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 (O-1(2)) generation capability of human serum albumin complexed with a tris(dicarboxymethylene)[60]fullerene C-3-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 ((CF)-C-3*) with lifetime of 46 mu s. In the presence of O-2, energy transfer occurred from HSA -(CF)-C-3* to O-2 to generate O-1(2); the quenching rate constant [k(q)(O-2)] 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 O-1(2) 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.