Modeling the Catalytic Site of Vanadium Bromoperoxidase:  Synthesis and Structural Characterization of Intramolecularly H-bonded Vanadium(V) Oxoperoxo Complexes, [VO(O2)(NH 2 pyg2)]K and [VO(O2)(BrNH 2 pyg2)]K

Vanadium haloperoxidases (VHPO) catalyze the peroxidative halogenation of organic substrates. Crystallographic studies suggest that hydrogen bonding from a lysine side chain to the vanadium(V)-bound peroxo group may facilitate oxidation of halides (Cl-, Br-, I-). A ligand with pendant NH2 functionality, N-(2-pyridylmethyl-6-amino) iminodiacetic acid (H2 NH 2 pyg2·2HCl) has been designed to explore the effects that H-bonding from Lys may have on peroxide activation. The first structural characterization of VBrPO model complexes [VO(O2)(NH 2 pyg2)]K and [VO(O2)(BrNH 2 pyg2)]K which demonstrate direct intramolecular H-bonding between an amine functionality and V(V)-bound peroxide is reported. The distances between NH2 proton and bound peroxo moiety {(d(N(1)−H···O): 2.637(4) Å in [VO(O2)(NH 2 pyg2)]K, and 2.640(8) and 2.6919(8) Å in [VO(O2)(BrNH 2 pyg2)]K} are indicative of intramolecular H-bonding. The intramolecular H-bond strength in [VO(O2)(BrNH 2 pyg2)]- is estimated at 6 kcal/mol by 1H NMR studies and demonstrates that the H-bond interaction is also significant in solution.