Electron spin resonance line-shape analysis of x-doxylstearic acid spin probes in dihexadecyl phosphate vesicles and effects of cholesterol addition

Journal Article · Thu Jul 15 04:00:00 EDT 1993 · Journal of Physical Chemistry; (United States)

DOI:https://doi.org/10.1021/j100130a041· OSTI ID:5865751

Bratt, P J ^[1]; Kevan, L ^[2]

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1. Univ. of London (United Kingdom)
2. Univ. of Houston, TX (United States)

Electron spin resonance spectra of a series of x-doxylstearic acids (x = 5, 7, 10, 12, and 16), solubilized in anionic dihexadecyl phosphate vesicles containing 10, 30, and 50 mol % cholesterol, are analyzed by employing spectral line-shape 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 the order parameter (S) and the rotational diffusion rate perpendicular to the alkyl chain (R[sub PRP]). The simulations show that the order parameter decreases with increasing x, suggesting a relatively extended conformation, unlike the U-shaped, bent conformation of the x-doxylstearic acid alkyl chain found previously in cationic dioctadecyldimethylammonium chloride vesicles. Furthermore, the headgroup region of the vesicle is less ordered in anionic dihexadecyl phosphate than in cationic dioctadecyldimethylammonium chloride vesicles. This result in liquid vesicle solutions corroborates the same x-doxylstearic conformations found in frozen vesicle solutions by electron spin echo modulation spectroscopy. The effect of cholesterol is found to decrease the observed order parameter for all doxyl positions. 36 refs., 4 figs., 2 tab.

• OSTI ID: 5865751
• Journal Information: Journal of Physical Chemistry; (United States), Journal Name: Journal of Physical Chemistry; (United States) Vol. 97:28; ISSN JPCHAX; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400102 -- Chemical & Spectral Procedures
400201* -- Chemical & Physicochemical Properties
99 GENERAL AND MISCELLANEOUS
990200 -- Mathematics & Computers
AMMONIUM COMPOUNDS
CHOLESTEROL
COLLOIDS
COMPUTERIZED SIMULATION
DATA
DIFFUSION
DISPERSIONS
ELECTRON SPIN RESONANCE
EXPERIMENTAL DATA
HYDROXY COMPOUNDS
INFORMATION
MAGNETIC RESONANCE
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
RESONANCE
SIMULATION
SPECTROSCOPY
STEROIDS
STEROLS