Complexes of hydroxamates IX: Binary and ternary complexes involved in thesystems methioninehydroxamic acid and glycylglycine with Co(II), Zn(II) and Cd(II)

The stability constants of the binary complexes between Co2+, Zn2+ or Cd2(M2+) and methioninehydroxamic acid (MX) were determined by potentiometric pH titration in aqueous solution (I = 0.15 M, NaCl) at 25 degrees C. The st abilities of the ternary complexes containing glycylglycine (Glygly) in add ition were also calculated. The ternary enhancements were determined from K -1 (beta(111k)/beta(101i) beta(011j)), K-2 (beta(111k)(2)/beta(201i) beta(0 21j)) and K-22 (beta(2220)/beta(1110)(2)). Differential pulse polarographic (DPP) techniques were performed to study t he reduction properties of these metal ions in the presence of the binary a nd ternary systems. With the aid of the potentiometric study, differential peaks were assigned to some binary and ternary species. The metal oxidation states (II) were more stable in ternary systems than in binary systems. Ho wever, Co(II) systems were not stabilized in the presence of these ligands.