AN ELECTRON-SPIN-RESONANCE STUDY OF THE SOY BEAN PHOSPHATIDYLCHOLINE-BASED REVERSED MICELLES

The ESR spectra of toyl-2-stearoyl-(n-doxyl)-glycero-3-phosphocholine spin label positional isomers (n = 5, 7, 10, 12 and 16) have been stud ied in soy bean phosphatidylcholine (SPC)based microemulsions with var ious volume fractions of disperse phase over the wide temperature rang e. The maximum hyperfine splitting 2A(max) and the order parameters S were taken as indices of the rotational mobility and the motion spatia l restrictions of the labeled lipid chain segments. It is found that t he temperatures T-tr at which sharp enhancements of 2A(max) and S occu r depend on concentration and size of the reversed micelles in solutio ns. To explain this, a plausible model, taking into account capability of the SPC molecule hydrocarbon chains to change a tilt angle with re spect to the surface of a polar head group as temperature varies, is p roposed. The estimations of the correlation times tau(sI) obtained fro m the lineshape characteristics of the ESR spectra provided the possib ility to suggest that these correlation times characterize the reorien tations of the SPC chain axis about the normal to the surface of a pol ar head group of a reversed micelle.