New determination of quadrupole coupling constants of Li isotopes in single crystals LiIO3 andLiNbO3

Quadrupole effects in NMR spectra of⁸Li(I =2⁺;T _1/2=0.84 s) in LiIO₃ andLiNbO₃ single crystals have been detected by use of a modified -NMR. The coupling constants for both crystals are in agreement with known ones. Field gradients in the crystals were measured by detecting pulsed-Fourier transformed NMR of⁷Li. The quadrupole moments deduced from both samples agree, and|Q(⁸Li; 2⁺)|=32.7±0.6 mb has been determined.     

High-Pressure Synthesis, Crystal Structure, and Metal–Semiconductor Transitions in the Tl2Ru2O7−δPyrochlore

Thallium ruthenium oxides, Tl₂Ru₂O_7−δ, with the pyrochlore structure were synthesized under a pressure of 1–5 GPa and 1173 K and characterized by resistivity, magnetization, and TOF neutron-diffraction measurements. The oxygen vacancy,δ, varied with the synthesis conditions and significantly affected their electrical properties. The pyrochlores synthesized at high pressure and atmospheric pressure are classified into four groups which depend on their oxygen nonstoichiometry. (i) Nonstoichiometric Tl₂Ru₂O_6.71shows a metallic conductivity with almost temperature-independent magnetization. (ii) Stoichiometric Tl₂Ru₂O₇synthesized under high oxygen pressure using KClO₄shows a metallic–semiconducting transition at 120 K with magnetization anomalies at 120 and 40 K. (iii) Slightly nonstoichiometric Tl₂Ru₂O_6.96shows spin-glass-like behavior around 40 K accompanying a resistivity increase at the transition. (iv) Tl₂Ru₂O₇synthesized at 773 K and atmospheric pressure is semiconducting with magnetization anomalies at 120 and 40 K. The change from the metallic to semiconducting state is discussed from the viewpoint of structure changes.     

Synthesis of the JK/LM-ring model of prymnesins, potent hemolytic and ichthyotoxic polycyclic ethers isolated from the red tide alga Prymnesium parvum: confirmation of the relative configuration of the K/L-ring juncture

Synthesis of the JK/LM-ring model of prymnesins, polycyclic ether toxins isolated from the red tide phytoflagellate, Prymnesium parvum, is described. Comparison of the ¹H and ¹³C NMR data of the synthetic model with those reported for prymnesins confirmed the reported configurational assignment of the K/L-ring juncture.     

Synthesis of aromatic polyimines by the condensation of aromatic dialdehyde and diamine

Film-forming aromatic polyimines were prepared by low temperature solution polymerization of aromatic dialdehyde and aromatic diamine usingm-cresol. The polymerization proceeded rapidly to give high molecular weight polyimine solutions. Fibrous polymers were precipitated by pouring the solutions into anhydrous methanol. Lemon yellow-to-orange films were cast in situ from the reaction solutions. The polymers showed typical C=N stretching absorption near 1620 cm^?1 in infrared spectra and had high glass transitions of over 200 ?C but showed low crystallinity.     

Atomic force microscopy studies of ganglioside GM1alpha in dioleoylphosphatidylcholine/dipalmitoylphosphatidylcholine mixed monolayers and hybrid bilayers

The membrane states of the alpha-series ganglioside GM1alpha in 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) mixed monolayers and hybrid bilayers were investigated using atomic force microscopy (AFM). The AFM image for the GM1alpha/DOPC/DPPC ternary monolayers showed the formation of GM1alpha-raft in the DOPC matrix. As increase of the surface pressure, GM1alpha are condensed in DPPC-rich domains; long and slender GM1alpha-rafts are separated from the DPPC-rich domains into the DOPC matrix. The GM1alpha/DOPC/DPPC ternary monolayers were deposited on mica coated with the first layer (1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine: DPPE) using the Langmuir-Schaeffer technique. The AFM image for the hybrid bilayers showed that same molecules were heterogeneously concentrated according to increase of the surface pressure to form GM1alpha-raft, DPPC-rich domain and DOPC matrix, being in agreement with the observation on the monolayer experiment. The found phenomenon implies that a binding of lectin to GM1alpha causes the increase of the surface pressure, the localization of GM1alpha and the succeeding formation of the raft as a first step of a specific signal transduction.     

Photochemical and thermal reactions of a kinetically stabilized 9-silaanthracene: the first spectroscopic observation of a 9,10-Dewar-9-silaanthracene isomer

A kinetically stabilized 9-silaanthracene (1) underwent unique photochemical and thermal reactions to afford 9,10-Dewar-9-silaanthracene 2a and the head-to-tail [4 + 4] dimer 3, respectively. The structure of 2a was confirmed by 1H, 13C, and 29Si NMR spectra, and the kinetic parameters for the thermal reversion of 2a to 1 were obtained by the measurement of UV/vis spectra. The dimer 3 was thermally stable, and the molecular structure of 3 was determined by X-ray crystallographic analysis. It was experimentally demonstrated for the first time that 9-silaanthracene, as well as anthracene, can afford either the Dewar isomer or [4 + 4] dimer, depending on the reaction conditions.     

Studies on propagating species in cationic polymerization of styrene derivatives by acetyl perchlorate or iodine. I. Bimodal molecular weight distribution of polymers produced by acetyl perchlorate or iodine

To investigate the nature of the propagating species in cationic polymerization of para-substituted styrenes, p-chlorostyrene (pCIS), p-methylstyrene (pMS), and p-methoxystyrene (pMOS), were polymerized with acetyl perchlorate or iodine in various solvents at 0°C, and the molecular weight distribution (MWD) of the polymers was measured by means of gel-permeation chromatography. When ClO_4? was a counterion, poly(pCIS) having a bimodal MWD was produced, while polymers of pMOS and pMS possessed a unimodal MWD, regardless of the solvent polarity. When more nucleophilic I^? (or I₃^?) was a counterion, however, polymers having a bimodal MWD were produced from pMOS and pMS. These results showed that either dissociated or nondissociated propagating species existed in the cationic polymerization of styrene derivatives with acetyl perchlorate or iodine, and that the type of MWD was strongly dependent on the stability of the growing cation and the nucleophilicity of the counterion.     

Characterization of a neutral polysaccharide having activity on the reticuloendothelial system from the rhizome of Curcuma longa.

A neutral polysaccharide, named ukonan D, was isolated from the rhizome of Curcuma longa L. It produced a single band on electrophoresis and a single peak on gel chromatography, and its molecular mass was estimated to be 28,000. It showed remarkable reticuloendothelial system-potentiating activity in a carbon clearance test. Ukonan D is composed of L-arabinose: D-galactose: D-glucose: D-mannose in the molar ratio of 1:1:12:0.2, in addition to small amounts of peptide moiety. Methylation analysis, carbon-13 nuclear magnetic resonance and enzymic degradation studies indicated that its structural features include mainly both alpha-1,5-linked L-arabino-beta-3,6-branched D-galactan type and alpha-4,6-branched D-glucan type structural units. The influence of degradation with alpha-amylase followed by the elimination of glucan side chains on its immunological activity was discussed.     

Triazole antifungals. IV. Synthesis and antifungal activities of 3-acylamino-2-aryl-2-butanol derivatives.

New triazole compounds were designed and synthesized as potential inhibitors of the fungal cytochrome P-450 14 alpha-demethylase. In testing for antifungal activity against a mouse systemic Candida albicans infection, (2R,3R)-3-acylamino-2-aryl-2-butanol derivatives III exhibited remarkably high efficacy after oral or parenteral administration. The structure-activity relationships of these amidoalcohols were evaluated.