Structural characterization of zinc bicarbonate compounds relevant to the mechanism of action of carbonic anhydrase

Abstract

The tris(3-t-butyl-5-methylpyrazolyl)hydroborato and tris(2-pyridylthio)methyl derivatives, [Tp^But,Me]ZnOCO₂H and [κ⁴-Tptm]ZnOCO₂H, are the first pair of terminal zinc bicarbonate complexes to be structurally characterized by using X-ray diffraction. In both cases, the bicarbonate ligand coordinates in a unidentate manner, comparable to that in human carbonic anhydrase I. While the bicarbonate complex [κ⁴-Tptm]ZnOCO₂H is obtained by treatment of {[κ³-Tptm]Zn(μ–OH)}₂ with CO₂ in the presence of water, the bridging carbonate complex [Tptm]Zn(μ-CO₃)Zn[Tptm] is obtained in the absence of water. The reactivity of {[κ³-Tptm]Zn(μ–OH)}₂ towards CO₂ is sufficiently high that the carbonate complex is obtained upon exposure to air.