Phase and mixing behavior of dilauroylphosphatidylcholine (DLPC)/distearoylphosphatidylcholine (DSPC) lipid mixtures are studied by molecular dynamics simulations with use of a coarse-grained model over a wide range of concentrations. The results reveal that phase transformations from the fluid to the gel state can be followed over a microsecond time scale. The changes in structure suggest regions of phase coexistence allowing us to outline the entire phase diagram for this lipid mixture using a molecular based model. We show that simulations yield good agreement with the experimental phase diagram. We also address the effect of macroscopic phase separation on the determination of the transition temperature, different leaflet composition, and finite size effects. This study may have implications on lateral membrane organization and the associated processes dependent on these membrane regions on different time and length scales.
"In this work the authors were able to reproduce semiquantitatively the experimental phase behavior of mixtures of larger ratios of DSPC than DLPC. In a followup study (Bennun et al., 2007b) both phase and mixing behavior of DLPC and DSPC lipid mixtures were studied for both larger and smaller ratios of the short tail lipids with respect to the long tail lipids at larger time and length scales. It was found that properties of the mixtures were not linearly dependent on composition; DSPC and DLPC present a demixing in the ideal fluid phase with a nonideal gel phase. "
[Show abstract][Hide abstract] ABSTRACT: Molecular modeling of phospholipids on many scales has progressed significantly over the last years. Here we review several membrane models on intermediate to large length scales restricting ourselves to particle based coarse-grained models with implicit and explicit solvent. We explain similarities and differences as well as their connection to experiments and fine-grained models. We neglect any field descriptions on larger scales. We discuss then a few examples where we focus on studies of lipid phase behavior as well as supported lipid bilayers as these examples can only be meaningfully studied using large-scale models to date.
Chemistry and Physics of Lipids 07/2009; 159(2):59-66. DOI:10.1016/j.chemphyslip.2009.03.003 · 2.42 Impact Factor
"Qualitatively, one might imagine that lipid mixtures formed by two components having very different structures (and transition temperatures) might prove more prone to phase-separate than mixtures of lipids having very similar structures. Such intuition is supported by a growing number of studies reporting lipid miscibility in simple, binary systems (Bennun et al., 2007; Feigenson and Buboltz, 2001; McConnell, 2005; Silvius, 1982; Veatch and Keller, 2002, 2005). These results, however, have something of a 'scatter shot' character to them and little work has been done to identify anything more than qualitative, guiding principles. "
[Show abstract][Hide abstract] ABSTRACT: In this contribution, we discuss several important technical aspects which are relevant for the molecular modeling of biomembranes in aqueous environments. We study the effect of coarse-grained water models on free and supported systems and show that the choice of water model has dramatic repercussions on the phase behavior. We characterize the phase behavior of a widely used water model and discuss the technical implications of modeling solid supports for biomembrane simulations. Finally, we compare the effect of anisotropic pressure coupling with surface tension coupling in atomistic bilayer simulations including alcohols.
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