296 Abstracts

~029 h4orx~DEm~M(v1) AND TUNGSTEN(VI) CATALYZED OXIDATION OF BROMIDE BY HYDROGEN PEROXIDE: FUNCTIONAL MIMICS OF VANADIUM BROMOPEROXIDASE

G.E. Meister and A, Butler, Departlnent of Chemistry, University of California, Santa Barbara, California, 93106

Vanadium bromoperoxidase is a vanadium(V) containing enzyme which catalyzes the peroxidative oxidation of halides and the halide-assisted disproportionation of hydrogen peroxide [ 11. The role of the essential vanadium(V) is not easily addressed by conventional spectroscopic techniques; however, functional mimics including VO2+ have helped to

establish the mechanism [2]. In acidic aqueous solution VO2+ forms mono- and diperoxo complexes, both of which oxidize bromide; turnover rates are 10-J that of the enzyme, which functions optimally at neutral pH.

We are now investigating the reactivity of other transition metals as catalysts of halide peroxidation. In similar acidic conditions, Moo3 and W03 catalyze the oxidation of bromide by hydrogen peroxide at rates about

ten times faster than VO2+. Moo3 and W03 coordinate two equivalents of peroxide wliidl c&ii oxidrzc vrtimidc.

. . L. .

A mechanism is proposed in Scheme 1. In this scheme, Mo0(02)2 reacts

_HyMoqy-‘

MoOy(OL) [Moo(~,~- 1 with bromide to generate an unknown adduct which releases an oxidized Hz0

bromine species (HOBr= Br2=Br3-) which can then brominate an appropriate =4oqtoL) q+

HOBriTcbyEq-

- MoOj +MoO(OL)? BrTMB organic substrate. Molybdenum rapidly

MO@ + 2H202 - MoO(O2)2 + 4H20

recoordinates peroxide to Scheme 1

regenerate Mo0(02)2. In order to better elucidate the mechanism of oxidation of bromide by

M00(02)2 and WO(O2)2, l&and effects and halide competition are also being investigated.

1. R.I. de la Rosa, M.J. Clague, and A. Butler, J. Ant. Chem. Sm., 114, 760 (1992). 2. A. Butler, in Bioinorpnic Catalysis, J. Reedijk, E&Marcel-Dekker, New York, 1993, p. 425.