An analysis of ionic conductivity in polymer electrolytes

Conductivities for a wide variety of ionically conducting polymer electrolytes with a range of salt compositions have been investigated over the temperature region T_g to 370 K. When the conductivity data are analyzed as a function of temperature using the empirical Vogel-Tammann-Fulcher (VTF) equation a common trend is observed in that deviations in the fits to the data invariably occur in the temperature range 1.2 T_g to 1.4 T_g for all of the samples investigated. This deviation is interpreted as a decoupling of the ions from polymer segmental motion. Recent ²³Na NMR and ²²Na positron annihilation studies of sodium salt-based polymer electrolytes support this interpretation with evidence of a change in dynamics at about 1.2T_g. © 1994 John Wiley & Sons, Inc.     

Stereochemistry of organophosphorus cylic compounds—XV: Synthesis of tetramethylammonium salt of 2-oxo-2-thio-1,3,2,-oxazaphosphorinan and its crystal and molecular structures

2-Hydroxy-1,3,-2-oxazaphosphorinan-2-thione (5) was prepared by alkaline hydrolysis of 2-chloro-1,3,2-oxazaphosphorinan-2- thione (6). Treatment of the latter with sodium methoxide afforded the 2-methoxy-derivative 7 from which the tetramethylammonium salt of the thioacid 5 was obtained by the action of trimethylamine. The structure of this salt has been determined by the direct method and refined by least-squares to R = 0.0734, a = 12.303(4), b = 9.041(3), c = 10.419(2) Å, space group P2₁2₁2₁. The 2-oxo-2-thio-1,3,2-oxazaphosphorinanyl anion is in the chair form with the exocylic S and O atoms in an axial and equatorial position, respectively. An intermolecular H-bond between S and the endo-cyclic N atom is present in the solid-state structure.     

The modified talcs as semi-active fillers of rubbers

We present a new modification method to additonally micronize talcs to a particle diameter of 0.8 m using silane and titanate coupling agents, thus allowing an increase of acitvity against elastomers. It appears that the silane modification proceeds in greater extent when acid medium is used. After the modifications, the wettability of talcs in water and benzene was measured by the calorimetric technique. A direct correlation between heats of immersionh _i ^W andh _i ^B of silane (titanate) surface coverage has also been found.     

Solution- and solid-phase synthesis of components for tethered bilayer membranes

The synthesis of the novel compound PhCH(2)SS(C(24)H(44)N(4)O(10))(C(20)H(41)) (5) for the preparation of tethered bilayer membranes is described. The compound is the all-amide analogue of the previously reported ester-containing membrane-forming material PhCH(2)SS(C(24)H(40)O(14))(C(20)H(41)) (1). The advanced intermediate (C(20)H(41)) C(16)H(28)N(3)O(8) (17) was prepared from the same starting materials using both solution-phase (13% yield) and solid-phase (81% yield) techniques. Monolayers on gold derived from 5 have been analyzed by ellipsometry and FTIR. The monolayers exhibit thicknesses similar to monolayers derived from 1 and possess H-bonded amide functionality.     

Metal-free catalysts for the hydrolysis of RNA derived from guanidines, 2-aminopyridines, and 2-aminobenzimidazoles

2-aminopyridine and 2-aminobenzimidazole were chosen as structural analogues to substitute guanidinium groups in receptor molecules designed as phosphoryl transfer catalysts. Shifting the pKa of the guanidinium analogues toward 7 was expected to raise catalytic activities in aqueous buffer. Although the pKa's of both heterocycles are similar (6.2 and 7.0), only 2-aminobenzimidazole led to active RNA cleavers. All cleavage assays were run with fluorescently labeled substrates and a DNA sequencer. RNase contaminations would degrade RNA enantioselectively. In contrast, achiral catalysts such as 9b and 10b necessarily induce identical cleavage patterns in RNA and its mirror image. This principle allowed us to safely rule out contamination effects in this study. The most active catalysts, tris(2-aminobenzimidazoles) 9b and 10b, were shown by fluorescence correlation spectroscopy (FCS) to aggregate with oligonucleotides. However, at very low concentrations the compounds are still active in the nonaggregated state. Conjugates of 10b with antisense oligonucleotides or RNA binding peptides, therefore, will be promising candidates as site specific artificial ribonucleases.     

Enthalpies of hydrogen-bonds in alpha-helical peptides. An ONIOM DFT/AM1 study

We report the enthalpy differences between alpha-helical and extended beta-strand conformations of acetyl(Ala)nNH2, for n = 8, 10, 12-17, calculated using molecular (MO) orbital theory from complete vibrational analyses of the optimized species. The calculations used the ONIOM method with B3LYP/D95(d.p) as the high and AM1 as the low levels. The incremental change in enthalpy upon addition of one Ala to a growing beta-strand defined using the hypothetical polycondensation reaction, n Ala + CH3COOH + NH3 --> acetyl(Ala)nNH2 + n H2O, reaches its asymptotic limit of -1.4 kcal/mol at n = 10, while that for the alpha-helix continues to increase in magnitude at n = 17. The asymptotic limit of the enthalpic preference of the alpha-helix over beta-strand is estimated to be about 3 kcal/mol, while that for n = 17 is 11.99 kcal/mol or about 0.8 kcal/mol/H-bond, which is similar to measured values for polyalanines of this size in aqueous solution.     

Crystal and molecular structures of (±)cadinene dihydrochloride (1) and (−)cadinene dihydrochloride (2)

Two compounds, racemic (±)cadinene dihydrochloride C₁₅H₂₆C1₂ (1) and (–)cadinene dihydrochloride C₁₅H₂₆Cl₂ (2), prepared by treating germacrene D fromSolidago canadensis L, and sesquiterpene fraction of essential oil fromPinus silvestris L, respectively, with gas HCl were investigated. Compound (1) crystallizes in monoclinic system, but (2) in orthorhombic (Table 1). The structures were found by direct methods and were refined with full matrix least-squares techniques to R value of 0.039 and 0.044, respectively, for (1) and (2).     

Synthesis,thermal, spectroscopic,and X-ray studies of (dichloroacetato)(triphenylphosphine)gold(I)

The synthesis, thermal, spectroscopic, and X-ray investigation of (dichloroacetato) (triphenylphosphine)gold(I), [Au(C₂HCl₂O₂)(C₆H₅)₃P] are reported. The thermal analysis showed that the decomposition of the studied complex is a two step process and the mechanism of the decomposition has been proposed. IR and¹³C NMR spectra of the complex are given. The compound crystallizes in the monoclinic space groupP2 ₁/n with four molecules per unit cell.M _r =587.19,a=11.455(1),b=12.398(3),c=14.718(2)Å,=104.95(1)°,V=2019.5(6)ų,D _x=1.931g/cm³,(Cu K)=172.6 cm^–1,F(000)=1120. FinalR=0.059 for 2780 absorption-corrected reflections. The crystals are not isostmctural with acetato(triphenylphosphine) gold(I) and (trifluoroacetato)-(triphenylphosphine)gold(I). The Au-O1 bond length is of 2.049(9), Au-P of 2.210(3)Å with O1-Au-P angle of 176.9(2)°.