The stepwise and the overall stability constants of the complexes formed by manganese (II) ion and twelve (12) amino acids have been determined. The dissociation constants, pKa, of the amino acids determined are; alanine (10.29), arginine (12.02), asparagine (9.39), glycine (9.87), histidine (7.01), lysine (9.28), methionine (9.68), phenyalanine (9.61), proline (10.54), threonine (10.31), tryptophan (9.77), and valine (9.99). The average number of amino acids coordinated to manganese (II) ion determined is 3. The Stepwise Stability Constants of manganese (II) amino acid complexes determined were found to decrease in the order K1 > K2 > K3 for all the complexes. The values of the overall stability constants of the complexes obtained are relatively high indicating
good stability for the complexes.
Keywords: Amino acids, dissociation constant, potentiometry, stability constant