<i>p</i>-Ferrocenylaniline and <i>p</i>-Ferrocenylphenol:  Promising Materials for Analytical Biochemistry and Bioelectrochemistry

Abstract

New substrates of horseradish peroxidase and laccase incorporating advantages of ferrocenes, on one hand, and typical aromatic substrates of peroxidase, on the other, viz. p -ferrocenylaniline (FcC 6 H 4 NH 2 - p ) and p -ferrocenylphenol (FcC 6 H 4 OH- p ), have been introduced. The new substrates are superior in terms of (i) high reactivity, i.e., the second-order rate constants for their oxidation by the peroxidase compound II equal ca. 1 × 10 7 M - 1 s - 1 at 25 °C, pH 5.0, which are 10 2 times higher than the corresponding 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); (iii) the products are water-soluble and do not inactivate enzymes. p -Ferrocenylaniline 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 slopes of potential versus pH plots are less than 30 mV. p -Ferrocenylaniline is also electrochemically active when adsorbed on a carbon electrode from an acetone solution. It has been demonstrated that the electrodeposited and adsorbed p -ferrocenylaniline films mediate the electro-oxidation of NADH with the sensitivity of 1.4 and 0.25 μA/mM cm 2 at pH 5 and 7.2, respectively.