Kinetics and mechanism of aluminum(III)/siderophore ligand exchange: mono(deferriferrioxamine B)aluminum(III) formation and dissociation in aqueous acid solution

The kinetics and mechanism of a linear trihydroxamic acid siderophore (deferriferrioxamine B, H4DFB⁺) ligand exchange with Al(H2O)6³⁺ to form mono(deferriferrioxamine B)aluminum(III) (Al(H2O)4H3DFB)³⁺ have been investigated at 25 °C over the [H⁺] range 0.001-1.0 M and I = 2.0 M (HClO4/NaClO4) by ²⁷Al NMR. Kinetic results are consistent with Al(H2O)4(H3DFB)³⁺ formation and dissociation proceeding through a parallel path mechanistic scheme involving Al(H2O)6³⁺(k2/k-1) and Al(H2O)5(OH)²⁺(k2/k-2) where k1 = 0.13 M^-1 s^-1, k-1 = 8.7 × 10^-3 M^-1 s^-1, k2 = 2.7 × 10³ M^-1 s^-1, and k-2 = 9.6 × 10^-4 s^-1. Relative complex formation rates at Al(H2O)6³⁺ and Al(H2O)5OH²⁺, and comparison with kinetic data for a series of synthetic hydroxamic acids, suggest that an interchange mechanism is operative. These results are also discussed in relation to kinetic data for the corresponding iron(III)-deferriferrioxamine B system. © 1987.

Duke Scholars

Author Alvin L. Crumbliss Chemistry