Nonequilibrium acoustic phonons in ZnTe at liquid-helium temperatures: Effect of impurities and structural defects on the phonon mean free path

ZnTe crystallites isolated from a druse of coarse-grained polycrystalline ZnTe, prepared by chemical vapor synthesis at a temperature of ～650°C, were studied using x-ray diffractometry, luminescence, and the heat pulse technique. The crystallites are stacked in {110}-oriented macroscopic layers with a common twin system. The {111} twin planes separated at a distance of 50–100 μm are perpendicular to the (110) growth layers. Acoustic phonon propagation was studied using the heat pulse technique. A comparison of the responses to the arrival of differently polarized phonons in a given sample with the responses obtained on high-purity coarse-grained ZnTe with randomly distributed twin systems with a separation of 5–10 μm and on twin-free single-crystal ZnTe suggests that twins radically affect the scattering of acoustic phonons. The mean free paths of LA, FTA, and STA phonons were determined by comparing the experimental responses with Monte Carlo calculations.     

C→N migration of methoxycarbonyl and acetyl groups in reactions of functionally substituted carbanions with aryl isocyanates. Kinetics and mechanism of the reactions

The kinetics and mechanism of C→N migrations of methoxycarbonyl and acetyl groups in the reactions of the sodium derivative of methyl (2-cyano-2-phenyl)acetate and 1,1-diacetyl-2-phenyl-2-tributylphosphonioethanide with aryl isocyanates were studied by spectrophotometry. The reactions afford a prereaction complex via a concerted mechanism, according to which the nucleophilic attack of the carbanionic center to the carbon atom of the isocyanate group and the subsequent nucleophilic attack of the nitrogen atom to the carbonyl carbon atom, resulting in the C-C bond cleavage, occur almost simultaneously in the framework of the same transition state. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 850–853, May, 2006.     

De novo sequencing of antimicrobial peptides isolated from the venom glands of the wolf spider Lycosa singoriensis

Antimicrobial peptides (AMPs), named lycocitin 1, 2 and 3, and a peptide with a monoisotopic molecular mass of 3038.70 Da were detected in the venom glands of the wolf spider Lycosa singoriensis. Two of the peptides, lycocitin 1 and 2, are new AMPs whereas lycocitin 3 is highly homologous to lycotoxin II isolated from the venom of spider Lycosa carolinensis. In addition, two other peptides with monoisotopic masses of 2034.20 and 2340.28 Da showing the motif typical for antimicrobial peptides were also identified. These peptides and lycocitin 1, 2 and 3 were de novo sequenced using electron capture dissociation and low-energy collisional tandem mass spectrometry. The amino acid sequence of lycocitin 1 was determined as GKLQAFLAKMKEIAAQTL-NH(2). Lycocitin 2 differs from lycocitin 1 by a replacement of a lysine residue for an arginine residue at the second position. Lycocitin 3 differs from the known lycotoxin II consisting of 27 amino acid residues by a deletion of Gly-26. Both lycocitin 1 and 2 inhibit growth of Gram-positive (Staphylococcus aureus, Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria and fungi (Candida albicans, Pseudomonas aeruginosa) at micromolar concentrations.     

The Behavior of Dimethylamino-substituted 2,5-Diaryloxazoles and 2,5-Diaryl-1,3,4-oxadiazoles Under Vilsmeier-Haack Conditions

It has been shown that dimethylamino-substituted 2,5-diaryloxazoles and 2,5-diaryl-1,3,4-oxadiazoles undergo heterocyclization under Vilsmeier-Haack conditions with the participation of the dimethylamino group to form quinazolinium salts. The oxazole ring can also be formylated at the free 4 position. In alkaline medium the quinazolinium ring is readily hydrolyzed with desalkylation.     

Synthesis and ion-selective properties of 1,2-bis[2-((2-diphenylphosphorylmethyl)phenoxy)ethoxy]cyclohexane (L) and its structural analogs. Crystal structure of L

Potentially hexadentate phosphoryl podands 1,2-bis[2-((2-diphenylphosphorylmethyl)phenoxy) ethoxy]cyclohexane (L), 1,2-bis[2-((2-diphenylphosphoryl)phenoxy)ethoxy]cyclohexane (L¹), and 1,2-bis[2-((2-diphenylphosphorylmethyl)phenoxy)ethoxy]benzene (L²) are synthesized. Stability constants of complexes formed by L, L¹, and L² with alkali-metal 2,4-dinitrophenolates in mixed THF—CHCl₃ solutions (4: 1 by volume) are determined. Electroanalytical characteristics of ion-selective electrodes with hexadentate phosphoryl podands having different structures used as active components of their plasticized membranes are compared for cations of alkali and alkaline-earth metals. The IR spectra are described. The crystal structure of L is studied by X-ray diffraction.     

Carboxylate Phosphabetaines Containing Chiral Carbon Atom: Synthesis and NMR Spectroscopy Data

Russian Journal of General Chemistry - The nucleophilic addition reactions of tertiary phosphines and unsaturated carboxylic acids have led to the formation of mono- and dicarboxylate...