IN-SITU FTIR THIN-LAYER REFLECTANCE SPECTROSCOPY OF FLAVIN ADENINE-DINUCLEOTIDE AT A MERCURY GOLD ELECTRODE

In this work, in situ FTIR thin-layer spectroelectrochemistry has been employed at a flat mercury-based electrode to obtain, uniquely, the s pectrum of the reduced form of flavin adenine dinucleotide (FAD) in ne utral (pH 7) solutions. The flat mercury surface was achieved by the o pen-circuit amalgamation of gold and it was found to display the advan tageous electrochemical properties, including the high hydrogen overpo tential, of mercury. This electrode facilitated the determination of t he difference in infrared absorbance resulting from the reduction of a solution of FAD. The spectrum of reduced FAD was recovered from the d ifference spectrum by adding to it the conventionally determined solut ion spectrum of the stable oxidized form of the redox couple. The obse rved shifts in band frequencies for the reduced vs. oxidised forms of FAD are consistent with the prior band assignments by normal coordinat e analysis and with the previously proposed sites of the redox chemist ry of FAD.