Photophysical, photodynamical, redox properties and BSA interactions of novel isomeric tetracationic peripheral palladium(ii)-bipyridyl porphyrins

Abstract

New isomeric tetra-cationic porphyrins containing peripheral [Pd(bpy)Cl]⁺ units attached to pyridyl substituents were synthesized and fully characterized. The porphyrins present an intense Soret band located in the blue spectral region and an additional four weaker red-shifted Q bands in the visible spectral region (about 500–700 nm). The obtained Strickler–Berg parameters indicate fully spin and symmetry allowed transitions for all the observed absorption bands. Both porphyrins present two fluorescence emission bands, an intense one located around 650 nm and an additional weak red-shifted emission at ∼710 nm. Fluorescence decay time profiles were obtained showing bi-exponential decay. The interaction of the porphyrins with bovine serum albumin (BSA) was studied in detail by a fluorescence quenching method and molecular docking analysis. In addition, the photodynamical activity of the porphyrins in the photooxidation of BSA was determined and compared with the light-induced formation of reactive oxygen species (ROS) by electron paramagnetic resonance (EPR) allied with the spin trapping method. The results show that the Pd(II)-bypyridyl tetra-cationic porphyrins are promising candidates for the photooxidation of biological substrates used in photodynamic therapy (PDT).