10.1021/ic0001659.s001
Hakim Boukhalfa
Hakim
Boukhalfa
Alvin L. Crumbliss
Alvin L.
Crumbliss
Multiple-Path Dissociation Mechanism for Mono- and Dinuclear Tris(hydroxamato)iron(III)
Complexes with Dihydroxamic Acid Ligands in Aqueous Solution
American Chemical Society
2000
Aqueous Solution Linear
dihydroxamic acid siderophores
L 8
L 2
dihydroxamic acid complexes
H 2 L n
hexadentate trihydroxamic acid counterparts
L n
ligand dissociation proceeds
Fe 2
H 2 O
CH
L 2 H
ligand dissociation paths
II
bidentate monohydroxamic acid
ligand dissociation processes
2000-08-24 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Multiple-Path_Dissociation_Mechanism_for_Mono-_and_Dinuclear_Tris_hydroxamato_iron_III_Complexes_with_Dihydroxamic_Acid_Ligands_in_Aqueous_Solution/3599193
Linear synthetic dihydroxamic acids ([CH<sub>3</sub>N(OH)Cī»O)]<sub>2</sub>(CH<sub>2</sub>)<i><sub>n</sub></i>; H<sub>2</sub>L<i><sup>n</sup></i><sup></sup>) with short (<i>n</i> = 2) and long (<i>n</i> = 8)
hydrocarbon-connecting chains form mono- and dinuclear complexes with Fe(III) in aqueous solution. At conditions
where the formation of Fe<sub>2</sub>(L<i><sup>n</sup></i><sup></sup>)<sub>3</sub> is favored, complexes with each of the two ligand systems undergo [H<sup>+</sup>]-induced
ligand dissociation processes via multiple sequential and parallel paths, some of which are common and some of
which are different for the two ligands. The pH jump induced ligand dissociation proceeds in two major stages
(I and II) where each stage is shown to be comprised of multiple components (I<i><sub>x</sub></i>, where <i>x</i> = 1ā3 for L<sup><i>2</i></sup> and L<sup><i>8</i></sup>,
and II<i><sub>y</sub></i>, where <i>y</i> = 1ā3 for L<sup><i>2</i></sup> and <i>y</i> = 1ā4 for L<sup><i>8</i></sup>). A reaction scheme consistent with kinetic and independent
ESI-MS data is proposed that includes the tris-chelated complexes (coordinated H<sub>2</sub>O omitted for clarity) {Fe<sub>2</sub>(L<i><sup>n</sup></i><sup></sup>)<sub>3</sub>, Fe<sub>2</sub>(L<sup><i>2</i></sup>)<sub>2</sub>(L<sup><i>2</i></sup>H)<sub>2</sub>, Fe(L<i><sup>n</sup></i><sup></sup>H)<sub>3</sub>, Fe(L<sup><i>8</i></sup>)(L<sup><i>8</i></sup>H)}, bis-chelated complexes {Fe<sub>2</sub>(L<i><sup>n</sup></i><sup></sup>)<sub>2</sub><sup>2+</sup>, Fe(L<i><sup>n</sup></i><sup></sup>H)<sub>2</sub><sup>+</sup>, Fe(L<sup><i>8</i></sup>)<sup>+</sup>}, and
monochelated complexes {Fe(L<i><sup>n</sup></i><sup></sup>H)<sup>2+</sup>}. Analysis of kinetic data for ligand dissociation from Fe<sub>2</sub>(L<i><sup>n</sup></i><sup></sup>)(L<i><sup>n</sup></i><sup></sup>H)<sup>3+</sup> (<i>n</i> =
2, 4, 6, 8) allows us to estimate the dielectric constant at the reactive dinuclear Fe(III) site. The existence of
multiple ligand dissociation paths for the dihydroxamic acid complexes of Fe(III) is a feature that distinguishes
these systems from their bidentate monohydroxamic acid and hexadentate trihydroxamic acid counterparts and
may be a reason for the biosynthesis of dihydroxamic acid siderophores, despite higher environmental molar
concentrations necessary to completely chelate Fe(III).