Abstract

Background: Meso-tetra-4-actophenyl-porphyrin (TAcPPH₂) was synthesized by reacting 4- acetyl-benzaldehyde with pyrrole in propionic acid, and used as a ligand for the synthesis of palladium (II) complex (PdTAcPP). The structure of the ligand and the complex were characterized by NMR and electronic spectroscopy.

Methods: The antioxidant activity and the binding parameters of both the ligand and its complex with superoxide anion radical . (O₂ -) were measured using cyclic voltammetry based assay. The assays were based on the measurement of the anodic peak current density of . O₂− electrochemically generated by reduction of molecular oxygen in DMF.

Results: The complex PdTAcPP showed the highest antioxidant activity (0.73 ± 0.01 mg/mL) which is four times higher than that of the standard antioxidant α-tocopherol (3.04 ± 0.03 mg/mL).

Discussion: Binding parameters like binding constants, the ratio of binding constants and binding free energies were also measured.

Conclusions: The value of the binding free energy ranging from -7.89 kJmol-1 for TAcPPH₂ to -17.59 kJ.mol-1for PdTAcPP suggests an electrostatic interaction of . O₂− with TAcPPH2 and PdTAcPP which has been found to be the dominant interaction mode. The kinetics of the interaction reaction of the ligand and complex was quantified having second-order rate constant values equal to 0.2 and 1.3 M-1 s-1, respectively.

Keywords: Porphyrin, homogeneous rate constant, cyclic voltammetry, superoxide anion radical, binding parameters, antioxidant activity coefficient.