Multielement standards for instrumental neutron activation analysis of biological materials

Standards for instrumental neutron activation analysis (INAA) of biological materials are proposed. The standards are multielement solid solutions in phenol-formaldehyde resole resin (PFR) moulded as pellets weighing 30 to 50 mg. The concentrations of trace elements in the standards are selected so that, firstly, they are commensurable with their concentrations in the biological materials and, secondly, that the analytical lines of each of the elements incorporated in PFR are resolved with the aid of modern equipment. The principal standard contains 21 trace elements from among those of greatest interest for INAA of biological materials. This standard is recommended for work on high-resolution equipment. At the same time, standards of simpler trace element composition have been prepared and studied which can be used in work on simpler equipment or in solving particular problems in determination of certain groups of chemical elements.     

13C-13C Coupling Constants in Structural Studies: XXXIII. Stereochemical Study of the Pyranose Ring

¹³C-¹³C coupling constants for all aldopyranoses of the D-series were calculated in terms of the self-consistent finite perturbation theory. General relations holding in the stereochemical behavior of the ¹³C-¹³C coupling constants for the pyranose ring were found. The results obtained make it possible to perform conformational analysis and assign configuration of the anomeric center in molecules of carbohydrates and products of their metabolism, containing a pyranose fragment.     

13C-13C Spin-Spin Coupling Constants in Structural Studies: XXXVII. Rotational Conformations of Hydroxy Groups in Pyranose, Furanose, and Septanose Rings

Rotational surfaces for ¹³C-¹³C coupling constants with respect to two dihedral angles at C¹ and C² in model structures of aldopyranoses, aldofuranoses, and aldoseptanoses of the D-series were calculated in terms of the self-consistent finite perturbation theory. Internal rotation of the hydroxy groups exerts an appreciable effect (within 2.5 Hz) on the ¹³C-¹³C coupling constants of all cyclic forms of monosaccharides, which provides the possibility for performing conformational analysis of carbohydrates and their metabolites containing pyranose, furanose, and septanose fragments.     

13C NMR spectra of biologically active compounds. II. 11-Deoxy-16- and 17-aryloxyprostaglandins

The¹³C NMR spectra of the initial ω-aryloxy chains and the final 16-and 17-aryloxyprostaglandins of the 11-deoxy series have been investigated, and stereochemical assignments have been made for the diastereomeric pairs. A weakening of the diastereotopic effects in the spectra of the 15- and 16-methyl-substituted 16- and 17-phenoxypropstaglandins to 0.1 ppm has been shown.     

Catalytic and Physicochemical Properties of Oxidative Condensation Products in the Oxidative Dehydrogenation of Propane by Sulfur Dioxide on SiO2

The effect of the deposition of oxidative condensation products in the reaction of oxidative propane dehydrogenation in the presence of SO₂ on the catalytic, acid–base, and texture characteristics of silica was studied. It was found that the oxidative condensation products exhibited high catalytic activity in this reaction. The carbonization of silica from 0 to 40 wt % was accompanied by an increase in the yield of propylene from 3.4 to 46 mol % (640°C; a C₃H₈/SO₂/He + N₂ mixture, 10 : 10 : 80 vol %). Further accumulation of condensation products resulted in a considerable decrease in the pore volume and radius; this imposed diffusion limitations on both propane conversion and selectivity to propane conversion products. The nature of active and deactivated condensation products was studied by DRIFT spectroscopy, diffuse-reflectance UV–VIS spectroscopy, EPR spectroscopy, XPS, thermal analysis, and electron microscopy.     

Reactions of 2-and 3-methylbenzothiophenes in the presence of heterogeneous acid catalysts

In the presence of catalysts (Al₂O₃, Al₂O₃ activated by HCl, and 5, 10, and 20% ZnCl₂/Al₂O₃), 2- and 3-methylbenzothiophenes undergo mutual isomerization, dealkylation, and disproportionation to benzothiophene and 2,3-dimethylbenzothiophene at 250–450°C and space velocities of 0.1 and 0.8 h^–1. An ionic mechanism is proposed for the isomerization reaction.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1079–1082, August, 1977.     

Investigation of lasing of dyes under the influence of the radiation of copper-vapor lasers

A study is made of the possibility of improving the laser properties of dyes pumped by the radiation of a copper-vapor laser, the choice of dye mixtures optimal from the point of view of producing stimulated emission, and the influence of the solvent on these properties, the aim being to obtain optimal energy parameters in an instrument based on a copper-vapor laser and an optical attachment.Translated from Izvestiya Vysshikh Uchebnhykh Zavedemii, Fizika, No. 10, pp. 44–48, October, 1980.     

Unusual Reaction of Sodium 1,6-Dioxo-2,4-alkadiene-3,4-diolates under Acid Hydrolysis Conditions

The reaction of sodium 1,6-dioxo-2,4-alkadiene-3,4-diolates with HCl solution afforded unexpected hydrolysis products, namely (2Z)-2-hydroxy-4-oxobut-2-enoic (2,4-dioxobutanoic) acid esters. The structural features of the synthesized compounds were discussed on the basis of IR, ¹H NMR spectroscopy, mass spectrometry and X-ray diffraction analysis data.     

Phase transitions in compounds with the Ca<Subscript>3</Subscript>Ga<Subscript>2</Subscript>Ge<Subscript>4</Subscript>O<Subscript>14</Subscript> structure

Possible structural changes described by the group-subgroup relationships in the Ca₃Ga₂Ge₄O₁₄-type structure (sp. gr. P321) are considered. The most probable phase transitions seem to be those accompanied by lowering of the symmetry to the maximal non-isomorphic subgroups P3 and C2. It is shown that only destructive phase transitions accompanied by symmetry rise up to the minimal non-isomorphic supergroups for the given structure type can take place. The change of the trigonal symmetry to monoclinic is revealed in La₃SbZn₃Ge₂O₁₄, whose crystal structure is refined as a derivative structure of the Ca₃Ga₂Ge₄O₁₄ structure type within the sp. gr. A2 (C2). At ～250°C, La₃SbZn₃Ge₂O₁₄ undergoes a reversible phase transition accompanied by symmetry rise, A2 ? P321. Similar phase transitions, P321 ? A2, are also observed in La₃Nb_0.5Ga_5.5O₁₄ and La₃Ta_0.5Ga_5.5O₁₄ under the hydrostatic pressures 12.4(3) and 11.7(3) GPa, respectively. The mechanisms of compression and phase transition are based on the anisotropic compressibility of a layer structure. With the attainment of the critical stress level in the structure, the elevated compressibility in the (ab) plane gives rise to a phase transition accompanied by the loss of the threefold axis. Attempts to reveal low-temperature phase transitions in a number of representatives of the langasite family have failed.     

Selenophene Synthesis in Thermal Reactions of Dialkyl Selenides with Acetylene in the Presence of Methanol

Russian Journal of Organic Chemistry -