Potentiometeric study of protonation and complex formation of some amino acids with Zn (II) , Co(II) and Ni (II) in aqueous solution

The stability constants and complexation reaction between L-glutamine, L-arginine and glycine with Zn (II) , Co (II) and Ni (II) were studied potentiometrically in aqueous solution at 25° C and μ=0.1 M KNO3. The overall stability constants log β´ s of all species are obtained by computer refinement of pH-volume data using BEST computer program. Several models were tested and the lowest δFIT, the best one is accepted. The main species in binary complexes MHL, ML, ML2, MLOH, ML(OH)2 and for ternary complexes are ML1L2, ML1L2H, ML1L2OH, ML1L2(OH)2. The order found for the resulting stability constants vary as Co (II) < Ni (II)