Stable and Biocompatible Monodispersion of C-60 in Water by Peptides

The lack of solubility in water and the formation of aggregates hamper many opportunities for technological exploitation of C-60. Here, different peptides were designed and synthesized with the aim of monomolecular dispersion of C-60 in water. Phenylalanines were used as recognizing moieties, able to interact with C-60 through pi-pi stacking, while a varying number of glycines were used as spacers, to connect the two terminal phenylalanines. The best performance in the dispersion of C-60 was obtained with the FGGGF peptidic nanotweezer at a pH of 12. A full characterization of this adduct was carried out. The peptides disperse C-60 in water with high efficiency, and the solutions are stable for months both in pure water and in physiological environments. NMR measurements demonstrated the ability of the peptides to interact with C-60. AFM measurements showed that C-60 is monodispersed. Electrospray ionization mass spectrometry determined a stoichiometry of C-60@(FGGGF)(4). Molecular dynamics simulations showed that the peptides assemble around the C-60 cage, like a candy in its paper wrapper, creating a supramolecular host able to accept C-60 in the cavity. The peptide-wrapped C-60 is fully biocompatible and the C-60 "dark toxicity" is eliminated. C-60@(FGGGF)(4) shows visible light-induced reactive oxygen species (ROS) generation at physiological saline concentrations and reduction of the HeLa cell viability in response to visible light irradiation.