ELECTROOXIDATIVE NITRATION OF PHENOLS AT COPPER ELECTRODES

p-Cresol, as a small-molecule model for tyrosine residues in proteins, undergoes electrooxidative nitration in the presence of a nitrogen so urce, for example ammonia, in mildly alkaline aqueous solution at pote ntials in the range 0.8 to 1.4 V (vs sce). Anodized copper is the best electrode material of those studied and nitrogen sources in the incre asing order of effectiveness are amides < amines congruent to proteins < ammonia, the latter giving a total of nitrocresols of similar to 30 % from an initial p-cresol concentration of 0.5 mM. Azulene also nitra tes in these conditions, but phenylethers (4-methyl methoxybenzene and 1,2-dimethoxy benzene) do not. The protein hen egg-white lysozyme (HE WL), in the absence of any other nitrogenous species, acts as a Source of nitrating agent in the electrooxidative nitration of p-cresol, thu s substantiating our earlier finding of selective tyrosine nitration i n proteins in the absence of any other nitrogen source. This electroni tration reaction, unique in that there is no N-O bond in any initial s pecies, provides a novel and environmentally friendly route in mild co nditions and is of particular benefit in the selective covalent modifi cation of proteins. (C) 1997 Elsevier Science Ltd.