Potentiometric studies of mixed complexes of cobalt(II) and copper(II) with l‐Asparagine and adenine

Abstract

A potentiometric titration technique has been used to determine the stability constants for the various complexes of Co(II) and Cu(II) with L-asparagine and from DNA base, e.g. adenine. Stability constants of ternary systems have been evaluated by the method suggested by IrwingRossotti. 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 determined 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= 5.25 for Co(II)-L-asparagine-adenine; log K= 9.30 for Cu(II)-L-asparagine-adenine. The ionic strength was kept constant at I = 0.20 with NaClO 4 .

Stability Constants of Mixed Ligand Complexes of Nickel(II) with Adenine and Some Amino Acids

“…The stability constants of these complexes, which were formed, were calculated (according to ( 1 ) and ( 2 )) at 0.1 mol·L −1 KNO 3 ionic medium and 25.0°C temperature with BEST computer program and given in Table 2 . From these results, it was seen that the results presented in the previous literature were coherent with the values of this research [ 34 , 35 ].…”

“…Protonation constants of all of the ligands determined in this study were listed in Table 1 . It is clear that all protonation constants (log 10 ⁡ K 1 , log 10 ⁡ K 2 , and log 10 ⁡ K 3 ) of Ade and L-amino acids identified in this research are very close to previously reported values for those ligands ( Table 1 ) [ 24 – 32 ].…”

Equilibrium Study of the Mixed Complexes of Copper(II) with Adenine and Amino Acids in Aqueous Solution

“…The obtained values are in good agreement with data found in the literature [37][38][39][40][41][42][43].…”

“…3, 4) were calculated by utilizing the pH values in the potentiometric titration curves using of the BEST computer software [36]. In 0.1 molÁL -1 KNO 3 at 25.00°C under a nitrogen atmosphere; the results are presented in Table 2 and it was observed that these stability constants are in line with the values found in the literature [38,39,[47][48][49][50]. …”

“…The stability constants of these complexes (Eqs. 1, 2) were calculated with the BEST software at 0.1 molÁL -1 KNO 3 ionic medium at 25.00°C; these are presented in Table 2 and determined to be in line with the values found in the literature [38,44,45]. They show that the larger metal ions (such as Cd(II) (ionic radius = 95 pm) or Hg(II) (102 pm) will coordinate in a chelate fashion between the N(3) and N(9) while the smaller metal ion Zn(II) (74 pm) will fit better in the smaller chelate ring size between N(7) and N(10) for adenine ( Fig.…”