Ei. Michonova-alexova et Ip. Sugar, Size distribution of gel and fluid clusters in DMPC/DSPC lipid bilayers. AMonte Carlo simulation study, J PHYS CH B, 105(41), 2001, pp. 10076-10083
Proteins and lipid components are organized into domains in many biological
membranes. With different experimental techniques vastly different cluster
sizes have been measured in an equimolar mixture of a DMPC/DSPC two-compon
ent lipid bilayer: very small ones in the nanometer range and very large on
es of size comparable with the size of the bilayer. In this paper the later
al distribution of gel and fluid lipid molecules in a DMPC/DSPC bilayer is
simulated by using a two-state, Ising type model with the application of Mo
nte Carlo methods. The same model has been able to predict the excess heat
capacity curves, FRAP threshold temperatures, average coherence length betw
een DSPC clusters, and the fractal dimension of gel clusters, in agreement
with the respective experimental data. In this work, similarly to the exper
imental results, the calculated equilibrium distributions of cluster size s
how that, between the onset temperature of the gel-to-fluid transition and
the percolation threshold temperature of the gel clusters, nanometer size g
el clusters coexist with a gel cluster of size comparable to the bilayer's
size itself. The calculated upper bound for the size of the small clusters,
8 +/- 1.5 nm is very close to the experimental estimate of 10 nm. More tha
n one large gel clusters might be present in the case of nonequilibrium lat
eral distributions. By means of the calculated temperature dependence of th
ree different cluster size averages we can get insight into the process of
cluster growth.