2-Aminothiophene derivatives in a novel synthesis of phthalimidines

New aminophthalides were synthesized from o-formylbenzoic acid and substituted 2-aminothiophenes. Two of these compounds underwent recyclization in boiling Ac₂O to give the previously unknown 3-acetoxy-2-(3-cyano-4,5-dimethylthiophen-2-yl)-1,3-dihydroisoindol-1-one and 3-acetoxy-2-(3-cyano-4,5-tetramethylenethiophen-2-yl)-1,3-dihydroisoindol-1-one. The possible reaction mechanism and factors preventing the recyclization, in particular, the formation of intramolecular hydrogen bonds in the starting phthalides, were discussed. Some reactions of the resulting compounds with C-nucleophiles in trifluoroacetic acid were investigated. Two derivatives containing 4-hydroxy-3,5-di-tert-butylphenyl substituents were studied by X-ray diffraction.     

In vitro effects of ultra-low and low doses of radiation produced by sources of different nature and power on enzymes

The effects of low and ultra-low doses of X-ray radiation and neutron fluxes produced by continuous-wave and pulsed sources of different nature and power on the activity of plant peroxidases and the bovine lung angiotensin-converting enzyme were studied. Certain ranges of doses (including ultra-low), the exposure to which under particular conditions causes the in vitro activation and/or inactivation of the enzymes, were found. Possible factors responsible for this phenomenon are discussed.     

Electrical and thermoelectric properties of the SiC/Si biomorphic composite at high temperatures

The electrical resistivity ρ and the thermopower coefficient α of a SiC/Si biomorphic composite fabricated from a porous carbon matrix [prepared through pyrolysis of wood (white eucalyptus)] by infiltrating molten Si into the empty channels of the matrix were measured in the temperature ranges 100–950 and 100–750 K, respectively. Silicon reacts chemically with the carbon of the matrix to produce 3C-SiC, which, in combination with the excess Si unreacted with carbon, forms the SiC/Si biomorphic composite. The SiC/Si samples studied had a concentration of “excess” Si of ～30 vol % and a porosity of ～13–15 vol %. Measurements of ρ were carried out on samples cut either along (ρ_∥) or across (ρ_⊥) the tree growth direction, and α was measured on a sample cut along the tree growth direction.     

Biplanar Epitaxial AlN/SiC/(n,p)SiC Structures for High-Temperature Functional Electronic Devices

Technical Physics - We investigate the possibility of integration of epitaxial SiC and AlN technologies using opposite faces of the common SiC substrate (AlN epitaxy is performed at the final...     

Radical cyclization of allyl α-bromocarboxylates into λ-butyrolactones. Effect of the ester structure on the cyclization

Allyl dibromoacetate, allyl α-bromopropionate, and allyl phenylbromoacetate undergo cyclization in benzene in the presence of increased concentration of Fe(CO)₅—DMF as the initiating system to give the corresponding bromo-substituted butyrolactones. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2210–2212, December, 1997.     

Correlation between the electric-field effect and weak-link type in YBa2Cu3−x Oy and YBa2Cu3−x Oy /Agx high-T c superconducting ceramics

An experimental study is reported of the effect of an electric field E⩽120 MV/m and of temperature T on the critical current I _c and I-V characteristics of yttrium-based high-T _c superconducting ceramics. The materials studied were copper-deficient ceramics, YBa₂Cu_3−x O_y (D samples), and YBa₂Cu_3−x O_y/Ag_x ceramics [S samples with silver present in amounts equal to the copper deficiency (0⩽x⩽0.4)]. It has been established that in D samples at 77 K, the electric field increases I _c and reduces substantially R for I>I _c, whereas in S samples no field effect is observed. Measurements of the I _c(T) dependence near the critical temperature showed that they can be described for all samples by a relation of the type I _c =const(1−T/T _c )^α, where α≈1 for the D samples, and α≈2 for the S samples. The results obtained suggest that the electric-field effect correlates with the existence in the ceramic of SIS-type weak links at grain boundaries. Fiz. Tverd. Tela (St. Petersburg) 40, 1195–1198 (July 1998)     

Grain size refinement due to relaxation of disclination junction configurations in the course of plastic deformation of polycrystals

A model is proposed for the formation of the substructure in polycrystals during plastic deformation. According to this model, fragmentation of a grain occurs through the formation of a system of diagonal low-angle boundaries, which originate at the edges of a rectangular grain. Misorientation boundaries form through relaxation of a nonsymmetric junction quadrupole disclination configuration accumulated at the grain corners under severe deformation when the disclination strength reaches a certain critical value. The energetics of this process is analyzed. A general case is considered where the disclinations at the junctions of the chosen grain differ in strength. The energetic approach used makes it possible to determine the misorientation angle ω_x of the resulting boundaries corresponding to the maximum energy gain and to find the dependence of this angle on the degree of asymmetry of the quadrupole configuration of junction disclinations. According to the proposed model, the splitting of a grain with a short edge greater than 0.5 μm is energetically favorable and decreases the latent energy of the grain for any ratio between the junction disclination strengths if the grain length-to-width ratio is less than 30. It is shown that the minimum possible grain size in the proposed model does not exceed 0.1 μm.     

Asymptotic Expansions for the Distribution of the Crossing Number of a Strip by Sample Paths of a Random Walk

The complete asymptotic expansions are obtained for the distribution of the crossing number of a strip in n steps by sample paths of an integer-valued random walk with zero mean. We suppose that the Cramer condition holds for the distribution of jumps and the width of strip increases together with n; the results are proven under various conditions on the width growth rate. The method is based on the Wiener–Hopf factorization; it consists in finding representations of the moment generating functions of the distributions under study, the distinguishing of the main terms of the asymptotics of these representations, and the subsequent inversion of the main terms by the modified saddle-point method.     

Wild type and mutant forms of recombinant horseradish peroxidase C expressed inEscherichia coli

Two horseradish peroxidase C (HRPC) mutants with substitutions in the active center, i.e., Phe41→ His and Phel43→ Glu, were compared to the wild-type recombinant enzyme expressed in Escherichia coli in terms of the enzymatic activity and stability under irradiation. Both mutations caused a significant decrease in activity, but it was still possible to follow the effect of mutations on the key steps of the reaction mechanism. Phe41 can be considered a nonpolar barrier separating histidine residues in the active center and providing a firm noncovalent binding with the highly hydrophobic porphyrin ring. The replacement of Phe41 with the ionizable His residue destabilizes the enzyme. The Phel43→ Glu replacement creates a negative charge at the entrance of the heme-binding pocket, and protects the latter from both donor substrates and free radicals. The radiolytic inactivation of the wild-type and mutant forms of recombinant HRP suggested different binding sites for iodide, 2,2′-bis(3-ethylbenzothiasoline-6-sulfonate (ABTS), guaiacol, and o-phenylene diamine. The study of kinetics and inactivation is in agreement with the direct binding of iodide to the heme porphyrin ring. The results also suggest that the ABTS binding site is less accessible than that for o-phenylene diamine.