Interaction of Flavin Adenine Dinucleotide (FAD) with a Glassy Carbon Electrode Surface

AbstractThe interaction of flavin adenine dinucleotide (FAD) with a glassy carbon electrode (GCE) surface was investigated in terms of the FAD adsorption thermodynamics and kinetics, the subsequent electroreduction mechanism, and the corresponding electron‐transfer rate. The kinetics of FAD electroreduction at the GCE was found to be an adsorption‐controlled process. A set of electroreduction kinetic parameters was calculated: the true number of electrons involved in the FAD reduction, n=1.76, the apparent transfer coefficient, αapp=0.41, and the apparent heterogeneous electron‐transfer rate constant, kapp=1.4 s−1. The deviation of the number of exchanged electrons from the theoretical value for the complete reduction of FAD to FADH2 (n=2) indicates that a small portion of FAD goes to a semiquinone state during the redox process. The FAD adsorption was well described by the Langmuir adsorption isotherm. The large negative apparent Gibbs energy of adsorption (ΔGads=−39.7 ±0.4 kJmol−1) indicated a highly spontaneous and strong adsorption of FAD on the GCE. The energetics of the adsorption process was found to be independent of the electrode surface charge in the electrochemical double‐layer region. The kinetics of FAD adsorption was modeled using a pseudo‐first‐order kinetic model.