A computer simulation study of probe molecule behaviour in lipid bilayer systems

Abstract

Computer simulations are presented of the behaviour of elongated probe molecules anchored to the interface of lipid bilayers above the phase transition of the hydrocarbon chains. The simulations thus mimic the behaviour of the fluorescent probe 1-[4-(trimethylammonio)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH) and cholestane spin label in lipid systems. In contrast to any experimental technique the simulations follow the behaviour of both the lipid molecules and the probe within the bilayer structure. Thus the relation between the behaviour of the probe molecules and the order and dynamics of the lipid chains can be studied in detail. We find that the presence of probe molecules at the low concentrations used experimentally causes only a marginal perturbation in the intrinsic properties of the lipid chains. The simulations presented support for the conventional prescription for describing the orientational behaviour of probe molecules in lipid bilayers in terms of a local effective orienting potential. Th...