Electrochemical investigation of some aromatic redox mediators immobilisedon titanium phosphate

Some phenazines, phenoxazines, and phenothiazines as well as riboflavin wer e immobilised on amorphous titanium phosphate (TP) by adsorption from aqueo us solutions. The immobilised organic redox compounds revealed a reasonable electron transfer rate and with a formal potential (E degrees') at pH 7.0 more positive than that observed for their corresponding aqueous soluble co unterparts. This shift in the E degrees' was partly assigned to the acidity of TP. The E degrees' of the immobilised redox compound remained virtually constant with a variation of the solution pH between 1 and 8 and was attri buted to the protection effect of the matrix. Attenuated total reflectance infrared spectroscopy (ATRIS) of methylene blue and riboflavin adsorbed ont o TP deposited on ZnSe-prism was also used to shed further light on the int eraction between these aromatic redox compounds and TP, as ATRIS is sensiti ve to the mode of adsorption of molecules on surfaces. Four of the immobili sed compounds (Nile blue, methylene blue, toluidine blue O, methylene viole t) were shown to be efficient as electron transfer mediators to electrocata lytically oxidise NADH in aqueous solution at pH 7.0. The kinetic parameter s such as apparent Michaelis-Menten constant were obtained for these four i mmobilised mediators.