AMINOHYDROXAMIC ACIDS AS SEQUESTERING AGENTS IN LIVING SYSTEMS. POTENTIOMETRIC DETERMINATION OF PROTONATION AND FORMATION CONSTANTS FOR 2,6-DIAMINO-N-HYDROXYHEXANAMIDE AND COPPER(II), NICKEL(II), COBALT(II), AND HYDROGEN IONS IN AQUEOUS SOLUTION

Abstract

Abstract The systems H+, cobalt(II), nickel(II), and copper(II) with 2,6-diamino-N-hydroxyhexanamide (L-lysinehydroxamic acid hydrochloride = dahhe) have been investigated by potentiometric and spectrophotometric titrations at 25 ± 0.1˚C and I = 0.5 mol dm−3 (KCl). The protonation constants of the ligand and the overall formation constants of several metal complexes were calculated from potentiometric and spectrophotometric data with the aid of the SUPERQUAD and SQUAD programs, respectively. The following cumulative association constants (relative standard deviations are given in parentheses), β pqr = [M p H q L r ]/[M] p [H] q [L] r , were obtained: log β011 = 10.66 (1), log β021 = 19.55 (1), log β031 = 26.56 (1); CoII-dahhe, log β121 = 22.68 (2), log β111 = 15.72 (2), log β122 = 29.73 (3), log β101 = 8.68 (1); NiII-dahne, log β111 = 16.93 (8), log β122 = 34.87 (1), log β112 = 27.70 (4); CuII-dahhe, log β111 = 20.26 (1), log β212 = 41.53(2), log β122 = 40.56 (3), log β112 = 33.33 (10). Dahhe forms proton...