Phospholipid vesicles as a model system for biomineralization

Abstract

The tailoring of inorganic minerals such as iron oxides for functional use in biological systems for iron storage, structural support and magnetoreception involves biological regulation of crystal structure, particle size, morphology and crystallographic organization. The encapsulation of crystallochemical reactions within enclosed biological microvolumes enables control to be exerted over: (1) the chemical regulation, by passive or facilitated ion-transport, of localised supersaturation levels (2) the stereochemical requirements for ion-binding, redox and nucleation events at the organic matrix interface and (3) the spatial organization of crystal growth and morphology. Matrix-mediated growth of inorganic materials has not been systematically investigated in vitro even though it may have applications in crystal engineering and materials science. We have used phospholipid unilamellar vesicles of ∼300 Å diameter to study membrane-mediated processes of iron oxide crystal growth. Intravesicular deposits differ in structure, morphology and size from precipitates formed from reactions in bulk aqueous solution. Mediating factors include vesicle shape and dimension, diffusion-limited processes of ion-transport and ion-binding at the curved lipid headgroup surface. These results help elucidate biomineralization and have technological relevance to the controlled synthesis of monodisperse sols with catalytic and magnetic properties.