Biocatalytic oxidation of phenolic compounds by bovine methemoglobin in the presence of H2O2: Quantitative structure-activity relationships

In the present work, 13 p-substituted phenols with different functional groups have been systematically evaluated as metHb substrates by means of HPLC analysis. Non-hyperbolic kinetics were observed and Hill coefficients in the 037-1.00 range were obtained. The catalytic constants and the Hill coefficients were found to be quantitatively correlated with two independent variables: the energy level of the highest-occupied molecular orbital (E-HOMO), which describes the intrinsic redox activity of the substrates and the pK(a)-values, which are related to substrate ionization. Oxygen evolution in the presence of each phenol derivative was also measured, and good correlation between peroxidase-like and catalase-like activities of the protein was observed. It is also shown that bovine metHb, although less active than other peroxidases, may represent a good alternative from an economical point of view for phenol removal processes. The equations here obtained may serve as a basis to further explore the potential use of metHb-mediated reactions in the treatment of phenols in wastewaters and to predict which phenol will be removed most efficiently under this treatment with satisfactory reliability. (C) 2012 Elsevier B.V. All rights reserved.