Flavin Derivatives with Tailored Redox Properties: Synthesis, Characterization, and Electrochemical Behavior

Abstract

This study establishes structure-property relationships for four synthetic flavin molecules as bioinspired redox mediators in electro- and photocatalysis applications. The studied flavin compounds were disubstituted with polar substituents at the N1 and N3 positions (alloxazine) or at the N3 and N10 positions (isoalloxazines). The electrochemical behavior of one such synthetic flavin analogue was examined in detail in aqueous solutions of varying pH in the range from 1 to 10. Cyclic voltammetry, used in conjunction with hydrodynamic (rotating disk electrode) voltammetry, showed quasi-reversible behavior consistent with freely diffusing molecules and an overall global 2e(-) , 2H(+) proton-coupled electron transfer scheme. UV/Vis spectroelectrochemical data was also employed to study the pH-dependent electrochemical behavior of this derivative. Substituent effects on the redox behavior were compared and contrasted for all the four compounds, and visualized within a scatter plot framework to afford comparison with prior knowledge on mostly natural flavins in aqueous media. Finally, a preliminary assessment of one of the synthetic flavins was performed of its electrocatalytic activity toward dioxygen reduction as a prelude to further (quantitative) studies of both freely diffusing and tethered molecules on various electrode surfaces.

Substrate and pH‐dependent homogeneous electrocatalysis using riboflavin for oxygen reduction

“…Under oxygen saturated conditions, the same redox peak is observed with an additional reduction peak at -0.15 V which can be attributed to the ORR. Although this peak is overlapping with the ORR peak of blank GC, the higher current density and more positive potential indicate an electrocatalytic behavior of riboflavin, which is in accordance with a comparable CV graph of a synthetic flavin derivative by the first paper by Kormányos et al [23] In comparison to previous reports [16,34,35,44] on anthraquinone-based molecules for electrocatalytic ORR, these results using riboflavin look very promising. We prepared homogeneous solutions of riboflavin for investigating their electrocatalytic O 2 to H 2 O 2 reduction.…”

A Self‐Assembling Flavin for Visible Photooxidation

“…[18] The 2e À process happening at pH 7 is reversible where a clear linearity between the peak currents and the potential sweep rate can be observed (Figure S18, Supporting Information). In line with previously reported data, [19] changing the pH of the solutions significantly alters the electrochemical behavior of flavin 5, with redox potentials shifting towards more negative values when the acidity decreases and with the loss of reversibility, due to competing protonation/deprotonation reactions.…”

Sensor systems for bacterial reactors: A new flavin-phenol composite film for the in situ voltammetric measurement of pH

“…The custom flavin monomer is highlighted in Scheme 1 and, as with riboflavin, can undergo two core transformations -oxidation and reduction of the flavin (I → II and II → I) [23][21] [24]. The inclusion of the phenol substituent however provides a third electrode process through oxidation of the phenol (I → III).…”