SiMPLISTIC: A Novel Pairwise Potential for Implicit Solvent Lipid Simulations with Single-site Models

Implicit solvent, coarse-grained models with pairwise interactions can access the largest length and time scales in molecular dynamics simulations, owing to the absence of interactions with a huge number of solvent particles, the smaller number of interaction sites in the model molecules, and the lack of fast sub-molecular degrees of freedom. In this paper, we describe a maximally coarse-grained model for lipids in implicit water. The model is called SiMPLISTIC, which abbreviates for Single-site Model with Pairwise interaction for Lipids in Implicit Solvent with Tuneable Intrinsic Curvature. SiMPLISTIC lipids rapidly self-assemble into realistic non-lamellar and lamellar phases such as inverted micelles and bilayers, the spontaneous curvature of the phase being determined by a single free parameter of the model. Model membrane simulations with the lamellar lipids show satisfactory fluid and gel phases with no interdigitation or tilt. The model lipids follow rigid body dynamics suggested by empirical studies, and generate bilayer elastic properties consistent with experiments and other simulations. SiMPLISTIC can also simulate mixtures of lipids that differ in their packing parameter or length, the latter leading to the phenomenon of hydrophobic mismatch driven domain formation. The model has a large scope due to its speed, conceptual and computational simplicity, and versatility. Applications may range from large-scale simulations for academic and industrial research on various lipid-based systems, such as lyotropic liquid crystals, biological and biomimetic membranes, vectors for drug and gene delivery, to fast, lightweight, interactive simulations for gaining insights into self-assembly, lipid polymorphism, biomembrane organization etc.Comment: 17 pages, 11 figure

Phase Transitions In An Implicit Solvent Minimal Model Of Lipids: Role Of Head-Tail Size Ratio

We present Monte Carlo simulations under constant NVT conditions on a minimal three beads coarse grained implicit solvent model of lipid molecules, with the hydrophilic head represented by one bead and the hydrophobic tail represented by two beads. We consider two lipids, one with the head and tail bead sizes equal and the other with the tail beads smaller than the head. When cooled to the ambient temperature from an initial isotropic phase at high temperature, the first lipid transforms spontaneously to a lamellar phase while the second lipid transforms to a micellar phase, showing the crucial role of the head and tail size ratio on lipid phases.Comment: conference pape

A Simulation Study on Multicomponent Lipid Bilayer

Simulation of a multicomponent lipid bilayer having a fixed percentage of cholesterol is done to study phase transition leading to domain formation. The concept of random lattice has been used in simulation to account for the coupling between the internal and translational degrees of freedom of lipid molecules. Considering a canonical ensemble, dissimilar lipid molecules are allowed to exchange their positions in the lattice subject to standard metropolis algorithm. The steps involved in the process effectively takes into account for the movement of sphingolipids and cholesterol molecules helping formation of cholesterol rich domains of saturated lipids as found in natural membranes