Preparation and characterization of new hybrid organic/inorganic systems derived from calcium (aminoalkyl)-phosphonates and -phosphonocarboxylates

We have studied the phenomenon of calcium complexation by lab synthesized amphiphilic (α-aminoalkyl)-phosphonocarboxylic or -phosphonic acids. The electrical conductivity of aqueous solutions of sodium salts of all these acids was measured versus the volume of a calcium salt solution added. It appeared that calcium complexes are formed in a Ca/P atomic ratio close to 1. Calcium phosphonocarboxylates and calcium phosphonates were also precipitated by mixing aqueous solutions of disodium salts of phosphorus amphiphiles and calcium nitrate solutions. Before chemical analysis, these complexes were calcined to remove the organic part. In the mineralized products, calcium and phosphate were assayed: the Ca/P atomic ratio was equal to 1. X-ray diffraction and IR spectroscopy showed that they are made entirely of β pyrophosphate (Ca2P2O7), a result in agreement with previous chemical analysis. The chemical formula of the starting calcium complexes could be written as CaL·2H2O (L= ligand). The SEM micrographs of these complexes show plate-like structures. XRD patterns are characteristic of layered structures. These facts suggest that calcium complexes are composed of alternating bimolecular layers of calcium alkylphosphonocarboxylates or calcium alkylphosphonates, the chains being tilted and partially interdigitated

Colloidal synthesis and characterization of monocrystalline apatite nanophosphors

Here, we report the synthesis and characterization of 12 nm long, ultrafine, individualized calcium phosphate nanorods. Synthesis of these nanobuilding blocks involved the preparation of a calcium phosphate hybrid precursor containing an aminophosphate ligand. Colloidal calcium phosphate nanoparticles were achieved through the reorganization of an amorphous hybrid precursor at high temperature during a post-ageing step. These nanoparticles can be described as monocrystalline deficient calcium hydroxyapatite Ca102x(PO4)62x(HPO4)x(OH)22x, with surfaces stabilized by [PO3 22–O(CH2)2NH3 +] groups. A model is proposed in which the [ab] plane of the nanoparticles is formed by 9 unit cells surrounded by a peripheral layer composed of twelve aminoethyl phosphate (AEP)-calcium phosphate (xCa9(PO4)6 2 yCa-(AEP)2) hybrid units. Our ultrafine individualized calcium phosphate nanophosphors, synthesized in aqueous medium and displaying amino groups on their surface, are good candidates for use as fluorescent probes in biological imaging

Colloidal and monocrystalline Ln3+ doped apatite calcium phosphate as biocompatible fluorescent probes

Ultrafine individualised mono crystalline Ca102x(PO4)62x-(HPO4)x(OH)22x deficient calcium hydroxyapatite nanocrystals displaying fluorescence under visible excitation are proposed for utilisation as biocompatible biological probes

Synthèse de nanoparticules de phosphate de calcium et de magnetite pour l'imagerie dans le domaine du vivant

TOULOUSE-ENSIACET (315552325) / SudocSudocFranceF

Europium-doped calcium pyrophosphates : allotropic forms and photoluminescent properties

International audienceIn a search for new luminescent biological probes, we synthesized calcium pyrophosphates doped with europium up to an atomic Eu/(Eu+Ca) ratio of 2%. They were prepared by coprecipitating a mixture of calcium and europium salts with phosphate. After heating at 900°C in air, two phases coexisted, identified as the β calcium pyrophosphate form and EuPO4. Heating near 1250°C in air, during the β→ transformation, europium ions substitute for calcium ions in the * calcium pyrophosphate structure as demonstrated by the spectroscopic study. Europium ions with both valence states (divalent and trivalent) were observed in the samples. Following the synthesis procedure, partial reduction of Eu3+ took place even in an oxidizing atmosphere. The 0.5%-doped compound could serve as a sensitive probe in biological applications. Depending on the excitation wavelength, the luminescence occurs either in the red or in the blue regions, which discriminates it from parasitic signals arising from other dyes or organelles in live cells

Nanocrystalline apatites in biological systems: characterisation, structure and properties.

Nanocrystalline apatitic calcium phosphates play a crucial role in calcified tissues and biomaterials. One of the most interesting characteristics of biomimetic apatite nanocrystals is the existence of a surface hydrated layer essentially related to their formation process in solution. This hydrated layer shows specific spectroscopic characteristics. It seems to exist in its nascent state only in wet samples and is altered on drying. This surface-hydrated layer progressively disappears as the stable apatite domains develop. The surface ions can be rapidly and reversibly exchanged in solution, mainly with selected bivalent species. The exchange reactions clearly reveal the existence of two domains: the relatively inert apatite core and the very reactive surface-hydrated domains. The structure of the hydrated layer has been shown to be reversibly affected by the constituting ions. Such a surface layer in bone apatite nanocrystals could participate actively in homeostasis and probably other regulation processes. The specificity of biomimetic apatite nanocrystals also opens interesting possibilities in materials science. The mobility of the mineral ions on the crystal surface, for example, allows strong bonding and interactions either with other crystals or with different substrates. Inter-crystalline interactions have been described as a “crystal fusion” process in vivo and they could be involved in the setting reaction of biomimetic calcium phosphate cements. Ceramic-like materials using the surface interaction capabilities of the nanocrystals can be produced at very low temperature (below 200 C). The surface-hydrated layer could also be involved in interactions with macromolecules and polymeric materials or in the coating of implants. The ion exchange and adsorption capabilities of the nanocrystals could probably be used for drug release, offering a range of possible behaviours

Calcium phosphate interactions with titanium oxide and alumina substrates: an XPS study

Besides the excellent mechanical properties of titanium and alumina (Al2O3) in the case of load bearing applications, their bone-bonding properties are very different. In osseous environment, Al2O3 ceramic is encapsulated by fibrous tissues, whereas bone can bind directly to titanium, via its natural titanium dioxide (TiO2) passivation layer. So far, this calcification dissimilarity between TiO2 and Al2O3 was attributed to respectively their negative and positive surface charge under physiological conditions. The present study aims at studying the chemical interactions between TiO2 and Al2O3 (phase α) with the diverse ions contained in simulated body fluids (SBFs) buffered with trishydroxymethyl aminomethane (TRIS) at pH=6.0 and pH=7.4. After 1 h of immersion, TiO2 and α-Al2O3 powders were analyzed by X-ray photoelectron spectroscopy (XPS). The results indicated that Ca and HPO4 groups were present on TiO2 surface. In addition, HPO4 groups were found to be in a higher amount than Ca on TiO2, which does not comply with the surface charge theory. With regard to Al2O3, little HPO4 but no Ca was detected on its surface, and TRIS bound to Al2O3 substrate in all of the immersion experiments. The fact that both Ca and HPO4 were present at the vicinity of TiO2 might be at the origin of its calcification ability. On the other hand, Al2O3 did not show any affinity towards Ca and HPO4 ions. This might explain the inability of Al2O3 substrate to calcify