Synthesis and physical studies of pyridine and imidazole containing tridentate metal binding ligands

Several tridentate ligands incorporating pyridine and substituted imidazoles were prepared and their physical properties studied as models for the enzyme carbonic anhydrase (CA). The H+ and M2+ binding abilities (pKa and [Formula: see text]) were determined. In the case of the imidazole ligands, N-methylation reduces the metal binding ability of the ligand by some 3–4 [Formula: see text] units over the analogues in which the imidazole has N—H. 1H-nmr studies of the simple ligands as a function of [Zn2+] show that the ligands are bound symmetrically as 1:1 and 2:1 complexes depending upon the ligand/metal ratio. Increasing the steric bulk of the ligands by introduction of 4,5-diisopropyl substituents on the imidazole inhibits the 2:1 (ligand/metal) complex. Titration experiments of several ligands bound to equimolar Zn2+ and Co2+ are described and analysed.