Enzymatic and electrochemical oxidation of N-hydroxy compounds - Redox potential, electron-transfer kinetics, and radical stability

A series of N-hydroxyacetanilide and 1-hydroxybenzotriazole analogues deriv atized by various functional substituents were studied with regard to redox potential, oxidation by laccase, oxidative stability, and correlation to t he electronic and steric properties of the substituents. It was found that substituents carrying conjugative/pi -electron function influenced the redo x potential more than substituents carrying inductive/sigma -electron funct ion, and that the electron-transfer from an N-hydroxy moiety to laccase was significantly affected by the redox potential. Electron-withdrawing substi tuents tended to reduce the electron density on the N-hydroxy group, leadin g to higher redox potential and lower oxidation rate. Bulky substitution or absence of N-phenyl tended to increase the K-m of the N-hydroxy group, lea ding to lower oxidation rate. Oxidized N-hydroxy compounds were stabilized by N-phenyl or N-carbonyl group, but not by N-azo or highly strained struct ure. Potential implication of these effects on laccase-based, N-hydroxy com pound-mediated biocatalysis is discussed.