Electrochemical comparative study of riboflavin, FMN and FAD immobilized on the silica gel modified with zirconium oxide

Modified carbon paste electrodes were prepared by the adsorption of flavin on a silica gel modified with zirconium oxide ( Si: Zr: flavin). The electrochemical behavior of immobilized riboflavin, FMN and FAD was investigated. The formal potentials, E-o',for the flavins in these electrodes were found to be - 0.46 V vs. SCE, this being similar to their values obtained in solution. Their E-o' values remained pH dependent with certain invariance for riboflavin between 4 and 5. The composition of the supporting electrolyte did not affect the E-o' with exception of Ca2+, but in buffer systems and especially in phosphate a good rate of electron transfer was observed. The differences verified in the electrochemical behavior and UV-visible absorption spectra among the immobilized flavins are discussed in terms of different kinds of interaction.