Kinetics of Iron(III) Chelation from Polynuclear Oxo-Hydroxy Aggregates by Hydroxamic Acids:  Understanding Ferritin Iron(III) Sequestration

The kinetics of the sequestration of iron(III) from the polynuclear iron(III) complex, [Fe 11 O 6 (OH) 6 (O 2 CPh) 15 ]· H 2 O·2MeCN, a possible biomimetic model of ferritin, with a series of 11 primary and secondary hydroxamic acids in dry acetonitrile/dichloromethane solvent mixtures indicates an associative interchange (Ia) mechanism in accordance with the wide variation of Δ H ⧧ and Δ S ⧧ within the series. Comparison of the kinetics of this hydroxamic acid series with the simple binuclear iron complex (NEt 4 ) 2 [Fe 2 OC1 6 ] shows that steric effects are considerably more important for the Fe 11 complex than for the Fe 2 complex. These conclusions, based on kinetics studies, are relevant to the design of chelators for sequestration of iron from ferritin.