Probing the perturbaton of lecithin bilayers by unmodified C₆₀ fullerenes using experimental methods and computational simulations

In this study, we aimed to use physicochemical and theoretical tools to understand fundamental problems of the interaction between lipid bilayers (Egg-PC liposomes) and unmodified C₆₀ fullerenes. The morphology, the size, and the electrokinetic properties of plain and C₆₀-loaded liposomes were investigated by means of atomic force microscopy, dynamic light scattering, and ζ-potential studies, respectively. The incorporation of C₆₀ molecules into the liposomes increases their size; however, there was no effect on their electrokinetic properties. Visualization studies revealed that the presence of C₆₀ in the membranes induced distortion in vesicle morphology, resulting in nonspherical vesicles. To elucidate further the impact of C₆₀ molecules on lipid bilayers, we assessed their miscibility by fluorescence spectroscopy measurements. Fluorescence measurements showed that the presence of C₆₀ in liposomes causes a pronounced effect on the Nile red emission spectrum due to alterations to the packing of the lipid membrane. The release of vesicle-encapsulated calcein was used as a measure of the integrity of the liposomes. Plain liposomes were found to be more stable compared with C₆₀-loaded (PC) liposomes, suggesting that C₆₀ ruptures the liposome membrane. Toxicity studies of C₆₀ in liposomes were carried out on cultured cells [rodent fibroblasts (3T3)] to assess further their toxicity. The results suggest that fullerene cytotoxic effect was reduced significantly after its incorporation into the liposomal bilayer after 24 h of incubation with the rodent fibroblasts (3T3). Finally, energy minimization studies were employed to underpin the experimental observations. The theoretical calculations show that low concentration of fullerene molecules present in the membrane had no effect on the membrane integrity; however, at high concentrations of fullerenes significant enlargement of the surface area is observed, supporting the experimental findings.