Search

Your search keyword '"Wright, Adrian J."' showing total 131 results
Start Over Author "Wright, Adrian J."
131 results on '"Wright, Adrian J."'

20. From crystalline to amorphous calcium pyrophosphates:a solid state Nuclear Magnetic Resonance perspective

Author

Gras, Pierre, Baker, Annabelle, Combes, Christèle, Rey, Christian, Sarda, Stéphanie, Wright, Adrian J., Smith, Mark Edmund, Hanna, John V., Gervais, Christel, Laurencin, Danielle, Bonhomme, Christian, Gras, Pierre, Baker, Annabelle, Combes, Christèle, Rey, Christian, Sarda, Stéphanie, Wright, Adrian J., Smith, Mark Edmund, Hanna, John V., Gervais, Christel, Laurencin, Danielle, and Bonhomme, Christian

Abstract

Hydrated calcium pyrophosphates (CPP, Ca2P2O7·nH2O) are a fundamental family of materials among osteoarticular pathologic calcifications. In this contribution, a comprehensive multinuclear NMR (Nuclear Magnetic Resonance) study of four crystalline and two amorphous phases of this family is presented. 1H, 31P and 43Ca MAS (Magic Angle Spinning) NMR spectra were recorded, leading to informative fingerprints characterizing each compound. In particular, different 1H and 43Ca solid state NMR signatures were observed for the amorphous phases, depending on the synthetic procedure used. The NMR parameters of the crystalline phases were determined using the GIPAW (Gauge Including Projected Augmented Wave) DFT approach, based on first-principles calculations. In some cases, relaxed structures were found to improve the agreement between experimental and calculated values, demonstrating the importance of proton positions and pyrophosphate local geometry in this particular NMR crystallography approach. Such calculations serve as a basis for the future ab initio modeling of the amorphous CPP phases. Statement of significance The general concept of NMR crystallography is applied to the detailed study of calcium pyrophosphates (CPP), whether hydrated or not, and whether crystalline or amorphous. CPP are a fundamental family of materials among osteoarticular pathologic calcifications. Their prevalence increases with age, impacting on 17.5% of the population after the age of 80. They are frequently involved or associated with acute articular arthritis such as pseudogout. Current treatments are mainly directed at relieving the symptoms of joint inflammation but not at inhibiting CPP formation nor at dissolving these crystals. The combination of advanced NMR techniques, modeling and DFT based calculation of NMR parameters allows new original insights in the detailed structural description of this important class of biomaterials.

Published
2016

22. 87Sr,119Sn,127I Single and {1H/19F}-Double Resonance Solid-State NMR Experiments: Application to Inorganic Materials and Nanobuilding Blocks

Author

Laurencin, Danielle, primary, Ribot, François, additional, Gervais, Christel, additional, Wright, Adrian J., additional, Baker, Annabelle R., additional, Campayo, Lionel, additional, Hanna, John V., additional, Iuga, Dinu, additional, Smith, Mark E., additional, Nedelec, Jean‐Marie, additional, Renaudin, Guillaume, additional, and Bonhomme, Christian, additional

Published
2016
Full Text
View/download PDF

23. Synthesis, structural and magnetic characterisation of the fully fluorinated compound 6H-BaFeO2F

Author

Clemens, O, Wright, Adrian J., Berry, Frank J., Smith, Ronald, and Slater, Peter.R.

Subjects
QC Physics, QD Chemistry
Abstract

The compound 6H-BaFeO2F (P63/mmc) was synthesised by the low temperature fluorination of 6H-BaFeO3-d using polyvinylidenedifluoride (PVDF) as a fluorination agent. Structural characterisation by XRD and NPD suggests that the local positions of the oxygen and fluorine atoms vary with no evidence for ordering on the anion sites. This compound shows antiferromagnetic ordering at room temperature with antiparallel alignment of the magnetic moments along the c-axis. The use of PVDF also allows the possibility of tuning the fluorine content in materials of composition 6H-BaFeO3-dFy to any value of 0 < y ≤ 1. In addition, the oxygen content, and therefore the iron oxidation state, can be tuned by applying different partial pressures of oxygen during the reaction.

Published
2013

26. A cohesive premixed monetite biocement.

Author

Cox, Sophie C., Patel, Sarika, Gbureck, Uwe, Wright, Adrian J., and Grover, Liam M.

Subjects
SODIUM alginate, COHESION, CALCIUM phosphate, STRENGTH of materials, METHYLENE blue
Abstract

Sodium alginate was successfully utilized to improve cohesion and limit particulate debris of a premixed calcium phosphate cement ( pCPC) that following the exchange of water set to form monetite. Modified pastes using glycerol and 2 wt% alginate exhibited initial and final setting times of 60 ± 9 and 1355 ± 105 minutes, respectively. Despite these setting times being significantly longer than clinically recommended the improved washout resistance of this formulation would allow for wound closure during setting. Set monetite pastes exhibited a maximum compressive strength of 8.6 ± 3.5 MPa with a corresponding porosity of 59% compared to 15.6 ± 5.8 MPa and 25% for the unmodified aqueous brushite cement. Storage of the pCPC paste at 4°C for 14 days was shown to significantly ( P<0.05) increase the compressive strength of the harden matrix (13.2 ± 1.5 MPa), however, subsequent deterioration was observed after 90 days storage. Methylene blue was utilized to visualize perfusion into the matrix during setting, demonstrating that the use of glycerol altered mass transport and ultimately shifted the crystallization kinetics in favor of monetite. Samples >20 mm did not reach full saturation after 10 days of immersion, which for the first time suggests an upper volume limit that will form a homogeneous cement highlighting an important consideration for clinical translation of pCPCs. [ABSTRACT FROM AUTHOR]

Published
2017
Full Text
View/download PDF

29. Crystallographic and Magnetic Structure of the Perovskite-Type Compound BaFeO2.5: Unrivaled Complexity in Oxygen Vacancy Ordering

Author

Clemens, Oliver, primary, Gröting, Melanie, additional, Witte, Ralf, additional, Perez-Mato, J. Manuel, additional, Loho, Christoph, additional, Berry, Frank J., additional, Kruk, Robert, additional, Knight, Kevin S., additional, Wright, Adrian J., additional, Hahn, Horst, additional, and Slater, Peter R., additional

Published
2014
Full Text
View/download PDF

30. Enhanced stability and local structure in biologically relevant amorphous materials containing pyrophosphate

Author

Slater, Colin, Laurencin, Danielle, Burnell, Victoria, Smith, Mark E., Grover, Liam M., Hriljac, Joseph A., Wright, Adrian J., Slater, Colin, Laurencin, Danielle, Burnell, Victoria, Smith, Mark E., Grover, Liam M., Hriljac, Joseph A., and Wright, Adrian J.

Abstract

There is increasing evidence that amorphous inorganic materials play a key role in biomineralisation in many organisms, however the inherent instability of synthetic analogues in the absence of the complex in vivo matrix limits their study and clinical exploitation. To address this, we report here an approach that enhances long-term stability to >1 year of biologically relevant amorphous metal phosphates, in the absence of any complex stabilisers, by utilising pyrophosphates (P2O74−); species themselves ubiquitous in vivo. Ambient temperature precipitation reactions were employed to synthesise amorphous Ca2P2O7.nH2O and Sr2P2O7.nH2O (3.8 < n < 4.2) and their stability and structure were investigated. Pair distribution functions (PDF) derived from synchrotron X-ray data indicated a lack of structural order beyond 8 Å in both phases, with this local order found to resemble crystalline analogues. Further studies, including 1H and 31P solid state NMR, suggest the unusually high stability of these purely inorganic amorphous phases is partly due to disorder in the P–O–P bond angles within the P2O7 units, which impede crystallization, and to water molecules, which are involved in H-bonds of various strengths within the structures and hamper the formation of an ordered network. In situ high temperature powder X-ray diffraction data indicated that the amorphous nature of both phases surprisingly persisted to 450 °C. Further NMR and TGA studies found that above ambient temperature some water molecules reacted with P2O7 anions, leading to the hydrolysis of some P–O–P linkages and the formation of HPO42− anions within the amorphous matrix. The latter anions then recombined into P2O7 ions at higher temperatures prior to crystallization. Together, these findings provide important new materials with unexplored potential for enzyme-assisted resorption and establish factors crucial to isolate further stable amorphous inorganic materials.

Published
2011

33. Synthesis, structural characterisation and proton conduction of two new hydrated phases of barium ferrite BaFeO2.5−x(OH)2x.

Author

Knöchel, Patrick L., Loho, Christoph, Hahn, Horst, Clemens, Oliver, Keenan, Philip J., Wright, Adrian J., Slater, Peter R., Reitz, Christian, Witte, Ralf, and Knight, Kevin S.

Abstract

Materials exhibiting mixed electronic and proton conductivity are of great interest for applications ranging from electrodes for proton conducting ceramic fuel cells to hydrogen separation membranes. In this work, we report a detailed investigation of the effect of water incorporation in BaFeO2.5 on the structure and conductivity. BaFeO2.5 is shown to be topochemically transformed to two different hydrated modifications, low-water (LW-) and high-water (HW-) BaFeO2.5. A combined analysis of neutron and X-ray diffraction data was used to determine the crystal structure of LW-BaFeO2.5 (BaFeO2.33(OH)0.33), which shows a unique ordering pattern of anion vacancies for perovskite type compounds, with structural relaxations around vacancies being similar to the chemically similar compound BaFeO2.33F0.33. Approximate proton positions were determined using the bond valence method. Conductivity studies of hydrated and pure BaFeO2.5 (with additional comparison to oxidized BaFeO2.5) show a significant enhancement of the conductivity on water incorporation, which can be attributed to proton conductivity. This is the first report of significant grain proton conduction (∼10−6 to 10−7 S cm−1) in an iron based perovskite. Water uptake is further shown to be completely reversible, with reformation of BaFeO2.5 when heating the compound to temperatures above ∼450 K under Ar. [ABSTRACT FROM AUTHOR]

Published
2016
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results