Characterization of the orientation and ordering of fatty acid pyrrolidine nitroxyls in lipid bilayers

Thomas Heimburg, K. Hideg, Derek Marsh

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

The electron spin resonance (ESR) spectra of a series of fatty acids bearing the paramagnetic pyrrolidin-N-oxyl ring have been studied in oriented bilayers of dimyristoylphosphatidylcholine:cholesterol (70:30 mol/mol) at pH 9.0. Nitroxyl fatty acids with the alkylcarboxy and alkyl substituents located respectively at the 2,2-, 3,2-, 2,4-, or 2,5-positions of the pyrrolidine ring were used. These disubstitutions correspond to different modes of incorporation of the nitroxyl ring into the chain. The order parameter of the nitroxyl z axis (principal hyperfine tensor element Azz = 32 G), SNO, was determined from the angular dependence of ESR spectra recorded at temperatures that were demonstrated to be in the motional narrowing regime. Combination of SNO with the segmental order parameters of the chain axis, Smol, allowed determination of the orientation, θ, of the nitroxyl z axis with respect to the chain diffusion axis in fluid lipid bilayers. The values of Smol were obtained from the ESR spectra of the appropriate positional isomers of n-(4,4-dimethyloxazolidin-N-oxyl)stearic acid, for which θ = 0. Values of θ = 0, 90, 40 ± 5, and 65 ± 5° were obtained for the 2,2-, 2,4-, 2,5-, and 3,2-disubstituted pyrrolidine fatty acids, respectively. Comparison with molecular modeling suggests that the rotational diffusion axis lies parallel to the fatty acid trans-chain axis for all molecular conformations except that of the 2,5-disubstituted fatty acid. This spectroscopic characterization of the pyrrolidine-based fatty acids is necessary for their use as lipid spin label probes in biological membranes.

Original languageEnglish
Pages (from-to)1950-1956
Number of pages7
JournalJournal of Physical Chemistry
Volume95
Issue number5
Publication statusPublished - 1991

Fingerprint

Lipid bilayers
fatty acids
Fatty acids
lipids
Fatty Acids
Paramagnetic resonance
electron paramagnetic resonance
Bearings (structural)
rings
Dimyristoylphosphatidylcholine
Trans Fatty Acids
Biological membranes
Spin Labels
Molecular modeling
Stearic acid
Isomers
Cholesterol
cholesterol
Tensors
Conformations

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Characterization of the orientation and ordering of fatty acid pyrrolidine nitroxyls in lipid bilayers. / Heimburg, Thomas; Hideg, K.; Marsh, Derek.

In: Journal of Physical Chemistry, Vol. 95, No. 5, 1991, p. 1950-1956.

Research output: Contribution to journalArticle

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