p-ferrocenylaniline and p-ferrocenylphenol: Promising materials for analytical biochemistry and bioelectrochemistry

New substrates of horseradlish peroxidase and laccase incorporating advanta ges of ferrocenes, on one hand, and typical aromatic substrates of peroxida se, on the other, viz. p-ferrocenylaniline (FcC(6)H(4)NH(2-p)) and p-ferroc enylphenol (FcC(6)H(4)OH-p), have been introduced. The new substrates are s uperior in terms of (i) high reactivity, i.e., the second-order rate consta nts for their oxidation by the peroxidase compound II equal ca. 1 x 10(7) M -1 s(-1) at 25 degrees C, pH 5.0, which are 10(2) times higher than the cor responding rate constants for oxidation of ferrocene, alkylferrocenes, and aniline; (ii) easy spectral control of redox transformations at 439 or 860- 1000 nm (products are colored and the extinction coefficients are high); (i ii) the products are water-soluble and do not inactivate enzymes, p-Ferroce nyl-aniline is readily electropolymerized on a rod carbon electrode in 0.1 M HCl by potential cycling in the range from -0.4 to +1.1 V(versus Ag/AgCl) . The peak potentials are weakly pH-dependent in the range 0.5-7 and the sl opes of potential versus pH plots are less than 30 mV. p-Ferrocenylaniline is also electrochemically active when adsorbed on a carbon electrode from a n acetone solution. It has been demonstrated that the electrodeposited and adsorbed p-ferrocenylaniline films mediate the electro-oxidation of NADH wi th the sensitivity of 1.4 and 0.25 mu A/mM cm(2) at pH 5 and 7.2, respectiv ely.