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 (¹O₂) 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 (³CF*) with lifetime of 46 μs. In the presence of O₂, energy transfer occurred from HSA−³CF* to O₂ to generate ¹O₂; the quenching rate constant [k_q(O₂)] was determined to be 2.2 × 10⁸ M⁻¹ s⁻¹. The HSA−CF showed strong photoresistence relative to HSA complexed with a protoporphyrin IX. The quantum yield of ¹O₂ 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.