A Novel Water-Soluble Tripodal Imidazolyl Ligand as a Model for the Tris(histidine)Motif of Zinc Enzymes:Nickel,Cobalt and Zinc Complexes and a Comparison with Metal Binding in Carbonic Anhydrase

摘要

Tris[2-isopropylimidazo]-4(5)yl]phosphane(4-TIP~/PT),a novel model ligand for the tris(histidine)motif of many zinc enzymes,has been prepared.4-TIP~/Pr is hydrolytically stable and soluble in protic solvents.It readily forms chloro-and nitratocobalt,-nickel and -zinc complexes in aqueous methanol.The crystal structures of the solvates[(4-TIP~/Pr)Co(MeOH)(NO_3)NO_3.2Et_2O(3.2Et_2O),[(4-TIP~/Pr)Ni(MeOH)(NO_3)]NO_3.Et_2o.MeOH(4.Et_2O.MeOH),[(4-TIP~/Pr)CoCl]Cl.MeOH.2.5H_2O(5.MeOH.2.5H_2O),and [(4-TIP~/Pr)ZnCl]Cl.MeOH.2.5H_2O(6-MeOH.2.5H_2O)have been determined.The complex 3 shows striking structural similarities to the hydrogencarbonate complex of cobalt-substituted human carbonic anhydrase II(HCA II).