz) and found that the NCs protected by the mixed-proteins give rise to largely enhanced stability and fluorescence, enabling promising applications for chemosensing and bioimaging. The enhanced fluorescence of Au NCs was found to be exclusively quenched at the presence of Hg2+ ions with an ultralow detection limit up to ∼0.7 nM. It is also interesting to find that the BSA-Lyz-Au NCs are nontoxic and available for fluorescence imaging of Hg2+ detection in MCF-7 cells. The low cytotoxicity, good penetrability and fluorescence sensitivity of BSA-Lyz-Au NCs suggest promising biological applications. Similar observations were also addressed for the Ag system, indicating general applicability of this facile strategy based on BSA-Lyz mixed proteins for the protection of metal NCs.Download high-res image (139KB)Download full-size image

•Water-soluble and biocompatible Ag14(SG)12 nanoclusters are synthesized.•The composition and structure are determined via a joint of experimental and theoretical investigations.•NBO analysis reveals the charge-transfer interactions between silver and the ligand.•Interestingly found was that the fluorescence of Ag14 NCs can be largely enhanced due to the presence of lysozyme.•Fluorescence of Ag14NCs-Lys can be exclusively quenched with the addition of Hg2+ ions.Employing glutathione (HSG) as a protecting ligand, we have synthesized water-soluble and biocompatible Ag14(SG)12 nanoclusters (Ag14 NCs) of which the composition and structure are determined via high-resolution mass spectrometry, fingerprint spectroscopy and DFT calculations. Natural bond orbital (NBO) analysis on a basis of first-principles theoretical calculations demonstrates the donor–acceptor orbital overlaps and charge-transfer interactions between silver and the ligand HSG. Further, it is interestingly found that the fluorescence of Ag14 NCs can be largely enhanced at the presence of lysozyme distinguishing from other proteases which we have tested, revealing the feasibility of Ag14 NCs as chemosensing to identify lysozyme. Also found is that, the fluorescence on-state of the obtained Ag14NCs-Lys can be exclusively switched off at the addition of Hg2+ ions with an ultralow detection limit of ∼16.2 nM. This interesting finding reveals Ag14 NCs a versatile chemosensor to identify lysozyme from proteases and to detect mercury ions from various cations.Download high-res image (164KB)Download full-size image

•The water-soluble Au13 clusters under the protection of binary thiolates are synthesized.•The formula and structure are determined via experimental and theoretical investigations.•Natural bond orbital (NBO) analysis reveals the origin of the Au13 MPCs stability.•The water-soluble Au13 MPCs are found to be a decent candidate for chemosensing and bioimaging.Here we report a successful synthesis of water-soluble 13-atoms gold clusters under the monolayer protection of binary thiolates, glutathione and penicillamine, under a molecular formula of Au13(SG)5(PA)7. This monolayer-protected cluster (MPC) finds decent stability and is demonstrated to possess an icosahedral geometry pertaining to structural accommodation in contrast to a planar bare Au13 of local minima energy. Natural bond orbital (NBO) analysis depicts the interaction patterns between gold and the ligands, enlightening to understand the origin of enhanced stability of the Au13 MPCs. Further, the water-soluble Au13 MPCs are found to be a decent candidate for chemosensing and bioimaging.Download high-res image (75KB)Download full-size image

Utilizing a strong electron acceptor molecule tetracyanoquinodimethane (TCNQ) as probe, we demonstrate how the electronic features and geometric sites determine charge-transfer interactions of noble metal clusters with organic molecules. First-principle calculations by searching local minimum energies suggest that the TCNQ complexes with Ag13, Au12Ag1, Au1Ag12 and Au13 all favor edge-site adsorption, and their structures are highly comparable and possess metal–N–metal bonds. Further analysis on frontier molecular orbitals (FMOs) and natural population analysis (NPA) reveals that it's easier for Ag13/Au1Ag12 clusters to transfer electrons to TCNQ as compared with Au13/Ag1Au12. Spin density isosurfaces indicate that the charge transfer from these 13-atom clusters to TCNQ leads to electronic shell closure of the metal clusters. The difference in the electronegativities of Ag and Au, as well as the significant relativistic effect of gold, results in varying donor–accepter interactions sensitive to the coordination number of the doping atom for both Au12Ag1 and Au1Ag12 clusters.

We present here a joint theoretical and experimental study on the oxidation reactivity of glycerol catalysed by chemically pure small Au clusters in the absence and presence of H2O2. From high-resolution mass spectrometry, fruitful products of glyceraldehyde, glyceric acid, tartronic acid, mesoxalic acid and glycolic acid are observed pertaining to the successive Jones oxidation process associated with C–O and C–H bond activation. We then fully demonstrate the reaction pathways on the basis of a complementary-active-sites mechanism, revealing the favourable dehydration of glycerol followed by oxidation to form glyceraldehyde and carboxylic acids in the presence of small Au clusters and H2O2. It is found that the Aun/H2O2 system undertakes a heterolytic mechanism by firstly transferring an O-atom from H2O2 to the Au cluster forming an active intermediate, on which hydride abstraction and subsequent oxygen rebound become thermodynamically possible, promoting the C–H insertion reaction and further oxidation of aldehyde to carboxylic acids.

Three hydrogen-bonded organic–inorganic frameworks (HOIFs) are synthesized. Along with full characterization and a comparison with similarly synthesized deuterated counterparts, we reveal that hydrogen-bond interactions of the HOIFs dominate the thermostability, porosity and selectivity in dye filtration on alumina membranes.

Correction for ‘One-pot one-cluster synthesis of fluorescent and bio-compatible Ag14 nanoclusters for cancer cell imaging’ by Jie Yang, et al., Nanoscale, 2015, 7, 18464–18470.

Interactions between tetracyanoquinodimethane (TCNQ) and two typical silver clusters Ag13 and Ag20 are studied by first-principles DFT calculations. Charge transfer (CT) from silver clusters to TCNQ molecules initiates the Ag–N bond formation at selective sites resulting in the formation of different isomers of Ag13–TCNQ and Ag20–TCNQ complexes. We show here a comprehensive spectroscopic analysis for the two CT complexes on the basis of Raman and infrared activities. Furthermore, frontier molecular orbital (FMO) and natural bond orbital (NBO) analysis of the complexes provides a vivid illustration of electron cloud overlap and interactions. The behavior of TCNQ adsorbed on the tetrahedral Ag20 cluster was even found in good agreement with the experimental measurement of TCNQ molecules on a single-crystal Ag(111) surface. This study not only endeavors to clarify the charge-transfer interactions of TCNQ with silver, but also presents a finding of enhanced charge transfer between Ag13 and TCNQ indicating potential for candidate building blocks of granular materials.

Here we show a study of vibrational spectroscopic identification of a few typical organic compounds which are known as the main sources of organic aerosols (OAs) particle matter in air pollution. Raman and IR spectra of isoprene, terpenoids, pinenes and their mixture are meticulously examined, showing distinguishable intrinsic vibrational spectroscopic fingerprints for these chemicals, respectively. As a reference, first-principles calculations of Raman and infrared activities are also conducted. It is interestingly found that, the experimental spectra are peak-to-peak consistent with the DFT (Density Functional Theory)-calculated vibrational activities. Also found is that, in a certain case such as for β-pinene, a dimer model, rather than an isolated single molecular model, reproduces the experimental results, indicating unneglected intermolecular interactions. Starting with this study, we are endeavoring to advocate a database of Raman/IR fingerprint spectra for OA haze identification.We show here a vibrational spectroscopic study of isoprene, pinenes and their mixture endeavoring to provide fingerprint identification for the sources of organic aerosols (OAs) in air pollution.

Weak intermolecular interactions in aniline-pyrrole dimer clusters have been studied by the dispersion-corrected density functional theory (DFT) calculations. Two distinct types of hydrogen bonds are demonstrated with optimized geometric structures and largest interaction energy moduli. Comprehensive spectroscopic analysis is also addressed revealing the orientation-dependent interactions by noting the altered red-shifts of the infrared and Raman activities. Then we employ natural bond orbital (NBO) analysis and atom in molecules (AIM) theory to have determined the origin and relative energetic contributions of the weak interactions in these systems. NBO and AIM calculations confirm the V-shaped dimer cluster is dominated by N−H···N and C−H···π hydrogen bonds, while the J-aggregated isomer is stabilized by N−H···π, n→π* and weak π···π* stacking interactions. The noncovalent interactions are also demonstrated via energy decomposition analysis associated with electrostatic and dispersion contributions.

We present here an in-depth study upon the interaction between a neutral cluster Al13 and a typical ligand tetrahydrofuran (THF) via density functional theory (DFT) calculation. It is found that electron delocalization over the framework of Al13 and THF facilitates ligand-to-Al13 charge transfer leading to enhanced stability for the superhalogen cluster Al13. Further study on the stabilization of Al13(THF)n cluster complexes with n = 1–8 reveals that the adsorption of more THF ligands gradually enhances the total binding energy and the total electronic charge transfer from the ligand to Al13. The bonding nature and stabilization of Al13(THF)n cluster are then demonstrated by rationalizing the interactions between superatomic and molecular orbitals of Al13 and THF, respectively.

We summarize here the research advances on the reactivity of metal clusters. After a simple introduction of apparatuses used for gas-phase cluster reactions, we focus on the reactivity of metal clusters with various polar and nonpolar molecules in the gas phase and illustrate how elementary reactions of metal clusters proceed one-step at a time under a combination of geometric and electronic reorganization. The topics discussed in this study include chemical adsorption, addition reaction, cleavage of chemical bonds, etching effect, spin effect, the harpoon mechanism, and the complementary active sites (CAS) mechanism, among others. Insights into the reactivity of metal clusters not only facilitate a better understanding of the fundamentals in condensed-phase chemistry but also provide a way to dissect the stability and reactivity of monolayer-protected clusters synthesized via wet chemistry.

Small-molecule-protected silver nanoclusters have smaller hydrodynamic diameter, and thus may hold greater potential in biomedicine application compared with the same core-sized, macromolecule (i.e. DNA)-protected silver nanoclusters. However, the live cell imaging labeled by small-molecule-protected silver nanoclusters has not been reported until now, and the synthesis and atom-precise characterization of silver nanoclusters have been challenging for a long time. We develop a one-pot one-cluster synthesis method to prepare silver nanoclusters capped with GSH which is bio-compatible. The as-prepared silver nanoclusters are identified to be Ag14(SG)11 (abbreviated as Ag14, SG: glutathione) by isotope-resolvable ESI-MS. The structure is probed by 1D NMR spectroscopy together with 2D COSY and HSQC. This cluster species is fluorescent and the fluorescence quantum yield is solvent-dependent. Very importantly, Ag14 was successfully applied to label lung cancer cells (A549) for imaging, and this work represents the first attempt to image live cells with small-molecule-protected silver nanoclusters. Furthermore, it is revealed that the Ag14 nanoclusters exhibit lower cytotoxicity compared with some other silver species (including silver salt, silver complex and large silver nanoparticles), and the explanation is also provided. The comparison of silver nanoclusters to state-of-the-art labeling materials in terms of cytotoxicity and photobleaching lifetime is also conducted.

Nitrogen and oxygen doped hollow carbon spheres (HCSs) have been prepared by pyrolysis of poly(o-phenylenediamine) (PoPD) submicrospheres, which were synthesized by a facile polymerization procedure with an environmental-friendly dopant glycine. Utilizing o-phenylenediamine (oPD) and glycine as the precursors, we are also motivated by the recognition that effective heteroatom doping increases the supercapacitor performance of carbon materials. The as-prepared N- and O- doped HCSs exhibit an enlarged specific surface area (∼355 m2 g−1) and pore volume (∼0.14 cm3 g−1), and they have superior performance in supercapacitors owing to the synergies gained from effective heteroatom doping, their hollow structures, and their good mesoporosity. The reasonable capacitance performance coupled with the facile synthesis procedure suggests supercapacitor applications.

Ligand-protected metal nanoclusters (NCs) having hydrodynamic diameters and fluorescent properties have reasonable potential for ion detection and bio-imaging applications by taking advantage of their smaller sizes and degradability as compared with larger nanoparticles. By controlling the pH value, here we have synthesized a fluorescent silver nanocluster, Ag–glutathione, which is found to be a versatile chemosensor operative for the detection of both manganese (Mn2+) and iodine (I−) ions. Mn2+ and I− are further distinguished by the ratiometric absorption spectrometry method. Care was taken for sufficient spectral analyses, based upon which we have fully demonstrated the chemosensing mechanisms of Ag@glutathione (Ag@SG) NCs applied in ion detection. Having expounded this issue, we further investigated the potential application of Ag@SG NCs in bio-imaging. It is interesting to find that the as-prepared Ag@SG NCs are nontoxic and available for fluorescence imaging of MCF-7 cells, with on/off alternation of fluorescence emission in the presence of Mn2+ or I− ions. The low cytotoxicity, good penetrability and on/off fluorescence property of Ag@SG NCs in MCF-7 cells suggest promising biological applications.

We have synthesized monodispersed Au25 nanoclusters (NCs) stabilized with eco-friendly glutathione and report here an insight into their interactions with dye molecules. In the presence of such gold NCs, consistent fluorescence quenching was observed for all the dye molecules that we examined in this study regardless of their maximum emission wavelengths. The steady-state and time-resolved spectroscopic results demonstrate that the weakened luminance is associated with the protective ligand pertaining to a static quenching mechanism. Having expounded this issue, we further employed proper laser irradiation enabling dissociation of Au25(SG)18 so as to attain a transformation of nonplasmonic NCs into plasmonic gold nanoparticles (NPs) via photo-assisted aggregation of the dissociated gold clusters. As a result, emission enhancement for these dyes was observed, which is largely attributed to the local electromagnetic field enhancement of gold NPs. The alternation of fluorescence quenching to emission enhancement reflects an accommodation of quantum size effects upon the ligand-stabilized gold clusters.

Bridging the gap between atoms and macroscopic matter, clusters continue to be a subject of increasing research interest. Among the realm of cluster investigations, an exciting development is the realization that chosen stable clusters can mimic the chemical behavior of an atom or a group of the periodic table of elements. This major finding known as a superatom concept was originated experimentally from the study of aluminum cluster reactivity conducted in 1989 by noting a dramatic size dependence of the reactivity where cluster anions containing a certain number of Al atoms were unreactive toward oxygen while the other species were etched away. This observation was well interpreted by shell closings on the basis of the jellium model, and the related concept (originally termed “unified atom”) spawned a wide range of pioneering studies in the 1990s pertaining to the understanding of factors governing the properties of clusters.Under the inspiration of a superatom concept, advances in cluster science in finding stable species not only shed light on magic clusters (i.e., superatomic noble gas) but also enlightened the exploration of stable clusters to mimic the chemical behavior of atoms leading to the discovery of superhalogens, alkaline-earth metals, superalkalis, etc. Among them, certain clusters could enable isovalent isomorphism of precious metals, indicating application potential for inexpensive superatoms for industrial catalysis, while a few superalkalis were found to validate the interesting “harpoon mechanism” involved in the superatomic cluster reactivity; recently also found were the magnetic superatoms of which the cluster-assembled materials could be used in spin electronics. Up to now, extensive studies in cluster science have allowed the stability of superatomic clusters to be understood within a few models, including the jellium model, also aromaticity and Wade–Mingos rules depending on the geometry and metallicity of the cluster. However, the scope of application of the jellium model and modification of the theory to account for nonspherical symmetry and nonmetal-doped metal clusters are still illusive to be further developed. It is still worth mentioning that a superatom concept has also been introduced in ligand-stabilized metal clusters which could also follow the major shell-closing electron count for a spherical, square-well potential.By proposing a new concept named as special and general superatoms, herein we try to summarize all these investigations in series, expecting to provide an overview of this field with a primary focus on the joint undertakings which have given rise to the superatom concept. To be specific, for special superatoms, we limit to clusters under a strict jellium model and simply classify them into groups based on their valence electron counts. While for general superatoms we emphasize on nonmetal-doped metal clusters and ligand-stabilized metal clusters, as well as a few isovalent cluster systems. Hopefully this summary of special and general superatoms benefits the further development of cluster-related theory, and lights up the prospect of using them as building blocks of new materials with tailored properties, such as inexpensive isovalent systems for industrial catalysis, semiconductive superatoms for transistors, and magnetic superatoms for spin electronics.

We present here a study of gas-phase reactivity of cobalt sulfide cluster anions ComSn– with molecular oxygen. Nascent ComSn– clusters were prepared via a laser ablation source and reacted with oxygen in a fast flow reactor under thermal collision conditions. We chose 18O2 in place of 16O2 to avoid mass degeneration with sulfur, and a time-of-flight (TOF) mass spectrometer was used to detect the cluster distributions in the absence and presence of the reactant. It was found that oxygen–sulfur exchange occurs in the reactions for those with specific compositions (CoS)n– and (CoS)nS– (n = 2–5) according to a consistent pathway, “ComSn– + 18O2 → ComSn–118O– + S18O”. Typically, for “Co2S2– + 18O2” we have calculated the reaction coordinates by employing the density functional theory (DFT), where both the oxygen–sulfur exchange and SO molecule release are thermodynamically and kinetically favorable. It is noteworthy that the reaction with molecular oxygen (triplet ground state) needs to overcome a spin excitation as well as a large O–O activation energy. This study sheds light on the activation of molecular oxygen by cobalt sulfides on one hand and also provides insight into the regeneration mechanism of cobalt oxides from the counterpart sulfides in the presence of oxygen gas on the other hand.

We have investigated the gas-phase reactivity of silver clusters with ethanethiol in a fast-flow tube reactor. The primary cluster products observed in this reaction are AgnSH– and AgnSH2–, indicating C–S bond activation, together with interesting byproducts H3S– and (H3S)2–. Agn– clusters with an odd number of valence electrons (n = even) were observed to be more reactive than those with an even number of electrons—a feature previously only observed in the reactivity of Agn– with triplet oxygen, indicating that radical active sites play a role in their reactivity. Furthermore, the reactivity dramatically increases with large flow rate of ethanethiol being introduced in the flow tube. Theoretical investigations on the reactivity of Ag13– and Ag8– with ethanethiol indicate that both Ag13– and Ag8– face significant barriers to reactivity with a single ethanethiol molecule. However, Ag8– reacts readily in a cooperative reaction with two ethanethiol molecules, consistent with the dramatic increase in reactivity with a large flow rate. Further hydrogen-transfer reactions may then release an ethylene molecule or an ethyl radical resulting in the observed AgnSH– species.

Nitrogen and oxygen doped hollow carbon spheres (HCSs) have been prepared by pyrolysis of poly(o-phenylenediamine) (PoPD) submicrospheres, which were synthesized by a facile polymerization procedure with an environmental-friendly dopant glycine. Utilizing o-phenylenediamine (oPD) and glycine as the precursors, we are also motivated by the recognition that effective heteroatom doping increases the supercapacitor performance of carbon materials. The as-prepared N- and O- doped HCSs exhibit an enlarged specific surface area (∼355 m2 g−1) and pore volume (∼0.14 cm3 g−1), and they have superior performance in supercapacitors owing to the synergies gained from effective heteroatom doping, their hollow structures, and their good mesoporosity. The reasonable capacitance performance coupled with the facile synthesis procedure suggests supercapacitor applications.

Interactions between tetracyanoquinodimethane (TCNQ) and two typical silver clusters Ag13 and Ag20 are studied by first-principles DFT calculations. Charge transfer (CT) from silver clusters to TCNQ molecules initiates the Ag–N bond formation at selective sites resulting in the formation of different isomers of Ag13–TCNQ and Ag20–TCNQ complexes. We show here a comprehensive spectroscopic analysis for the two CT complexes on the basis of Raman and infrared activities. Furthermore, frontier molecular orbital (FMO) and natural bond orbital (NBO) analysis of the complexes provides a vivid illustration of electron cloud overlap and interactions. The behavior of TCNQ adsorbed on the tetrahedral Ag20 cluster was even found in good agreement with the experimental measurement of TCNQ molecules on a single-crystal Ag(111) surface. This study not only endeavors to clarify the charge-transfer interactions of TCNQ with silver, but also presents a finding of enhanced charge transfer between Ag13 and TCNQ indicating potential for candidate building blocks of granular materials.

We present here a joint theoretical and experimental study on the oxidation reactivity of glycerol catalysed by chemically pure small Au clusters in the absence and presence of H2O2. From high-resolution mass spectrometry, fruitful products of glyceraldehyde, glyceric acid, tartronic acid, mesoxalic acid and glycolic acid are observed pertaining to the successive Jones oxidation process associated with C–O and C–H bond activation. We then fully demonstrate the reaction pathways on the basis of a complementary-active-sites mechanism, revealing the favourable dehydration of glycerol followed by oxidation to form glyceraldehyde and carboxylic acids in the presence of small Au clusters and H2O2. It is found that the Aun/H2O2 system undertakes a heterolytic mechanism by firstly transferring an O-atom from H2O2 to the Au cluster forming an active intermediate, on which hydride abstraction and subsequent oxygen rebound become thermodynamically possible, promoting the C–H insertion reaction and further oxidation of aldehyde to carboxylic acids.