The enzyme PcpA is a ring-cleaving dioxygenase with an unusual preference for ortho-halogen substituents, both in hydroquinone substrates and phenol inhibitors (Machonkin, et al., Biochemistry, 2011, 50, 8899�8913). Metal-halogen secondary bonding has been proposed as one possible source of this specificity.  Metal complexes incorporating tris(pyrazolyl) borate (Tp) ligands were used to further explore metal-halogen secondary bonding with ortho-substituted phenols and hydroquinones. Complexes with two substituted Tp ligands [(tris(3,5-diisopropylpyrazolyl)borate and tris(3,5-diphenylpyrazolyl)borate] and three different divalent metals (Fe, Co, Ni) were synthesized, which in turn were reacted with ortho-substituted phenolates and hydroquinones to mimic substrate/inhibitor binding. Four iron(II) complexes were made using 2,6-dibromo-, 2,6-dichloro-, 2-chloro- and 2-methylphenolate. Two TpiPr,iPrFeII complexes were synthesized using 2,6-dichlorophenolate and 2,6-dichlorohydroquinone. Cobalt and nickel complexes were synthesized using the TpPh,Ph ligand with 2,6-dibromo-, 2,6-dichloro- and 2,6-dimethylphenolate. These complexes were analyzed by X-ray crystallography, 1H NMR spectroscopy and UV/vis/NIR spectroscopy.

Examining the origin of the substrate specificity of PcpA using synthetic model complexes

243rd National Meeting (2012)

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