ABSTRACT

In this study, a potentiometric titration technique has been used to determine stability constants for the various complexes of Zn(II), Co(II), Cd(II) and Mn(II) with creatinine and two amino acids. Stability constants of ternary systems have been evaluated by the method suggested by Irving-Rossotti at 25°C and 0.11M ionic strength (kept constant with NaC10₄ in aqueous solution. In addition, the conditional constants were calculated as a function of pH. The maximum values of the conditional formation constants were found to be in accordance with the mixed-ligand complex formation constants in a given pH region. In addition, the mole fractions of different species from mixed complexes were calculated by means of formation constants. The values of stability constants of mixed-ligand complexes at 25°C were calculated as follows: logK=3.20 for Zn(II)-L-cysteine-creatinine,logK₁=4 .24 and logK₂=3.58 for Co(II)-L-cysteinecreatinine₂, logK=3.22 for Cd(II) - L-cysteine - creatinine, logK=3.65 for Mn(II) - L-cysteine - creatinine and logK=5.34 for Co(II)-BDHL-cysteine-creatinine, logK=5.30 for Cd(II)-BDHL-cysteine-creatinine, logK₁=5.35 and logK₂ =3.93 for Zn(II) - BDHL-cysteine - creatinine₂, logK₁=5.40 and logK₂=3.49 for Mn(II) - BDHL-cysteine - creatinine_2.