Lipid−Ethanol Interaction Studied by NMR on Bicelles

Abstract

The interaction of ethanol with phospholipids was studied in bicelles at a physiologically relevant ethanol concentration of 20 mM and a lipid content of 14 wt % by high-resolution NMR. Transient association of ethanol with magnetically aligned bicelles imparts a small degree of anisotropy to the solute. This anisotropy allows detection of residual (1)H-(1)H and (1)H-(13)C dipolar couplings, which are superimposed on scalar couplings. Residual (2)H NMR quadrupole splittings of isotope-labeled ethanol were measured as well. The analysis of residual tensorial interactions yielded information on the orientation and motions of ethanol in the membrane-bound state. The fraction of phosphatidylcholine-bound ethanol was determined independently by gas chromatography and NMR. About 4% of ethanol is bound to phosphatidylcholine at a bicelle concentration of 14 wt % at 40 degrees C. Free and bound ethanol are in rapid exchange. The lifetime of ethanol association with phosphatidylcholine membranes is of the order of a few nanoseconds.

A layer model of ethanol partitioning into lipid membranes

“…Ethanol concentration declines steeply over the region of carbonyl groups of lipid hydrocarbon chains towards the bilayer center, with frequent incursions of ethanol molecules into the region of upper hydrocarbon chain segments. The lifetimes of association between lipid and ethanol are brief, on the order of nanoseconds only (Koenig and Gawrisch 2005a). Ethanol is in rapid exchange between the excess water phase and the lipid water interface.…”

When detergent meets bilayer: Birth and coming of age of lipid bicelles

“…RDCs were measured for ethanol [219]. The orientation and motion of ethanol in its membrane bound state could be inferred from these measurements.…”

Comprehensive Analysis of Lipid Dynamics Variation with Lipid Composition and Hydration of Bicelles Using Nuclear Magnetic Resonance (NMR) Spectroscopy

“…Experimentally measured heteronuclear dipolar couplings can provide atomic-level detailed information regarding segmental mobility and orientation of molecules 9,10,30-32. The order parameter gives a measure of the mobility of a chemical bond in a molecule with respect to a molecular frame and can be determined from the observed dipolar coupling 〈D ij 〉 values using the following equation:$$\langle D_{ij}\rangle =D_{ij}{S}_{ij}\langle 3{\cos }^2\theta -1\rangle$$$$\text{where}{D}_{ij}=\frac{({\mu }_0∕4\pi ){\gamma }_i{\gamma }_j}{r^3}$$ D ij is the static dipolar coupling between nuclei i and j , S ij is an order parameter (0 ≤ S ij ≤ 1), and θ is the angle between the i-j internuclear vector and the external magnetic field axis.…”