Potentiometric Studies on the Formation Equilibria of Binary and Ternary Complexes of Some Metal Ions with Dipicolinic Acid and Amino Acids

摘要

The binary and ternary complexes of Mg~(2+), Ca~(2+), Sr~(2+), Ba~(2+), Co~(2+), Ni~(2+), Mn~(2+), and Cd~(2+) metal ions with dipiolinic acid as a primary ligand and some selected mono-and dicarboxylic amino acids as biolgically relevant secodnary litgands were studied in solution using a ptoentiometric technique. The acidity constants of the ligands selected were determined potentiometrically and used for determining the stability constants of the complexes formed in aqueous solution at 25 deg C and ionic strength I = 0.10 mol dm~(-3) (NaNO_3). The lower stability of 1:2 binary complexes of amino acids compared to that of the corresponding 1:1 systems is in accord with statistical considerations. The formation of ternary complexes was found to take place in a stepwise manner. The order of stability of the binary and ternary complexes in terms of the nature of the amino acid is investigated and discussed .The values of #DELTA# log K for ternary systems involving amino acids have been evaluated and discussed.