Dependence of the structure of siloxane urethane elastomer on the conditions of synthesis

The morphology and thermal and mechanical properties of siloxane urethane block copolymers based on oligosiloxane- and oligoalkylene diols are investigated. The dependence of morphology on the conditions of synthesis is studied via atomic force microscopy and scanning electron microscopy.     

Study of the features of BaF<Subscript>2</Subscript> heteroepitaxy on CaF<Subscript>2</Subscript>/Si(100) layers obtained in the high-temperature growth mode

The surface morphology of BaF₂ epitaxial films grown by MBE (molecular beam epitaxy) in various modes on the surface of CaF₂/Si(100) is investigated by AFM. The CaF₂ layers on Si(100) are obtained in the high-temperature growth mode (Т _S = 750°C). It is shown that the epitaxy of BaF2 at a temperature of 600°C at the initial stage of growth leads to the formation of defects such as perforations in the epitaxial film, while epitaxy at a temperature of 750°C provides a defect-free film with a surface morphology suitable for the subsequent growth of semiconductors of IV–VI type and solid solutions based on them.     

Lithium Ascorbate as a Promising Neuroprotector: Fundamental and Experimental Studies of an Organic Lithium Salt

Given the observable toxicity of lithium carbonate, neuropharmacology requires effective and non-toxic lithium salts. In particular, these salts can be employed as neuroprotective agents since lithium ions demonstrate neuroprotective properties through inhibition of glycogen synthetase kinase-3β and other target proteins, increasing concentrations of endogenous neurotrofic factors. The results of theoretical and experimental studies of organic lithium salts presented here indicate their potential as neuroprotectors. Chemoreactomic modeling of lithium salts made it possible to select lithium ascorbate as a suitable candidate for further research. A neurocytological study on cerebellar granular neurons in culture under conditions of moderate glutamate stress showed that lithium ascorbate was more effective in supporting neuronal survival than chloride or carbonate, i.e., inorganic lithium salts. Biodistribution studies indicated accumulation of lithium ions in a sort of “depot”, potentially consisting of the brain, aorta, and femur. Lithium ascorbate is characterized by extremely low acute and chronic toxicity (LD50 > 5000 mg/kg) and also shows a moderate antitumor effect when used in doses studied (5 or 10 mg/kg). Studies on the model of alcohol intoxication in rats have shown that intake of lithium ascorbate in doses either 5, 10 or 30 mg/kg did not only reduced brain damage due to ischemia, but also improved the preservation of myelin sheaths of neurons.     

A new transformation of aminopyridines upon diazotization in acetonitrile with the formation of N-pyridinylacetamides

Russian Chemical Bulletin - Diazotization of aminopyridines upon treatment with NaNO2 and H3PO4 in acetonitrile led to the formation of N-pyridinylacetamides. This reaction constitutes a convenient...     

Synthesis of chalcogenide and pnictide crystals in salt melts using a steady-state temperature gradient

Some examples of growing crystals of metals, alloys, chalcogenides, and pnictides in melts of halides of alkali metals and aluminum at a steady-state temperature gradient are described. Transport media are chosen to be salt melts of eutectic composition with the participation of LiCl, NaCl, KCl, RbCl, CsCl, AlCl₃, AlBr₃, KBr, and KI in a temperature range of 850–150°C. Some crystals have been synthesized only using a conducting contour. This technique of crystal growth is similar to the electrochemical method. In some cases, to exclude mutual influence, some elements have been isolated and forced to migrate to the crystal growth region through independent channels. As a result, crystals of desired quality have been obtained using no special equipment and with sizes sufficient for study under laboratory conditions.     

Variations of Atmospheric Muons and Background Measured with Large Volume Detector

Physics of Atomic Nuclei - The analysis of atmospheric muons detected in the LVD underground experiment (Gran Sasso, Italy) has been completed. Atmospheric muons and the low-energy background that...     

Modification of Styrene-Containing Oligomer Based on Bottoms from Toluene Distillation in Production of Polybutadiene

Chemical modification of styrene-containing oligomer with maleic anhydride was studied. The process conditions and content of maleic anhydride were optimized.     

15N NMR studies of the No?NH3?O2 reaction over ZSM-5 type zeolites and vanadia supported catalysts

¹⁵N nuclear magnetic resonance spectra produced by adsorption of NO together with O₂ and NH₃ on H-ZSM-5 and V₂O₅/Al₂O₃ catalysts have been examined. Several surface species and reaction intermediates have been identified by their characteristic¹⁵N NMR spectra. The intermediate complexes between the products of disproportionation and partial oxidation of NO, on one hand, and ammonia, on the other hand, were found to be formed in the reaction. On V₂O₅/Al₂O₃ catalyst the reaction proceeds more rapidly compared with ZSM-5 but some details of the mechanism are similar for both catalysts.     

Tautomerism of peroxyacetic acid derivatives: a quantum chemical study

The electronic and molecular structures and the relative stabilities of organic peracids X=C(R)-COOH and their cyclic tautomers, dioxiranes

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, with R = Me, CF₃; X = O, NH, were studied using the ab initio Hartree-Fock method and the density functional theory (B3LYP version) as well as at the MP2-MP4 Møller-Plesset levels of perturbation theory. Geometry optimization was performed by the UHF and B3LYP methods with the 6-31G** basis set and at the MP2/cc-pvtz level of theory. The acyclic form of the peracid is more stable than the cyclic dioxirane form irrespective of the nature of the substituent. The energy difference between these tautomers increases as the CF₃ and NH groups are replaced by Me and O, respectively. Parameters of the activation barrier to tautomeric conversion increase in parallel with enhancement of the electron-accepting properties of both substituents. The transition state of tautomeric interconversion, which is topologically similar to the acyclic structure of the carbonyl oxide derivative R(HX)C=O⁺-O^?, was found and characterized taking peroxyacetic acid as an example. The characteristic features of the transition state are an intramolecular “multicenter” H-bond and the charge distribution that is inconsistent with the canonical structure mentioned above. An appropriate reaction coordinate for the transformation of the quasi-tetrahedral dioxirane structure into a planar peroxyacetic acid structure is provided by the dihedral angle. Deprotonated anionic systems are characterized by much smaller differences between the relative stabilities of the open and closed forms of isomers and by much lower activation barriers to isomeric conversions.

     

4-Hydroxy-2-quinolenes. 20.* Synthesis and chemical conversions of ehtyl esters of the chloro-substituted quinoline-3-carboxylic acids

Preparative methods for the synthesis of ethyl esters of 2,4-dichloro- and 2-oxo-4-chloroquinoline-3-carboxylic acids were developed. The behavior of the compounds indicated was studied under conditions of alkaline and acidic hydrolysis, in reactions with some nucleophilic reagents, as well as in reductive dehalogenation. Results of the study of the antimicrobial and antiinflammatory activity of the synthesized compounds are presented.Okrainian Pharmaceutical Academy, Khar'kov 310002. Translated from Khimiya Geterosiklicheskikh Soedinenii, No. 2, pp. 195–203, February, 1995. Original article submitted May 6, 1994.