Nanoscale iron(III) oxyhydroxy aggregates formed in the presence of functional water-soluble polymers: models for iron(III) biomineralisation processes

Superparamagnetic clusters of iron(III) oxyhydroxide in the form of poorly crystalline ferrihydrite (formally, 5Fe(2)O(3). 9H(2)O) have been synthesis ed in the presence of the polymers polyvinyl alcohol (PVA), polyacrylic aci d (PAA) and alginic acid. The solutions have been characterised by viscosit y studies and the resultant arrays isolated from these solutions have been imaged under an electron microscope and their magnetic properties determine d by Fe-57-Mossbauer spectroscopic studies at 293 and 77 K and magnetisatio n measurements at 293 and 5 K. The magnetic data show that the iron(III) ox yhydroxy particles are superparamagnetic. All preparations show hysteretic behaviour with coercive fields being approximately half or less than half o f that of ferrihydrite (3.4 kOe) and values of magnetic moment per iron par ticle less than that of ferrihydrite. Nanoscale aggregates (2-4 nm) are for med in the presence of PVA and PAA while, with alginic acid, extended branc h-like structures are observed, their formation being facilitated by the co mparatively rigid polysaccharide chain, a process related to iron biominera lisation in diverse biological systems. (C) 2000 Elsevier Science Inc. All rights reserved.