The study of complex formations between essential amino acids and some metal ions by electrochemical methods

Abstract

In this thesis, the complex formations between the 8 essential amino acids for human namely L-isoleucine, L-leucine, L-lysine, L-methionine, L-phenylalanine, L-threonine, L-tryptophan and L-valine with interesting transition metal ions, Mn(II), Cd(II) and Pb(II) ion, sampled representatively from the first, second and the third rows, respectively, were investigated by two electrochemical techniques, pH-metric titration and polarography. The experimental conditions used were the constant ionic strength of 0.10 M KC1 and the constant temperature of 37.0 ± 0.5℃. By pH-metric titration technique, the stepwise stability constants, K1 and K2 respectively, were found to be in the order of seventh and sixth for the Cd(II)-essental amno aid complexes. The stability constants, K1, were found to be in the order of third for the Mn(II)-essential amino acid complexes and the precipitate was taken place for the Pb(II)-essential amino acid systems. By polarographic technique, the coordination numbers of the Cd(II)-essential amino acid were found to be 1 and 2 corresponding to the 1:1 and 1:2 complexes with the stability constants, log β1and log β2 respectively, of the range of 8 and 15. The coordination number was found to be 1 corresponding to the 1:1 complexes of Mn(II)-essential amino acid and Pb(II)-essential amino acid with the stability constants, log β1, of the range of 3 and 4, respectively. The comparison of the stability constants determined from two techniques was generally in good agreement and these values decreased in the following order; Cd > Pb > Mn.