Disruption of Lipid Raft-like Domains by Acetonitrile: Insights from Experiments and Monte Carlo Simulations

Predicting the impact of additional molecules on lipid rafts─crucial phase-separated domains in biological membranes─remains a major challenge in physicochemical and biophysical research. This influence arises from modifications in phase patterns within multicomponent lipid membranes, which may be induced by external molecules and can be investigated using model membrane systems. Here, we investigate the effect of acetonitrile (MeCN) molecules on the phase behavior in lipid membranes. MeCN is a hazardous substance capable of producing cyanide upon oxidation, and it modifies the membrane properties upon incorporation. Our inferences herein indicate that the addition of MeCN to ternary lipid membranes composed of saturated lipids, unsaturated lipids, and cholesterol lowers miscibility transition temperatures. The region of the liquid-ordered (L_o) domain, which corresponds to the lipid raft, gradually shrinks and disappears as the MeCN molecules gradually penetrate the lipid membranes at 28 °C. The change in miscibility transition temperature, T_mix, is determined based on the relationship between the fraction of phase-separated liposomes and temperature. T_mix is reduced from approximately 34 to 28 °C by the addition of MeCN from 0 to 10 vol %. We simulated and assessed the effect of MeCN molecules on the phase behaviors of lipid membranes by using the Monte Carlo method and the two-dimensional (2D) Ising model. The simulation results resemble the experimental results. We hypothesize that the incorporation of MeCN molecules into ternary lipid membranes alters the free energy for molecular mixing and disrupts phase separation and raft-like microdomains. These findings provide a foundation for future investigations of lipid rafts.