Structure, Photophysical Property, and Cytotoxicity of Human Serum Albumin Complexed with Tris(dicarboxymethylene)[60]fullerene

We present structure, photoexcited triplet-state property, and singlet oxygen ((1)O 2) generation capability of human serum albumin complexed with a tris(dicarboxymethylene)[60]fullerene C3-isomer (HSA-CF). Small angle X-ray scattering measurements showed that a globular size-dimension and surface charge distribution of HSA were unaltered by monomolecular complexation of CF into the hydrophobic cavity. Laser flash photolysis to the HSA-CF solution yielded a photoexcited triplet state of the CF chromophore ((3)CF*) with lifetime of 46 mus. In the presence of O2, energy transfer occurred from HSA-(3)CF* to O2 to generate (1)O2; the quenching rate constant [k q(O2)] was determined to be 2.2 x 10 (8) M (-1) s (-1). The HSA-CF showed strong photoresistence relative to HSA complexed with a protoporphyrin IX. The quantum yield of (1)O2 production for this artificial protein was compared to those of other photosensitizing agent. The HSA-CF did not show a dark cytotoxicity, but induced cell death efficiently under visible light irradiation.