Models of the active sites of zinc-containing enzymes: the structure of acetato[hydrotris(3-tert-butyl-5-methylpyrazol-1-yl)borato]zinc(II)

Abstract

The zinc complex acetato[hydrotris(3-tert-butyl-5-methylpyrazol-1-yl)borato]zinc(II) has been prepared and structurally characterised as a model of the active sites of the zinc-containing enzymes carbonic anhydrase and dihydroorotase. Crystals are monoclinic, space group P2₁/n, a 15.995(2), b 19.861(4), c 10.530(2)Å, β 90.00(2)°, Z 4 and the structure has been refined to a residual of 0.048 based on 4096 reflections. The complex deviates from C₃ symmetry as a consequence of interactions between the tripod ligand and the fourth ligand bound to the Zn atom. The Zn–N (tripod) bond lengths are affected by the degree of steric crowding but bonds to the fourth ligand are not. Comparison with the I^–, OH^– and HCO₃^– forms of human carbonic anhydrase I confirms that the complexes with tripodal ligands are excellent structural models for the active site of this enzyme.