Electron spin resonance spectra of a series of x-doxylstearic acids (x = 5, 7, 10, 12, and 16) solubilized in cationic dioctadecyldimethylammonium chloride vesicles were recorded 298-328 K and analyzed by employing spectral line simulation. The spectra from the vesicle phase are well reproduced by using the microscopic order-macroscopic disorder model of Freed and co-workers with Brownian rotational diffusion. The partial averaging of the magnetic interactions by local anisotropic motions in the vesicles is quantified mainly by an order parameter (S) and the rotational diffusion rate perpendicular to the alkyl chain (R perpendicular-to). The simulations show that the doxyl position becomes progressively less ordered (S decreases) as x increases up to x = 12 but inverse more ordered at x = 16. This suggests a U-shaped bent conformation of the doxylstearic acid alkyl chain. R perpendicular-to shows a similar, but inverse, correlation; that is, R perpendicular-to increases, plateaus, and decreases with increasing x. The U-shaped conformation of the spin probe alkyl chain in liquid vesicle solutions is the same as deduced previously in frozen vesicle solutions measured by electron spin echo modulation spectroscopy.
原文链接
分享
引用
