Water-mediated structuring of bone apatite

International audienceIt is well known that organic molecules from the vertebrate extracellular matrix of calcifying tissues are essential in structuring the apatite mineral. Here, we show that water also plays a structuring role. By using solid-state nuclear magnetic resonance, wide-angle X-ray scattering and cryogenic transmission electron microscopy to characterize the structure and organization of crystalline and biomimetic apatite nanoparticles as well as intact bone samples, we demonstrate that water orients apatite crystals through an amorphous calcium phosphate-like layer that coats the crystalline core of bone apatite. This disordered layer is reminiscent of those found around the crystalline core of calcified biominerals in various natural composite materials in vivo. This work provides an extended local model of bone biomineralization

GIPAW (gauge including projected augmented wave) and local dynamics in C-13 and Si-29 solid state NMR: the study case of silsesquioxanes (RSiO1.5)(8)

Octameric silsesquioxanes (RSiO1.5)(8) are versatile and interesting nano building blocks, suitable for the synthesis of nanocomposites with controlled porosity. In this paper, we revisit the Si-29 and C-13 solid state NMR spectroscopy for this class of materials, by using GIPAW (gauge including projected augmented wave) first principles calculations [Pickard & Mauri, Phys. Rev. B, 2001, 63, 245101]. Full tensorial data, including the chemical shift anisotropies (CSA) and the absolute orientation of the corresponding principal axes systems (PAS), were calculated. Subsequent averaging of the calculated tensors (due to fast reorientation of the R groups around the Si-C bonds) allowed for the interpretation of the strong reduction of CSA and dipolar couplings for these derivatives. Good agreement was observed between the averaged calculated data and the experimental parameters. Interesting questions related to the interplay between X-ray crystallography and solid state NMR are raised and will be emphasized

Calcium phosphates: First-principles calculations vs. solid-state NMR experiments

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First principles calculations of NMR parameters in biocompatible materials science: The case study of calcium phosphates, beta- and gamma-Ca(PO3)(2). combination with MAS-J experiments

First principles calculations of NMR parameters in biocompatible materials science: The case study of calcium phosphates, beta- and gamma-Ca(PO3)(2). combination with MAS-J experiment

Dipolar and J- Derived Solid State NMR Techniques and First Principles Calculations Applied to the Structure of Silicophosphates and to the Characterization of Phosphonate Grafting on Silica Nanoparticles

International audienceJ-derived (HMQC, INEPT) and D-derived (double and triple resonance) experiments were applied to the detailed characterization of crystalline and amorphous silicophosphate derivatives. 31P/29Si and 1H/31P/29Si CP MAS experiments were suitable for the description of complex silicophosphate gels, which can act as precursors for biocompatible materials. First principles calculations involving the GIPAW approach (first developed by Mauri and Pickard) were applied for the determination of CSA (29Si, 31P, 17O) and quadrupolar (17O) parameters. Excellent agreement between experimental and calculated data was obtained

Interfacial Ca2+ environments in nanocrystalline apatites revealed by dynamic nuclear polarization enhanced 43Ca NMR spectroscopy

International audienceThe interfaces within bones, teeth and other hybrid biomaterials are of paramount importance but remain particularly difficult to characterize at the molecular level because both sensitive and selective techniques are mandatory. Here, it is demonstrated that unprecedented insights into calcium environments, for example the differentiation of surface and core species of hydroxyapatite nanoparticles, can be obtained using solid-state NMR, when combined with dynamic nuclear polarization. Although calcium represents an ideal NMR target here (and de facto for a large variety of calcium-derived materials), its stable NMR-active isotope, calcium-43, is a highly unreceptive probe. Using the sensitivity gains from dynamic nuclear polarization, not only could calcium-43 NMR spectra be obtained easily, but natural isotopic abundance 2D correlation experiments could be recorded for calcium-43 in short experimental time. This opens perspectives for the detailed study of interfaces in nanostructured materials of the highest biological interest as well as calcium-based nanosystems in general