Nature of mechanically induced defects in polycrystalline hydrargillite and Al2O3-A1(OH)3 studied by radiation methods

Mechanical treatment of hydrargillite Al(OH)₃ in a vibrational grinder and in a ball-mill grinder increases the dispersion, the specific surface area, and the unit-cell constants. An x-ray amorphous phase forms. Differences in the nature and in the concentration of paramagnetic centers arise on irradiation (77 K) of the mechanically treated samples. Anion vacancies and oxygen ions with disrupted short-range order appear in the mechanically treated samples. Their concentration increases with increased time of mechanical treatment. Pulsed thermal treatment of hydrargillite forms the Al₂O₃-Al(OH)₃ system and anneals the mechanically induced defects.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1463–1467, July, 1990.     

Use of reference pools to compare the qualitative and quantitative determination of polychlorinated biphenyls by packed and capillary gas chromatography with electron capture detection. Part 1. Serum

Serum for reference pools of in vivo polychlorinated biphenyls (PCBs) was obtained from four goats that had received one dose (100 mg kg-1) of a selected technical Aroclor (AR) (1016, 1242, 1254 or 1260) and were allowed to recover for 30 d. These pools were used to assess the differences in an analytical method that determines and quantifies PCBs using packed-column gas chromatography (PCGC) (quantified on the basis of mean mass percent. data for grouped PCB peaks) and capillary-column gas chromatography (CCGC) (quantified on the basis of percent. composition data for specific congeners). With CCGC, results were statistically significantly different (p less than or equal to 0.0002) from results with PCGC for ARs 1016, 1242 and 1254 but not for AR 1260 (p = 0.23). When comparing these gas chromatographic methods using bovine serum spiked in vitro with the same ARs at 17-25 p.p.b., it was found that the methods were not statistically significantly different for any of the ARs (p = 0.30-0.92). Levels of serum PCB determined by the two methods for 12 persons, divided into two groups according to exposure, were compared using the paired t-test. Group 1 consisted of three persons with dietary and/or environmental exposure; one with dietary and/or environmental exposure in addition to occupational exposure dating back 20 years. Group 2 consisted of eight persons with recent occupational exposure.(ABSTRACT TRUNCATED AT 250 WORDS)     

The molecular structure of tetrathiofulvalene-13C (TTF) from proton magnetic resonance studies using nematic solvents

The molecular structure of TTF dissolved in nematic liquid crystalline solvents has been determined from the proton magnetic resonance including couplings due to ¹³C in natural abundance. The molecule is puckered in a boat conformation with the SCHCHS planes making a dihedral angle of 13 ± 2° with the S₂C  CS₂ plane. The other structural parameters obtained are r_CH = 1.085 ± 0.014 Å and the angel CCH = 123.7 ± 1.5°.     

Studies on Ziegler-Natta catalysts. Part II. Reactions between α- or β-TiCl3 and AlMe3, AlMe2Cl,or AlEt3 at various temperatures

The following reactions, carried out in the absence of solvents, has been studied: α-TiCl₃ + Al(CH₃)₃ at 20°C., β-TiCl₃ + Al(CH₃)₃ at 65°C., α-TiCl₃ + Al(CH₃)₂Cl at 20 and 65°C., and α-TiCl₃ + Al(C₂H₅)₃ between 30 and 65°C. It appears that a general reaction mechanism, such as discussed in the preceding paper of this series, applies to all these reactions between TiCl₃ and aluminum alkyls. The differences in overall stoichiometry between some of these systems may be linked to differences in stability of the intermediate Ti? C bonds. In the case of α-TiCl₃ + Al(CH₃)₂Cl, alkylation is probably accompanied by fixation of the AlCH₃Cl₂ on the nonvolatile product.     

Intramolecular hydrogen bond in substituted 3-hydroxypyridines

To explain the character of the intramolecular hydrogen bond in substituted 3-hydroxypyridines, the chemical shifts in the NMR spectra of the hydroxyl group and the IR spectra were studied. It was established that the stability of the intramolecular hydrogen bond of the O-HNR₂ type in substituted 3-hydroxypyridines increases when compared with the corresponding phenols, while an opposite pattern is observed for bonds of the O-H0₂ N type. An approximate evaluation of the energy of the intramolecular hydrogen bond in substituted 3-hydroxypyridines was achieved. When reacting with bases of the same strength, 3-hydroxypyridine forms more stable complexes than phenol.     

Arylhydroxyacetic acids and amino acids derived from ethinylphenols

Conclusions A method of synthesis of arylhydroxyacetic acids and ammo acids derived from ethinylphenols has been developed in view of possible physiological activity of these compounds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1170–1172, May, 1970.     

Kinetics and mechanism of polymerization yielding stereoblock poly(methyl methacrylate) with VCl4-Al(C2H5)3 catalyst system

Methyl methacrylate was polymerized at 40°C with the VCl₄–AlEt₃ catalyst system in n-hexane. The rate of polymerization was proportional to the catalyst and monomer concentration at Al/V ratio of 2, indicating a coordinate anionic mechanism of polymerization. NMR spectra were further used to confirm the mechanism of polymerization and stability of active sites responsible for isotacticity.     

EMISSION SPECTRA FROM SYNTHETIC POLYNUCLEOTIDES AND DEOXYRIBONUCLEIC ACID IN AQUEOUS SOLUTIONS†

A study has been made of the emission spectra at 77°K from poly A, poly U, poly C, their complexes, and from native and heat-denatured DNA in buffered aqueous solutions containing 0·25 per cent glucose: no emission was observed from these polynucleotides at room temperature. The spectra differed from those obtained in the polyalcoholic glasses used by other workers. The principal differences between the emission spectra of poly A and adenosine at pH 7 in a water-glucose mixture were: (a) a decrease in both P/F and the overall intensity in poly A; (b) absence of the structure normally found in adenosine phosphorescence; and (c) appearance of a new short-lived component in the phosphorescence decay. Further changes in the emission characteristics (e.g. the increase of P/F, the proportional increase of the short-lived component in the phosphorescence decay) from poly A were observed at pH 5. These can not be explained solely by protonization of adenosine residues, but rather appear to depend upon exciton interactions of the most intense π–π* transition in double-stranded poly A. and perturbation of the lowest-lying emitting band. When poly A or poly C is complexed with poly U or poly I the luminescence intensity decreases in two-strand complexes and is completely quenched in poly (A + 2U), poly (A+2I) and poly (C⁺+I); no emission was observed from either, single-strand poly I or poly U. Identical emission patterns were obtained from native and heat-denatured samples of DNA. The comparison of polynucleotide emission spectra in the water-glucose medium with those obtained from polyalcoholic glasses leads to the conclusion that the emission spectra depend most critically upon the relative proportions of base-solvent and base-base interactions in each environment: the possible importance of proton tunneling and/or triplet-triplet transfer mechanisms is briefly discussed.     

Determination of the energy of the bond formed by carbon with the surface of a nickel catalyst

Summary Calculations were made of the energy of the bond formed by carbon with the surface of a nickel catalyst on the assumtion that the excess of free energy of the surface compounds is determined mainly by the excess of free energy of the surface of the catalyst.We express our deep thanks to A. A. Balandin for his interest in our work.