Metal ion-buffer interactions. Complex formation of N,N-bis(2-hydroxyethyl)glycine (bicine) with various biologically relevant ligands

摘要

Ternary 1:1:1 complexes of some metal ions Cu(II), Ni(II), and Co(II) with NN-bis(2-hydroxyethyl)glycine (bicine) and some aliphatic carboxylic acids (succinic, oxalic, malic, maleic, and tartaric), aromatic carboxylic acids (5-sulfosalicylic, salicylic, and phthalic), and hydroxamic acids (benzohydroxamic acid and salicylhydroxamic acid) are described. The formation constants of the 1:1:1 ternary complexes were determined potentiometrically at (298.15 ± 0.1) K and 0.10 mol(.)dm(-3) (NaNO3) ionic strength. The ternary complex formation was found to take place in a stepwise manner. The stability of the ternary complex is also discussed in relation to that of the binary complexes of secondary ligands. An evaluation of the effects of temperature and ionic strength of the medium on the stability of the ternary system Cu(II) + bicine + ligands has been studied. The thermodynamic parameters (&UDelta; H°, &UDelta; G°, and &UDelta; S°) were calculated and discussed. The stability constant of the above-mentioned ternary system has been investigated in a dioxane-water solution. Confirmation of the ternary complexes in solution has been carried out using differential pulse polarography, square wave voltammetry, conductometric measurements, and V-visible spectroscopic measurements.