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. 2022 May;169(5):055501.
doi: 10.1149/1945-7111/ac6a13. Epub 2022 May 4.

Cobalamin-Mediated Electrocatalytic Reduction of Ethyl Chloroacetate in Dimethylformamide

Benjamin H R Gerroll  1 , Jared C Lewis  1 , Lane A Baker  2
Affiliations

Cobalamin-Mediated Electrocatalytic Reduction of Ethyl Chloroacetate in Dimethylformamide

Benjamin H R Gerroll et al. J Electrochem Soc. 2022 May.

Abstract

The catalytic reduction of ethyl chloroacetate (ECA) by hydroxocobalamin (HOCbl) in dimethylformamide was studied electrochemically and spectroelectrochemically to identify initial steps in the reaction between the electrogenerated Co(I) center of cobalamin (cob(I)alamin) and ECA. Cyclic voltammograms of HOCbl in the presence of ECA show a small increase in current related to reduction of Co(II) to Co(I), and a new peak at more negative potentials related to reduction of an ethyl carboxymethyl-Cbl intermediate. The oxidation state of HOCbl during catalysis was monitored by means of spectroelectrochemical controlled-potential bulk electrolysis. Addition of ECA to electrogenerated cob(I)alamin initially generates the Co(II) form (cob(II)alamin) followed by a gradual formation of an ethyl carboxymethyl-Cbl intermediate. Controlled-potential bulk electrolysis was performed to identify products formed from catalytic reduction of ECA by electrogenerated cob(I)alamin and quantify the number of electrons transferred per molecule of ECA. Product distributions and coulometric results, together with the results of voltammograms and spectroelectrochemical controlled-potential bulk electrolysis, were interpreted to propose a reaction mechanism.

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Figures

Scheme 1.
Scheme 1.
Routes of Co(II) and Co(III)-R Intermediate Formation
Figure 1.
Figure 1.
a) Structure of hydroxocobalamin (HOCbl). b) Cyclic voltammograms recorded at 100 mV/s for 1 mM HOCbl at a circular planar glassy carbon electrode (area = 0.071 cm2) in oxygen-free DMF containing 0.1 M TBABF4.
Figure 2.
Figure 2.
a) Cyclic voltammograms recorded at 100 mV/s of 1 mM ECA (dashed red), 1 mM HOCbl (solid black), and 1 mM HOCbl in the presence of 1 mM ECA (solid red) at a circular planar glassy carbon electrode (area = 0.071 cm2) in oxygen free DMF containing 0.1 M TBABF4. b) Cyclic voltammograms recorded at 100 mV/s of 1 mM HOCbl (solid black) in the presence of 1 mM ECA (solid red), 5 mM ECA (solid blue) and 10 mM ECA (solid green) at a circular planar glassy carbon electrode in oxygen free DMF containing 0.1 M TBABF4.
Figure 3.
Figure 3.
Absorbance spectra collected during bulk reduction of 0.07 mM HOCbl and reaction of electrogenerated cob(I)alamin with 5 mM ECA. Spectra were collected at 30 second intervals, and a cathodic potential was maintained at all times. For clarity, only selected spectra were plotted and presented. a) Absorbance spectra collected during the Co(III)/Co(II) transition. Representative spectra for cob(III)alamin and cob(II)alamin labeled respectively. b) Absorbance spectra collected during the Co(II)/Co(I) transition. Representative spectra for cob(II)alamin and cob(I)alamin labeled respectively. c) Absorbance spectra collected after the addition of 5 mM ECA to the spectroelectrochemical cell.
Scheme 2.
Scheme 2.
Proposed mechanistic scheme for catalystic reduction of ethyl chloroacetate
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