title: Structural studies of hydrated samples of amorphous calcium phosphate and phosphoprotein nanoclusters.
abstract: There are abundant examples of nanoclusters and inorganic microcrystals in biology. Their study under physiologically relevant conditions remains challenging due to their heterogeneity, instability, and the requirements of sample preparation. Advantages of using neutron diffraction and contrast matching to characterize biomaterials are highlighted in this article. We have applied these and complementary techniques to search for nanocrystals within clusters of calcium phosphate sequestered by bovine phosphopeptides, derived from osteopontin or casein. The neutron diffraction patterns show broad features that could be consistent with hexagonal hydroxyapatite crystallites smaller than 18.9 Å. Such nanocrystallites are, however, undetected by the complementary X-ray and FTIR data, collected on the same samples. The absence of a distinct diffraction pattern from the nanoclusters supports the generally accepted amorphous calcium phosphate structure of the mineral core.
authors.affiliation: EPSAM, Keele University, Staffordshire, ST5 5BG, UK.|Institut Laue-Langevin, 71 Avenue des Martyrs, 38042, Grenoble Cedex 9, France.|School of Physics and Astronomy, Astbury Center for Structural Molecular Biology, University of Leeds, LS2 9JT, Leeds, UK.
authors.forename: Samuel
authors.initials: S
authors.lastname: Lenton
authors.affiliation: Division of Physical Chemistry, Department of Chemistry, Lund University, 124, Lund, S221 00, Sweden.
authors.forename: Tommy
authors.initials: T
authors.lastname: Nylander
authors.affiliation: Institute of Molecular, Cell, and Systems Biology, University of Glasgow, Glasgow, G12 8QQ, UK.
authors.forename: Carl
authors.initials: C
authors.lastname: Holt
authors.affiliation: Structural Biochemistry Group, University of Edinburgh, Roger Land Building, The King's Buildings, Mayfield Road, EH9 3JR, Edinburgh, UK.
authors.forename: Lindsay
authors.initials: L
authors.lastname: Sawyer
authors.affiliation: Institut Laue-Langevin, 71 Avenue des Martyrs, 38042, Grenoble Cedex 9, France.
authors.forename: Michael
authors.initials: M
authors.lastname: Härtlein
authors.affiliation: European Synchrotron Radiation Facility, CS 40220, 38043, Grenoble, France.
authors.forename: Harrald
authors.initials: H
authors.lastname: Müller
authors.affiliation: EPSAM, Keele University, Staffordshire, ST5 5BG, UK. teixeira@ill.fr.|Institut Laue-Langevin, 71 Avenue des Martyrs, 38042, Grenoble Cedex 9, France. teixeira@ill.fr.
authors.forename: Susana C M
authors.identifier: http://orcid.org/0000-0002-1967-0026
authors.initials: SC
authors.lastname: Teixeira
mesh_terms: D000818:Animals; D002130:Calcium Phosphates / Q000737:chemistry*; D002417:Cattle; D053758:Nanoparticles / Q000737:chemistry*; D053495:Osteopontin / Q000737:chemistry; D010748:Phosphopeptides / Q000737:chemistry; D010750:Phosphoproteins / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D002130:Calcium Phosphates; D010748:Phosphopeptides; D010750:Phosphoproteins; C519480:amorphous calcium phosphate; D014867:Water; D053495:Osteopontin
keywords: Amorphous calcium phosphate; Biomineralization; Casein; Neutron diffraction; Osteopontin; Phosphoproteins