Studies on the stability of group II B metal ion-alpha-amino acids-diketooxime ternary systems

The protonation constants of 3,3,9,9-tetramethyl-4,8-diazaundecane-2,10-dio xime (PnAO) and six alpha-amino acids, the stability constants of Zn(II), C d(II), Hg(II)-PnAO, Zn (II), Cd(II), Hg(II)-alpha-amino acids binary comple xes and Zn(II), Cd(II), Hg(II)-PnAO-alpha-amino acids ternary complexes hav e been determined by pH titration method at (35 +/- 0.1)degrees C, I = 0.1 mol/L KNO3. The results show that the Linear Free Energy Relationship (LFER ) has been found to exist between the protonation constants of alpha-amino acids and the corresponding stability constants of Zn(II), Cd(II), Hg(II)-P nAO-alpha-amino acids ternary system. The cause of existence of LFER has be en discussed by means of the stereo structures of the ternary complexes. Th e trend of change of the stability for the title systems is governed by the sequence Zn(II)>Cd(II)<Hg(II), and the internal cause has been discussed i n terms of the charge/radius effect and ionization potential of the metal i ons.