“Polyaniline”: Interconversion of Metallic and Insulating Forms

Abstract

“Polyaniline” has been synthesized in various forms both chemically and electrochemically in aqueous media. The qulnoid-benzenoid-diimine form, an insulator, is doped by dilute aqueous protonic acids to the metallic regime ([sgrave] = 5 ohm^?1cm^?1; compressed pellet) to give the corresponding iminium salt. This represents a new type of p-doping phenomenon in a conducting polymer. Both these forms are stable in the presence of air and/or water. The doping process is reversed by treatment with aqueous alkali. Cyclic voltammetry studies in an aqueous electrolyte show excellent reversibility between selected reduced and oxidized forms of polyaniline.     

“Bands” and “Torsads” Textures in Films and Threads of Hydroxypropyl Cellulose

The present paper deals with films and threads of a mesomorphic cholesteric polymer: the hydroxypropyl cellulose. The steady flow behaviour and the shear induced textures (observed by optical microscopy under crossed polars) of films of lyotropic solutions of this polymer have been studied. A detailed analysis of the banded structures, of either the sheared solutions or the dried films obtained by solvent evaporation, is reported. We point out the existence of transverse striated patterns—“torsads”—superposed on the main banded structures, which are associated with the rewinding of the cholesteric structure following the cessation of the shear stress. The torsads, also observed in some threads, originate from the same relaxation phenomena and are discussed in the last part of the paper.     

Characteristics of Guajazulene Based Chemosensor Toward CN− and F− Anions

A chemosensor having electron pushing donor and pulling acceptor material based on conjugation bridges, namely D-π-A structural chemosensor, was herein designed and synthesized. This chemosensor 3 contained guajazulene and indole moieties, which was synthesized through a one-step condensation reaction. The synthesized material showed very selective sensing properties towards anions. Upon the addition of CN- and F-, the remarkable changes in absorption spectra were monitored. However, each of others did not show any noticeable optical changes. The original intramolecular charge transfer system of chemosensor 3 was altered by the formation of N- at iindole moiety with anion reaction: caused by the deprotonation of NH at the indole moiety of chemosensor. With intermolecular charge transfer system between chemosensor 3 and anions, the electron density and distribution were determined by frontier calculation method.     

Optical and Electrooptical Properties of “Guest-Host” Effect in Twisted Liquid Crystal Layers

Abstract

Optical and electro-optical characteristics of a positive dichroic dye-doped Twisted Nematic Liquid Crystal Layer (TNLCL) for two different orientations of the input light polarization to the NLC director α (α = 0°, α = 90°) and various NLC optical path lengths A = Δnd/λ (Δn = real part of birefringence, d = cell thickness, λ = wavelength) are investigated. In the case of one polarizer, the maximum contrast ratio is obtained for A ? 1.2 (α = 0°) and A ～ 0 (α = 90°), regardless of whether Δn or d is changed. The viewing characteristics of a dye doped TNLCL with one polarizer are shown to be more uniform than those for a “pure” TNLCL between parallel polarizers.     

Optimization of the Compositions of Solid Electrolytes Pb1 – xRxF2 + x with Fluorite-Type Structure in Conductivity and Thermal Stability

Crystallography Reports - The compositions of nonstoichiometric phases Pb1 – xRxF2 + x (CaF2 type, R is a rare-earth element) have been optimized with...     

Growth,Compositions, and Mechanical Characteristics of Sodium–Gadolinium Molybdate Single Crystals

Crystallography Reports - A concentration series of sodium–gadolinium molybdate single crystals have been grown by the Czochralski method from melts of stoichiometric and some...     

Lattice Variation and Stability of NaCl?KCI Mixed Crystals Grown from Aqueous Solutions

An attempt to improve the stability of NaCl KCl mixed system was made by adding KBr to it. Crystals were grown by the slow evaporation method and characterized by X-ray diffraction measurements. A large improvement in stability was observed with crystals grown from (NaCl)_x (KCl)_0.9−x(KBr)_0.1 than from Na_xK_1−xCl solutions.     

X-ray mapping in heterocyclic design: 17. Crystal and molecular structures of the “molecule of the month”; and its hydrogenated form

The structures of 2,8-dimethyl-5-[2-(6-methylpyridin-3-yl)ethyl]-2,3,4,4a,5,9b-hexahydro1H-pyrido[4,3-b]indole trihydrobromide (I) (a = 12.865(4) ?, b = 14.281(3) ?, c = 13.553(3) ?, Z = 4, sp. gr. Pna2₁) and 2,8-dimethyl-5-[2-(6-methylpyridin-3-yl)ethyl]-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole dihydrobromide (II) (a = 13.9704(14) ?, b = 14.4447(15) ?, c = 10.7819(12)?, β = 107.58(1)°, Z = 4, sp. gr. P2₁/c) were studied by single-crystal X-ray diffraction. The structures were solved by direct methods and refined by the full-matrix least-squares method with anisotropic displacement parameters to the R factors of 0.0603 and 0.0446, respectively. All Br⁻ anions form hydrogen bonds with protonated nitrogen atoms. The synthesis and physicochemical parameters of these two compounds are reported.     

Use of conduction models in the study of “low temperature” carbons

The frequency (10-10⁸ Hz) and temperature (100–400 K) dependence of the ac conductivity of anthracene carbons is explained within two theoretical models. The properties of carbon heat treated up to 600°C are correctly explained by means of a model where the current flow is due to electron hops over a potential barrier between localized sites.The conductivity of the carbon heat-treated up to 650°C is interpreted using a theory proposed by Mott and Davis. The spatial densities of states are determined in both cases.     

A review of: “Liquid Cvystuls Topics in Physical Chemistry”

Abstract

Edited by H, Stegemeyer, Steinkopff Verlag, Darmstadt, 1994, X, 231pp, Hardcover, DM 44.80, ISBN 3-7985-0924-7     

Refinement of the crystal structures of low-rare-earth and “typical” burbankites by the Rietveld method

The crystal structures of two samples of burbankite from the Khibiny massif, namely, low-rare-earth burbankite (Na_1.82Ca_1.02Y_0.02)_2.86(Sr_2.32Ba_0.43Ca_0.17La_0.06Ce_0.02)_3.00(CO₃)₅ from pectolite metasomatites and burbankite of the characteristic composition (Na_2.22Ca_0.65Y_0.03)_2.97 × × (Sr_2.10Ba_0.33Ce_0.23Ca_0.15La_0.12Nd_0.05Pr_0.02)_3.00(CO₃)₅ from alkaline hydrothermolites, were refined by the Rietveld method. The experimental data were collected on an ADP-2 diffractometer (λCuK _α radiation, Ni-filter; 15.00° < 2θ < 155.00°; 2θ scan with steps 0.02°; the exposure time per step, 15–20 s; the number of (α₁ + α₂) reflections 556–570). All the calculations were performed using the WYRIET program (version 3.3) in the sp. gr. P6₃ mc. For low-rare-earth burbankite: a = 10.5263(1) Å, c = 6.5392(1) Å, R _P = 3.52, R _wp = 4.49, R _B = 4.10, and R _F = 4.11. For burbankite from alkaline hydrothermolites: a = 10.5313(1) Å, c = 6.4829(1) Å, R _P = 2.54, R _wp = 3.23, R _B = 3.06, and R _F = 3.44. The structures were refined using the anisotropic thermal parameters of cations.     

Study of Bronze Statues “John the Baptist” and “Dancing Cupid” from the Collections of the Pushkin State Museum

Crystallography Reports - Bronze statues “John the Baptist” and “Dancing Cupid” from the collections of the Pushkin State Museum of Fine Arts have been investigated at the...     

Structural Study of Membrane Glycoprotein-Precursor of β-Amyloid and Proteins Involved in Its Proteolysis

Crystallography Reports - Alzheimer’s disease is the most widespread form of neurodegenerative disease in the world. Its clinical manifestations are explained by selective degeneration of...