Lipid Membranes as Solvent for Carbon Nanoparticles

Abstract

C60 fullerene has a wide variety of applications, from nanomedicine to energy production. Most of these applications require fullerene to be dissolved, at one point. However, dissolving fullerene is difficult because of its low solubility in most common solvents, including apolar ones like alkanes. Despite low solubility in alkanes, fullerene has been shown to permeate and spread in lipid bilayers under certain conditions. The interior of a lipid bilayer is chemically identical to alkanes, so it is not clear why fullerene behavior in bilayers and alkanes would be different.We used molecular dynamics simulations and the MARTINI coarse-grained force field to understand the different behavior of fullerene in alkanes vs lipid bilayers. We find that the free energy of association between fullerenes in bilayers is lower than in alkanes, and the difference is due mostly to enthalpic contributions, not entropic ones. Confinement of fullerene in the bilayer thickness and alignment of the lipid chains do not contribute to fullerene dissolution in membranes. On the contrary, high solvent density and limited perturbation of solvent-solvent interactions upon solute aggregation favor fullerene dissolution in bilayers. Lipid bilayers are ubiquitous in living systems and their physical properties can easily be tuned by altering head group composition and chain length. We conclude that lipid bilayers are effective, tunable and biocompatible solvents for C60 fullerene.