Dynamics of an interfacial methylene in dimyristoylphosphatidylcholine vesicles using carbon-13 spin relaxation

Abstract

The dynamic and conformational properties of the 2-methylene on the sn-2 chain of dimyristoylphosphatidylcholine were investigated in small unilamellar vesicles. An analysis of the spin relaxation of a proton-coupled 13C nucleus was used to provide the additional information necessary to propose a specific geometry for motion. A model with 3 motions in addition to vesicle tumbling is suggested; a slow axial rotation of the entire molecule about the bilayer normal (.tau. .simeq. 2 .times. 10-8 s); torsional oscillations about C.sbd.C bonds on a very fast time scale; and rapid jumps (.tau. = 6 .times. 10-10 s) between 2 conformers having approximate gauche+ and gauche- conformations about the C2.sbd.C3 bond of the sn-2 chain. The proposed conformations are compared to those previously predicted on the basis of crystal structures, spectroscopic data and energy-minimization calculations.