title: Ion-association complexes unite classical and non-classical theories for the biomimetic nucleation of calcium phosphate.
abstract: Despite its importance in many industrial, geological and biological processes, the mechanism of crystallization from supersaturated solutions remains a matter of debate. Recent discoveries show that in many solution systems nanometre-sized structural units are already present before nucleation. Still little is known about the structure and role of these so-called pre-nucleation clusters. Here we present a combination of in situ investigations, which show that for the crystallization of calcium phosphate these nanometre-sized units are in fact calcium triphosphate complexes. Under conditions in which apatite forms from an amorphous calcium phosphate precursor, these complexes aggregate and take up an extra calcium ion to form amorphous calcium phosphate, which is a fractal of Ca(2)(HPO(4))(3)(2-) clusters. The calcium triphosphate complex also forms the basis of the crystal structure of octacalcium phosphate and apatite. Finally, we demonstrate how the existence of these complexes lowers the energy barrier to nucleation and unites classical and non-classical nucleation theories.
authors: Eindhoven University of Technology, Department of Chemical Engineering and Chemistry, Laboratory of Materials and Interface Chemistry and Soft Matter Cryo-TEM Research Unit, PO Box 513, 5600 MB Eindhoven, The Netherlands.
authors: Wouter J E M
authors: WJ
authors: Habraken
authors: Jinhui
authors: J
authors: Tao
authors: Laura J
authors: LJ
authors: Brylka
authors: Heiner
authors: H
authors: Friedrich
authors: Luca
authors: L
authors: Bertinetti
authors: Anna S
authors: AS
authors: Schenk
authors: Andreas
authors: A
authors: Verch
authors: Vladimir
authors: V
authors: Dmitrovic
authors: Paul H H
authors: PH
authors: Bomans
authors: Peter M
authors: PM
authors: Frederik
authors: Jozua
authors: J
authors: Laven
authors: Paul
authors: P
authors: van der Schoot
authors: Barbara
authors: B
authors: Aichmayer
authors: Gijsbertus
authors: G
authors: de With
authors: James J
authors: JJ
authors: DeYoreo
authors: Nico A J M
authors: NA
authors: Sommerdijk
mesh_terms: D000818:Animals; D040761:Biomimetic Materials / Q000737:chemistry*; D002118:Calcium / Q000032:analysis; D002130:Calcium Phosphates / Q000737:chemistry*; D002417:Cattle; D003094:Collagen / Q000737:chemistry; D020285:Cryoelectron Microscopy; D017886:Durapatite / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007477:Ions; D007700:Kinetics; D018625:Microscopy, Atomic Force; D008956:Models, Chemical; D008958:Models, Molecular; D053758:Nanoparticles / Q000737:chemistry / Q000648:ultrastructure; D010316:Particle Size; D011108:Polymers / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D055672:Static Electricity; D017356:Synchrotrons; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D002130:Calcium Phosphates; D007477:Ions; D011108:Polymers; C519480:amorphous calcium phosphate; D003094:Collagen; D017886:Durapatite; D002118:Calcium