Ternary Complexes of Essential Metal Ions with L-Arginine and Succinic Acid in Cationic Surfactant Medium

Chemical speciation of ternary complexes MLX, ML2X and MLXH formed by Co(II), Ni(II), Cu(II) and Zn(II) with L-arginine as primary ligand (L) and succinic acid as secondary ligand (X) was studied in various concentrations (0.0-2.5% w/v) of cationic surfactant solution maintaining an ionic strength of 0.16 mol dm-3 (NaNO3) at 303K. Titrations were carried out in the presence of different relative concentrations (M: L: X =1:2:2, 1:2:4, 1:4:2) of metal to L-arginine to succinic acid with sodium hydroxide as titrant. The observed extra stability of ternary complexes compared to their binary complexes was explained based on the electrostatic interactions of the side chains of the ligands, charge neutralization, chelate effect, stacking interactions and hydrogen bonding. The trend in log β values with mole fraction of the surfactant and distribution diagrams were presented. Structures of plausible ternary complexes were also presented.