Kinetic deuterium isotope effect in the oxidation of veratryl alcohol promoted by lignin peroxidase and chemical oxidants

Abstract

The intramolecular kinetic deuterium isotope effects (k_H/k_D = 4.6–4.9) determined in the H₂O₂-induced oxidation of the racemic and enantiomeric forms of α-monodeuterated veratryl alcohol catalysed by lignin peroxidase (LiP) are very similar to those determined in the oxidation of racemic α-monodeuterated veratryl alcohol promoted either by a LiP model compound (a water soluble iron porphyrin using m-chloroperbenzoic acid as the oxidant) (k_H/k_D = 4.2) or by potassium 12-tungstocobalt(III)ate, a genuine one-electron oxidant (k_H/k_D = 4.5). These results indicate that very likely veratryl alcohol radical cation, once generated by the LiP–H₂O₂ system, is released from the enzyme and is deprotonated by the medium.