Equilibrium study and Stability constants of mixed Ligand complexes of Bio- molecules and Amino acids with Metal ions by Potentiometric method

Research of metal complexes with biologically active ligand is one of high scientific and practical interest. Formation of binary and ternary complexes of metal ions such as Cu(II), Co(II), Pb(II), Zn(II) and Cd(II) with biologically important ligand were investigated. Where nucleic acid Adenine (A) used as primary ligand and amino acid Histidine (B) used as secondary ligand. Potentiometric technique was applied for determination of complexation behavior of binary and ternary species in aqueous media at 37±1° C under ionic strength I = 0.1 M NaNO3. Stability constant have been determined through the method suggested by Irving & Rossetti and further refined through SCOGS computer program. The mixed ligand ternary complexes were occurring simultaneously in most cases generally at high pH with gradually declination of binary complexes of particular metal complexes. The percentage of ternary species of 56 at 6.4 pH for A-Cu(II)-B, 67.7 at 6.3 pH for A-Co(II)A, 65.56 at 7.2 pH for A-Pb(II)-B, 48.5 at 7.4 pH for A-Zn(II)-B and 56.5 at 7.3 pH for A-Cd(II)-B. The overall stability constant of mixed ligand Adenine(A)-M(II)-Histidine(B) ternary system are obtained in the following order A-Cu(II)-B > ACo(II)-B> A -Pb(II)-B > A-Zn(II)-B> A-Cd(II)-B.