Reaction mechanism and the role of copper in the photooxidation of alcohol over Cu/Nb2O5

Loading of a small amount of copper on Nb(2)O(5) significantly enhances the activity of alcohol photooxidation without organic solvents. Alcohol is adsorbed on the Lewis acid site (Nb(V)) to form an alkoxide species. Photogenerated holes and electrons on Cu/Nb(2)O(5) are trapped by the adsorbed alkoxide and Cu(II) species to form the alkoxide carbon radical and Cu(I) species. The formed alkoxide carbon radical is converted to a carbonyl compound and then desorbed. Finally, the reduced Cu(I) sites are reoxidized by reaction with O(2). The alcohol photooxidation over Nb(2)O(5) takes place under not only UV irradiation but also under visible light irradiation up to 450 nm, although the band gap of Nb(2)O(5) is 390 nm (3.2 eV). DFT calculations reveal that 1) the surface donor level derived from the adsorbed alkoxide species is located in the forbidden band, 2) direct electron transition from the surface donor level to the conduction band takes place by absorbing a photon, 3) the excitation energy from surface donor level to the Nb 4d conduction band is lower than that from the O 2p valence band to Nb 4d. The kinetic study and FT/IR spectra suggest that Cu(I) acts as an effective desorption site for the products. Based on these results, we conclude that copper functions as an effective redox promoter and desorption site for the product.     

Kinetics and dynamics in physisorption of CH3Cl on HOPG: surface temperature and molecular orientation dependence

We report a study of kinetics and dynamics in physisorption of CH(3)Cl on a highly-oriented pyrolytic graphite (HOPG). Thermal energy atom scattering (TEAS) was used to probe the kinetics of thermal CH(3)Cl adsorption on HOPG during the coverage evolution. The desorption energy of CH(3)Cl on HOPG changes from 0.25 to 0.30 eV with increasing surface coverage, suggesting the attractive interaction between CH(3)Cl molecules on the surface. On the other hand, the oriented molecular beam scattering was used to monitor the dynamical interaction of CH(3)Cl with HOPG at zero coverage, demonstrating that the CH(3)Cl scattering intensity depends on the molecular orientation of the incident CH(3)Cl. The observed steric preference is not sensitive to the surface temperature. These results suggest that the moderate anisotropy in the interaction potential induces the molecular-orientation dependence of energy dissipation during the transient trapping into the physisorption well.     

Thermal decomposition of 2-butanol as a potential nonfossil fuel: a computational study

The thermochemistry and kinetics of the pyrolysis of 2-butanol have been conducted using ab initio methods (CBS-QB3 and CCSD(T)) and density functional theory (DFT). The enthalpies of formation and bond dissociation energies of some alcohols including 2-butanol and its derived radicals have been calculated. A variety of simple and complex dissociations have been examined. The results indicated that dehydration to 1- and 2-butene through four-center transition states is the most dominant channel at low to moderate temperatures (T ≤ 700 K), where formation of butenes is kinetically and thermodynamically more favorable than other complex and simple bond scission reactions. Although the C-C bond fission channels require more energy than needed for some complex decomposition reactions, the former pathways predominate at higher temperatures (T ≥ 800 K) due to the higher values of the pre-exponential factors. The progress of the complex decomposition reactions has been followed through intrinsic reaction coordinate (IRC) calculations to understand the mechanism of transformation of 2-butanol to different products.     

Total synthesis of (+)-papulacandin D

A total synthesis of (+)-papulacandin D has been achieved in 31 steps, in a 9.2% overall yield from commercially available materials. The synthetic strategy divided the molecule into two nearly equal sized subunits, the spirocyclic C-arylglycopyranoside and the polyunsaturated fatty acid side-chain. The C-arylglycopyranoside was prepared in 11 steps in a 30% overall yield from triacetoxyglucal. The fatty acid side-chain was also prepared in 11 steps in a 30% overall yield from geraniol. The key strategic transformations in the synthesis are: (1) a palladium-catalyzed, organosilanolate-based cross-coupling reaction of a dimethylglucal-silanol with an electron-rich and sterically hindered aromatic iodide and (2) a Lewis-base catalyzed, enantioselective allylation reaction of a dienal and allyltrichlorosilane. A critical element in the successful execution of the synthesis was the development of a suitable protecting group strategy that satisfied a number of stringent criteria.     

Total synthesis of (+)-negamycin and its 5-epi-derivative

(+)-Negamycin was prepared in 13 steps in an overall yield of 31% from commercially available ethyl (R)-(+)-4-chloro-3-hydroxybutanoate. The key step in the reaction sequence was a highly stereoselective asymmetric Michael addition of chiral amine (−)-21 [(1S,2R)-(−)-2-methoxybornyl-10-benzylamine] into the α,β-unsaturated carbonyl moiety of key intermediate 8, thus establishing the second chiral center in (+)-negamycin. 5-epi-Negamycin was also prepared in a similar fashion.     

Potential Response of Monolayer‐Modified Indium Tin Oxide Electrodes to Indole Compounds

Potential response of indium tin oxide (ITO) electrode modified by treatment with disuccinimidyl suberate (DSS) was investigated to various target molecules. Distinctively, the DSS‐modified ITO electrode exhibited a potential shift to the molecules possessing an indole group such as tryptophan, tryptamine and indole propionic acid, while little response to benzoic acid, phenylalanine, proline, proline amide, and arginine was observed. In addition, the combination of this specificity to indoles and enantioselective affinity of human serum albumin (HSA), which was additionally immobilized on the DSS‐modified ITO electrode, brought about enantioselective potential response to tryptophan.     

An artificial model of photosynthetic photosystem II: visible-light-derived O2 production from water by a di-μ-oxo-bridged manganese dimer as an oxygen evolving center

Visible-light-derived O(2) production was yielded by conjugating water oxidation catalysis by [(OH(2))(terpy)Mn(μ-O)(2)Mn(terpy)(OH(2))](3+) as an oxygen evolving center model and photo-sensitization of [Ru(bpy)(3)](2+) as a photoexcitation center model at an interlayer of mica.