Spin Polarization of Fluorine Nuclei in the Si/CaF<Subscript>2</Subscript> Nanostructure Under Optical Excitation

The laws of fluorine nuclear spin polarization in the Si/CaF₂ nanostructure under optical excitation of the charge carriers in it has been considered theoretically. It has been shown that maximum values (up to 3% of the concentration of nuclei in the lattice) are attained under a high rate of optical excitation (>10⁻⁹ sec⁻¹) when the nuclear spin diffusion process and the Auger recombination prevail. In this case, the nuclear relaxation time in an individual layer reaches 100–300 sec and the spin diffusion radius decreases to 0.3 nm. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 397–403, May–June, 2005.     

Surfaces with maximal curvature of the Grassmann image

Translated from Matematicheskie Zametki, Vol. 48, No. 3, pp. 12–19, September, 1990.     

Investigation of inelastic interactions of 400 GeV protons with emulsion nuclei

The basic experimental characteristics of incoherent interactions of 400 GeV protons on emulsion nuclei, such as the multiplicity of charged secondaries, one-particle distributions and two-particle correlations, are reported and discussed in details. They are compared with the results of other experiments on hadron-nucleus interactions at lower energies. We have shown from both the quantitative and qualitative comparison of the data presented with predictions of various model approaches to nuclear production, that most of them cannot explain the complete set of experimental observations.An analysis of the experimental data presented gives strong support to the idea that the production mechanism in high-energy hadron-nucleus interactions has two or multi-component character.     

Nitroxides scavenge myeloperoxidase-catalyzed thiyl radicals in model systems and in cells

Nitroxide radicals possess important antioxidant activity in live tissues because of their ability to scavenge reactive radicals. Despite the fact that, in cells, damaging free radicals are primarily quenched by glutathione (GSH) with subsequent formation of harmful glutathionyl radical (GS(*)), interactions of nitroxide radicals with GS(*) and thiols have not been studied in detail. In addition, intracellular metabolic pathways leading to the formation of secondary amines from nitroxides are unknown. Here we report that GS(*) radicals react efficiently and irreversibly with nitroxides to produce secondary amines. We developed a sensitive method for the detection of GS(*) based on their specific interaction with Ac-Tempo, a nonfluorescent conjugate of fluorogenic acridine with paramagnetic nitroxide Tempo, and used it to characterize interactions between nitroxide and thiyl radicals generated through phenoxyl radical recycling by peroxidase. During reaction of Ac-Tempo with GS(*), Tempo EPR signals decayed and acridine fluorescence concurrently increased. DMPO and PBN, spin traps for GS(*), inhibited this interaction. Using combined HPLC and mass spectrometry, we determined that 90% of the Ac-Tempo was converted into fluorescent acridine (Ac)-piperidine; GSH was primarily oxidized into sulfonic acid. In myeloperoxidase-rich HL-60 cells, Ac-piperidine fluorescence was observed upon stimulation of GS(*) generation by H(2)O(2) and phenol. Development of fluorescence was prevented by preincubation of cells with the thiol-blocking reagent N-ethylmaleimide as well as with peroxidase inhibitiors. Furthermore, Ac-Tempo preserved intracellular GSH and protected cells from phenol/GS(*) toxicity, suggesting a new mechanism for the free-radical scavenging activity of nitroxides in live cells.     

Structures of the radical P[N(SiMe3)2](NPri2), its dimer, cation and chloro derivative

Treatment of PCl[N(SiMe3)2](NPri2) (1) with potassium-graphite in thf afforded the colourless, crystalline diphosphine [P[N(SiMe3)2](NPri2)]2 (2) in good yield. Sublimation of 2 in vacuo yielded the yellow phosphinyl radical P[N(SiMe3)2](NPri2) (3), which upon cooling reverted to 2; the latter in C6D6 at 298 K was a mixture of rac and meso diastereoisomers. The yellow, crystalline phosphenium salt [P[N(SiMe3)2](NPri2)][AlCl4] (4) was obtained from 1 and 1/2Al2Cl6 in CH2Cl2. By single-crystal X-ray diffraction (XRD) the structures of the known compound 1 and of 2 and 4 were determined. The structure of the radical 3, formed by the thermal homolytic dissociation of the diphosphine 2, was determined in the gas phase by electron diffraction (GED), utilising data from UMP2/6-31+G*ab initio calculations. The model of the molecule in the GED structure analysis was described by a set of internal coordinates and an initial set of Cartesian coordinates from ab initio calculations, facilitating the structure analysis. The experimental data were found to be consistent with the presence of a single conformer of the radical in the gas phase. The computed standard homolytic dissociation enthalpy of the P-P bond in the corresponding diphosphine 2, corrected for BSSE, 54 kJ mol(-1), is substantially reduced compared to the dissociation enthalpy of tetramethyldiphosphine by the reorganisation energies of the fragments that form upon dissociation. The intrinsic energy content of the P-P bond in the diphosphine 2 was estimated to be 286 kJ mol(-1), in agreement with the results of previous work on a series of crowded diphosphines.