Synthesis of Decacationic C₇₀ Bisadducts by Incorporating Covalently BoundElectron-Donors for Enhancement of Radical-Based Type-I PDT

We designed, synthesized, and characterized two types of highly water-soluble C 70 monoadduct, C 70 [>M(C 3 N 6 + C 3 ) 2 ]-(I ‒ ) 10 (LC17), and bisadducts, C 70 [>M(C 3 N 6 + C 3 ) 2 ][>M(C 3 N 6 C 3 ) 2 ] (LC18). Each of these compounds consist of a well-defined decacationic quaternary ammonium iodide moiety with ten positive charges per C 70 for increasing water-solubility and the ability to target pathogenic bacterial cells. The structural modification enables them to act as broad-spectrum antibacterial nano-PDT drugs. We found that white light was more effective with LC17 while UVA light was more effective with LC18 to the antimicrobial effects against human pathogens, Gram-positive ( Staphylococcus aureus ) and Gram-negative species ( Escherichia coli and Acinetobacter baumannii ). Both compounds were effective in a mouse model of Gram-negative 3 rd -degree burn infections. The observation led to our proposition that the attachment of an additional electron-donating deca(tertiary ethylenylamino)malonate arm to C 70 , giving a product of LC18, allowed the moiety to act as a potent electron source and increased the generation yield of hydroxyl radicals under UVA illumination. This demonstrated a new approach in enhancing HO·-induced radical-killing (Type-I photochemistry) of pathogenic bacteria.