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 coex istence region of an equimolar DC16PC-DC22PC lipid mixture has been studied by means of Monte Carlo computer simulation, fluorescence, and Fourier tra nsform infrared spectroscopy. The results reveal that the nonequilibrium ph ase separation process after a sudden temperature or pressure quench of the binary mixture from the one-phase fluid region into the two-phase gel-flui d coexistence region has a strong influence on the lateral membrane organiz ation on different length scales. This is manifested as the formation of a heterogeneous lateral bilayer structure composed of long-living gel and flu id 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 li pid structure of ordered DC16PC lipids is formed at the dynamically changin g network of domain boundaries. Our combined theoretical and experimental i nvestigations 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 importan ce for a deeper understanding of properties that control membrane compartme ntalization which in turn might be of relevance for membrane processes that take place in localized membrane regions.