Experimental evidence and structural modeling of nonstoichiometric (010) surfaces coexisting in hydroxyapatite nano-crystals

[Display omitted] ► HRTEM crystal simulation reveal the coexistence of two HA (010) terminations. ► A Ca-rich (B layer) and PO4-rich (A layer) were identified. ► The HA nano-crystal along [100] is formed by integer numbers of the BAA sequence. ► Water molecules are differently adsorbed on each cryst...

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Bibliographic Details
Published in:Colloids and surfaces, B, Biointerfaces B, Biointerfaces, 2012-01, Vol.89 (1), p.15-22
Main Authors: Ospina, C.A., Terra, J., Ramirez, A.J., Farina, M., Ellis, D.E., Rossi, A.M.
Format: Article
Language:English
Subjects:
calcium
Channels
colloids
Computer simulation
Durapatite - chemistry
Electronic structure
HRTEM
Hydroxyapatite
Microscopy, Electron, Transmission
Modeling
Models, Molecular
Nanocrystals
Nanoparticles
Powder Diffraction
Reconstruction
Spectroscopy, Fourier Transform Infrared
Surface analysis
Surface Properties
Terminations
transmission electron microscopy
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Summary:[Display omitted] ► HRTEM crystal simulation reveal the coexistence of two HA (010) terminations. ► A Ca-rich (B layer) and PO4-rich (A layer) were identified. ► The HA nano-crystal along [100] is formed by integer numbers of the BAA sequence. ► Water molecules are differently adsorbed on each crystal surface. High-resolution transmission electron microscopy (HRTEM) and ab initio quantum-mechanical calculations of electronic structure were combined to investigate the structure of the hydroxyapatite (HA) (010) surface, which plays an important role in HA interactions with biological media. HA was synthesized by in vitro precipitation at 37°C. HRTEM images revealed thin elongated rod nanoparticles with preferential growth along the [001] direction and terminations parallel to the (010) plane. The focal series reconstruction (FSR) technique was applied to develop an atomic-scale structural model of the high-resolution images. The HRTEM simulations identified the coexistence of two structurally distinct terminations for (010) surfaces: a rather flat Ca(II)-terminated surface and a zig-zag structure with open OH channels. Density functional theory (DFT) was applied in a periodic slab plane-wave pseudopotential approach to refine details of atomic coordination and bond lengths of Ca(I) and Ca(II) sites in hydrated HA (010) surfaces, starting from the HRTEM model.
ISSN:0927-7765
1873-4367
DOI:10.1016/j.colsurfb.2011.08.016