Deuteron N.M.R. relaxation studies of phospholipid membranes

Abstract

Bilayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), specifically deuteriated at various positions of the sn-2-chain, have been studied by N.M.R. relaxation methods. Analysis of the experiments, employing a density matrix treatment based on the stochastic Liouville equation, provides new information about the dynamic organization of the different membrane phases (liquid-crystalline, intermediate and gel phases). The complex molecular dynamics are characterized by a super-position of inter- and intramolecular motions, comprising overall reorientation of phospholipid molecules and trans-gauche isomerization of individual chain segments. In addition, there is evidence for two-site rotational jumps of the sn-2-chains in the plane of the membrane. The results clearly demonstrate the particular advantage of N.M.R. relaxation studies in characterizing complex chemical and biological systems.