Di‐ and tri‐phenyltin chlorides transfer across a model lipid bilayer

A compound's ability to penetrate the plasma membrane of a cell is the critical parameter that determines its potential to become a biologically potent factor. A well‐known group of organotin compounds that exhibit toxic properties in relation to biological systems are phenyltins. There are as yet no studies that in a direct manner have established whether organotin compounds such as diphenyltin dichloride (DPhT) and triphenyltin chloride (TPhT) diffuse, or not, through the lipid bilayer, although we know that at least some organotins absorb in both liposome and biological membranes. In this paper we present a series of experiments that show transfer of these compounds across the lipid membrane using the stopped‐flow technique. The results obtained demonstrate that DPhT and TPhT first adsorb onto the lipid bilayer surface, in a diffusion‐controlled manner and within a very short time (0.05 s), whereas the membrane crossing was observed to be on the order of a minute. The adsorption process was easily fitted with a single exponential for both the compounds studied, indicating a single process phenomenon. The longer time kinetics (characteristic of membrane crossing) showed a complex dependence on compound concentration and the presence of cholesterol in the membrane. On passing from the outer to the inner surface of the bilayer, organotins undergo desorption and enter the liposome interior, which has been shown in lipid monolayer desorption studies. In conclusion, it can be stated that amphiphilic DPhT and TPhT permeate the liposome membrane. Copyright © 2005 John Wiley & Sons, Ltd.     

Thermal conductivity of Tb2(MoO4)3 crystals at low temperatures

Thermal conductivity of the improper ferroic Tb₂(MoO₄)₃ was measured in the range 0.3 K–100 K by the method of the stationary heat flow. An additional maximum in thermal conductivity observed at 0.45 K is due to the anomaly of specific heat corresponding to the antiferromagnetic phase transition. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Elastic properties of zinc tris(thiourea) sulphate in a wide temperature range studied by Brillouin spectroscopy

The elastic properties of the zinc tris (thiourea) sulphate crystal were studied by Brillouin spectroscopy in the range 80 – 300 K. The measurements were made on single crystals obtained by the isothermal method. The temperature dependences of the Brillouin shift were determined for the crystal in the principal directions and in a few mixed directions on a tandem type spectrometer. The results revealed anomalies in the bulk wave propagation rate and in a few elastic constants at about 138 K. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

General theory of the translation equation

Summary This paper gives a survey of the results of the general theory of translation equation which appeared after 1973.     

A viscoplastic model combined smedamage and smeared crack for softening of concrete

A viscoplastic model accounting for developing damage in concrete is proposed by assuming the rate of damage to be dependent on viscous strain and stress rates. The damage is measured by a scalar parameter affecting both the yield stress and the material viscosity. For a post-critical range of deformation, the localized mode occurs for which additional constitutive equations are specified. The model is applied to simulate uniaxial strain rate controlled and creep response for the concrete.     

Catalysis of hydrosilylation XIII. Gas-phase hydrosilylation of acetylene by trichlorosilane on functionalised silica supported rhodium and ruthenium phosphine complexes

Gas-phase hydrosilylation of acetylene by tri-chlorosilane catalyzed in a continuous flow apparatus by rhodium and ruthenium phosphine complexes immobilized on the silica via mercapto, phosphine, amine and nitrile ligands has been studied. GLC analysis of the reaction products showed vinyltrichlorosilane to be accompanied by products of double hydrosilylation of acetylene and the redistribution of trichlorosilane followed by the hydrosilylation and hydrogenative hydrosilylation of acetylene with dichlorosilane. A scheme for this complex competitive–consecutive reaction was proposed. The yield and selectivity of vinyltrichlorosilane can be much improved under special reaction conditions, e.g. rate flow of the particular substrates, temperature, given catalyst and others. Kinetic measurements carried out in the range of 115–140°C allowed us to evaluate the activation energy, E_a, for the vinyltrichlorosilane synthesis, which varied between 20.5 and 27.6 kJ mol^?1 for the selected rhodium and ruthenium supported complexes.     

New Acyclic Dimers of Cholic Acid with Oxamide and Hydrazide Spacers

Three new acyclic dimers of cholic acid with oxamide and isomeric hydrazide (N,N′-diacylhydrazine) spacers were obtained. The oxamide spacers bind two identical steroidal subunits through position 3 (head-to-head dimer) or position 23 (tail-to-tail dimer). In the case of a third dimer the hydrazine moiety binds two molecules of cholic acid through position 24 (tail-to-tail dimer).     

Solute-solvent interactions in acid-base dissociation: nine protonated nitrogen bases in water-DMSO solvents

A titration method utilizing glass electrodes and silver-silver chloride electrodes in a cell without liquid junction has been used to determine the acidic dissociation constants at 15, 25, and 35°C of nine protonated nitrogen bases in mixtures of water and dimethyl sulfoxide (DMSO). The mole fraction of DMSO in the mixed solvents was 0.2, 0.4, 0.6, and 0.8. The cell was calibrated with HCl (molality=0.01 mole-kg^?1) in the mixed solvents, and the ionic strength and chloride molality remained substantially unchanged during the titration with added base. This method minimizes the errors resulting from the formation of AgCl ₂ ^? in the media rich in DMSO. The pK _a of all the protonated bases passes through a minimum at a solvent composition close to that at which H₂O-DMSO mixtures display a maximum solvent structure. The results are discussed in terms of the preferential solvation of ions by the two types of solvent molecules. They are consistent with the hypothesis that increased solvent structure is accompanied by increased desolvation of the cation acids.     

Simultaneous Determination of Major Constituents of Honeybee Venom by LC-DAD

The aim of the study was to develop an LC method for honeybee venom analysis, using cytochrome c as an internal standard. The SynChropack C8 6.5 μm, 4.6 × 100 mm column was applied. The bee venom was separated by linear gradient 5–80% B at 30 min (eluent A—0.1% TFA in water, eluent B—0.1% TFA in acetonitrile:water (80:20)). The flow rate of mobile phase was maintained at 1 mL min⁻¹, injection volume: 40 μL, separation temperature: 25 °C. The analysis was monitored at 220 nm. Several honeybee venom constituents were separated and the content of four of them (apamine, mast cell degranulating peptide, phospholipase A₂ and melittin) were determined. By applying this methodology differences in chemical composition of honeybee venom were evaluated. In order to confirm the data obtained, the following steps and parameters were taken into account for the validation of the method: selectivity, precision (injection repeatability, analysis repeatability), accuracy (recovery), linearity and operating range, limit of detection and limit of quantitation. All steps of validation proved that the developed analytical procedure was suitable for its intended purpose (standardization). Due to its simplicity, the developed method can be easily automated and incorporated into routine operations both in the bee venom identification, quality control and assay tests.