Katsutoshi Ohkubo

Structures and binding energies of benzene–methane and benzene–benzene complexes. An ab initio SCF/MP2 study

Ab initio SCF/MP2 potentials are calculated on benzene–methane and benzene–benzene complexes. Although no energy stabilization appears at the Hartree–Fock level, a small but non-negligible stabilization in energy is observed at the MP2 level in both complexes, indicating the importance of the dispersion energy. Besides the dispersion energy, the electrostatic interaction plays some role in determining the relative stabilities in several cases. The most stable structure of the benzene–methane complex adopts a C3v symmetry with methane lying on the benzene C6 axis and one hydrogen atom pointing towards benzene. The binding energy of this structure is –1.95 kcal mol–1 from MP2/MIDI-4** calculations and –1.09 kcal mol–1 from MP2/6-31G** calculations, where a p-polarization function is added only on the H atoms of methane. The benzene–methane complex is much less stable than the benzene–benzene complex.

Ligand effects of ruthenium 2,2′-bipyridine and 1,10-phenanthroline complexes on the electrochemical reduction of CO2

Electrochemical reduction of CO2catalysed by [RuL1(L2)(CO)2]2+[L1,L2=(bipy)2, (bipy)(dmbipy), (dmbipy)2, or (phen)2], [Ru(phen)2(CO)Cl]+(phen = 1,10-phenanthroline), and [RuL(CO)2Cl2][L = 2,2′-bipyridine (bipy) or 4,4′-dimethyl-2,2′-bipyridine (dmbipy)] were carried out by controlled-potential electrolysis at –1.30 V vs. saturated calomel electrode in acetonitrile–water (4 : 1, v/v), MeOH, or MeCN–MeOH (4 : 1, v/v). In acetonitrile–water (4 : 1, v/v) no difference in activities between the catalysts was observed, however in MeOH the amounts of carbon monoxide produced became larger than those of HCO2– upon introduction of the dmbipy ligand. This is attributed to the equilibrium constants among the reaction intermediates [RuL1(L2)(CO)2]2+, [RuL1(L2)(CO)-{C(O)OH}]+, and [RuL1(L2)(CO)(C02–)]+ which become smaller on substitution of bipy by dmbipy, because of the donor property of the CH3 group.

A novel photocatalytic asymmetric synthesis of (R)-(+)-1,1′-bi-2-naphthol derivatives by oxidative coupling of 3-substituted-2-naphthol with Δ-[Ru(menbpy)3]2+[menbpy = 4,4′-di(1R,2S,5R)-(–)-menthoxycarbonyl-2,2′-bipyridine], which posseses molecular helicity

The asymmetric synthesis of (R)-(+)-1,1′-bi-2-naphthol [or (R)-(+)-1,1 ′-bi-3-methoxy-2-naphthol] from 2-naphthol (or 3-methoxy-2-naphthol) is performed photocatalytically by using the chiral ruthenium complex, M(C3)-Δ-[Ru(menbpy)3]2+[M(C3)= counterclockwise molecular helicity along the C3 axis, menbpy = 4,4′-di(1R,2S,5R)-(–)-menthoxycarbonyl-2,2′-bipyridine] as a photosensitizer and[Co(acac)3](acac–= acetylacetonato) as an oxidant.

Catalytic activity of a novel water-soluble cross-linked polymer imprinted by a transition-state analogue for the stereoselective hydrolysis of enantiomeric amino acid esters

Abstract A novel water-soluble cross-linked polymer catalyst containing l -histidine and quarternary trimethylammonium groups, which was imprinted by a racemic transition-state analogue of phenyl 1-benzyloxycarbonyl-3-methylpentylphosphonate for the hydrolysis of p -nitrophenyl N -(benzyloxycarbonyl)- l (or d )-leucinate (Z- l (or d )-Leu-PNP), exhibited the notable substrate stereospecificity for Z- l -Leu-PNP in the hydrolyses of enantiomeric amino acid p -nitrophenyl esters in 10 vol% DMSO (or MeCN)—Tris buffer pH 7.15) at 303 K.

Successful photocatalytic reduction of methylviologen (MV2+) with [Cu(NN)(PPh3)2]+ (NN = 2,9-dimethyl-1,10-phenanthroline or 4,4',6,6'-tetramethyl-2,2'-bipyridine) upon near-UV-light irradiation and a novel solvent effect on its catalytic activity

Le methylviologene (MV 2+ ) est reduit photocatalytiquement par les complexes du titre dans un solvant alcool-eau. Les rendements quantiques diminuent de dimephen>tetrabipy>dibipy>phen. Mecanisme

Rate-enhancement of hydrolysis of long-chain amino acid ester by cross-linked polymers imprinted with a transition-state analogue: Evaluation of imprinting effect in kinetic analysis

Acceleration property of a cross-linked polymer catalyst for the hydrolysis of N-dodecanoyl leucine-p-nitrophenyl ester is attributed to the molecularly imprinting of phenyl-1-undecylcarbonylamino-3-methylbutyl phosphonate as the template of transition-state analogue (TSA) and 4-[(3 � -methacryloylamino)ethyl]imidazole as the binding site of the polymer catalyst. Equimolar complex of the template of the TSA and the binding site of imidazole-containing monomer through the electrostatic interaction and hydrophobic effect was confirmed by 1 H NMR measurements and the complex was copolymerized with hydrophobic styrene monomer and 10% divinylbenzene cross-linker. A control polymer without the template, but with the cross-linker, was also prepared. After removal of the template, imidazole-containing imprinted polymer gave a ca. two-fold rate-enhancement in comparison to the non-imprinted polymer.

Theoretical study on oxygen exchange accompanying alkaline hydrolysis of esters and amides. The role of water for the exchange reaction

Abstract The hydrolysis of esters and amides accompanies a fast reaction, which results in exchange of carbonyl 18O to 16O coming from solvent water. The present study considered two paths as the oxygen exchange mechanism. One, Path 1 called the direct path, is the mechanism that a proton of the OH fragment directly moves from the OH to the 18O fragment in the tetrahedral intermediate. The other, Path 2 called the water-assisted mechanism, is that one water molecule assists transferring a proton to make an 18OH fragment. The MP2/6-31+G* level of theory estimated rather high ΔEgas‡(TD) for the direct path of methylacetate and N-methylacetamide (21.8 and 19.7 kcal mol−1, respectively). The ΔEgas‡(H2O), the activation barrier for the water-assisted mechanism, is very low both for the ester (3.8 kcal mol−1) and for the amide (2.8 kcal mol−1). The ΔG‡(H2O) and ΔG‡(OH), calculated activation free energies including solvent effect, are small in comparison with those observed for the breakdown of TD intermediates to exchange or hydrolysis products. The present MO calculation suggests that one solvent water acts as one of the reactants and facilitates both proton transfer from the OH fragment and proton acceptance from the water to form the new 18OH fragment. It is likely that the oxygen exchange reaction accompanying hydrolysis of esters and amides proceeds via the water-assisted mechanism.

Influence of cross-linking monomer and hydrophobic styrene comonomer on stereoselective esterase activities of polymer catalyst imprinted with a transition-state analogue for hydrolysis of amino acid esters

Abstract Polymer catalysts, cross-linked with N,N′-ethylene (C2) {or butylene (C4)}-bisacrylamide containing l -histidine and quaternary trimethylammonium groups were imprinted with a racemic transition-state analogue of phenyl 1-benzyloxycarbonyl-3-methylpentylphosphonate for the hydrolysis of p-nitrophenyl N-(benzyloxycarbonyl)- l (or d )-leucinate {Z- l (or d )-Leu-PNP}. Maximal stereoselectivity ( l / d =8.4) was obtained by using N,N′-C4-bisacrylamide cross-linked polymer catalyst, which was copolymerized with hydrophobic styrene monomer.

The Artificial Evolution of an Enzyme by Random Mutagenesis: The Development of Formaldehyde Dehydrogenase

A unique variant of glutathione independent formaldehyde dehydrogenase of Pseudomonas putida was obtained by random mutagenesis using the PCR-reaction. This YM042 mutant, S318G, was a cold-adapted formaldehyde dehyrogenase. The activity at 29 °C of the variant was 1.7-fold higher than that of the wild type. The Km values of the mutant at 37 °C were 0.40 mM for NAD+ and 2.5 mM for formaldehyde, while those of the wild-type were 0.18 mM for NAD+ and 2.1 mM for formaldehyde. The catalytic efficiency for formaldehyde was about 1.5-fold greater in the mutant than in the wild-type enzyme. The optimum pHs and temperatures of the mutant and the wild-type enzyme were 7.5, and 8.0 and 37 °C, and 47 °C, respectively. The thermal stability of the mutant was lower than that of the wild type.

Enantioselective and photocatalytic oxidation of 1,1′-bi-2-naphthol with a chiral ruthenium complex which includes molecular helicity

Abstract 1,1′-Bi-2 -naphthol was oxidized catalytically and enantioselectively ( ≤ 15.2 % e.e.), by using the chiral ruthenium complex, Δ-[Ru (menbpy) 3 ] 2+ (menbpy = 4,4′-dimenthoxycarbonyl-2,2′-bipyridine) as a photocatalyst and [Co (acac) 3 ] (Hacac=pentane-2,4-dione) as an oxidant under photoirradiation.