Abstract

A general model for NMR relaxation studies of fluid bilayer systems is introduced, combining a mesoscopic Brownian dynamics description of the bilayer with an atomistic molecular dynamic (MD) simulations. Example is given for a ²H₂O in DPPC and compared with experiment. Experimental agreement is within a factor of 2 in the water relaxation rates, based on a postulated model with fixed parameters, which are largely available from the MD simulation. Relaxation rates are particularly sensitive to the translational diffusion of water perturbed by the interface dynamics and structure. Simulation results suggest that a notable deviation in the relaxation rates may follow from the commonly used small-angle approximation of bilayer undulation. The method has potential to overcome the temporal and spatial limitations in computing NMR relaxation with atomistic MD, as well as the shortcomings of continuum models enabling a consistent description of experiments performed on solvent lipid and added spinprobes. The work opens for possibilities to understand relaxation processes involving systems such as micelles, multilamellar vesicles, red blood cells etc. at biologically relevant timescales in great detail.