Significance of the Henri–Michaelis–Menten theory in abiotic catalysis: catechol oxidation by δ-MnO 2

Abstract

The Henri–Michaelis–Menten theory, for more than eight decades, was only restricted to homogeneous enzymatic catalysis. A mimic of an enzymatic kinetics based on the Henri–Michaelis–Menten concept was experimentally observed in heterogeneous catalysis in the present study with δ-MnO 2 as an abiotic catalyst in the oxidation of catechol (1,2-dihydroxybenzene). Using the derived linear forms of Lineweaver–Burk or Hofstee, the data show that similar to the enzyme tyrosinase, the kinetics of the catechol oxidation catalyzed by δ-MnO 2 can be described by the Henri–Michaelis–Menten equation, V 0= V max S/( K m+ S), where V max is the maximum velocity and K m the concentration of the substrate ( S) corresponding to an initial velocity ( V 0) half of V max. By analogy to the enzymatic kinetics, the parameters V max and K m for an heterogeneous abiotic catalysis were derived for the first time. Further, based on the concentration of the active centers of the mineral oxide, the kinetic constants k cat and k cat/ K m, respectively, representing the turnover frequency and the efficiency of the mineral catalyst, were also determined from the derived general rate equation of Briggs and Haldane. As an abiotic catalyst, δ-MnO 2 has a paramount role in the oxidation of phenolic compounds in soil, sediment and water environments. Therefore, the present observation is of fundamental and practical significance in elucidating the affinity between an abiotic catalyst and a substrate based on the Henri–Michaelis–Menten theory.