N-Aryl-N-hydroxy urethanes as peroxidase substrates

N-Aryl-N-hydroxy urethanes (AHUs), which are promising N-OH mediators for o xidoreductase catalysis, are electrochemically active redox compounds with a redox potential of 0.35-0.40 V vs. SCE (0.59-0.64 V vs. NHE). Alkyl subst ituents in the carbamic acid residue have, as expected, only little influen ce on the redox potential. The highest potential was noticed for N-hydroxy- N-(4-cyanophenyl)-carbamic acid methyl ester. Recombinant Coprinus cinereus peroxidase (rCiP) catalyzes oxidation of the AHUs with apparent bimolecula r constants k(ox) of 2.5 . 10(4)-7.5 . 10(4) M(-1)s(-1) at pH = 8.5 and 25 degreesC. Structure-function connectivities of the substrates were analysed within th e framework of the Marcus cross relationship and by using ab initio quantum chemical calculations. An excellent correlation of the redox potentials an d the HOMO energies could be found. However, no correlation of log(k(ox)) w ith redox potential and HOMO energy was indicated as predicted by theory. T his was explained by specific docking of the substrates in the active cente r of rCiP.