Study of the Methionine Electrooxidation at an Electrode Modified with Vitamin B12 and Multi-Walled Carbon Nanotubes

Abstract

The electrochemical behavior of methionine at an electrode modified with vitamin B12 and multi-walled carbon nanotubes has been studied in this work. A possible mechanism of redox processes occurring on the modified electrode is proposed. When the electrode is formed, vitamin B12 is fixed on the surface of a carboncontaining electrode modified with multi-walled carbon nanotubes due to adsorption. In the process of cathodic polarization, cobalt(III) in cobalamin is reduced to cobalt(II) to which a partially negatively-charged sulfur atom in the methionine molecule is attached due to electrostatic interactions. During anodic polarization, cobalt(II) in the complex is oxidized up to Co3+, the methyl group from methionine is transferred to cobalamin, and homocysteine passes into the solution, which is proved by Raman spectra. Based on the study of the dependence of current and potential on the sweep speed, it was found that the oxidation process is not reversible, the limiting stage is adsorption, and one proton and one electron participate in the electrochemical stage. The following optimal conditions for recording an analytical signal were selected: the background electrolyte is a tartrate buffer solution with pH = 4.01; the electrolysis potential is 1.6 V; the accumulation time is up to 180 s. The metrological characteristics of the procedure for determining methionine were estimated. The accuracy index did not exceed 29 %, the repeatability and intermediate precision indices did not exceed 14 % and 16 %, respectively. The range of detectable contents was (1–50)×10–7; the detection limit was 5.0×10–8 M. It was shown that a 10-fold excess of ascorbic acid, tryptophan, glycine, cysteine and tyrosine does not have a noticeable distorting effect on the procedure for determining methionine.