Ab initio calculation of the electronic structure and the barrier to pyramidal inversion for H3S+

The electronic structure of H₃S⁺ is examined by ab initio MO calculations (STO 3G) and is compared with those of other XH₃ type molecules. The barrier to pyramidal inversion and the proton affinity of H₂S are calculated to be 34.8 and 225.05 kcal/mol respectively. Computations are made with respect to a model A₃S⁺ which is employed to discuss the barrier to pyramidal inversion of H₃S⁺, where A corresponds to an electromagnetive substituent or an electron donating one.     

Thermal degradation mechanisms of liquid crystalline aromatic polyesters studied by pyrolysis–gas chromatography/mass spectrometry

The thermal degradation mechanisms of liquid crystalline aromatic polyesters (LCPs) prepared from p-hydroxybenzoic acid (PHB), biphenol (BP), and terephthalic acid (TA) were studied by pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS). The LCP containing deuterated terephthalate units and the LCPs that have different comonomer ratios were examined. On the basis of the pyrolysis products determined, the origin of the main pyrolysis products (benzene, phenol, biphenyl, phenyl benzoate, etc.) from the corresponding comonomer units were estimated and their thermal degradation mechanisms were eventually discussed in detail.     

Products of the reaction between alpha- or gamma-tocopherol and nitrogen oxides analyzed by high-performance liquid chromatography with UV-visible and atmospheric pressure chemical ionization mass spectrometric detection

The reaction products of alpha- or gamma-tocopherol with nitric oxide in the presence of molecular oxygen were isolated and characterized. The consumption of tocopherols and the formation of the major products were monitored by high-performance liquid chromatography (HPLC) by a gradient elution method. The quantitative analysis of these compounds with UV-Vis detectors, however, was interfered by several minor products having similar UV spectra and retention times as those of the major ones. In order to establish a quantitative analytical method for the products, we investigated other detection methods, and found that atmospheric pressure chemical ionization (APCI), LC-MS was a more selective and better analytical method for these compounds.     

Flavonoids that mimic human ligands from the whole plants of Euphorbia lunulata

In our investigation of a cell proliferation-based screening assay using human ligand-dependent cell lines for medicinal herbal extracts, the acetone extract of the whole plants of Euphorbia lunulata (EL) was observed for its proliferation activity for insulin- and interleukin-10 (IL-10)-dependent cell lines. Fractionation of the active extract led to the isolation of one new flavonoid galactoside, quercetin 3-O-(2',3'-digalloyl)-beta-D-galactopyranoside (1), and four known ones, quercetin 3-O-(2'-galloyl)-beta-D-galactopyranoside (2), hyperin (3), quercetin (4), and gallic acid (5). Compounds 1 and 2 showed insulin-like activity. Compounds 4 and 5 showed IL-10-like activity. This is the first report of these activities of EL, and 1 and 2 will become the seed compounds for the development of a nonpeptidyl insulin substitutional medicine. Compounds 4 and 5 support the pharmacological use of EL, which has been employed as an herbal medicine for the treatment of bronchial asthma.     

Protected amino acids as a nonbonding source of chirality in induction of single-handed screw-sense to helical macromolecular catalysts

Chiral nonbonding interaction with N-protected amino acid methyl esters used as chiral additives in achiral solvents allows dynamic induction of single-handed helical conformation in poly(quinoxaline-2,3-diyl)s (PQX) bearing only achiral substituents. Ac-l-Pro-OMe, for instance, allows induction of energy preference of 0.16 kJ mol⁻¹ per monomer unit for the M-helical structure over the P-helix in t-butyl methyl ether (MTBE). With this new mode of screw-sense induction, homochiral screw-sense has been induced in virtually achiral poly(quinoxaline-2,3-diyl)s 1000-mer containing phosphine pendants (PQXphos). Use of PQXphos as a helically dynamic ligand along with Ac-Pro-OMe (l or d) as a chiral additive in MTBE allowed a highly enantioselective Suzuki–Miyaura coupling reaction with up to 95% enantiomeric excess.

Achiral poly(quinoxaline-2,3-diyl) containing Ar₂P groups undergo dynamic induction of M-helical conformation through nonbonding interaction with protected AA such as Ac-l-Pro-OMe, serving as a chiral ligand in asymmetric cross-coupling with up to 95% ee.     

An ab initio molecular orbital study on the stacking interaction between nucleic acid bases: Dependence on the sequence and relation to the conformation

The stacking interaction energies between nucleic acid bases in A DNA and B DNA are calculated by means of the ab initio molecular orbital method. The calculated values agree well with the experimental values of stacking enthalpy changes. The stacking interaction energy is shown to be highly sequence dependent, particularly when the sequence includes guanine or cytosine. The possibility is shown that the conformation of a DNA double helix fragment is determined by the constituent stacking interaction. Electrostatic energy is the cause of the sequence dependency of the stacking energy, while charge transfer and dispersion energies contribute to the overall stability.     

Preparation and properties of silicon containing polyamides

Silicon containing polyamides were prepared by melt polycondensation method with a 1,3-bis(3-aminopropyl)tetramethyldisiloxane and aliphatic dicarboxylic acids having various numbers of methylene groups. Only one endothermic peak appeared in the DTA curve of the quenched sample for polyamides having an even number of methylene groups in the repeating unit. Two endothermic peaks, however, appeared for the sample kept for a week in dry air at ambient temperature after quenching: the peak at the higher temperature is called peak I; and the peak at the lower one, peak II. By heat treatment at the higher temperature, peak II shifted to a higher temperature and increased its peak area, and peak I decreased its peak area while keeping its temperature unchanged. This behavior suggests the existence of two types of crystalline states. The peak temperature of peak I alternatively decreased with the increase of the number of methylene groups. The Young's modulus and the tensile strength increased with increase of annealing time at ambient temperature. The solubilities in various solvents, the resistance to alkali solution, and the thermal stability were acceptable. Both the permeation coefficient of oxygen (P) and the separation ratio (P/P) increased with the increase of silicon content in the repeating unit.     

13C NMR Spectroscopy on the Complexation of α-Cyclodextrin with 1-Alkanols and 1-Alkanoate Ions

Binding constants for -cyclodextrin ( -CD) complexes with 1- alkanols and 1- alkanoate ions were determined by analyzing changes ( ) in chemical shifts of guest ¹³C NMR signals with -CD concentration. The guests gave well-separated ¹³C NMR signals. The curve-fitting analyses of for individual carbons upon assumption of a simple 1:1 complexation gave virtually the same binding constants (K₁) in the cases of guests with relatively short alkyl chains, such as 1-propanol, 1-butanol, 1- pentanol , 1- butanoate , 1- pentanoate , and 1-hexanoate. However, thus obtained individual K₁ values were significantly different from one another, when the guests had relatively long alkyl chains such as 1- hexanol , 1- heptanol , and 1-octanoate. In these guests, satisfactorily consistent K₁ values were obtained by the curve-fitting analyses of for individual carbons upon an assumption that not only 1:1 but also 2:1 (host:guest) complexation occurs.     

Determination of D- and L-amino acids in mouse kidney by high-performance liquid chromatography.

A method for the enantiomeric analysis of amino acids of mammalian tissues is described. An excellent resolution of D- and L-enantiomers of common protein amino acids was achieved by employing a combination of thin-layer chromatography and high-performance liquid chromatography. D-Enantiomers and L-enantiomers of glutamate, aspartate, glutamine, asparagine, serine, threonine, alanine, proline, tyrosine, valine, methionine, isoleucine, leucine, phenylalanine and histidine, as well as glycine were derivatized with 1-fluoro-2,4-dinitrophenyl-5-L-alanine amide. The amino acid diastereomers were separated by two-dimensional thin-layer chromatography. Each amino acid diastereomer was then analysed by reversed-phase high-performance liquid chromatography for the resolution of D- and L-enantiomers. Very sharp peaks were obtained using a conventional octadecylsilyl-bonded column, and the possibility of analysing these amino acids (except tyrosine and histidine) in subnanomole amounts was indicated. The method was used to demonstrate the presence of D-enantiomers of alanine, proline and serine in mouse kidney.     

Ternary liquid—liquid equilibria and their representation by modified NRTL equations

Experimental liquid—liquid equilibrium data are reported for the systems acetonitrile—acetone—cyclohexane at 318.15 K and acetonitrile—methyl acetate—cyclohexane at 313.15 K. Two modified forms of the NRTL equation proposed by Renon are presented by substituting local surface fractions for local mole fractions and further by including Guggenheim's combinatorial entropy for athermal mixtures whose molecules differ in size and shape. The resultant equations involve three adjustable parameters and are extended to multicomponent systems without adding ternary (or higher) parameters. Calculated results of vapor—liquid and liquid—liquid equilibria for typical binary and ternary mixtures are presented.