Electron Spin Echo Modulation Studies of Doxylstearic Acid Spin Probes in Frozen Vesicles: Interaction of the Spin Probe with D2O and Effects of Cholesterol Addition

Article abstract of DOI:10.1021/j100341a075

Electron spin echo studies have been carried out for a series of x-doxylstearic acid ( x=5, 7, 10, 12, and 16 ) spin probes in frozen deuteriated aqueous solutions of phospholipid vesicles and cationic dioctadecyldimethylammonium chloride (DODAC) vesicles.Modulation effects due to interactions of the nitroxide group of the spin probes with D2O give information about the conformations of the probes and the degree of hydration of the surfactant headgroups as well as about the degree of packing of the alkyl chain.We show that DODAC headgroups are more hydrated than choline headgroups and that the doxylstearic acid probes show a larger tendenncy for bending in DODAC vesicles than in phospholipid vesicles.Upon addition of cholesterol into phospholipid vesicles, the headgroups are separated and their degree of hydration increases.