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 DC 16 PC−DC 22 PC 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 DC 16 PC 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.