Water sandwiched by a pair of aromatic rings in a proton-conducting metal-organic framework.

The interactions between water molecules and aromatic rings are known to be common and important in physics, chemistry and life sciences. Benzene-water complexes are the main prototype systems for O-Hπ and lone-pair (lp)π interactions in theoretical research, however solid state examples are very rare. Here, the solid state example of water sandwiched by a pair of aromatic rings is observed in a silver-mellitate framework, where lpπ and O-Hπ interactions coexist. The coexistence of these two interactions has been further verified by theoretical calculations. In addition, ammonium ions and water molecules as proton sources, and strongly H-bonded nets as the pathway of proton transport, make the reported MOFs (metal-organic frameworks) exhibit distinct proton conduction.

Energetics and kinetics of Cu atoms and clusters on the Si(111)-7 × 7 surface: first-principles calculations.

Exploring the properties of noble metal atoms and nano- or subnano-clusters on the semiconductor surface is of great importance in many surface catalytic reactions, self-assembly processes, crystal growth, and thin film epitaxy. Here, the energetics and kinetic properties of a single Cu atom and previously reported Cu magic clusters on the Si(111)-(7 × 7) surface are re-examined by the state-of-the-art first-principles calculations based on density functional theory. First of all, the diffusion path and high diffusion rate of a Cu atom on the Si(111)-(7 × 7) surface are identified by mapping out the total potential energy surface of the Cu atom as a function of its positions on the surface, supporting previous experimental hypothesis that the apparent triangular light spots observed by scanning tunneling microscopy (STM) are resulted from a single Cu atom frequently hopping among adjacent adsorption sites. Furthermore, our findings confirm that in the low coverage of 0.15 monolayer (ML) the previously proposed hexagonal ring-like Cu6 cluster configuration assigned to the STM pattern is considerably unstable. Importantly, the most stable Cu6/Si(111) complex also possesses a distinct simulated STM pattern with the experimentally observed ones. Instead, an energetically preferred solid-centered Cu7 structure exhibits a reasonable agreement between the simulated STM patterns and the experimental images. Therefore, the present findings convincingly rule out the tentative six-atom model and provide new insights into the understanding of the well-defined Cu nanocluster arrays on the Si(111)-(7 × 7) surface.

Self-assembly of an unprecedented polyoxomolybdate anion [Mo20O66]12- in a giant peanut-like 62-core silver-thiolate nanocluster.

A polyoxometalate-templated silver thiolate nanocluster, [Ag62(S(t)Bu)40(Mo20O66)(Mo6O19)3(CH3CN)2]·(CF3SO3)4 (1), has been isolated, in which a giant peanut-like silver(i)-thiolate cluster [Ag62(S(t)Bu)40](22+) encapsulates an unprecedented [Mo20O66](12-) polyoxoanion core. It opens a new approach for the synthesis of both elusive polyoxometalates and high-nuclearity silver(i)-thiolate nanoclusters.

A highly sensitive C3-symmetric Schiff-base fluorescent probe for Cd2+.

A new C3-symmetric Schiff-base fluorescent probe (L) based on 8-hydroxy-2-methylquinoline has been developed. As expected, the probe L can display high fluorescent selectivity for Cd(2+) over Zn(2+) and most other common ions in neutral ethanol aqueous medium. Moreover, the mechanism of the L-Cd(2+) complex has been confirmed by X-ray crystallography and density functional theory calculation results. More importantly, L could be used to image Cd(2+) within living cells.

Highly enantioselective catalytic system for asymmetric copolymerization of carbon dioxide and cyclohexene oxide.

A new ligand can be easily prepared, and its intramolecular dinuclear zinc complexes act as a high performance catalyst for the asymmetric alternating copolymerization of cyclohexene oxide and CO2 under very mild conditions (1 atm CO2 , room temperature), affording completely alternating polycarbonates with up to 93.8 % enantiomeric excess (ee) and 98 % yield. A high Mn value of 28 600 and a relatively narrow polydispersity (Mw /Mn ratio) of 1.43 were also achieved.

A new fluorescent probe for Al(3+) based on rhodamine 6G and its application to bioimaging.

A water-soluble rhodamine-based derivative (L) has been rationally designed for selective recognition of Al(3+) in aqueous medium with good sensitivity. The addition of Al(3+) to the aqueous solution of L induces a remarkable fluorescence enhancement along with obvious color change detected by the naked eye, due to the ring-opening mechanism of the rhodamine spirolactam, which has been proved by single crystal diffraction analyses directly. The recognizing behavior has been investigated both experimentally and computationally. Furthermore, the fluorescent probe can also be used as a bioimaging reagent for detection of Al(3+) in living cells.

DFT investigation on mechanisms and stereoselectivities of [2 + 2 + 2] multimolecular cycloaddition of ketenes and carbon disulfide catalyzed by N-heterocyclic carbenes.

The first theoretical investigation using density functional theory (DFT) methods to study the detailed reaction mechanisms of stereoselective [2 + 2 + 2] multimolecular cycloaddition of ketene (two molecules) and carbon disulfide (CS2, one molecule) which is catalyzed by N-heterocyclic carbene (NHC) is presented in this paper. The calculated results indicate that this reaction occurs through four steps: the complexation of NHC with ketene (channel 1a) rather than with CS2 (channel 1b), addition of CS2 (channel 2b) but not dimerization of ketene (channel 2a), formal [4 + 2] cycloaddition with a second molecule of ketene (channel 3a) rather than intramolecular [2 + 2] cycloaddition (channel 3b), and finally regeneration of NHC. The second step is revealed to be the rate-determining step. Moreover, the stereoselectivities associated with the chiral carbon center and the carbon double bond are predicted to be respectively determined in the second and third steps and respectively R and E configurations dominated, which are in good agreement with the experimental results. Furthermore, the possible mechanisms of the identical [2 + 2 + 2] cycloaddition catalyzed by N,N-dimethylpyridin-4-amine (DMAP) have also been investigated to help understand the ring closure mechanism proceeding in the third step.

N-heterocyclic carbene catalyzed reaction of phthalaldehydes: controllable stereoselective synthesis of polyhydroxylated spiro- and fused indenones dictated by the structure of NHC catalysts.

The N-heterocyclic carbene catalyzed stereoselective dimerization reactions of phthalaldehydes produced polyhydroxylated spiro- or fused indenones. The reaction pathways were dictated by the structures of NHC catalysts. Under the catalysis of a imidazole carbene, phthalaldehydes produced dihydroxylspiro[indene-2,1'-isobenzofuran]-3-ones in good to excellent yields, whereas a triazole carbene catalyzed reaction of phthalaldehydes afforded fully cis-trihydroxylindeno[2,1-a]inden-5-ones in high yields. This work not only provides a highly efficient method for the construction of valuable polyhydroxyl substituted indene derivatives that are not easily assembled by other synthetic means but also reflects the versatility of organocatalysis using N-heterocyclic carbenes.

A 1,8-naphthyridine-based fluorescent chemodosimeter for the rapid detection of Zn2+ and Cu2+.

A novel fluorescent chemodosimeter based on 1,8-naphthyridine exhibits high selectivity to Zn(2+) and Cu(2+). When 1-(7-acetamino-1,8-naphthyridyl)-2-(6-diacetaminopyridyl)ethene was mixed with CuCl2, hydrolysis of the acetamino group catalyzed by Cu(2+) complex was first observed. Resulting from coordination and hydrolysis catalyzed by the corresponding complex of Zn(2+) or Cu(2+), the highly effective fluorescent detection of Zn(2+) and Cu(2+) is realized with Zn(2+)-selective dual-emission and Cu(2+)-selective ON-OFF behavior.

[A quantum chemistry investigation on antimalarial mechanism of Qinghaosu based on cleavage of the peroxide bridge].

AIM: To investigate antimalarial mechanism of Qinghaosu ( QHS) and its derivatives. METHODS: The electronic structure of QHS and its derivatives were completely optimized and calculated at B3LYP/6-31G * level, while the route was at HF/STO-3G level. RESULTS: The peroxide bridge is the active center of QHS and induced by ferrous iron to produce cyclic product. CONCLUSION: Heme can link with QHS derivatives.