Charge transfer in biology

Most living organisms utilize electron transport chains in order to obtain energy. Riboflavin, commonly known as vitamin B2, is the central component of the redox coenzymes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN). These cofactors serve as a prosthetic group to flavoproteins and function as the energy-carrying molecules in electron transfer reactions. In this study, the different ionization and oxidation states of riboflavin were identified and quantified as a function of solution potential and pH. To accomplish this task, spectroelectrochemical reductions of riboflavin at different pH were performed. Spectroscopic data offer clues concerning the identity of underlying species, such as oxidation/ionization states and the controlling equilibria. The large data sets obtained from these experiments were analyzed and the acid dissociation constant for reduced riboflavin was determined.