Formation and evolution of hydrated surface layers of apatites

Nanocrystalline apatites exhibit a very fragile structured hydrated surface layer which is only observed in aqueous media. This surface layer contains mobile ionic species which can be easily exchanged with ions from the surrounding fluids. Although the precise structure of this surface layer is still unknown, it presents very specific spectroscopic characteristics. The structure of the hydrated surface layer depends on the constitutive mineral ions: ion exchanges of HPO42- ions by CO32- ions or of Ca2+ by Mg2+ ions result in a de-structuration of the hydrated layer and modifies its spectroscopic characteristics. However, the original structure can be retrieved by reverse exchange reaction. These alterations do not seem to affect the apatitic lattice. Stoichiometric apatite also shows HPO42- on their surface due to a surface hydrolysis after contact with aqueous solutions. Ion exchange is also observed and the environments of the surface carbonate ions seem analogous to that observed in nanocrystalline apatites. The formation of a hydrated layer in aqueous media appears to be a property common to apatites which has to be taken into account in their reactivity and biological behavior

On symmetric X-ray beam splitting with high efficiency by use of reflection gratings with rectangular profile in the extreme off-plane configuration.

In order to be reflected or diffracted off a surface structure soft X-rays and hard X-rays need to impinge at grazing angles of incidence onto the surface. In case of a reflection grating of highly symmetric structure with rectangular groove profile these grooves can be oriented parallel to the beam trajectory. In such a symmetric situation the distribution of the diffracted intensity with respect to the plane of incidence is then expected to be symmetric. This is indeed observed with symmetrically oriented diffraction peaks. It can be predicted that for appropriate structure parameters the intensity can be contained mostly in two symmetrically oriented diffraction peaks. This will also be the case for hard X-rays. The diffraction efficiency will be particularly high, when the angle of grazing incidence is chosen in the total reflection regime below the critical angle of the grating coating. These predictions were experimentally verified in this work for hard X-rays with photon energies between 4 keV and 12.4 keV. In the experiment of the order of 30% of the incident intensity was diffracted into the two first orders. This is to be compared to reflectivities of the order of 50% measured at the same coating in an unruled area of the substrate. Consequently the relative structural diffraction efficiency for each first order was about 30%, while ideally it could have been 40%. The presented grating structure will thus be a rather efficient amplitude beam splitter for hard X-rays, e.g. in the coherent beam from a free electron laser. In addition such object could then be used as the first component in Michelson interferometers for the beam characterisation or for introducing a time delay between two coherent beams

Preliminary characterization of calcium chemical environment in apatitic and non-apatitic calcium phosphates of biological interest by X-ray absorption spectroscopy

Several reports have mentioned the existence of non-apatitic environments of phosphate and carbonate ions in synthetic and biological poorly crystalline apatites. However there were no direct spectroscopic evidences for the existence of non-apatitic environment of calcium ions. Xray Absorption Spectroscopy, at the K-edge of calcium, allows the discrimination between different calcium phosphates of biological interest despite great spectral similarities. A primary analysis of the spectra reveals the existence, in synthetic poorly crystalline apatites, of variable features related to the maturation stage of the sample and corresponding to the existence of nonapatitic environments of calcium ions. Although these features can also be found in several other calcium phosphate salts, and do not allow a clear identification of the ionic environments of calcium ions, they give a possibility to directly determine the maturity of poorly crystalline apatite from calcium X-ray Absorption Near Edge Structure spectra

Biological mineralizations based on calcium phosphates

The mineral fractions of bones and teeth are non-stoichiometric apatite crystals. Their morphology, dimensions, composition and reactivity are adapted to their biological function. Bone apatites are made of very reactive nanocrystals possessing, on their surface, a structured hydrated layer responsible for their biological properties. This unstable layer becomes progressively and unavoidably transformed into a relatively inert apatite lattice. In spite of very different time periods, the laws that determine the biological and diagenetic evolution of bone mineral are the same, especially in processes involving dissolution-re-precipitation phenomena

qualifying label components for effective biosensing using advanced high throughput seira methodology

The multiplexed SEIRA analysis of antibody-functionalized NP biolabels that can be exploited for specific assay platforms in view of high-performance readout

The use of SR-FTIR microspectroscopy for a preliminary biochemical study of the rat hippocampal formation tissue in case of pilocarpine induced epilepsy and neutroprotection with FK-506

The main aim of the work was the biochemical analysis of the hippocampal formation tissue in the case of epileptic rats treated with the neuroprotective agent FK-506. Three groups of animals were compared: rats with pilocarpine induced seizures treated and non-treated with tacrolimus as well as naive controls. Synchrotron radiation Fourier transform infrared (SR-FTIR) microspectroscopy was used for the biomolecular analysis of studied samples. The measurements were carried out at SISSI beamline of ELETTRA. A Bruker IFS 66v/S interferometer coupled to a Bruker Hyperion 2000 microscope was used. The tissue samples were analyzed in transmission mode with a beam defined by a small aperture and spatial resolution steps of 10 mu m which allowed us to probe the selected cross-line of the sample at cellular resolution. The obtained results enabled to compare the distributions of proteins and lipids in the three hippocampal cellular layers, i.e. in molecular, multiform and granular layers. For epileptic animals both treated and non-treated with FK-506, the tendency for increase of the ratio of the absorbance at around 1548 and 1658 cm(-1) (amide II/amide I ratio) was observed, however only for the multiform layer these changes were statistically significant. Similar relation was noticed in case of the ratio of the absorbance at around 1631 and 1658 cm(-1). The mentioned results may suggest conformational changes of proteins in the direction of beta-sheet secondary structure. Additionally, a statistically significant increase in the lipid massif and a decrease of the ratio of absorbance at around 2921 and 2958 cm(-1) were observed for epileptic animals treated with tacrolimus comparing to the control group

SYNCHROTRON BASED MICRO-MAPPING AND XAFS INVESTIGATION OF Fe-Mn AND EPIGENETIC INTERGROWTH WITHIN THE CAMBRIAN SHALLOW MANGANESE DEPOSITS, SOUTH JORDAN

The current work investigates the Cambrian Manganese ore deposits from Wadi Dana at central Wadi Araba region. This investigation aims to unravel the chemistry and micro-textures of the mineral paragenetic sequence for these manganese ore deposits. Particularly the Fe–Mn intimate intergrowth micro texture and the epigenetic Mn mineralization associated with Cu minerals. The combination of the synchrotron-based X-ray fluorescence (syn-XRF) micro-mapping and X-ray absorption fine structure (XAFS) techniques were used. They provide a clear picture of the elemental distribution of Mn, Fe, Cu, and Pb and other elements presented within the ore micro textures. Besides, it determines the exact elemental speciation. The results obtained gave a better understanding of the elemental atomic structures and eventually the depositional environment. Particularly, the syn-XRF micro-mapping reveals the existing of many successive evolution stages in the Mn ores. Besides, the X-ray Absorption Near Edge Structure (XANES) results showed that the micro-rhythmic texture is changing from Mn+4 (Pyrolusite) into Fe+3 (Hematite). This is evidence for the role of Eh as the main controlling factor during the ore formation. Eventually, indicating tentatively the paleoceanography setting of the Mn deposits. This is related to the continuous transgression-regression on the sea level in a semi-closed sea

Naica's "Cueva de los Cristales": Synchrotron radiation characterization of the wall-crystal interface

Naica's "Cueva de los Cristales" was discovered in 2000. It has been considered particularly interesting for its beauty and the challenges it poses to crystallography. This article focuses on the study of the wall-selenite interface by various techniques, particularly X-ray diffraction (XRD), scanning electron microscopy (SEM), with emphasis on micro-X-ray fluorescence (micro-XRF) and micro-X-ray absorption near edge structure (micro-XANES). The main phases calcite, quartz, goethite and montmorillonite were identified by XRD, as well as the association of crystalline and amorphous minor and trace phases of Zn, Mn, Cu, As and Pb. The latter were identified in micro-XRF maps and micro-XANES spectra. The results for the morphology and the chemical description of the crystal-wall interface may contribute to propose a nucleation and growth mechanism for Naica megacrystals

Abstracts from the 8th International Conference on cGMP Generators, Effectors and Therapeutic Implications

This work was supported by a restricted research grant of Bayer AG

Étude de la réactivité de surface d'apatites de synthèse nanocristallines

Ce mémoire porte sur l'étude de la réactvité d'apatites nanocristallines analogues au minéral osseux, et plus particulièrement sur leurs propriétés de surface. Les apatites nanocristallines obtenues par précipitation en milieu aqueux présentent des carctéristiques physico-chimiques similaires à celles du minéral osseux. Elles possèdent une couche superficielle hydratée, responsable de leur réactivité, à laquelle sont associés des ions minéraux "non-apatitiques" aisément mobilisables. Ils participent à divers processus de régulation et de substitution ioniques ; ils sont également soupçonnés d'affecter les propriétés physico-chimiques de la surface et de jouer un rôle important dans l'activité des cellules osseuses. Ces couches hydratées peuvent être considérées comme réservoirs d'ions échangeables. La plupart des études concernant le minéral osseux ou ses analogues de synthèse ont été effectuées sur des produits secs souvent obtenus par séchage sous vide. Dans une première partie, nous avons essayé de caractériser, en milieu humide, les phases qui se forment au cours de la précipitation de phosphates de calcium de synthèse et de préciser les réactions chimiques impliquées dans les phénomènes de maturation à l'aide des techniques telles que la spectroscopie infrarouge (ATR) ou la RMN du solide. Nous avons montré l'existence, dans les analogues humides juste après précipitation, d'une phase hydratée transitoire et extrêmement fragile, détruite par toute étape de séchage, et qui évolue vers la formation d'une phase apatitique. Dans une seconde partie, nous nous sommes intéressés aux modifications de surface des apaties mal cristallisées par échange ionique (cationique et anionique) afin de mieux appréhender leur réactivité et les propriétés de cette phase hydratée. Nous avons pu montrer que la structure et la composition de la couche hydratée sont profondément modifiées au cours de ces substitions. Ces travaux mettent en évidence la grande réactivité des apatites nanocristallines en suggérant l'utilisation de méthodes de caractérisation en milieu humide, notamment pour des échantillons biologiques.TOULOUSE-ENSIACET (315552325) / SudocSudocFranceF