Phenazines electrochemistry

Although hydronium ion (H30+) (Chapter 8) and dioxygen (02) (Chapter 9) are the most studied of the molecules and ions without metal atoms, several of the molecules that contain sulfur, nitrogen, or carbon also are electroactive. The results for representative examples are presented to illustrate the utility of electrochemical measurements for die evaluation of the redox thermodynamics and bond energies for non-metal-containing molecules. In particular, die electrochemistry for several sulfur compounds [S8, S02, HS(CH2)3SH], nitrogen compounds [-NO, HON=0, N20, H2NOH, hydrazines (/ NHNH/ ), amines, phenazine], and carbon compounds (C02, CO, NCT) is summarized and interpreted. 

Crooks, R. M. and Bard, A. J. (1988a) Electrochemistry in near-critical and supercritical fluids. Part VI. The electrochemistry of ferrocene and phenazine in acetonitrile between 25 and 300°C. J. Electroanal. Chem. 243, 117-131. 

Fig. 1.8. Adsorption events monitored by SPR-electrochemistry in situ of LDH on gold evaporated electrodes modified with ligand-free (a) and Ll-anchored (B) MPA-DAB monolayers, before and after several runs of electroenzymatic reaction (E) Addition of a 2.64 x 10 M LDH solution in 50 mM Na-phosphate buffer, pH 7.0. (W) Washing with 50 mM Na-phosphate buffer, pH 7.0. (b) Changing the buffer to 100 mM Tris—HCl, 100 mM KCl, pH 8.0, switching the potential to +100mM (Ag/AgCl) and addition of 2.5 mM NAD" " and 0.25 mM phenazine methosulfate. (R) Addition of 20 mM lactate to the reaction mixture at +100 mV (Ag/AgCl). Reproduced from [241] with permission.

The electrochemistry of both NAD+ and NADH at clean electrodes occurs at high overvoltages (of the order of 1V) and hence causes imwanted side reactions, which tend to foul the electrode [142-144]. One way around this problem is to use mediators (two electron-proton acceptor/donors) such as o-quinone [145-147] or p-phenylenediamine derivatives [148], arylnitro derivative such as 2-nitro-9-fluorenone [149], PQQ with Ca " [150] and polyaromatic dye molecules, i.e., phenazine, phenoxazine and phenothiazine derivatives [11] that substantially lower the voltage for needed NADH oxidation. 

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See also in sourсe #XX -- [ , ]

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