Stable and Biocompatible Monodispersion of C₆₀ in Water by Peptides

The lack of solubility in water and the formation of aggregates hamper many opportunities for technological exploitation of C₆₀. Here, different peptides were designed and synthesized with the aim of monomolecular dispersion of C₆₀ in water. Phenylalanines were used as recognizing moieties, able to interact with C₆₀ through π-π stacking, while a varying number of glycines were used as spacers, to connect the two terminal phenylalanines. The best performance in the dispersion of C₆₀ was obtained with the FGGGF peptidic nanotweezer at a pH of 12. A full characterization of this adduct was carried out. The peptides disperse C₆₀ 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 C₆₀. AFM measurements showed that C₆₀ is monodispersed. Electrospray ionization mass spectrometry determined a stoichiometry of C₆₀@(FGGGF)₄. Molecular dynamics simulations showed that the peptides assemble around the C₆₀ cage, like a candy in its paper wrapper, creating a supramolecular host able to accept C₆₀ in the cavity. The peptide-wrapped C₆₀ is fully biocompatible and the C₆₀ "dark toxicity" is eliminated. C₆₀@(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.