Molecular Dynamics Evaluation of the Effect of Cholinium Phenylalaninate Biocompatible Ionic Liquid on Biomimetic Membranes

Toward the search of sustainable green solvents, choline amino acid ([Ch][AA]) ionic liquids (ILs), mainly derived from renewable feedstocks, have emerged as a promising atoxic alternative to the conventional solvents. Recent studies have shown the remarkably benign nature of cholinium-based ILs against biomimetic phospholipid membranes. However, few of the contemporaneous experimental studies have contradicted the aforesaid ecofriendly nature of these ILs with anions comprising longer alkyl or aromatic tails. Aiming to understand the influence of amino acid side-chain variation in a particular bio-IL on biomembranes, herein, we have evaluated the effect of cholinium phenylalaninate ([Ch][Phe]) IL on the structural stability of homogeneous biomimetic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) lipid bilayers using atomistic molecular dynamics simulations. Although we observe spontaneous intercalation of aromatic rings of [Phe](-) anions in the hydrophobic region of the bilayers, the polar backbone of the anion remains coordinated with the lipid polar part through strong electrostatic and H-bonding interactions. Besides, the [Ch](+) cations get accumulated at the lipid-water interface to counter the excess negative charge density. The intercalation of the anionic rings causes significant perturbations in the lipid structural arrangement while still maintaining the bilayer integrity. The quantitative evaluation to probe the deteriorating effect of this bio-IL application establishes anions as the principal component causing the observed structural perturbations. The analysis of the structural properties along with the free energy assessment reveals the higher efficacy of [Ch][Phe] bio-IL to perturb the POPE bilayer structure than the POPC bilayer.