MOLECULAR-DYNAMICS SIMULATIONS OF A LIPID BILAYER AND OF HEXADECANE -AN INVESTIGATION OF MEMBRANE FLUIDITY

Molecular dynamics simulations of a fluid-phase dipalmitoyl phosphatid ylcholine lipid bilayer in water and of neat hexadecane are reported a nd compared with nuclear magnetic resonance spin-lattice relaxation an d quasi-elastic neutron scattering data. On the 100-picosecond time sc ale of the present simulations, there is effectively no difference in the reorientational dynamics of the carbons in the membrane interior a nd in pure hexadecane. Given that the calculated fast reorientational correlation times and the ''microscopic'' lateral diffusion of the lip ids show excellent agreement with the experimental results, it is conc luded that the apparently high viscosity of the membrane is more close ly related to molecular interactions on the surface rather than in the interior.