Hydrogen-bonding abilities for phenols assessed by quantitative analyses of their partition coefficients derived from different partitioning systems

We recently proposed a new hydrogen-accepting scale, S(HA), on the basis of the heat of formation calculated by the conductor-like screening model (COSMO) method. In this work, the same approach was applied to a series of compounds with a common hydrogen-donor group. Thus the S(HA) values for monosubstituted phenols were calculated and used for correlating their log P(oct) values (P(oct): 1-octanol/water partition coefficient) with log P(CL) (P(CL): chloroform/water partition coefficient) and log P(E) (P(E): butyl ether/water partition coefficient). It was demonstrated that the S(HA) parameter works effectively, providing excellent correlations whose physicochemical meanings are well rationalized in terms of hydrogen-bonding characteristics of the substituents.     

A recyclable catalyst for asymmetric transfer hydrogenation with a formic acid-triethylamine mixture in ionic liquid

A novel task-specific ionic ligand with an imidazolium salt moiety was synthesized, and its catalytic ability and recyclability for asymmetric transfer hydrogenation of acetophenone derivatives with a formic acid-triethylamine azeotropic mixture in an ionic liquid [bmim][PF6] was examined.     

Inversion of enantioselectivity of asymmetric biocatalytic decarboxylation by site-directed mutagenesis based on the reaction mechanism

The introduction of two mutations (G74C/C188S) based on the estimated reaction mechanism resulted in the inversion of enantioselectivity of arylmalonate decarboxylase, which catalyses the asymmetric decarboxylation of arylmethylmalonate to give optically active arylpropionate.     

13C-Spingitter-Relaxationszeiten von verschiedenen Polymethacrylaten in Lösung

Ohne Zusammenfassung     

Resonance Raman spectrum of selenium thin film

The resonance Raman spectrum of a selenium thin film at 20 K has been measured with the 514.5 nm excitation. A series of overtones, nv₇ (n = 1–5), v₂ + nv₇ (n = 0–3) and v₁₀ have been observed where v₇, v₂ and v₁₀ are the fundamental vibrations of the Se₈ ring molecule. The broadness of these bands at 20K suggests that the thin film contains randomly orientated Se₈ ring molecules.     

Experimental and theoretical study on cation radicals of cyclopropane,cyclobutane and cyclopentane

Cation radicals of cycloalkanes have been produced for the first time in γ-irradiated rigid solutions using fluoromethane as a matrix. Observed ESR spectra are analyzed by ab initio MO calculations; molecular geometries of the cations are optimized for several low-lying doublet states by the energy gradient method. Based on the optimized geometry thus determined the hyperfine splitting constants are calculated by the pseudo-orbital theory. Large Jahn-Teller distortions are calculated for the carbon rings and the H-C-H frames of the cation radicals. The distortions are consistent with the nodal picture of singly occupied orbitals. The calculated hfs constants are sensitive to the change in geometry due to a large contribution of spin-delocalization. The average of the calculated proton hfs constants is compatible with the observed ESR spectra which indicates that all the protons of the individual cations have become equivalent owing to the dynamic Jahn-Teller distortion.     

Transient behavior of secondary emission of ZnTe under band-to-band excitation

Time characteristics of secondary emissions have been measured in ZnTe at 82K under the excitation into the fundamental absorption band by subnanosecond light pulses. The decay time of polariton luminescence has been determined to be about 100 ps. On the other hand, the time behavior of the intensity of the sharp 2LO-phonon line has been found to coincide with that of the exciting pulse. This result is consistent with the resonance Raman scattering mechanism.     

Critical behavior of a non-uniform system

The correlation function of the local order parameter fluctuations in a non-uniform system with an interface is calculated by means of the mean field approximation. Some special limits are of particular interest and there the explicit forms of the correlation are given in three dimensions as well as in four dimensions.