title: Tuning hardness in calcite by incorporation of amino acids.
abstract: Structural biominerals are inorganic/organic composites that exhibit remarkable mechanical properties. However, the structure-property relationships of even the simplest building unit-mineral single crystals containing embedded macromolecules-remain poorly understood. Here, by means of a model biomineral made from calcite single crystals containing glycine (0-7 mol%) or aspartic acid (0-4 mol%), we elucidate the origin of the superior hardness of biogenic calcite. We analysed lattice distortions in these model crystals by using X-ray diffraction and molecular dynamics simulations, and by means of solid-state nuclear magnetic resonance show that the amino acids are incorporated as individual molecules. We also demonstrate that nanoindentation hardness increased with amino acid content, reaching values equivalent to their biogenic counterparts. A dislocation pinning model reveals that the enhanced hardness is determined by the force required to cut covalent bonds in the molecules.
authors.affiliation: School of Chemistry, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK.
authors.forename: Yi-Yeoun
authors.identifier: 0000-0002-8503-4554
authors.initials: YY
authors.lastname: Kim
authors.affiliation: Department of Materials Science and Engineering, 214 Bard Hall, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Carloni
authors.affiliation: BioArCh, Departments of Chemistry and Archaeology, University of York, York YO10 5DD, UK.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Demarchi
authors.affiliation: Department of Materials Science and Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK.
authors.forename: David
authors.initials: D
authors.lastname: Sparks
authors.affiliation: Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK.
authors.forename: David G
authors.initials: DG
authors.lastname: Reid
authors.affiliation: Department of Materials Science and Engineering, 214 Bard Hall, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Miki E
authors.initials: ME
authors.lastname: Kunitake
authors.affiliation: Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE, UK.
authors.forename: Chiu C
authors.initials: CC
authors.lastname: Tang
authors.affiliation: Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK.
authors.forename: Melinda J
authors.initials: MJ
authors.lastname: Duer
authors.affiliation: Department of Materials Science and Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK.
authors.forename: Colin L
authors.initials: CL
authors.lastname: Freeman
authors.affiliation: Department of Materials Science and Engineering and the Russell Berrie Nanotechnology Institute, Technion Israel Institute of Technology, Haifa 32000, Israel.
authors.forename: Boaz
authors.initials: B
authors.lastname: Pokroy
authors.affiliation: BioArCh, Departments of Chemistry and Archaeology, University of York, York YO10 5DD, UK.
authors.forename: Kirsty
authors.initials: K
authors.lastname: Penkman
authors.affiliation: Department of Materials Science and Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK.
authors.forename: John H
authors.initials: JH
authors.lastname: Harding
authors.affiliation: Department of Materials Science and Engineering, 214 Bard Hall, Cornell University, Ithaca, New York 14853, USA.|Kavli Institute at Cornell for Nanoscale Science, 420 Physical Sciences Building, Ithaca, New York 14853, USA.
authors.forename: Lara A
authors.initials: LA
authors.lastname: Estroff
authors.affiliation: Department of Materials Science and Engineering, 214 Bard Hall, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Shefford P
authors.initials: SP
authors.lastname: Baker
authors.affiliation: School of Chemistry, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK.
authors.forename: Fiona C
authors.initials: FC
authors.lastname: Meldrum