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

The dynamic and conformational properties of the 2-methylene on the sn-2 chain of dimyristoylphosphatidylcholine have been investigated in small unilamellar vesicles. An analysis of the spin relaxation of a proton-coupled 13C nucleus has been used to provide the additional information necessary to propose a specific geometry for motion. The results suggest a model with three motions in addition to vesicle tumbling: (1) a slow axial rotation of the entire molecule about the bilayer normal (tau congruent to 2 X 10(-8) s); (2) torsional oscillations about C-C bonds on a very fast time scale; and (3) rapid jumps (tau = 6 X 10(-10) s) between two conformers having approximate gauche+ and gauche- conformations about the C2-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.