Formation constants in the ternary systems: Co(II)‐L‐Cysteine ‐ Adenine & Zn(II)‐L‐Cysteine‐Adenine2

A potentiometric titration technique has been used to determine stability constants for the various complexes of Co(II) and Zn(II) with L‐cysteine and from DNA bases i.e. Adenine. Stability constants of ternary systems have been evaluated by the method suggested by Irwing‐Rossotti. 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 at a given pH region. Furthermore, the molar 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 are as follows: log K=9.50 for Co(II)‐L‐cysteine‐Adenine; log K 1 = 6.85 and log K 2 = 6.00 for Zn(II)‐L‐cysteine‐Adenine2. The ionic strength was kept constant at I = 0.20 with NaClO4.