Partitioning behaviour of 1-hexanol into lipid membranes as studied by deuterium NMR spectroscopy

Abstract

Deuterium nuclear magnetic resonance (NMR) spectroscopy was used to study the partitioning behaviour of 1-hexanol specifically deuterated in the α-position into model lipid bilayers. In all systems studied, the observed deuterium NMR lineshapes were time-dependent. Initially, 1-hexanol- d 2 gave rise to an isotropic deuterium resonance with a different chemical shift from that of aqueous 1-hexanol- d 2. After equilibration over a period of days, a broader spectral component characteristics of a spherically-averaged powder-pattern was observed. The quadrupole anisotropy of the 1-hexanol- d 2 giving rise to the broad spectrum depended upon the cholesterol content of the membrane. From quantitation of the anisotropic to isotropic deuterium NMR spectra, the partition coefficients of 1-hexanol- d 2 in a number of bilayer systems (asolectin and phosphatidylcholine bilayers (the latter with and without cholesterol)) were determined. The partitioning of 1-hexanol- d 2 into red blood cell membranes, and a suspension of lipids extracted from red blood cell membranes, was also examined. It is suggested that 1-hexanol, and probably other lipophiles, can partition to either the bilayer surface or the bilayer interior in a time-dependent manner.