Role of Cholesterol in Interaction of Ionic Liquid with Model Lipid Membranes and Associated Permeability

In this work, we have investigated the impact of composition of cholesterol in the lipid membrane composed of phosphatidylcholine (POPC) or phosphatidylglycerol (POPG) on the membrane permeability induced by 1-dodecyl-3-methylimidazolium bromide ([C12MIM]+Br-) ionic liquid using various biophysical techniques. We investigated four different compositions of cholesterol (10, 20, 30, and 40 mole%) both with POPC and POPC phospholipids. Membrane permeability was determined using steady-fluorescence-based dye leakage assay. Further, interaction of ionic liquid with lipid membranes was investigated using ζ-potential measurements, and dynamic light scattering for measuring the size distribution. POPC and POPG membranes both show a reduction in [C12MIM]+ induced membrane permeability in the presence of cholesterol which continues with a further increase in cholesterol content. The overall reduction in membrane permeability is more in POPG LUVs in the presence of 30 and 40 mol% cholesterol content. Besides this, cholesterol also impacts the [C12MIM]+Br--induced fusion of POPC and POPG LUVs at higher ionic liquid concentrations. POPG membranes become more fusion prone in the presence of cholesterol as compared to POPC lipid membrane.