DISTRIBUTION AND DIFFUSIVITY OF A HYDROPHOBIC PROBE MOLECULE IN THE INTERIOR OF A MEMBRANE - THEORY AND SIMULATION

We propose a simple model for the distribution of position and orienta tion and the diffusion of a hydrophobic probe molecule embedded in a m embrane, The molecule experiences both a Maier-Saupe orienting potenti al as well as an enclosing potential of repulsion from the membrane wa lls, A statistical thermodynamics treatment of the model provides pred ictions of the location and orientation of the molecule within the mem brane. In particular, we evaluate the order parameter of the molecule in terms of the model constants, The diffusivity of the probe is studi ed by Brownian dynamics simulation. For rotational diffusion, we check an available analytical approximate treatment that allows for the pre diction of the dynamics in terms of equilibrium quantities, We also pa y attention to quantities related to the initial and mean reorientatio nal rate of the probe, For translational diffusion, we use the simulat ion results to analyze some general aspects of lateral and transversal diffusion.