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 67 Zn 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 « OH. Calculations on the methylimidazole complex [(MelmH) 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.