A stopped-flow study on the kinetics and mechanism of CO<Subscript>2</Subscript> uptake by chromium(III) complexes with histamine and pyridoxamine

The mechanism and kinetics of the reaction between an aqueous solution of CO₂ and coordinate ions, cis-[Cr(C₂O₄)(L–L)(OH₂)₂]⁺, where L–L denotes histamine (hm) or pyridoxamine (pm), were investigated using the stopped-flow technique. The studies were carried out at 5 to 25 °C over the pH range 6.04–8.15 at a fixed ionic strength solution (1 M NaClO₄). The results enabled determination of the number of steps of the reactions studied. Based on the kinetic equations, rate constants were determined for each step. Finally, thermodynamic activation parameter values H, were calculated for the reaction studied from temperature relationships.     

DTA-untersuchung der Umwandlungen des Amorphen Schwefels

DTA was applied to investigate amorphous sulfur samples remelted at different temperaturesT _f. For the sample remelted atT _f<159 °C, an exothermic process I occurs in the range 30–40°C. Transformation of orthorhombic to monoclinic sulfur, melting and polymerization ofS ₈ rings was observed at higher temperatures. For the sample remelted atT _f > 159 °C, a new, fast exothermic process II occurs at ambient temperature, followed by an exothermic process III at slightly higher temperature. The next, also exothermic process IV is detected in the vicinity of the melting point. The heats of the thermal effects for all the above-mentioned processes, and the part of sulfur insoluble in CS₂, were determined. An attempt was made to evaluate the mechanism of the transformations.     

Studies of Dehydration Process for Isostructural Series of Lanthanide(III) 2,6-dihydroxybenzoates

Dehydration kinetics of lanthanide 2,6-dihydroxybenzoates has been studied by thermogravimetry using the model-fitting method of calculation. Several kinetic models gavea good representation of the measured thermogravimetric (TG) curves but the calculation method allowed to propose the most probable dehydration mechanism. The activation energies of dehydration for isostructural 2,6-dihydroxybenzoates of lanthanides are similar for a given kinetic model. A change in the heating rate did not alter the dehydration mechanism. A linear correlation between the activation energy and the heating rate was observed for the systems studied. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rational rotation numbers for maps of the circle

We consider families of maps of the circle of degree 1 which are homeomorphisms but not diffeomorphisms, that is maps like

QENS study of molecular motions in partially deuterated liquid crystal 4BT

Molecular rotational dynamic in the crystalline and smectic E phases of selectively deuterated (in the outer phenyl ring) 4-n-butyl-isothiocyanatobiphenyl was investigated by means of quasielastic neutron scattering. The 120° reorientation of the methyl group in the crystal phase could be identified at 125 K. Additionally, ring flips were seen at 200 K. The structure of crystal and smectic E phases was obtained by X-ray measurements and the data give the identification of type of solid phases.     

The complexation of anions by chloro- and cyanoacetanilides; IR, 1H-NMR and computation study

Complexation ability of simple chloro- and cyanoacetanilides has been determined using IR as well as ¹H-NMR titration experiments. Only 1:1 anion–amide complex stoichiometry has been found. The structures of several free anilides and their complexes with bromide anion have been studied by DFT calculation.     

Unknown thermal properties of ZnSb2O6 and Zn7Sb2O12 compounds

The investigations by XRD, DTA/TG and IR methods show that two compounds: ZnSb₂O₆ and Zn₇Sb₂O₁₂ are formed in the ZnO-α-Sb₂O₄ system in air. Oxygen contained in the air participates in the synthesis of these compounds. ZnSb₂O₆ was observed as an intermediate phase, during the Zn₇Sb₂O₁₂ synthesis. The temperature of the β→α-Zn₇Sb₂O₁₂ transition was fixed at 1225±10°C. The mechanisms of the reactions of ZnSb₂O₆ and Zn₇Sb₂O₁₂ thermal decomposition have been proposed. The IR studies of α and β-Zn₇Sb₂O₁₂ have initially indicated that the structures of both polymorphous forms differ in the reciprocal connection of the SbO₆ and ZnO₆ octahedra and the ZnO₄ tetrahedra.     

Kinetics of small molecule adsorption studied using precision ellipsometry

On the basis of a miniature polarisation modulator, a precision ellipsometry system has been made, enabling real-time measurement of subnanometre thin layers on reflecting substrates. This system monitored the kinetics of adsorption and desorption of propanol, or ethanol, or methanol on oxidised Si substrates. While adsorption of propanol and ethanol increased the thickness, adsorption of methanol showed surprising kinetics: the thickness first increased, then decreased. To explain this, a model of substitutional (or competitive) adsorption has been used, where the target molecule is adsorbed only when it substitutes another one leaving an adsorption site. The model fits the experimental data quantitatively and can predict processes involving several components on solid surfaces. Precision ellipsometry demonstrated its high analytical potential in investigation of surfaces at molecular level.