title: Ion exchange in hydroxyapatite with lanthanides.
abstract: Naturally occurring hydroxyapatite, Ca5(PO4)3(OH) (HAP), is the main inorganic component of bone matrix, with synthetic analogues finding applications in bioceramics and catalysis. An interesting and valuable property of both natural and synthetic HAP is the ability to undergo cationic and anionic substitution. The lanthanides are well-suited for substitution for the Ca(2+) sites within HAP, because of their similarities in ionic radii, donor atom requirements, and coordination geometries. We have used isothermal titration calorimetry (ITC) to investigate the thermodynamics of ion exchange in HAP with a representative series of lanthanide ions, La(3+), Sm(3+), Gd(3+), Ho(3+), Yb(3+) and Lu(3+), reporting the association constant (Ka), ion-exchange thermodynamic parameters (ΔH, ΔS, ΔG), and binding stoichiometry (n). We also probe the nature of the La(3+):HAP interaction by solid-state nuclear magnetic resonance ((31)P NMR), X-ray diffraction (XRD), and inductively coupled plasma-optical emission spectroscopy (ICP-OES), in support of the ITC results.
authors.affiliation: Medicinal Inorganic Chemistry Group, Department of Chemistry, University of British Columbia , 2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1.
authors.forename: Jacqueline F
authors.initials: JF
authors.lastname: Cawthray
authors.forename: A Louise
authors.initials: AL
authors.lastname: Creagh
authors.forename: Charles A
authors.initials: CA
authors.lastname: Haynes
authors.forename: Chris
authors.initials: C
authors.lastname: Orvig
mesh_terms: D017886:Durapatite / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D007477:Ions; D028581:Lanthanoid Series Elements; D017886:Durapatite