title: Selective formation of metastable ferrihydrite in the chiton tooth.
abstract: Metastable precursors are thought to play a major role in the ability of organisms to create mineralized tissues. Of particular interest are the hard and abrasion-resistant teeth formed by chitons, a class of rock-grazing mollusks. The formation of chiton teeth relies on the precipitation of metastable ferrihydrite (Fh) in an organic scaffold as a precursor to magnetite. In vitro synthesis of Fh under physiological conditions has been challenging. Using a combination of X-ray absorption and electron paramagnetic resonance spectroscopy, we show that, prior to Fh formation in the chiton tooth, iron ions are complexed by the organic matrix. In vitro experiments demonstrate that such complexes facilitate the formation of Fh under physiological conditions. These results indicate that acidic molecules may be integral to controlling Fh formation in the chiton tooth. This biological approach to polymorph selection is not limited to specialized proteins and can be expropriated using simple chemistry.
authors.affiliation: Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, IL 60201 (USA).
authors.forename: Lyle M
authors.initials: LM
authors.lastname: Gordon
authors.forename: Jessica K
authors.initials: JK
authors.lastname: Román
authors.forename: R Michael
authors.initials: RM
authors.lastname: Everly
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Cohen
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Wilker
authors.forename: Derk
authors.initials: D
authors.lastname: Joester
mesh_terms: D000818:Animals; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000138:chemical synthesis*; D049916:Polyplacophora / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy; D014961:X-Ray Diffraction
chemical_list: D005290:Ferric Compounds; C092844:ferric oxyhydroxide
keywords: biomineralization; ferrihydrite; iron oxides; metastable compounds; organic matrix