Covalent functionalization of fullerene C₆₀ with polyethyleneimine

Fullerene C₆₀ derivatives have been evaluated as potential photosensitizers (PSs) for the inactivation of microorganisms. Fullerenes exhibit several attractive features, including high photostability, absorption in the visible region of the spectrum, and the ability to generate reactive oxygen species (ROS). However, one of the main limitations for their application as PSs is their low solubility in polar solvents, which leads to aggregation in aqueous solutions and biological media, ultimately impairing efficient photoactivity. Nevertheless, advances in fullerene C₆₀ covalent chemistry have enabled the attachment of various functional groups to the spherical carbon cage, thereby enhancing their biological activity.

In this work, a PS derived from fullerene C₆₀ covalently linked to polyethyleneimine (PEI) was developed. PEI is a polymer that acquires positive charges at physiological pH and is capable of interacting with microbial cell membranes. The reaction was carried out in DMF in the presence of TEA at room temperature. The C₆₀-PEI conjugate was purified by dialysis in water for one week to eliminate the rest of the reagents that remained unreacted. UV-visible absorption in H₂O and N,N-dimethylformamide (DMF) indicated that the properties of the C₆₀ are preserved in the conjugate. Moreover, C₆₀-PEI generates singlet oxygen yielding a quantum yield value of 0.15 and 0.07 in DMF and H₂O, respectively. Thus, this methodology enabled the development of a fullerene-derived PS with promising properties for applications in polar environments.