Improvement of Photodynamic Activity by a Stable System Consisting of a C 60 Derivative and Photoantenna in Liposomes.

A dyad system comprising a lipid membrane-incorporated fullerene derivative with an N , N -dimethylpyrrodinium group (C 60 - 1 ) and a photoantenna molecule (DiD) did not exhibit the high photodynamic activity expected based on its singlet oxygen generation ability. Comparison with a fullerene derivative with an amide substituent (C 60 - 2 ) suggested the cause to be that some of the fullerene derivative had been released from the liposomes, partly disrupting the dyad system. The dyad system of C 60 - 2 and DiD exhibited about twice the photodynamic activity toward HeLa cells as that of C 60 - 1 and DiD, due to the suppression of the release of the fullerene derivative from the liposomes. The hydrophobicity/hydrophilicity balance of the substituent in fullerene derivatives was shown to be very important to obtain a dyad system in liposomes characterized by high photodynamic activity.