Sensitivity and Resilience of Phosphatidylcholine and Phosphatidylethanolamine Lipid Membranes against Cholinium Glycinate Biocompatible Ionic Liquid

Choline amino acid ([Ch]­[AA]) based ionic liquids (ILs) are considered to be highly biodegradable and biocompatible solvents. The toxicological scrutiny and environmental fate analysis of these ILs are fundamental requisites to employ these ILs on large scale applications. In the present work, we investigate how the presence of the simplest form of [Ch]­[AA] ILs, cholinium glycinate ([Ch]­[Gly]), affects the structure and stability of homogeneous 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) lipid bilayers by using atomistic molecular dynamics simulation. The study reveals a considerable compression of the POPC bilayer along with an enhanced ordering of hydrocarbon lipid tails on increasing the concentration of [Ch]­[Gly] IL. On the other hand, the stability and structure of the POPE bilayer is hardly affected at lower concentration of [Ch]­[Gly]; however, at higher concentration (20 mol %), the structure of the bilayer is slightly changed. The H-bond analysis reveals that [Ch]⁺ cations have greater propensity to H-bond with phosphate and ester group oxygens of POPE than POPC lipid molecules. The structural properties of the POPE bilayer are influenced by [Ch]­[Gly] IL to a lesser extent compared to the POPC bilayer, which appears to be a direct consequence of the ability of POPE lipids to form a strong inter- as well as intramolecular H-bonding network among themselves and adapting a more compact packed bilayer structure. Enhanced accumulation of [Gly]⁻ anions at water–membrane interfacial regions is unambiguously observed for both POPC and POPE bilayers.