The site of complex formation of the imidazole molecule has been determined to be the pyridine nitrogen by comparing data on the N-methylimidazole complex with the imidazole complex of Ag(I). The preparation and characterization of a dual system of imidazole and imidazolate complexes is presented for Ni(II), Cu(II), Zn(II), and Ag(I). Total heats of formation of these complexes have been determined.
The thermodynamic parameters for the complexation reactions of serine, threonine, homoserine, isoserine, 4-amino-3-hydroxybutyric acid, and /3-aminobutyric acid with copper(II) and nickel(II) in aqueous solution at 25°and µ = 0.16 are reported. Values for the formation constants were obtained from potentiometric titrations and enthalpy values determined calorimetrically. The -amino acids studied, as well as /3-aminobutyric acid, were postulated to form the typical amino-carboxyl chelates with copper(II) and nickel(II). The formation of a sixmembered chelate ring was found to be less favorable thermodynamically than the formation of a five-membered chelate ring for both copper(II) and nickel(II) complexes. The thermodynamic data seem to indicate the formation of a chelate ring involving the amino and hydroxy groups of the isoserine with the copper(II). The isoserine ligand was postulated to be functioning as either a bidentate or tridentate ligand with copper(II).It has been shown that for a number of aliphatic amino acids the formation of copper(II) complexes proceeds in a stepwise manner to form the mono and bis copper(II) species.2 These complexes are formed by the elimination of a proton from the zwitterion form of 1 and 2 moles of amino acid, respectively. Chelation occurs between the carboxyl and amino groups of the amino acid and the copper(II) ion. The formation of nickel(II) complexes with aliphatic amino acids proceeds in the same manner, except that a third mole of amino acid can be chelated to the nickel(II) ion to form the tris nickel(II) species. In the case of amino acids interacting with copper(II) there seems to be some dis-agreement3-5 as to whether or not the amino acid zwitterion can function as a monodentate ligand. Recent studies of the interaction of copper(II) with gly-(1) Based on the dissertation of J. E. Letter submitted to the Graduate
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