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A DENSITY FUNCTIONAL THEORY STUDY OF THE OXIDATION OF BROMIDE BY PEROXOMETAL COMPLEXES Maruf Khan and Martha S. Reynolds Colgate University A peroxometal complex is involved in the oxidation of bromide by vanadium bromoperoxidase, an enzyme found in seaweed. The resulting hypobromite ion combines with an organic molecule to form an irritant that protects against bacteria, fungi and predators. This project focuses on the mechanism for the oxidation of bromide by several synthetic analogues of the enzyme. A simplified system with MoO(O2)(NH3)(H2O) and MoO2(NH3) as the metal-containing reactant and product, respectively, was examined. Molybdenum was used because experimental data have shown that peroxomolybdenum complexes are more reactive than their vanadium counterparts.1 Gaussian98 was employed to optimize geometries using density functional theory (B3PW91) with the MIDI! basis set, and double zeta valence polarized basis (DZVP) functions for the metal. After optimization of reactant and product geometries, a transition state search was done. The transition state was sought using the QST2 function of Gaussian, which searches for a saddle point on the energy surface by requiring that one eigenvalue of the matrix of second-order energy derivatives be negative at every optimization step. Gaussian returned a transition state with the bromide attached to one of the oxygen atoms in the peroxo group. The following diagram shows the positions of the different species on the reaction profile: O H3N O Mo H2O transtion state O Br- O H3N O H3N O Mo Mo H2O O H2O O Br- + OBr product reactant A transition state is now being sought for bromide oxidation by an experimentally more realistic molecule— MoO(O2)(dipic)(H2O) (dipic is 2,6-pyridinedicarboxylate). Optimization of reactant and product geometries is complete, but the transition state structure is still being sought. Similar calculations will then be done for MoO(O2)(mpic)(H2O) (mpic is 6-hydroxymethyl-2pyridinecarboxylate), MoO(O2)(pdm)(H2O) (pdm is 2,6-pyridinedimethanol), and the peroxovanadium complexes of the same ligands. 1 Reynolds, M. S.; Butler, A. Inorg. Chem. 1996, 35, 2378—2383