Effect of the medium of a living organism on the vulcanization of silicone rubber

Conclusions The vulcanization process of SKTN silicone rubber in a living organism significantly depends on the chemical nature of the catalyst. The organism accelerates this process if cross-linking of the rubber occurs in the presence of tin dioctyldilaurate (Sn⁴⁺) and may retard this process if tin octoate (Sn²⁺) serves as the catalyst.Presented to the Second All-Union Conference on Biomechanics, Riga, April 1979.Translated from Mekhanika Kompozitnykh Materialov, No. 2, pp. 345–349, March–April, 1980.     

Cathodic deprotonation of 5-substituted isoxazoles

The regularities of electroreduction of 5-substituted isoxazoles are studied by examining their cyclopropyl and phenyl derivatives. It is found that this process proceeds on a steel electrode according to the mechanism of direct cathodic deprotonation and is accompanied by the removal of a proton from the 3rd position of the isoxazole ring with the formation of a corresponding carbanion, which is readily isomerized to enolate anion of an open type. The same mechanism is realized also in the electroreduction of 5-substituted isoxazoles on cathodes with a high overpotential of hydrogen evolution (C, Hg). An alternative process, namely, an indirect cathodic deprotonation of 5-substituted isoxazoles, can be realized with the use of MeOH or t-BuOH as the prebases.     

Solvent induced cooperativity of Zn(II) complexes cleaving a phosphate diester RNA analog in methanol

The kinetics of cyclization of 2-hydroxypropyl p-nitrophenyl phosphate (1) promoted by two mononuclear Zn(II) catalytic complexes of bis(2-pyridylmethyl)benzylamine (4) and bis(2-methyl 6-pyridylmethyl)benzylamine (5) in methanol were studied under (s)(s)pH-controlled conditions (where (s)(s)pH refers to [H(+)] activity in methanol). Potentiometric titrations of the ligands in the absence and presence of Zn(2+) and a non-reactive model for 1 (2-hydroxylpropyl isopropyl phosphate (HPIPP, 6)) indicate that the phosphate is bound tightly to the 4:Zn(II) and 5:Zn(II) complexes as L:Zn(II):6(-), and that each of these undergoes an additional ionization to produce L:Zn(II):6(-):((-)OCH(3)) or a bound deprotonated form of the phosphate, L:Zn(II):6(2-). Kinetic studies as a function of [L:Zn(II)] indicate that the rate is linear in [L:Zn(II)] at concentrations well above those required for complete binding of the substrate. Plots of the second order rate constants (defined as the gradient of the rate constant vs. [complex] plot) vs. (s)(s)pH in methanol are bell-shaped with rate maxima of 23 dm mol(-1) s(-1) and 146 dm mol(-1) s(-1) for 4:Zn(II) and 5:Zn(II), respectively, at their (s)(s)pH maxima of 10.5 and 10. A mechanism is proposed that involves binding of one molecule of complex to the phosphate to yield a poorly reactive 1 : 1 complex, which associates with a second molecule of complex to produce a transient cooperative 2 : 1 complex within which the cyclization of 1 is rapid. The observations support an effect of the reduced polarity solvent that encourages the cooperative association of phosphate and two independent mononuclear complexes to give a reactive entity.     

Plastic motion and mixing in deformable mixes of metals

The article continues the publication of experimental results from the study of plastic motions in thin layer-heterogeneous sandwich samples and contains data on how the microhardness ratio of the metals in the sandwich affects these motions. We consider nonequilibrium plastic deformation structures in heterogeneous materials and their role in the mixing of metals.Novokuznetsk Pedagogical Institute. Translated from Izvetiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 10–15, February, 1994.     

Mechanistic studies of La3+- and Zn2+-catalyzed methanolysis of aryl phosphate and phosphorothioate triesters. Development of artificial phosphotriesterase systems

The methanolyses of a series of O,O-diethyl O-aryl phosphates (2,5) and O,O-diethyl S-aryl phosphorothioates (6) promoted by methoxide and two metal ion systems, (La3+)2(-OCH3)2 and 4:Zn2+:-OCH3 (4 = 1,5,9-triazacyclododecane) has been studied in methanol at 25 degrees C. Br?nsted plots of the logk2 values vs. pKa for the phenol leaving groups give beta(lg) values of -0.70, -1.43 and -1.12 for the methanolysis of the phosphates and -0.63, -0.87 and -0.74 for the methanolysis of the phosphorothioates promoted by the methoxide, La3+ and Zn2+ systems respectively. The kinetic data for the metal-catalyzed reactions are analyzed in terms of a common mechanism where there is extensive cleavage of the P-XAr bond in the rate-limiting transition state. The relevance of these findings to the mechanism of action of the phosphotriesterase enzyme is discussed.     

Two-particle correlation function and dihadron correlation approach

It is shown that, in the case of asymmetric nuclear interactions, the application of the traditional dihadron correlation approach to determining a two-particle correlation function C may lead to a form distorted in relation to the canonical pair correlation function _C². This result was obtained both by means of exact analytic calculations of correlation functions within a simple string model for proton–nucleus and deuteron–nucleus collisions and by means of Monte Carlo simulations based on employing the HIJING event generator. It is also shown that the method based on studying multiplicity correlations in two narrow observation windows separated in rapidity makes it possible to determine correctly the canonical pair correlation function C₂ for all cases, including the case where the rapidity distribution of product particles is not uniform.     

HgTe/CdHgTe double quantum well with a spectrum of bilayer graphene and peculiarities of its magnetotransport

Free expansion of Bose–Einstein condensates of rubidium atoms at finite temperatures has been analyzed experimentally and theoretically. It has been shown that the interaction between condensed and noncondensed atoms is manifested most clearly by a decrease in the density of atoms in the center of the expanding cloud as compared to the theoretical prediction for a pure condensate.     

Scaling in the quantum Hall effect regime in n-InGaAs/GaAs nanostructures

The longitudinal ρ _xx (B) and Hall ρ _xy (B) magnetoresistances are investigated experimentally in the integer quantum Hall effect (QHE) regime in n-InGaAs/GaAs double quantum well nanostructures in the range of magnetic fields B = (0–16) T and temperatures T = (0.05–70) K before and after IR illumination. The results are evaluated within the scaling hypothesis with regard to electron-electron interaction.