Nonequilibrium lipid domain growth in the gel-fluid two-phase region of a DC16PC-DC22PC lipid mixture investigated by Monte Carlo computer simulation, FT-IR, and fluorescence spectroscopy

The nonequilibrium ordering dynamics of lipid domains in the gel-fluid coexistence region of an equimolar DC16PC-DC22PC lipid mixture has been studied by means of Monte Carlo computer simulation, fluorescence, and Fourier transform infrared spectroscopy. The results reveal that the nonequilibrium phase separation process after a sudden temperature or pressure quench of the binary mixture from the one-phase fluid region into the two-phase gel-fluid coexistence region has a strong influence on the lateral membrane organization on different length scales. This is manifested as the formation of a heterogeneous lateral bilayer structure composed of long-living gel and fluid lipid domains characterized by a relaxation time on the order of hours. In the early time stage of the phase separation process a distinct local lipid structure of ordered DC16PC lipids is formed at the dynamically changing network of domain boundaries. Our combined theoretical and experimental investigations suggest that nonequilibrium effects may be a strong modulator of lateral membrane heterogeneity and lead to the formation of local lipid structures on various length and time scales. Such results are of importance for a deeper understanding of properties that control membrane compartmentalization which in turn might be of relevance for membrane processes that take place in localized membrane regions.