Synthesis and characterization of benzimidazole-based zinc complexes as structural carbonic anhydrase models and their applications towards CO₂ hydration
2011
Ibrahim, Mohamed M. | Amin, Mahmoud A. | Ichikawa, Kazuhiko
The tripod ligand tris(2-benzimidazolylmethyl)amine L¹ and its methylated derivative tris(N-methyl-2-benzimidazolylmethyl)amine L² were used for the preparation of chloro complexes [L¹Zn–Cl](PF₆) 1 and [L²Zn–Cl](PF₆) 2. These complexes reacted with AgPF₆ in aqueous acetone to form the corresponding aqua complexes [L¹Zn–OH₂](PF₆)₂3, [L²Zn(H₂O)](PF₆)₂4, which were deprotonated by using KOH to form the hydroxide complexes [L¹Zn–OH)](PF₆) 5 and [L²Zn–OH)](PF₆) 6. ¹H NMR titration of the ligands with Zn(II) ions gave detailed information about the structure of the resulting zinc complexes and the evidence for the existence of the zinc-bound hydroxo species. Complex 3 reacted with CO₂ gas in the presence of triethylamine to give the bicarbonate complex [L¹Zn–OCO₂H)](PF₆), which was characterized by IR and ¹³C NMR spectroscopes. The X-ray structure of [L¹Zn–NCS]₂[Zn(NCS)₄] 7 as structural carbonic anhydrase inhibitor was determined and adopted slightly distorted tetrahedral ZnN₄ coordination geometries with the equatorial positions occupied by three benzimidazole nitrogen atoms and apical position by nitrogen atom from the thiocyanate anion.
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