Mechanism of the CO oxidation reaction on O-precovered Pt(111) surfaces studied with near-edge x-ray absorption fine structure spectroscopy

The mechanism of CO oxidation reaction on oxygen-precovered Pt(111) surfaces has been studied by using time-resolved near-edge x-ray absorption fine structure spectroscopy. The whole reaction process is composed of two distinct paths: (1) a reaction of isolated oxygen atoms with adsorbed CO, and (2) a reaction of island-periphery oxygen atoms after the CO saturation. CO coadsorption plays a role to induce the dynamic change in spatial distribution of O atoms, which switches over the two reaction paths. These mechanisms were confirmed by kinetic Monte Carlo simulations. The effect of coadsorbed water in the reaction mechanism was also examined.     

Conformational peculiarities of alcohols incorporated in lyotropic and thermotropic liquid crystals

Conformational characteristics of 1-butanol incorporated not only in hexagonal and lamellar aggregates formed by a lyotropic liquid crystal composed of sodium octanoate, 1-butanol, and water but also in a thermotropic liquid crystal, 4'-methoxybenzylidene-4-n-butylaniline (MBBA), have been investigated from 2H NMR quadrupolar splittings of the perdeuterated and partially deuterated compounds. In the lyotropic phases, 1-butanol shows strong trans preferences and renders itself extended, and octanoate decreases the trans fraction toward the methyl terminal to fill the inner space of the aggregate on behalf of 1-butanol. In MBBA, 1-butanol prefers globular conformations. This tendency was also indicated from the phase behaviors of 1-butanol/MBBA and 1-decanol/MBBA systems. In the nematic field, two successive C-C bonds of 1-butanol mostly adopt g+/-g+/- conformations, which are formed in the vicinity of the headgroup of 1-decanol in the lamella of the sodium octanoate/1-decanol/water system. A large degree ofconformational freedom near the hydroxyl group of alcohols, being shown by ab initio molecular orbital calculations at the Gaussian-2 level, permits them to change conformation for each environment.     

Laser-induced orientational change of nematic liquid crystalline molecules mediated by photochromic reactions of surface azobenzenes

The alignment of nematic liquid crystalline (LC) molecules with respect to the LC cell surface was regulated between the homeotropic (H) state and the parallel (P) state by the photochromic trans—cis isomerization of surface-attached azobenzene (Az) moieties. By bringing the angular-selective photoreaction into the system, the orientational order in the P state was significantly improved to attain a universal orientational axis over the entire irradiated area, which was rotatable and erasable photochemically. Laser pulse experiments revealed that the allignment relaxation time τ was reduced from 1000 to 30 ms by increasing the pulse intensity from 10 to 20 mJ cm⁻². Strong coupling between the LC and Az molecules was indicated.     

Regioselective lithiation of II-(arene)chromium tricarbonyl complexes

Chromium tricarbonyl complexes of 3-methoxybenzyl alcohol and related compounds were selectively lithiated at the 4-position in contrast to the corresponding metal free arene compounds. The resulting 4-lithio complexes were converted to the 4-substituted arene compounds in moderate to excellent yields through the reactions with proper electrophiles and subsequent demetalation.     

NAD(P)+-NAD(P)H model. 38. Reduction of aldehyde by 1,4-dihydroquinolin derivative

Benzaldehyde are reduced to benzyl alcohol by a model compound of NAD(P)H almost quantitatively. Reductions of some other aldehydes are also mentioned.     

Optically active copolyamides by melt and solution condensation polymerization

The melt and solution condensation copolymerization of nylon salts which were prepared from d-camphoric acid and adipic acid with hexamethylenediamine were carried out, and optically active copolyamides were obtained. The copolyamides obtained had a positive specific rotation. The specific rotations for the copolyamides increased with increasing content of d-camphoryl units in the copolymers. The optical rotatory dispersion of the copolyamides had positive curves and were found to fit the simple Drude equation. The λ_c values of the polymers obtained by the melt and solution condensation polymerization were 241 mμ and 245 mμ, respectively.     

High performance liquid chromatography equipped with a cathodic detector and column-switching device as a high-throughput method for a phosphatase assay with p-nitrophenyl phosphate

A preparative high-speed counter-current chromatography (HSCCC) method for isolation and purification of coumarin compounds from the Chinese medicinal plant Peucedanum decursivum (Miq.) Maxim (Zihuaqianhu in Chinese) was successfully established by using light petroleum-ethyl acetate-methanol-water (5:5:7:4, v/v) as the two-phase solvent system. The upper phase of light petroleum-ethyl acetate-methanol-water (5:5:7:4, v/v) was used as the stationary phase of HSCCC. Nodakenetin (2.8 mg), 6.1 mg of Pd-C-IV, 7.3 mg of Pd-D-V, 4.7 mg of ostruthin, 7.8 mg of decursidin and 11.2 mg of decursitin C with the purity of 88.3%, 98.0%, 94.2%, 97.1%, 97.8% and 98.4%, respectively, were separated successfully in one-step separation from 150 mg of crude sample from P. decursivum (Miq.) Maxim. After purified by HSCCC again with light petroleum-ethyl acetate-methanol-water (5:5:4:5, v/v) as the two-phase solvent system, the purity of (I) can reach 99.4%. The structures of all the compounds were identified by 1H NMR and 13C NMR.     

General synthesis of sugar-pendant 1,3-propanediamines containing a C-glycoside linkage

A straightforward route to C-glycoside linked sugar-pendant 1,3-propanediamines is described. The three-step preparation procedure involves (1) C-glycosylation of an OH-protected α-glycosyl halide with malononitrile, (2) catalytic hydrogenation of the nitriles to amines, and (3) deprotection of acetyl groups via acid-catalyzed hydrolysis. In the case of the galactose derivative, excess sodiomalononitrile promotes the second addition of a carbanion in the first step. The β-anomeric configuration was confirmed by X-ray crystallography of the glycosylated intermediates. This method demonstrates a general method to access a new class of carbohydrate-pendant C-glycoside chelators.     

Kinetic study of the electron-transfer oxidation of the phenolate anion of a vitamin E model by molecular oxygen generating superoxide anion in an aprotic medium

Electron-transfer reduction of molecular oxygen (O2) by the phenolate anion (1-) of a vitamin E model, 2,2,5,7,8-pentamethylchroman-6-ol (1H), occurred to produce superoxide anion, which could be directly detected by a low-temperature EPR measurement. The rate of electron transfer from 1- to O2 was relatively slow, since this process is energetically unfavourable. The one-electron oxidation potential of 1- determined by cyclic voltammetric measurements is sufficiently negative to reduce 2,2-bis(4-tert-octylphenyl)-1-picrylhydrazyl radical (DOPPH*) to the corresponding one-electron reduced anion, DOPPH-, suggesting that 1- can also act as an efficient radical scavenger.     

Retention behavior of bile acid derivatives using cyclodextrin in the mobile phase in high-performance liquid chromatography

The retention behavior of 3-(1-anthroyl)bile acids together with bile acid glucuronides, sulfates, and 12-dehydro derivatives is examined by the addition of cyclodextrin to the mobile phase in reversed-phase high-performance liquid chromatography. The data suggest that the functional group at the 12 position of the steroid moiety may be the important factor for the formation of the inclusion complex from the solute and cyclodextrin. The separation of these bile acid derivatives is much improved by this inclusion chromatography.