Structural Unit Determination in Silica Nanoparticles Using Infrared Micro-Reflectance Spectroscopy.

A method based on infrared (IR) micro-reflectance measurements for the structural characterization of glassy nanomaterials is presented. Near-specular reflectance spectra of pressed pellets can be analyzed using a model relating the structure of silicate glasses to their dielectric response and an effective medium approximation to account for the effect of porosity. The integrated intensities of phenomenological bands attributed to Q2, Q3, and Q4 structural units allow quantifying their relative populations. These values are in good agreement with those obtained with magic-angle spinning nuclear magnetic resonance, which serves as validation of the method and proves the feasibility of extracting quantitative information about glass structure from IR micro-reflectance experiments.

A computationally-guided non-equilibrium synthesis approach to materials discovery in the SrO-Al2O3-SiO2 phase field.

Glass-crystallisation synthesis is coupled to probe structure prediction for the guided discovery of new metastable oxides in the SrO-Al2O3-SiO2 phase field, yielding a new ternary ribbon-silicate, Sr2Si3O8. In principle, this methodology can be applied to a wide range of oxide chemistries by selecting an appropriate non-equilibrium synthesis route.

Zinc-Doped Bioactive Glass/Polycaprolactone Hybrid Scaffolds Manufactured by Direct and Indirect 3D Printing Methods for Bone Regeneration.

A novel organic-inorganic hybrid, based on SiO2-CaO-ZnO bioactive glass (BG) and polycaprolactone (PCL), associating the highly bioactive and versatile bioactive glass with clinically established PCL was examined. The BG-PCL hybrid is obtained by acid-catalyzed silica sol-gel process inside PCL solution either by direct or indirect printing. Apatite-formation tests in simulated body fluid (SBF) confirm the ion release along with the hybrid's bone-like apatite forming. Kinetics differ significantly between directly and indirectly printed scaffolds, the former requiring longer periods to degrade, while the latter demonstrates faster calcium phosphate (CaP) formation. Remarkably, Zn diffusion and accumulation are observed at the surface within the newly formed active CaP layer. Zn release is found to be dependent on printing method and immersion medium. Investigation of BG at the atomic scale reveals the ambivalent role of Zn, capable of acting both as a network modifier and as a network former linking the BG silicate network. In addition, hMSCs viability assay proves no cytotoxicity of the Zn hybrid. LIVE/DEAD staining demonstrated excellent cell viability and proliferation for over seven weeks. Overall, this hybrid material either non-doped or doped with a metal trace element is a promising candidate to be translated to clinical applications for bone regeneration.

Long-Term Fate and Efficacy of a Biomimetic (Sr)-Apatite-Coated Carbon Patch Used for Bone Reconstruction.

Critical bone defect repair remains a major medical challenge. Developing biocompatible materials with bone-healing ability is a key field of research, and calcium-deficient apatites (CDA) are appealing bioactive candidates. We previously described a method to cover activated carbon cloths (ACC) with CDA or strontium-doped CDA coatings to generate bone patches. Our previous study in rats revealed that apposition of ACC or ACC/CDA patches on cortical bone defects accelerated bone repair in the short term. This study aimed to analyze in the medium term the reconstruction of cortical bone in the presence of ACC/CDA or ACC/10Sr-CDA patches corresponding to 6 at.% of strontium substitution. It also aimed to examine the behavior of these cloths in the medium and long term, in situ and at distance. Our results at day 26 confirm the particular efficacy of strontium-doped patches on bone reconstruction, leading to new thick bone with high bone quality as quantified by Raman microspectroscopy. At 6 months the biocompatibility and complete osteointegration of these carbon cloths and the absence of micrometric carbon debris, either out of the implantation site or within peripheral organs, was confirmed. These results demonstrate that these composite carbon patches are promising biomaterials to accelerate bone reconstruction.

Theoretical and Experimental Studies of Gallate Melilite Electrides from Topotactic Reduction of Interstitial Oxide Ion Conductors.

A nonstoichiometric La1.5Sr0.5Ga3O7.25 melilite oxide ion conductor features active interstitial oxygen defects in its pentagonal rings with high mobility. In this study, electron localization function calculated by density functional theory indicated that the interstitial oxide ions located in the pentagonal rings of gallate melilites may be removed and replaced by electron anions that are confined within the pentagonal rings, which would therefore convert the melilite interstitial oxide ion conductor into a zero-dimensional (0D) electride. The more active interstitial oxide ions, compared to the framework oxide ions, make the La1.5Sr0.5Ga3O7.25 melilite structure more reducible by CaH2 using topotactic reduction, in contrast to the hardly reducible nature of parent LaSrGa3O7. The topotactic reduction enhances the bulk electronic conduction (σ ∼ 0.003 S/cm at 400 °C) by ∼ 1 order of magnitude for La1.5Sr0.5Ga3O7.25. The oxygen loss in the melilite structure was verified and most likely took place on the active interstitial oxide ions. The identified confinement space for electronic anions in melilite interstitial oxide ion conductors presented here provides a strategy to access inorganic electrides from interstitial oxide ion conductor electrolytes.

In vivo effectiveness of carbonated calcium-deficient hydroxyapatite-coated activated carbon fiber cloth on bone regeneration.

We have previously shown that activated carbon fiber cloth (ACC) either uncoated or coated with carbonated calcium-deficient hydroxyapatite (CDA), namely ACC and ACC/CDA, were biocompatible in vitro with human osteoblasts. Here we hypothesized that ACC and ACC/CDA could be used as tissue patches in vivo to accelerate wounded bone healing. In a model of rat femoral defect, we have compared spontaneous cortical bone regeneration with regeneration in the presence of ACC and ACC/CDA patches. At Day 7, 14, and 21, bone formation was evaluated using microcomputed tomography, magnetic resonance imaging, and histological analysis. Our results demonstrate first that these ACC tissues are highly biocompatible in vivo, and second that ACC/CDA patches apposition results in the acceleration of bone reconstruction due to a guiding action of the ACC fibers and an osteogenic effect of the CDA phase. We guess that this approach may represent a valuable strategy to accelerate bone regeneration in human.

Complementary Nuclear Magnetic Resonance-Based Metabolomics Approaches for Glioma Biomarker Identification in a Drosophila melanogaster Model.

Human malignant gliomas are the most common type of primary brain tumor. Composed of glial cells and their precursors, they are aggressive and highly invasive, leading to a poor prognosis. Due to the difficulty of surgically removing tumors and their resistance to treatments, novel therapeutic approaches are needed to improve patient life expectancy and comfort. Drosophila melanogaster is a compelling genetic model to better understanding human neurological diseases owing to its high conservation in signaling pathways and cellular content of the brain. Here, glioma has been induced in Drosophila by co-activating the epidermal growth factor receptor and the phosphatidyl-inositol-3 kinase signaling pathways. Complementary nuclear magnetic resonance (NMR) techniques were used to obtain metabolic profiles in the third instar larvae brains. Fresh organs were directly studied by 1H high resolution-magic angle spinning (HR-MAS) NMR, and brain extracts were analyzed by solution-state 1H-NMR. Statistical analyses revealed differential metabolic signatures, impacted metabolic pathways, and glioma biomarkers. Each method was efficient to determine biomarkers. The highlighted metabolites including glucose, myo-inositol, sarcosine, glycine, alanine, and pyruvate for solution-state NMR and proline, myo-inositol, acetate, and glucose for HR-MAS show very good performances in discriminating samples according to their nature with data mining based on receiver operating characteristic curves. Combining results allows for a more complete view of induced disturbances and opens the possibility of deciphering the biochemical mechanisms of these tumors. The identified biomarkers provide a means to rebalance specific pathways through targeted metabolic therapy and to study the effects of pharmacological treatments using Drosophila as a model organism.

Iterative baseline correction algorithm for dead time truncated one-dimensional solid-state MAS NMR spectra.

We present an algorithm suitable for automatically correcting rolling baseline coming from time-domain truncation induced by the dead time in pulse-acquire one-dimensional MAS NMR spectra. It relies on an iterative estimation of the baseline restricted in the time-domain by the dead time duration combined with a histogram filter allowing adaptive selection of the baseline points. This method does not make any assumption regarding the NMR resonances line shapes or widths and does not modify the acquired free induction decay points. This makes it suitable for accurate deconvolution and quantification of single-pulse MAS NMR spectra. The baseline correction accuracy is evaluated on synthetic solid-state spectra of 19F, 71Ga, and 23Na by comparing the fitted baseline to the theoretical one. The versatility of the algorithm is also exemplified on three additional solid-state spectra of 23Na and 71Ga. The algorithm is made available to the community through a user-friendly standalone Matlab® application.

Atomic Insights into Aluminium-Ion Insertion in Defective Anatase for Batteries.

Aluminium batteries constitute a safe and sustainable high-energy-density electrochemical energy-storage solution. Viable Al-ion batteries require suitable electrode materials that can readily intercalate high-charge Al3+ ions. Here, we investigate the Al3+ intercalation chemistry of anatase TiO2 and how chemical modifications influence the accommodation of Al3+ ions. We use fluoride- and hydroxide-doping to generate high concentrations of titanium vacancies. The coexistence of these hetero-anions and titanium vacancies leads to a complex insertion mechanism, attributed to three distinct types of host sites: native interstitial sites, single vacancy sites, and paired vacancy sites. We demonstrate that Al3+ induces a strong local distortion within the modified TiO2 structure, which affects the insertion properties of the neighbouring host sites. Overall, specific structural features induced by the intercalation of highly polarising Al3+ ions should be considered when designing new electrode materials for polyvalent batteries.

Spatially-resolved metabolic profiling of living Drosophila in neurodegenerative conditions using 1H magic angle spinning NMR.

Drosophila flies are versatile animal models for the study of gene mutations in neuronal pathologies. Their small size allows performing in vivo Magic Angle Spinning (MAS) experiments to obtain high-resolution 1H nuclear magnetic resonance (NMR) spectra. Here, we use spatially-resolved 1H high-resolution MAS NMR to investigate in vivo metabolite contents in different segments of the fly body. A comparative study of metabolic changes was performed for three neurodegenerative disorders: two cell-specific neuronal and glial models of Huntington disease (HD) and a model of glutamate excitotoxicity. It is shown that these pathologies are characterized by specific and sometimes anatomically localized variations in metabolite concentrations. In two cases, the modifications of 1H MAS NMR spectra localized in fly heads were significant enough to allow the creation of a predictive model.

X-ray Diffraction, NMR Studies, and DFT Calculations of the Room and High Temperature Structures of Rubidium Cryolite, Rb3AlF6.

A crystallographic approach incorporating multinuclear high field solid state NMR (SSNMR), X-ray structure determinations, TEM observation, and density functional theory (DFT) was used to characterize two polymorphs of rubidium cryolite, Rb3AlF6. The room temperature phase was found to be ordered and crystallizes in the Fddd (no. 70) space group with a = 37.26491(1) Å, b = 12.45405(4) Å, and c = 17.68341(6) Å. Comparison of NMR measurements and computational results revealed the dynamic rotations of the AlF6 octahedra. Using in situ variable temperature MAS NMR measurements, the chemical exchange between rubidium sites was observed. The ß-phase, i.e., high temperature polymorph, adopts the ideal cubic double-perovskite structure, space group Fm3m, with a = 8.9930(2) Å at 600 °C. Additionally, a series of polymorphs of K3AlF6 has been further characterized by high field high temperature SSNMR and DFT computation.

Highly Transparent Fluorotellurite Glass-Ceramics: Structural Investigations and Luminescence Properties.

Crystallization from glass can lead to the stabilization of metastable crystalline phases, which offers an interesting way to unveil novel compounds and control the optical properties of resulting glass-ceramics. Here, we report on a crystallization study of the ZrF4-TeO2 glass system and show that under specific synthesis conditions, a previously unreported Te0.47Zr0.53OxFy zirconium oxyfluorotellurite antiglass phase can be selectively crystallized at the nanometric scale within the 65TeO2-35ZrF4 amorphous matrix. This leads to highly transparent glass-ceramics in both the visible and near-infrared ranges. Under longer heat treatment, the stable cubic ZrTe3O8 phase crystallizes in addition to the previous unreported antiglass phase. The structure, microstructure, and optical properties of 65TeO2-35ZrF4Tm3+-doped glass-ceramics, were investigated in detail by means of X-ray diffraction, scanning and transmission electron microscopies, and 19F, 91Zr, and 125Te NMR, Raman, and photoluminescence spectroscopies. The crystal chemistry study of several single crystals samples by X-ray diffraction evidence that the novel phase, derived from α-UO3 type, corresponds in terms of long-range ordering inside this basic hexagonal/trigonal disordered phase (antiglass) to a complex series of modulated microphases rather than a stoichiometric compound with various superstructures analogous to those observed in the UO3-U3O8 subsystem. These results highlight the peculiar disorder-order phenomenon occurring in tellurite materials.

Mechanism of Calcium Incorporation Inside Sol-Gel Silicate Bioactive Glass and the Advantage of Using Ca(OH)2 over Other Calcium Sources.

Calcium is an essential component of osteogenesis and is often required for imparting significant bioactivity to synthetic bone substitutes and, in particular, silicate-based materials. However, the mechanism of calcium incorporation inside sol-gel silicates is poorly understood. In this work, we shed light on the determinant parameters for incorporation of calcium into acid-base-catalyzed sol-gel silicates at ambient temperature: increasing the pH above the isoelectric point of silicic acid and the nature of the calcium counterion in the calcium precursor are found to be the key. Based on our proposed reaction sequence, we were able to compare calcium precursors and select an ideal candidate compound for the synthesis of bioactive glasses (BG) and organic-inorganic hybrids at ambient temperature. Reproducible syntheses and gel times of SiO2-CaO BG were obtained using calcium hydroxide (CH), and we demonstrate its usability in the synthesis of promising BG-polycaprolactone hybrid scaffolds. BG and hybrids prepared with CH were able to form nanocrystalline nonstoichiometric apatite in simulated body fluid. The increased reliability of low-temperature syntheses associated with the use of a stable and inexpensive alkaline-earth precursor are major steps toward the translation of calcium silicate hybrids or other alkaline-earth silicates from bench to clinic.

Insight into the factors influencing NMR parameters in crystalline materials from the KF-YF3 binary system.

Solid state NMR signals are very sensitive to the local environment of the observed nucleus; however, their interpretation is not straightforward. On the other hand, first-principles DFT calculations of NMR parameters can now be applied to periodic compounds to predict NMR parameters. Thus, ab initio calculations can help to interpret the NMR spectra exhibited by complex materials, to assign NMR lines to structural environments, and even to enlighten the environmental factors influencing the NMR parameters for a given nucleus. Both techniques have been applied to crystalline compounds of the KF-YF3 binary system, γ-K3YF6, K2YF5, KYF4, ß-KY2F7 and α-KY3F10, which present a variety of YFn and KFm polyhedra. First, the structure of K2YF5 was refined in the Pnma space group and, for all compounds, atomic positions were optimized by DFT. The 19F, 89Y and 39K NMR spectra have been recorded and the measured NMR parameters are compared to those calculated from the first-principles DFT method, allowing unambiguous assignments of NMR lines to crystallographic sites. Linear correlations between the experimental δiso and calculated σiso values for the three nuclei are used to predict the theoretical 19F spectra of KYF4 (24 F sites) and ß-KY2F7 (19 F sites) as well as the 39K spectrum of KYF4 (6 K sites). For 89Y and 39K, both computational and experimental results show a decrease of the isotropic chemical shift values when the cation coordination number increases. Above all, 89Y isotropic chemical shift values correlate with the number of K atoms present in the Y second coordination sphere. For 19F, the combination of isotropic chemical shift and chemical shift anisotropy allows for distinguishing four kinds of F environments.

Cooperative mechanisms of oxygen vacancy stabilization and migration in the isolated tetrahedral anion Scheelite structure.

Tetrahedral units can transport oxide anions via interstitial or vacancy defects owing to their great deformation and rotation flexibility. Compared with interstitial defects, vacancy-mediated oxide-ion conduction in tetrahedra-based structures is more difficult and occurs rarely. The isolated tetrahedral anion Scheelite structure has showed the advantage of conducting oxygen interstitials but oxygen vacancies can hardly be introduced into Scheelite to promote the oxide ion migration. Here we demonstrate that oxygen vacancies can be stabilized in the BiVO4 Scheelite structure through Sr2+ for Bi3+ substitution, leading to corner-sharing V2O7 tetrahedral dimers, and migrate via a cooperative mechanism involving V2O7-dimer breaking and reforming assisted by synergic rotation and deformation of neighboring VO4 tetrahedra. This finding reveals the ability of Scheelite structure to transport oxide ion through vacancies or interstitials, emphasizing the possibility to develop oxide-ion conductors with parallel vacancy and interstitial doping strategies within the same tetrahedra-based structure type.

Evaluation of Ligands Effect on the Photophysical Properties of Copper Iodide Clusters.

Luminescent materials based on copper complexes are currently receiving increasing attention because of their rich photophysical properties, opening a wide field of applications. The copper iodide clusters formulated [Cu4I4L4] (L = ligand), are particularly relevant for the development of multifunctional materials based on their luminescence stimuli-responsive properties. In this context, controlling and modulating their photophysical properties is crucial and this can only be achieved by thorough understanding of the origin of the optical properties. We thus report here, the comparative study of a series of cubane copper iodide clusters coordinated by different phosphine ligands, with the goal of analyzing the effect of the ligands nature on the photoluminescence properties. The synthesis, structural, and photophysical characterizations along with theoretical investigations of copper iodide clusters with ligands presenting different electronic properties, are described. A method to simplify the analysis of the 31P solid-state NMR spectra is also reported. While clusters with electron-donating groups present classical luminescence properties, the cluster bearing strong electron-withdrawing substituents exhibits original behavior demonstrating a clear influence of the ligands properties. In particular, the electron-withdrawing character induces a decrease in energy of the unoccupied molecular orbitals, that consequently impacts the emission properties. The modification of the luminescence thermochromic properties of the clusters are supported by density functional theory (DFT) calculations. This study demonstrates that the control of the luminescence properties of these compounds can be achieved through modification of the coordinated ligands, nevertheless the role of the crystal packing should not be underestimated.

Phosphonate-Mediated Immobilization of Rhodium/Bipyridine Hydrogenation Catalysts.

RhL2 complexes of phosphonate-derivatized 2,2'-bipyridine (bpy) ligands L were immobilized on titanium oxide particles generated in situ. Depending on the structure of the bipy ligand-number of tethers (1 or 2) to which the phosphonate end groups are attached and their location on the 2,2'-bipyridine backbone (4,4'-, 5,5'-, or 6,6'-positions)-the resulting supported catalysts showed comparable chemoselectivity but different kinetics for the hydrogenation of 6-methyl-5-hepten-2-one under hydrogen pressure. Characterization of the six supported catalysts suggested that the intrinsic geometry of each of the phosphonate-derivatized 2,2'-bipyridines leads to supported catalysts with different microstructures and different arrangements of the RhL2 species at the surface of the solid, which thereby affect their reactivity.

Design and properties of a novel radiopaque injectable apatitic calcium phosphate cement, suitable for image-guided implantation.

An injectable purely apatitic calcium phosphate cement (CPC) was successfully combined to a water-soluble radiopaque agent (i.e., Xenetix® ), to result in an optimized composition that was found to be as satisfactory as poly(methyl methacrylate) (PMMA) formulations used for vertebroplasty, in terms of radiopacity, texture and injectability. For that purpose, the Xenetix dosage in the cement paste was optimized by injection of the radiopaque CPC in human cadaveric vertebrae under classical PMMA vertebroplasty conditions, performed by interventional radiologists familiar with this surgical procedure. When present in the cement paste up to 70 mg I mL-1 , Xenetix did not influence the injectability, cohesion, and setting time of the resulting composite. After hardening of the material, the same observation was made regarding the microstructure, mechanical strength and alpha-tricalcium phosphate to calcium deficient apatite transformation rate. Upon implantation in bone in a small animal model (rat), the biocompatibility of the Xenetix-containing CPC was evidenced. Moreover, an almost quantitative release of the contrast agent was found to occur rapidly, on the basis of in vitro static and dynamic quantitative studies simulating in vivo implantation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2786-2795, 2018.

ZSM-5 Zeolite: Complete Al Bond Connectivity and Implications on Structure Formation from Solid-State NMR and Quantum Chemistry Calculations.

Al site distribution in the structurally complex and industrially important ZSM-5 zeolite is determined by studying the spectroscopic response of Al(OSi)4 units and using a self-consistent combination of up-to-date solid-state NMR correlations (29Si-27Al and 1H-27Al D-HMQC) and quantum chemistry methods (DFT-D). To unravel the driving forces behind specific Al sitting positions, our approach focuses on ZSM-5 containing its more efficient OSDA, tetrapropylammonium.

Local Disorder and Tunable Luminescence in Sr1-x/2Al2-xSixO4 (0.2 ≤ x ≤ 0.5) Transparent Ceramics.

Eu-doped Sr1-x/2Al2-xSixO4 (x = 0.2, 0.4, and 0.5) transparent ceramics have been synthesized by full and congruent crystallization from glasses prepared by aerodynamic levitation and laser-heating method. Structural refinements from synchrotron and neutron powder diffraction data show that the ceramics adopt a 1 × 1 × 2 superstructure compared to the SrAl2O4 hexagonal polymorph. While the observed superstructure reflections indicate a long-range ordering of the Sr vacancies in the structure, 29Si and 27Al solid-state NMR measurements associated with DFT computations reveal a significant degree of disorder in the fully polymerized tetrahedral network. This is evidenced through the presence of Si-O-Si bonds, as well as Si(OAl)4 units at remote distances of the Sr vacancies and Al(OAl)4 units in the close vicinity of Sr vacancies departing from local charge compensation in the network. The transparent ceramics can be doped by europium to induce light emission arising from the volume under UV excitation. Luminescence measurements then reveal the coexistence of Eu2+ and Eu3+ in the samples, thereby allowing tuning the emission color depending on the excitation wavelength and suggesting possible applications such as solid state lighting.