LANGEVIN DYNAMICS OF THE CHOLINE HEAD GROUP IN A MEMBRANE ENVIRONMENT

Computer simulations of dipalmitoylphoshatidylcholine (DPPC) have been performed using Langevin dynamics and a Marcelja-type mean field. Thi s work has focused on the dynamics of the choline head group to parame terize the empirical constraints against phosphorus-carbon dipolar cou plings (D-p-c) as measured by nuclear magnetic resonance (C-13-NMR). T he results show good agreement with experimental values at constraints equivalent to the choline tilt observed in joint refinement of x-ray diffraction and neutron diffraction scatterings. Quadrupolar splitting s for the alpha and beta positions are also calculated and compared wi th H-2-NMR experiments. The model predicts torsional transition rates around the alpha-beta bonds and for the two C-O-P-O torsions. it also predicts T-1 relaxation times for the alpha and beta carbons.