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

Abstract

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