Reactivity and aging in hydroxy-iron(III) polymers, analogs of ferritin cores

Abstract

The aging of hydrolytic polymers of ferric iron, analogs of the hydroxy-iron cores of ferritin, has been monitored via increases in light absorption, sedimentation velocity, and resistance to attack by acid. Two concurrent, yet distinct aging processes are observed, which can be associated with structural change and with growth via particle accretion. The acid decomposition kinetics are first order in the number of polymerized iron(III) ions in solution and first order in nitric acid concentration. Moreover the polymer particles shrink in proportion to the amount of acid consumed. The kinetic evidence suggests that either the particles harden outward from the center, or that they are accessible to the solvent over much of their interior. The polymers can be annealed in solution, rapidly decreasing their reactivity.