Photophysicochemical consequences of bovine serum albumin binding to non-transition metal phthalocyanine sulfonates

The interactions between bovine serum albumin (BSA) and sulfonated metallophthalocyanine (MPc) complexes of aluminum (AlPcSmix), zinc (ZnPcSmix), silicon (SiPcSmix), germanium (GePcSmix) and tin (SnPcSmix) are studied using fluorescence quenching of BSA by MPc complexes. The fluorescence quantum yields of the non-aggregated MPc complexes (AlPcSmix, GePcSmix and SiPcSmix) decreased in the presence of BSA, but increased for the aggregated ZnPcSmix and SnPcSmix complexes. The BSA: MPc conjugates were less stable than the corresponding MPc complexes. The quenching constants were much higher for the non-aggregated complexes. The aggregated nature of the complexes also affected the rate constants (kF, kIC, kISC) for the deactivation of the excited singlet state.