Influence of Albumin on the Spectroscopic Properties and Existence State of Mono-Substituted Phthalocyanine Zinc()

Interaction between 1-[4-(2-carboxyl-ethyl-)phenoxy] phthalocyanine Zinc() (ZnPcC₁) and albumin (human serum albumin or bovine serum albumin) was studied. ZnPcC₁ can be covalently bound to albumin through amide bond formation. The molar ratios of ZnPcC₁ to albumins are found to be about 7:1 in the covalent bioconjugates. On the other hand, there are strong non-covalent interactions between ZnPcC₁ and albumins with a binding constant of ca. 1.0×10⁵ mol^-1·L. Binding sites competition experiments suggest that the binding site locates in subdomain B of human serum albumin. When conjugated to albumin, no matter covalent conjugation or non-covalent conjugation, the ZnPcC₁ exhibit more distinctive characteristic monomer absorption than the free ZnPcC₁, which is a property beneficial to photodynamic therapy. Covalent conjugation results in the Q-band of ZnPcC₁ red-shifting about 5 nm, whereas non-covalent conjugation does not lead to red-shift.