The electrochemical behavior of flavin adenine dinucleotide in neutral solutions

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Abstract
A detailed investigation of the electrochemical behavior of flavin adenine dinucleotide (FAD) in neutral solutions has been carried out at Hg and glassy carbon electrodes. At FAD concentrations of about 10−4 M, cyclic voltammetry (CV) shows a pair of anodic and cathodic peaks having a peak separation at low sweep rates indicative of a two-electron transfer process and yielding a formal redox potential for FAD of −0.206 ± 0.003 V vs. NHE at pH 7. Evidence for FAD adsorption was obtained in experiments at high sweep rates, from the effect of time of exposure of the electrode surface to FAD in solution and from the effect of the potential limits on the cyclic voltammetric response. The process of FAD adsorption was studied in detail in dilute FAD solutions (ca 10−6 M) using a hanging mercury drop electrode and the techniques of CV and ac voltammetry. Three distinct stages of FAD adsorption were observed and a model of the orientation of FAD on the electrode surface as a function of time and potential is presented. In addition, the kinetics of oxidation and reduction of adsorbed FAD was studied for each of the stages of FAD deposition, and a surface standard rate constant of ca. 40 s−1 was obtained for Stages II and III of FAD adsorption.