Solid-state 67Zn NMR spectroscopic studies and ab initio molecular orbital calculations on a synthetic analogue of carbonic anhydrase

The tris(pyrazolyl)hydroborato zinc complexes [Tp(But,Me)]ZnX (where X = Br, Cl, and OH) have been examined by low-temperature solid-state Zn-67 NMR spectroscopy. The value of the quadrupole coupling constant, Cq, for the zinc increased monotonically with the electronegativity of the bound substituent X, e.g., Br < Cl much less than OH. Calculations on the methylimidazole complex [(MeImH)(3)Zn(OH)](+) as a model for the active site of carbonic anhydrase indicate that the computed electric field gradient tensor is in good agreement with the experimental and calculated values for [Tp(But,Me)]ZnOH.