Modeling the catalytic site of vanadium bromoperoxidase: synthesis and structural characterization of intramolecularly H-bonded vanadium(V) oxoperoxo complexes, [VO(O(2))((NH)2pyg(2))]K and [VO(O(2))((BrNH)2pyg(2))]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 - , l - ). A ligand with pendant NH 2 functionality, N-(2-pyridylmethyl-6-amino) iminodiacetic acid (H 2 N H 2 pyg 2 .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(O 2 )( N H 2 pyg 2 )]K and [VO(O 2 )( B r N H 2 pyg 2 )]K which demonstrate direct intramolecular H-bonding between an amine functionality and V(V)-bound peroxide is reported. The distances between NH 2 proton and bound peroxo moiety {(d(N(1)-H...O): 2.637(4) A in [VO(O 2 )( N H 2 pyg 2 )]K, and 2.640(8) and 2.6919(8) A in [VO(O 2 )( B r N H 2 pyg 2 ))]K} are indicative of intramolecular H-bonding. The intramolecular H-bond strength in [VO(O 2 )-( B r N H 2 pyg 2 )] - is estimated at 6 kcal/mol by 1 H NMR studies and demonstrates that the H-bond interaction is also significant in solution.