Mamj. Vanzandvoort et al., DISTRIBUTION OF HYDROPHOBIC PROBE MOLECULES IN LIPID BILAYERS .1. MONTE-CARLO DYNAMICS COMPUTER-SIMULATIONS, JOURNAL OF PHYSICAL CHEMISTRY B, 101(20), 1997, pp. 4142-4148
Lattice dynamics techniques are used to simulate the orientational dyn
amics of the hydrophobic probe molecules 1,6-diphenyl-1,3,5-hexatriene
DPH and perylene in lipid bilayer systems. It is shown that these mol
ecules are essentially found in two distinct environments: in the midd
le of the bilayer and in the two regions near the bilayer interfaces.
This partition arises from the competition between the entropic effect
s of free volume and the interaction of the probes with the lipid mole
cules. Each probe population exhibits a distinct orientational and dyn
amical behavior. The probe molecules move through the bilayer on a tim
e scale slow compared to their rotational motions such that the two po
pulations are effectively in dynamic equilibrium. The simulations reve
al, furthermore, inherent ambiguities in the analysis of time-resolved
fluorescence anisotropy measurements on such heterogeneous systems. T
his problem is illustrated in the accompanying paper, where a detailed
analysis of time-resolved fluorescence anisotropy of perylene molecul
es in lipid vesicle systems is presented.