title: From crystalline to amorphous calcium pyrophosphates: A solid state Nuclear Magnetic Resonance perspective.
abstract: Hydrated calcium pyrophosphates (CPP, Ca2P2O7·nH2O) are a fundamental family of materials among osteoarticular pathologic calcifications. In this contribution, a comprehensive multinuclear NMR (Nuclear Magnetic Resonance) study of four crystalline and two amorphous phases of this family is presented. (1)H, (31)P and (43)Ca MAS (Magic Angle Spinning) NMR spectra were recorded, leading to informative fingerprints characterizing each compound. In particular, different (1)H and (43)Ca solid state NMR signatures were observed for the amorphous phases, depending on the synthetic procedure used. The NMR parameters of the crystalline phases were determined using the GIPAW (Gauge Including Projected Augmented Wave) DFT approach, based on first-principles calculations. In some cases, relaxed structures were found to improve the agreement between experimental and calculated values, demonstrating the importance of proton positions and pyrophosphate local geometry in this particular NMR crystallography approach. Such calculations serve as a basis for the future ab initio modeling of the amorphous CPP phases.
  
  
  CONCLUSIONS
  The general concept of NMR crystallography is applied to the detailed study of calcium pyrophosphates (CPP), whether hydrated or not, and whether crystalline or amorphous. CPP are a fundamental family of materials among osteoarticular pathologic calcifications. Their prevalence increases with age, impacting on 17.5% of the population after the age of 80. They are frequently involved or associated with acute articular arthritis such as pseudogout. Current treatments are mainly directed at relieving the symptoms of joint inflammation but not at inhibiting CPP formation nor at dissolving these crystals. The combination of advanced NMR techniques, modeling and DFT based calculation of NMR parameters allows new original insights in the detailed structural description of this important class of biomaterials.
authors.affiliation: CIRIMAT, INPT-CNRS-UPS, Université de Toulouse, ENSIACET, Toulouse, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Gras
authors.affiliation: School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
authors.forename: Annabelle
authors.initials: A
authors.lastname: Baker
authors.affiliation: CIRIMAT, INPT-CNRS-UPS, Université de Toulouse, ENSIACET, Toulouse, France.
authors.forename: Christèle
authors.initials: C
authors.lastname: Combes
authors.affiliation: CIRIMAT, INPT-CNRS-UPS, Université de Toulouse, ENSIACET, Toulouse, France.
authors.forename: Christian
authors.initials: C
authors.lastname: Rey
authors.affiliation: CIRIMAT, INPT-CNRS-UPS, Université de Toulouse, Université Paul Sabatier, Toulouse, France.
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Sarda
authors.affiliation: School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
authors.forename: Adrian J
authors.initials: AJ
authors.lastname: Wright
authors.affiliation: Vice-Chancellor's Office, University House, Lancaster University, Lancaster LA14YW, UK; Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Smith
authors.affiliation: Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
authors.forename: John V
authors.initials: JV
authors.lastname: Hanna
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS, Collège de France, UMR 7574, Chimie de la Matière Condensée de Paris, 75005 Paris, France.
authors.forename: Christel
authors.initials: C
authors.lastname: Gervais
authors.affiliation: Institut Charles Gerhardt de Montpellier, UMR 5253, CNRS-UM-ENSCM, Université de Montpellier, Montpellier, France.
authors.forename: Danielle
authors.initials: D
authors.lastname: Laurencin
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS, Collège de France, UMR 7574, Chimie de la Matière Condensée de Paris, 75005 Paris, France. Electronic address: christian.bonhomme@upmc.fr.
authors.forename: Christian
authors.initials: C
authors.lastname: Bonhomme
mesh_terms: D000369:Aged, 80 and over; D001672:Biocompatible Materials / Q000737:chemistry*; D001843:Bone Cements; D002118:Calcium / Q000737:chemistry; D002131:Calcium Pyrophosphate / Q000737:chemistry*; D003460:Crystallization; D003461:Crystallography; D006801:Humans; D006860:Hydrogen Bonding; D007249:Inflammation; D007477:Ions; D008958:Models, Molecular; D008968:Molecular Conformation; D019906:Nuclear Magnetic Resonance, Biomolecular; D010003:Osteoarthritis / Q000503:physiopathology; D011522:Protons; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D001672:Biocompatible Materials; D001843:Bone Cements; D007477:Ions; D011522:Protons; D014867:Water; D002118:Calcium; D002131:Calcium Pyrophosphate
keywords: (1)H; (31)P; (43)Ca solid state NMR; Amorphous calcium pyrophosphates; Crystalline calcium pyrophosphates; First principles GIPAW calculations