Partitioning and solubility of C60 fullerene in lipid membranes

Carbon nanoparticles (CNPs) are considered to be among the most promising nanomaterials, with applications in many different areas of technology. Most CNPs can enter both artificial lipid membranes and living cells, and are biologically active. The interaction of CNPs with lipid membranes is of great interest because biological activity requires crossing or breaking lipid membranes. Moreover, lipid bilayers have been proposed to be efficient solubilizing agents for C60 and C70 fullerenes. In this comment, we review the literature on fullerene partitioning and dispersion in lipid membranes, considering both the experimental and the simulation literature, and highlighting similarities and differences. Both experiments and simulations confirm that fullerenes partition to the membrane interior, although experimental information on the location of fullerene molecules is only qualitative. On the other hand, the fullerene dispersion state is difficult to assess experimentally, and appears to depend on the details of the methodology used for the preparation of fullerene-loaded liposomes. Although some degree of aggregation is confirmed by most experiments, the extent of the aggregation is uncertain. Large aggregates observed in the presence of lipid membranes are unlikely to be found within the membrane, as they are orders of magnitude larger than the membrane thickness. Simulations carried out so far yielded contrasting results. Both atomistic and some coarse-grained simulations indicated that fullerene dimerization in lipid membranes should be significantly less favorable than that in bulk alkanes, but the physical reasons for this are still unclear. (comment)