Electrical conductivity of π-conjugated polymers with nitro substituents

π-Conjugated polymers bearing nitro substituent(s), e.g., poly(aryleneethynylene) (PAE) type polymers and poly(4,8-dinitroanthraquinone-1,5-diyl) P(4,8-NO₂-1,5-AQ), show semiconducting properties with electrical conductivities of an order of 10⁻⁷ to 10⁻⁶ S · cm⁻¹ at room temperature without special oxidation and reduction of the polymer. P(4,8-NO₂-1,5-AQ) shows a large shift of phase in alternating current (ac) measurements and a unique magnetism at low temperature.     

Magnetic Circular Dichroism and Electronic Spectra of Tropothione

The magnetic circular dichroism (MCD) and electronic absorption spectra of tropothione have been measured. The circular-dichroism (CD) spectrum of the β-cyclodextrin complex with tropothione is also reported. The absorption bands of tropothione are assigned.     

FICA,a new chiral derivatizing agent for determining the absolute configuration of secondary alcohols by 19F and 1H NMR spectroscopies

Optically active 1-fluoroindan-1-carboxylic acid (FICA) was designed and prepared as its methyl ester for determining the absolute configuration of chiral molecules by both ¹H and ¹⁹F NMR spectroscopies. Enantiomerically pure isomers of FICA methyl esters (FICA Me esters) were obtained by chromatographic separation using HPLC with a Daicel Chiralcel OJ-H column. The absolute configuration of the (+)-FICA Me ester was deduced to be (S) by X-ray crystallographic analysis of the (+)-FICA amide of (R)-α-phenethylamine. Both enantiomers were derived to the diastereomeric esters of chiral secondary alcohols by an ester exchange reaction. In the ¹H NMR spectra, the signs of Δδ_H (δ_R ? δ_S) were consistent on each side of the FICA molecular plane. Therefore, the concept of the modified Mosher’s method could be successfully applied to the FICA-based procedure. Moreover, the consistency in the signs of Δδ_F (δ_R ? δ_S) values suggests that the FICA method would be reliable in assigning the absolute configurations of secondary alcohols based on ¹⁹F NMR spectroscopy.     

Synthesis and properties of polycarbosilanes with the meta-linkage bending unit by hydrosilylation polymerization

The polycarbosilanes (PCS) with meta-linkage bending unit ((SINGLE BOND)Me₂Si(SINGLE BOND)m(SINGLE BOND)C₆H₄(SINGLE BOND)Me₂Si(SINGLE BOND)CH₂CH₂(SINGLE BOND)) were successfully synthesized in mild conditions by hydrosilylation in the presence of [Pt{(CH₂(DOUBLE BOND)CHSiMe₂)₂O}₂]. The PCS obtained were soluble in various solvents owing to the lowering of the crystallinity. These properties are well compared with those of the PCS [(SINGLE BOND)Me₂Si(SINGLE BOND)p(SINGLE BOND)C₆H₄(SINGLE BOND)Me₂Si(SINGLE BOND)CH₂CH₂(SINGLE BOND)]_n. © 1996 John Wiley & Sons, Inc.     

Biotransformation of benzaldehyde-type and acetophenone-type derivatives by Pharbitis nil hairy roots

The glucosylation of some coumarin and flavone derivatives on incubation with the hairy roots of morning glory (Pharbitis nil) was previously reported. We further studied the biotransformation of benzaldehyde- and acetophenone-type derivatives. Vanillin and isovanillin were reduced to alcoholic derivatives and glucosylated at the phenolic and the alcoholic hydroxyl groups. In the case of 3,4-dihydroxybenzaldehyde, the formyl group was reduced and the 3-hydroxyl or 4-hydroxyl groups were glucosylated to give monoglucosides. The 3-hydroxyl group was predominantly glucosylated to the 4-hydroxyl group. 4-beta-D-Glucopyranosyloxy-3-methoxybenzylalcohol was obtained in low yield. In time-course experiments with vanillin, it was found that the high-level reduction of the formyl group and glucosylation of the phenolic hydroxyl group occurred, and finally 4-O-beta-D-glucopyranosylvanillylalcohol was obtained as the main product. In the case of 3,4-dimethoxybenzaldehyde, 3,4,5-trimethoxybenzaldehyde, and salicylaldehyde, the formyl groups were reduced, and then the hydroxyl groups at the benyl position were glucosylated to give alcoholic glucosides in relatively high yields. In 4-hydroxy-3-methoxyacetophenone, the 4-hydroxyl group was glucosylated and two dimerized glucosides, biphenyl and biphenylether types, were obtained in low yields. In acetophenone, 1-beta-D-glucopyranosyloxy-1-phenylethane and 2-beta-D-glucopyranosyloxyacetophenone were obtained. As mentioned above P. nil hairy roots showed various biotransformative activities including glucosylation of phenolic and benzylic hydroxyl groups, reduction of the formyl group near the benzene ring, and phenol oxidation dimerization. The glucosylation reaction was especially interesting for the production of valuable glucosides.     

Anhydrous Silicophosphoric Acid Glass: Thermal Properties and Proton Conductivity

Anhydrous silicophosphoric acid glass with an approximate composition of H₅Si₂P₉O₂₉ was synthesized and its thermal and proton-conducting properties were characterized. Despite exhibiting a glass transition at 192 °C, the supercooled liquid could be handled as a solid up to 280 °C owing to its high viscosity. The glass and its melt exhibited proton conduction with a proton transport number of ∼1. Although covalent O−H bonds were weakened by relatively strong hydrogen bonding, the proton conductivity (4×10⁻⁴ S cm⁻¹ at 276 °C) was considerably lower than that of phosphoric acid. The high viscosity of the melt was due to the tight cross-linking of phosphate ion chains by six-fold-coordinated Si atoms. The low proton conductivity was attributed to the trapping of positively charged proton carriers around anionic SiO₆ units (expressed as (SiO_6/2)²⁻) to compensate for the negative charges.     

Low-temperature reflection spectrum of K-TCNQ single crystal

Polarized reflection spectra of a K-TCNQ single crystal have been measured at 27,295 and 413 K. The absorption spectra were derived from the observed reflection spectra by Kramers-Kronig transformation. At 27 K, the near-infrared absorption band which is associated with the charged transfer between TCNQ^? ions, splits into a strong sharp peak at 8 × 10³ cm^?1 and a weak broad band at 11 × 10³ cm^?1. These bands were interpreted in terms of the strongly correlated extended Hubbard model including the nearest-neighbor Coulomb interaction.     

Structure,energy and solute segregation behaviour of [110] symmetric tilt grain boundaries in yttria-stabilized cubic zirconia

Yttria-stabilized cubic zirconia bicrystals with [110] symmetric tilt grain boundaries are systematically fabricated by the diffusion bonding method. It is revealed that the grain-boundary atomistic structures, excess energies and solute segregation behaviours are strongly dependent on the macroscopic geometries of the boundaries. High-resolution transmission electron microscopy combined with lattice statics calculations suggests that the grain-boundary structures are characterized by the accumulation of coordination-deficient cation sites at their cores, whose densities have a clear correlation with excess energies and amounts of solute segregation. The orientation dependence of grain-boundary properties in cubic zirconia can thus be linked and understood via local grain-boundary atomistic structures with the characteristic miscoordinated cation sites.     

Unified approach to catechin hetero-oligomers: first total synthesis of trimer EZ-EG-CA isolated from Ziziphus jujuba

A catechin hetero-trimer isolated from Ziziphus jujuba has been synthesized. Among three constituent monomers, (-)-epiafzelechin and (-)-epigallocatechin were prepared by de novo synthesis. Trimer formation relied on the unified approach to oligomers based on the bromo-capping and the orthogonal activation, reaching the reported structure of the natural product.     

First-principles supercell calculations for simulating a shallow donor state in Si

We present first-principles simulations of As-doped Si carried out using several cubic supercells of up to 10 648 atoms. The 1s As donor level in each supercell splits into three states, which have A₁, T₂, and E symmetries, respectively. The 1s(A₁) wavefunction is well converged in the largest cell, and its spread is close to those of the effective-mass theories. However, the calculated binding energies are smaller than experimental values. This discrepancy would be due to the self-interaction error within the approximated exchange-correlation density functional used in this calculation. Therefore, we also show perturbative calculations based on an impurity potential without the self-interaction error to estimate the binding energies of the 1s(A₁) donor state. The estimated binding energy in the largest supercell agrees well with the experimental value.