Photophysical, photooxidation, and biomolecule-interaction of meso-tetra(thienyl)porphyrins containing peripheral Pt(ii) and Pd(ii) complexes. Insights for photodynamic therapy applications

Abstract

We report the synthesis and characterization of two novel tetra-cationic porphyrins, containing Pt(II) or Pd(II) polypyridyl complexes attached at the peripheral position of N₄-macrocycle. Compounds were characterized through elemental analysis, molar conductivity, cyclic voltammetry, and spectroscopy analysis. Photophysical and photobiological parameters were also evaluated. Also, the binding capacity of each porphyrin with human serum albumin (HSA) was determined by UV–Vis, steady-state, and time-resolved fluorescence spectroscopy, combined with molecular docking calculations. The results suggest that the interaction of these compounds is spontaneous, weak to moderate, and probably occurs at site III (subdomain IB) by non-covalent forces, including van der Waals and H-bonding. Moreover, porphyrins containing peripheral complexes improve their interactions with biomolecules, show good photostability, generate reactive oxygen species under white light studied by electron paramagnetic resonance (EPR) analysis, and promote photo-damage of HSA.