A calorimetric unit for measurements of the thermal effects of reactions in solution

A calorimetric unit for measurements of the thermal effects of reactions in solution was created. The unit was designed following the classic scheme of a hermetic liquid calorimeter working under isoperibolic conditions, it had a thermometric sensitivity of 10⁻⁴ K and a calorimetric sensitivity of 10⁻² J. The accuracy of calorimeter operation was checked against the heats of solution of potassium chloride. The molar integral enthalpies of solution of glycine in water at 298 K were determined.     

Methionine equilibrium in aqueous solutions

Stepwise dissociation constants of D,L-methionine in aqueous solution at 298 K were measured by spectrophotometric method, and a possibility of analytical determination of the amino acid concentration was estimated. The integral enthalpy of dissolution of D,L-methionine in water, enthalpies of protonation of the amino group and neutralization of the carboxy group at 298 K were measured using a calorimetric method.     

Hydrogen sorption characteristics of magnesium-based composites with addition of Mg<Subscript>2</Subscript>Ni<Subscript>0.7</Subscript>Co<Subscript>0.3</Subscript> and graphite

Magnesium-based composites of 75 wt% Mg — (10, 15, 20) wt% Mg2Ni0.7Co0.3 — (15, 10, 5) wt% C mechanically activated for 30 min under argon in a planetary mill, were obtained. Their absorption-desorption characteristics were investigated under a pressure P = 1 MPa and temperatures of 623, 573, 473, 423 and 373 K. Desorption was carried out at 623 K and 573 K and a pressure of 0.15 MPa. All the three composites showed improved hydriding kinetics as compared to pure magnesium. However, the desorption temperature was somewhat higher than needed for practical application.      

Thermodynamical control of the grain size of LiCoPO4 powders

The control of the grain size distribution of the LiCoPO₄ compound was achieved by a thermodynamically monitored heating regime of the used ceramic route. For this purpose, on the basis of calorimetric (DSC-TG) measurements collected in non-isothermal and isothermal regime and then related to the grain size of the final product via equations, the irreversibility degree of the heating regime was determined. Grain size of the final product was revealed by scanning electron microscopy (SEM), while the purity of the final product was discussed from thermodynamic calculations (DSC and TG) and confirmed by X-ray diffraction analysis (XRD). The purity and the grain size of the product was tested a priori, using a series of heating regimes and then the accuracy of the established model was checked.     

Effect of Various Treatment Methods on Sorption Properties of Antimony(V)-based Simple and Mixed Oxohydrates

A comparative study of the sorption characteristics of crystalline antimonic acid and a silicon-phosphorus-antimony cationite subjected to thermal treatment in air and in a molten sodium nitrate was carried out. The possibility of regeneration of these sorbents, which are used in ion-exchange strengthening of glasses, was analyzed.     

Spatially periodic modulation of the level population upon saturation for centers with weak and strong electron-phonon interactions

Simple relationships are derived for describing a spatially periodic modulation of the difference between the diagonal elements of the density matrix for individual orientation groups of quantum systems in anisotropic crystals and for centers of the crystal as a whole. It is revealed that the modulation depth of the level populations upon saturation for centers with a strong electron-phonon interaction in the limit is two times greater than that for centers with pure electronic optical transitions. The effect of doubling of the wave number of the periodic structures induced by excited centers is described using crystals with a rutile structure and a four-fold optic axis as an example.     

Arylation of adamantanamines: V. Palladium-catalyzed amination of isomeric chloroquinolines with diamines of the adamantane series

Palladium-catalyzed arylation of diamines of the adamantane series with isomeric 2-, 4-, and 6-chloroquinoline was studied, and optimal conditions for the synthesis of the corresponding N,N′-diaryl derivatives were found. N,N-Diarylation products of primary amino groups in the diamines bearing 2-aminoethyl and 4-aminophenyl substituents were readily formed.     

Preparation and preliminary characterization of exopolysaccharides by yeast Rhodotorula acheniorum MC

The effects of various carbon and nitrogen sources on the synthesis of exopolysaccharides by Rhodotorula acheniorum MC were studied. The dynamic viscosity of cell-free culture broths during exopolysaccharide synthesis were measured. The highest values for the viscosity (10.14 MPa.s) and crude polysaccharide productivity (6.6 g/L) were obtained in a medium supplied with 5% sucrose. Ammonium sulfate was the most favorable nitrogen source for exopolysaccharide synthesis. The value of pH played a determinant role, and the obligatory condition for exopolysaccharide production was low (pH 1.7-2.0) during the fermentation. The chemical composition and sugar constituents of the crude exopolysaccharides were determined. Mannose was the main monosaccharide component, and its concentration was the highest (69.13%) in the crude exopolysaccharide synthesized in the medium that included 5% sucrose as a carbon source.     

Synthesis of optically active 2,7-disubstituted naphthalene derivatives and evaluation of their enantioselective recognition ability

The palladium-catalyzed amination was used to synthesize 2,7-diamino derivatives of naphthalene containing two chiral substituents and fluorophore groups (dansyl, 7-methoxycoumarin, 6,7-dimethoxycoumarin, 6-aminoquinoline). The synthesized compounds were studied by UV absorption and fluorescence spectroscopy in the presence of individual enantiomers of amino alcohols and salts of 21 metals. The possibility of using these compounds as fluorescent detectors for optically active compounds and metals was examined. In the presence of (S)-leucinol, the diquinoline derivative showed enhanced emission with a maximum at shorter wavelengths, which is not typical of its (R) isomer. This fact can be used for the recognition of these enantiomers. A number of naphthalene derivatives can be considered as potential fluorescent chemosensors for Cu^II cations due to the total fluorescence quenching in the presence of this metal.