Phenazine, phenothiazine, and phenoxazine are potential model compounds for flavins, minicking flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), and riboflavin (VB2); each showing significant reactivity toward β-dihydronicotinamide adenine dinucleotide (NADH) and its oxidized form, NAD+. In most cases, the reaction stoichiometry is 1:1 and the associated equilibrium constants are around 104. Besides the reactivity toward NAD+ and NADH, phenazine, phenothiazine and phenoxazine adsorb strongly on indium-tin oxide (ITO) electrodes. After being adsorbed on electrodes, they still preserve their reactivity toward NAD + and NADH. Phenazine, phenothiazine, and phenoxazine can also be attached to ITO electrodes via chemical modifications such as diazotization reduction and anodic polymerization. Irrespective of the approach, the adhesion force between the adsorbates and ITO was characterized to be >30 nN. Noticeably, when these artificial flavins were subjected to atomic force microscopy (AFM)-based field-induced local oxidation (ALO), they formed microstructures on the ITO substrates, indicating that they are potential ink molecules for electrochemical lithography, in addition to being active electron-transfer mediators for NADH/NAD+.
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