Probing the Molecular Interactions of Electrochemically Reduced Vitamin B₂ with CO₂

The electrochemical reduction of riboflavin (vitamin B₂) in a dimethyl sulfoxide solvent was examined under a CO₂ atmosphere and compared with results under an argon atmosphere. Variable-scan-rate cyclic voltammetry combined with controlled potential electrolysis (CPE) and analysis by UV-vis and EPR spectroscopies provided insights into the nature of interactions of reduced flavins with dissolved CO₂. Reductive exhaustive CPE experiments under CO₂ indicated an overall two-electron stoichiometry, compared to one-electron reduction under an argon atmosphere, due to the lowering of the formal one-electron reduction potential of the flavin radical anion to form the dianion, which can be rationalized by riboflavin-CO₂ molecular interactions. UV-vis spectroscopic measurements confirmed complete chemical reversibility of the redox transformations over extended time scales.