Abstract. The theory of electron spin relaxation in protein solutions taking into account the "two-motion" model of spin label mobility is developed. The relations obtained for the longitudinal and transverse relaxation rates describe the experimental results better than isotropic ("one-motion") model. The mechanism of longitudinal relaxation in solution of spin-labeled lysozyme is revealed and the correlation time of the inherent motion of spin label is evaluated. The linewidth analysis and study of ESR spectra under viscosity variation were used to obtaln the microdynamical parameters characterizing lysozyme molecular mobility. A discrepancy between the correlation time values obtained by viscosity-variation-technique and the results known from other methods is found and ascribed to the manifestation of the intermediatetime-scale mobility of protein.
The ESR spectra of I-palmitoyl-2-stearoyl-(n-doxyl)-glycero-3-phosphocholine spin label positional isomers (n = 5, 7, 10, 12 and 16) have been studied in soy bean phosphatidylcholine (SPC)-based microemulsions with various volume fractions of disperse phase over the wide temperature range. The maximum hyperfine splitting 2A... and the order parameters S were taken as indices of the rotational mobility and the motion spatial restrictions of the labeled lipid chain segments. It is found that the temperatures T,, at which sharp enhancements of 2A n, ax and S occur depend on concentration and size of the reversed micelles in solutions. To explain this, a plausible model, taking into account capability of the SPC molecule hydrocarbon chains to change a tilt angle with respect to the surface of a polar head group as temperature varies, is proposed. The estimations of the correlation times si obtained from the lineshape characteristics of the ESR spectra provided the possibility to suggest that these correlation times characterize the reorientations of the SPC chain axis about the normal to the surface of a polar head group of a reversed micelle.
Spin-lattice relaxation times of T12+ ions in potassium sulphate single crystals were measured in the temperature range 1.5 to 25 OK a t a frequency of about 9 GHz by electron spinecho method. The relaxation is due to direct and Raman processes: TT1 = 1.02' + 3.3 x x 10-5T7. Deviations from the T;l-T7 dependence at high temperatures allow to estimate the Debye tempeature of K,SO, to 0 = 120 OK. The anomalous temperature dependence of the Raman processes is discussed.MeToRoM 3JIeKTPOHHOrO CIIHHOBOK'O 3xa Ha YaCTOTe Z 9 GHZ B ~~l a n a a o~e
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