Contrasts between organic participation in apatite biomineralization in brachiopod shell and vertebrate bone identified by nuclear magnetic resonance spectroscopy |
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Authors: | Marianne T. Neary David G. Reid Matthew J. Mason Tomislav Fri??i? Melinda J. Duer Maggie Cusack |
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Affiliation: | 1.Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK;2.Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK;3.Department of Geographical and Earth Sciences, Gregory Building, University of Glasgow, University Avenue, Glasgow G12 8QQ, UK |
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Abstract: | Unusually for invertebrates, linguliform brachiopods employ calcium phosphate mineral in hard tissue formation, in common with the evolutionarily distant vertebrates. Using solid-state nuclear magnetic resonance spectroscopy (SSNMR) and X-ray powder diffraction, we compare the organic constitution, crystallinity and organic matrix–mineral interface of phosphatic brachiopod shells with those of vertebrate bone. In particular, the organic–mineral interfaces crucial for the stability and properties of biomineral were probed with SSNMR rotational echo double resonance (REDOR). Lingula anatina and Discinisca tenuis shell materials yield strikingly dissimilar SSNMR spectra, arguing for quite different organic constitutions. However, their fluoroapatite-like mineral is highly crystalline, unlike the poorly ordered hydroxyapatite of bone. Neither shell material shows 13C{31P} REDOR effects, excluding strong physico-chemical interactions between mineral and organic matrix, unlike bone in which glycosaminoglycans and proteins are composited with mineral at sub-nanometre length scales. Differences between organic matrix of shell material from L. anatina and D. tenuis, and bone reflect evolutionary pressures from contrasting habitats and structural purposes. The absence of organic–mineral intermolecular associations in brachiopod shell argues that biomineralization follows different mechanistic pathways to bone; their details hold clues to the molecular structural evolution of phosphatic biominerals, and may provide insights into novel composite design. |
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Keywords: | Lingula anatina Discinisca tenuis francolite hydroxyapatite fluoroapatite bone |
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