Thermodynamic and kinetic studies of the sulfonated derivative of the ironchelator TRENCAM, an analog of enterobactin

The solution coordination chemistry of TRENCAMS, the water soluble sulfonat ed derivative of the enterobactin analog TRENCAM, based on three catechol s ubunits connected to a tris(2-aminoetbyl)amine, is described. The protonati on constants of this ligand and the formation and protonation constants of its Fe(III) complex have been determined by potentiometric nd spectrophotom etric techniques. The ligand TRENCAMS has a chelating ability at pH 7.4, [L ](tot) = 10(-5) M, [Fe](tot) =10(-6) M stronger (pFe 29.6) than TRENCAM (pF e 27.8) and of the same order of magnitude as O-TRENSOX (pFe 29.5), a tripo dal ligand based on 8-hydroxyquino line subunits (Serratrice et al., Inorg. Chem. 36 (1997) 3898). The kinetics of formation of the Fe(III) complex sh ows a contribution from the [FeOH2+] species (k(1) = 3700 M-1 s (-1)) and f rom the [Fe-2(OH)(2)4(+)] species (k(2) = 2700 M-1 s(-1)). Both proton depe ndent and proton independent rate constants for acid hydrolysis of the comp lex were measured (k'(-1), = 0.191 M (-1) s (-1) and k(-1) = 0.018 s (-1), respectively). These rates and the mechanism are discussed and compared to the processes observed for the dissociation of Fe(III) complexes with catec hol or hydroxamate or other literature ligands. (C), 1999 Elsevier Science S.A. All rights reserved.