Thermische Zersetzung von CuInSe2, LiInSe2 und LiInTe2

The thermal decompositions of CuInSe₂, LiInSe₂ and LiInTe₂ in vacuum at high temperatures were studied by using TG/DTG coupled with mass spectrometry. For CuInSe₂, two steps were found to be significant. Up to 1000 °C Se₂ and In₂Se evaporate, followed later by Cu₂Se. The Li-containing compounds show similar behaviour. However, Li⁺ was already detected during the first step. Obviously, Li₂Se dissociates more readily than Cu₂Se. No Cu⁺ species were detected up to the complete evaporation of CuInSe₂.     

Second-order relativistic electron capture

Starting with the impulse approximation, we analyse second-order effects in relativistic electron capture. The relation of this model with relativistic distorted-wave approximations is clarified. In particular it is shown that the second-order spin-coupling terms in the RCDW theory are consistent with the correct form given by perturbation theory. In the semirelativistic limit, the RCDW results are shown to accord with the formulae of Moiseiwitsch for flip and nonflip transitions in the ultra-relativistic limit. This confirms that the continuum-distorted-wave model generalises to relativistic spinors, and highlights the defects of scalar models. We also present a new symmetric eikonal theory which gives reliable results for capture without change of spin, but leads to a divergent total cross section for spin-flip transitions in the second-order term. This effect, which is quite distinct from the spurious spin-flip amplitudes of the scalar symmetric eikonal theory, is taken as further evidence that the eikonal approximation is not valid for magnetic transitions.     

Xanthones from the roots ofSwertia iberica

From the roots ofSwertia iberica, together with the previously known swertiaperennin decussatin, gentiakochianin, and norswertianin, we have isolated two new xanthones — isogentiakochianin and swertiaiberin. On the basis of UV, IR, PMR, and mass spectroscopy, the structure of 1,3,8-trihydroxy-7-methoxyxanthone is proposed for isogentiakochianin, and that of 1,2,3-trihydroxy-7,8-dimethoxyanthone for swertiaiberin.All-Union Scientific-Research Institute of Medicinal Plants, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 190–195, March–April, 1980.     

Microelectrode for potassium ions based on a neutral carrier and comparison of its characteristics with a cation exchanger sensor

A potassium-selective liquid-membrane microelectrode based on valinomycin is described. Tip diameters of about 2 μm as well as high discrimination against Na⁺, H₃O⁺, acetylcholine and some other quaternary ammonium ions, allow the intracellular measurement of potassium ion activity changes. The inherently high membrane resistance of the neutral carrier-based microelectrodes is reduced by adding a lipophilic charge carrier to the valinomycin. Results are compared with those of classical microelectrodes.     

Thermal properties of tetrahydroperparine derivatives

The thermal behaviour of tetrahydroperparine (THP) and its derivatives with various acids has been investigated. The acid is liberated from the formate derivative basically in two steps, while the other aliphatic acids are released quantitatively before the thermal decomposition of the THP molecule. The thermoanalytical curves, electrical conductivity data measured in the molten phase, and infrared spectra prove that while part of the formic acid is hydrogen-bonded the other part is bound ionically in the molecule. It may be assumed that the marked biological activity of the compound can be explained by this difference in the nature of the bonds.     

Kinetics of the metal-exchange reaction of deuteroporphyrin and gematoporphyrin cadmium complexes with cobalt chloride in acetonitrile

The metal-exchange reaction of cadmium deuteroporphyrin (CdDP) and cadmium gematoporphyrin (CdGP) with cobalt chloride in acetonitrile is studied spectrophotometrically. The stoichiometry of the metal-exchange reaction is determined. The results are compared with the exchange reaction of cadmium mesoporphyrin and cadmium protoporphyrin with cobalt acetate in acetonitrile. Substituents in the 2,4-positions of cadmium complexes of protoporphyrins are shown to influence the rate of the metal-exchange reaction. The increasing order of the rates of the metal-exchange reaction between protoporphyrins and cobalt chloride in acetonitrile is established.     

Self-association of daunomycin antibiotic in various buffer solutions

The self-association of an antitumor antibiotic, daunomycin (DAU), in various buffer solutions, including water-salt solutions, phosphate buffer, HEPES, and TRIS, was studied by 1D and 2D ¹H NMR spectroscopy at 500 MHz. The two-dimensional NOESY spectra and the concentration and temperature dependences of the chemical shifts of antibiotic protons in the solvents studied showed that the self-association parameters of DAU were independent of the type of buffer solutions. The most probable two spatial structures of the dimer of DAU in solution were constructed by the method of molecular mechanics. The mutual orientation of the chromophores was parallel in one structure and antiparallel in the other.     

Glass forming ability and thermal stability in the system ZrF46BaF26PrF3

New glasses have been synthesized in the system ZrF₄6BaF₂6PrF₃. Glasses were prepared by conventional fusion method and the vitreous domain was established. For vitreous samples the thermal stability parameters were determined, so that the best compositions could be selected according to a compromise between high glass forming ability and thermal stability vs. crystallization.     

Diels—Alder reaction. Effect of internal and external factors on the reactivity of diene—dienophile systems

The key factors influencing the Diels—Alder reaction rate at ambient and elevated pressures were elucidated using data on the reactivity of various diene—dienophile systems in usual and Lewis acid-catalyzed Diels—Alder reactions, the reaction enthalpy, complex formation, dissolution, and solvation, and the donor-acceptor properties of the reactants. It was found that taking account of both the orbital interaction energy and the balance of bond rupture and formation energies allows correct prediction of the reaction rate in the absence or in the presence of Lewis acids.     

Isolation,purification, and characterization of two forms of lipase from the fungusMucor miehei

Two forms of lipases (A and B) have been isolated from the fungusMucor miehei UzLT-3 and purified to the homogeneous state, and molecular masses of 43 and 40 kDa have been established for them from the results of disk electrophoresis and gel filtration. The isoelectric points of the lipases are 4.7 for form A and 4.9 for form B. Institute of Microbiology, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax 41 71 29. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 673–676, September–October, 1994.