Electrochemical properties of Co(II) complexes with rutin in aqueous-alcoholic solutions

Abstract

Cyclic voltammetry and electrochemical impedance spectroscopy were used to study the effect of pH and the Co:Rut ratio on redox potentials and electrical conductivity of water-alcohol solutions of Co(II) complexes with rutin (Rut). It was found that the reduction potentials for the ratio Co:Rut=1:1 and 1:2 are in the range of –0.110 V to –0.197 V relative to the Ag/AgCl reference electrode, which is significantly higher than the potentials for known flavonoids. In an alkaline medium, the absolute value of the reduction potential increases regardless of the composition of the sample. The measured range of oxidizing potentials for all compounds is in the range of +0.02 V to +0.094 V relative to Ag/AgCl reference electrode, which corresponds to the potentials of compounds with self-oxidizing activity. It is assumed that an increase in oxidative potentials up to 0.094 V can characterize the antioxidant activity, which is associated with the manifestation of the autoxidizing properties of the complex in the presence of oxygen and is due to the participation of different binding sites in chelation with the metal. Using the data of electrochemical impedance spectroscopy, the capacity of electrical double layer of a platinum electrode in water–alcohol solutions containing Co(II) complexes with rutin was calculated. An increase in capacitance values by an order of magnitude was observed at a ratio of metal:ligand=2:1 in comparison with the complexes having a ratio of 1:1. The effect of an excess of hydroxyl ions on the charge distribution at the electrode/solution interface was experimentally established, leveling the effect of the Co:Rut ratio on the electrochemical properties.