Evaluation of intramolecular equilibria in complexes formed between substituted imidazole ligands and nickel(II), copper(II) or zinc(II)

• Published in: Journal of inorganic biochemistry 2000-01, Vol.78 (2), p.129-137
• Main Authors: Sigel, Helmut, Saha, Arati, Saha, Nityananda, Carloni, Paolo, Kapinos, Larisa E, Griesser, Rolf
• Format: Article
• Language: English
• Subjects: Cations, Divalent; Chelate formation; Chelating Agents; Copper - chemistry; Equilibrium analysis; Imidazole derivatives; Imidazoles - chemistry; Metal ion complexes; Nickel - chemistry; Organometallic Compounds - chemistry; Oxygen - chemistry; Solution structures; Zinc - chemistry
• ISSN: 0162-0134; 1873-3344
• DOI: 10.1016/S0162-0134(99)00219-6

The metal ion-binding properties of imidazole-4-acetate (ImA −), 4(5)-aminoimidazole-5(4)-carboxamide (AImC), 2,2′-biimidazole (BiIm) (I. Török et al., J. Inorg. Biochem. 71 (1998) 7–14), and bis(imidazol-2-yl)methane (BiImM) (K. Várnagy et al., J. Chem. Soc., Dalton Trans. (1994) 2939–2945) have been evaluated by using the recently published stability constants and by applying the recently established log  K ML M versus p K HL H straight-line plots (L.E. Kapinos, B. Song, H. Sigel, Inorg. Chim. Acta 280 (1998) 50–56) which hold for simple imidazole-type ligands. The indicated analysis regarding the intramolecular equilibrium between a monodentatally imidazole-nitrogen-coordinated (open) species and a chelated isomer provides various helpful insights, e.g., the formation degree of chelates is more favored if six-membered rings can be formed, as in the case with M(BiImM) 2+ compared to M(BiIm) 2+, though in both instances the formation degree of the chelates is large. The formation degree of chelates in the M(ImA) + complexes increases in the series Zn(ImA) + (87%)