CHARACTERIZATION OF AMINO HYDROXAMIC METAL-CHELATES AND THEIR ACTIVITY IN BIOLOGICAL-SYSTEMS - FORMATION-CONSTANTS BETWEEN2-AMINO-N,3-DIHYDROXYPR OPANAMIDE, AND 2-AMINO-N,3-DIHYDROXYBUTANAMIDEAND IRON(III) IONS IN AQUEOU S SOLUTION

Complex formation equilibria and relative stability constants for species present in aqueous solutions of ion(III) with ''L-serinehydroxamic acid'' (2-amino-N,3-dihydroxypropanamide, adhp) and ''DL-threoninehydroxamic acid'' (2-amino-N,3-dihydroxybutanamide, adhb) have been investigated by potentiometric titrations at 25 +/- 0.1-degrees-C and I = 0. 5 mol dm-3 (KCl). Overall formation constants of several metal complexes were computed from potentiometric data with the hyperquad program. The following cumulative association constants (relative standard deviation values are given in parentheses) beta(pqr) = [M(p)H(q)L(r)]/[M]p[H]q[L]r were obtained: adhp, log beta011 = 12.72(l), log beta021 = 21.62(1), log beta031 = 28.38(1), log beta122 = 32.88(6), log beta111 = 17.07(6), log beta112 = 28.80(6), log beta102 = 22.15(8), log beta123 = 41.17(7), log beta133 = 46.26(13), log beta113 = 34.83(7), log beta103 = 28.06(7), log beta2-22 = 22.51(12); adhb, log beta011 = 12.75(l), log beta021 = 21.61(1), log beta031 = 28.39(l), log beta122 = 32.73(3), log beta111 = 16.90(4), log beta112 = 28.55(3), log beta102 = 21.37(7), log beta123 = 41.16(3), log beta133 = 46.03(7), log beta113 = 34.89(3), log beta103 = 27.76(3), log beta2-22 = 22.34(7), log beta1-13 = 19.23(5). Since the two ligands show behaviour very similar to that of already investigated aminohydroxamic acids without the OH- group, it is suggested that the proton residing on the alcoholic group is not ionized when the complex formation takes place. Consequently, in the refinement process of the complex species, the H2L+ species with only two dissociable groups ( - NHOH, - NH3+) has been considered, taking into account log beta011 and log beta021 for the two ligands, respectively. Equilibrium constants for their formation and the probable structure of the chelated compounds formed in aqueous solution are the object of discussion in terms of possible significance to biological reactions. Stability is compared with that of analogous chelated compounds.