Hydrogen bonding in vitamin B6

Double-well potential energy surfaces for hydrogen bonding in crystalline vitamin B₆ have been associated with molecular environmental effects. New calculations, involving improved representations of a fragmentation model, include the introduction of a second pyridoxinium chloride system within the model in a “dimer-like” configuration. The new results confirm the double-well potential and the prediction of the experimentally observed position for the proton as being due essentially to environmental effects. Atomic difference maps are presented for the charge density distributions, which reflect the nature of the bonding as it depends on the proton position. Mulliken populations are examined particularly in relation to the “intermolecular” transfer of electrons.     

Low-lying (K π = 0+) states of gadolinium isotopes

The sd-interacting boson approximation (sd-IBA) and the df-interacting boson approximation (df-IBA) can be related to each other and the states of the interacting boson approximation model can be identified with the fully symmetric states in the sdf interacting boson approximation model. A systematic study of the sdf-IBA model showed that the constructed Hamiltonian can successfully describe the strong octupole correlations in the deformed nuclei. We showed that the interacting boson approximation may account for many of these K ^π ?=?0⁺ states. It was found that the calculated energy spectra of the gadolinium isotopes agree quite well with the experimental data. The observed B(E2) values were also calculated and compared with the experimental data.     

Cation migration upon adsorption of methanol in NaY and NaX faujasite systems: a molecular dynamics approach

Molecular dynamics simulations have been carried out to address the question of cation migration upon adsorption of methanol in NaY and NaX faujasite systems as a function of the loading. For NaY, it has been shown that, at low and intermediate loadings, SII cations can migrate toward the center of the supercage due to strong interactions with the adsorbates, followed by a hopping of SI' from the sodalite cage into the supercage to fill the vacant SII site. A SI' cation can also migrate across the double six ring and takes a SI' vacant position. SI cations mainly remain trapped in their initial sites whatever the loading. At high loading, only limited motions are observed for SII cations due to steric effects induced by the presence of adsorbates within the supercage. For NaX, the SIII' cations which occupy the most accessible adsorption sites are significantly moving upon coordination to the methanol molecules; the extent of this mobility exhibits a maximum for 48 methanol molecules per unit cell before decreasing at higher loadings due to steric hindrance. In addition, the SI' and SII cations remain almost trapped in their initial sites whatever the loading. Indeed, the most probable migration mechanism involves SIII' cation displacements into nearby SIII' sites.     

Modeling the concentration dependence of the methanol self-diffusivity in faujasite systems: comparison with the liquid phase

Molecular dynamics simulations were performed to understand further the concentration dependence of the self-diffusion of methanol in the faujasite zeolite systems. The evolution of the self-diffusivity was investigated as a function of coverage for DAY and NaY systems to study the effect of both the pore confinement and the presence of the extraframework cations within the supercage. It was found that the self-diffusivity decreases with loading for DAY, whereas for NaY it passes through a maximum at intermediate coverage, in agreement with pulse-field gradient NMR and quasi elastic neutron scattering data reported in similar systems. The activation energies of the methanol diffusion corresponding to a combination of both intra- and intercage motions were evaluated as a function of the coverage. The simulated trends are interpreted on the basis of the predominant interactions which take place in both systems. Finally, the preferential arrangement of the adsorbate molecules are provided and compared with those simulated in the liquid phase. For the fully loaded materials, it was seen that the methanol molecules form a one-dimensional hydrogen-bonded chain along the channels in DAY whereas only dimers are present in NaY.     

氮杂冠醚研究——Ⅲ.N-取代苯并氮杂冠醚的质谱研究

本文报道两种单取代苯并氮杂冠醚(1)和四种双取代苯并氮杂冠醚(2)的电子轰击(EI)质谱及其分子离子峰。化合物(1)的特征峰,m/z 372,342,236,192,136,121,109,56;化合物(2)的特征峰:m/z[M-109]~ ,[M/2]~ ,[M/2±13]~ 等。据此提出了单取代和双取代苯并氮杂冠醚经电子轰击断裂的可能途径。     

Three New Diarylpropanes from Dioscorea composita

Three new diarylpropanes were isolated from the dried rhizomes of Dioscorea composita Hemsl., and their structures were determined as 1, 3-bis-(2-hydroxy-4-methoxyphenyl) propane (1), 1, 3-bis-(2, 4-dihydroxyphenyl)propane (2), 1-(2′-hydroxy-4′-O-β-D- glucopymnosy-phenyl)-3-(2“, 4“-dihydroxyphenyl)propane (3), by spectroscopic analysis, respectively.     

A New Saponin Transformed from Ginsenoside Rh1 by Bacillus subtilis

A novel saponin was isolated from the transformed products of ginsenoside Rh1 by Bacillus subtilis. It‘s structure was determined to be 3-O-β-D-glucopyranosyl-6-O-β-D-glucopyranosyl-20 (S)-protopanaxatriol on the basis of the spectral data.     

A New Diterpene Acid from the Flowers of Heteropappus altaicus

A new compound, named heteraltaic acid was isolated from the flowers of Heteropappus altaicus (willd) Novopokr. The compound was elucidated as (5R, 6S, 8aS) -5-[2-(3-furyl) ethyl-5, 6, 8a-trimethyl-4a, 5, 6, 7, 8, 8a -hexahydro-l-naphthalenecarboxylic acid] by the combination of 1D and 2D NMR techniques (HSQC, HMBC) and X-ray analysis.     

Radiometric and fluorimetric determination of aminosilanes and protein covalently bound to thermally pretreated glass substrates

Derivatization of solid soda-lime glass spheres with aminosilanes and the stability of these groups near physiological pH in flow streams of aqueous buffered solutions are described. The presence of immobilized and adsorbed amines in the nanomolar range is confirmed by using two independent methods, one based on a radiotracer and the other on the fluorescent marker, fluorescamine. A method for covalently attaching bovine serum albumin to the beads is described.