Browsing by Author "Aitken, JB"

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    Chemical alterations to murine brain tissue induced by formation fixation: implications for biospectroscopic imaging and mapping studies of disease pathogenesis
    (Royal Society of Chemistry, 2011-07-21) Hackett, MJ; McQuillan, JA; El-Assaad, F; Aitken, JB; Levina, A; Cohen, DD; Siegele, R; Carter, EA; Grau, GE; Hunt, NH; Lay, PA
    Understanding biochemical mechanisms and changes associated with disease conditions and, therefore, development of improved clinical treatments, is relying increasingly on various biochemical mapping and imaging techniques on tissue sections. However, it is essential to be able to ascertain whether the sampling used provides the full biochemical information relevant to the disease and is free from artefacts. A multi-modal micro-spectroscopic approach, including FTIR imaging and PIXE elemental mapping, has been used to study the molecular and elemental profile within cryofixed and formalin-fixed murine brain tissue sections. The results provide strong evidence that amino acids, carbohydrates, lipids, phosphates, proteins and ions, such as Cl(-) and K(+), leach from tissue sections into the aqueous fixative medium during formalin fixation of the sections. Large changes in the concentrations and distributions of most of these components are also observed by washing in PBS even for short periods. The most likely source of the chemical species lost during fixation is the extra-cellular and intra-cellular fluid of tissues. The results highlight that, at best, analysis of formalin-fixed tissues gives only part of the complete biochemical "picture'' of a tissue sample. Further, this investigation has highlighted that significant lipid peroxidation/oxidation may occur during formalin fixation and that the use of standard histological fixation reagents can result in significant and differential metal contamination of different regions of tissue sections. While a consistent and reproducible fixation method may be suitable for diagnostic purposes, the findings of this study strongly question the use of formalin fixation prior to spectroscopic studies of the molecular and elemental composition of biological samples, if the primary purpose is mechanistic studies of disease pathogenesis.© 2011, Royal Society of Chemistry
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    Diffraction and spectroscopic study of pyrochlores Bi2−xFe1+xSbO7
    (Elsevier, 2014-03-15) Zhou, Q; Blanchard, PER; Kennedy, BJ; Ling, CD; Liu, S; Avdeev, M; Aitken, JB; Tadich, A; Brand, HEA
    The structural and electronic properties of the series Bi2−xFe1+xSbO7 (0 ⩽ x ⩽ 0.6) were investigated using a combination of diffraction and spectroscopy. Synchrotron and neutron diffraction analysis show that Fe3+ cations substitute for Bi3+ onto the A site with increasing x, which was further confirmed by analysis of the Fe K/L-edge X-ray absorption near-edge spectra. The diffraction analysis indicated the presence of displacive disorder along the A2O chains, likely the result of the Bi3+ 6s2 lone pair, as well as non-Vegard-like behaviour of the lattice parameters in the Fe-poor region. Fe K-edge extended X-ray absorption fine-structure analysis of Bi2FeSbO7 confirmed the displacive disorder of the Bi3+ cations as well as Sb5+ and Fe3+ disorder on the B site. © 2013 Elsevier B.V.
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    Investigating the local structure of lanthanoid hafnates Ln2Hf2O7 via diffraction and spectroscopy
    (American Chemical Society, 2013-02-07) Blanchard, PER; Liu, S; Kennedy, BJ; Ling, CD; Avdeev, M; Aitken, JB; Cowie, BCC; Tadich, A
    The lanthanoid hafnates Ln2Hf2O7 (Ln = La, Pr, Nd, Sm?Tm) were studied using a combination of synchrotron X-ray and neutron powder diffraction together with X-ray absorption and Raman spectroscopy. Spectroscopic methods revealed a gradual increase in disorder from the ideal pyrochlore structure to the defect fluorite structure as the size of the Ln cation increases. The line shape of the Hf L3-edge X-ray absorption near edge spectra which is sensitive to the local coordination environment changed with increasing disorder. The general line shape of the O K-edge XANES and Raman spectra also indicated an increase in disorder across the Ln2Hf2O7 series. Differences in the diffraction and spectroscopy analysis reflect the greater sensitivity of the spectroscopy techniques to local ordering. © 2013, American Chemical Society
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    Investigation of the mouse cerebellum using STIM and mu-PIXE spectrometric and FTIR spectroscopic mapping and imaging
    (Elsevier, 2011-10-15) Hackett, MJ; Siegele, R; El-Assaad, F; McQuillan, JA; Aitken, JB; Carter, EA; Grau, GE; Hunt, NH; Cohen, DD; Lay, PA
    The cerebral biochemistry associated with the development of many neurological diseases remains poorly understood. In particular, incomplete understanding of the mechanisms through which vascular inflammation manifests in tissue damage and altered brain function is a significant hindrance to the development of improved patient therapies. To this extent, a combination of spectrometric/spectroscopic mapping/imaging methods with an inherent ability to provide a wealth of biochemical and physical information have been investigated to understand further the pathogenesis of brain disease. In this study, proton-induced X-ray emission (PIXE) mapping was combined with scanning transmission ion microscopy (STIM) mapping and Fourier-transform infrared (FTIR) imaging of the same tissue sample to study directly the composition of the murine (mouse) cerebellum. The combination of the elemental, density and molecular information provided by these techniques enabled differentiation between four specific tissue types within the murine cerebellum (grey matter, white matter, molecular layer and micro blood vessels). The results presented are complementary, multi-technique measurements of the same tissue sample. They show elemental, density and molecular differences among the different tissue types. (C) 2011 Elsevier B.V.
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    Key role of Bismuth in the magnetoelastic transitions of Ba3BiIr2O9 and Ba3BiRu2O9 as revealed by chemical doping
    (America Chemical Society, 2013-12-24) Blanchard, PER; Huang, ZX; Kennedy, BJ; Liu, S; Miiller, W; Reynolds, EM; Zhou, QD; Avdeev, M; Zhang, ZM; Aitken, JB; Cowie, BCC; Jang, LY; Tan, TT; Li, S; Ling, CD
    The key role played by bismuth in an average intermediate oxidation state in the magnetoelastic spin-gap compounds Ba3BiRu2O9 and Ba3BiIr2O9 has been confirmed by systematically replacing bismuth with La3+ and Ce4+. Through a combination of powder diffraction (neutron and synchrotron), X-ray absorption spectroscopy, and magnetic properties measurements, we show that Ru/Ir cations in Ba3BiRu2O9 and Ba3BiIr2O9 have oxidation states between +4 and +4.5, suggesting that Bi cations exist in an unusual average oxidation state intermediate between the conventional +3 and +5 states (which is confirmed by the Bi L3-edge spectrum of Ba3BiRu2O9). Precise measurements of lattice parameters from synchrotron diffraction are consistent with the presence of intermediate oxidation state bismuth cations throughout the doping ranges. We find that relatively small amounts of doping (∼10 at%) on the bismuth site suppress and then completely eliminate the sharp structural and magnetic transitions observed in pure Ba3BiRu2O9 and Ba3BiIr2O9, strongly suggesting that the unstable electronic state of bismuth plays a critical role in the behavior of these materials. © 2013 American Chemical Society.
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    Mechanisms of murine cerebral malaria: multimodal imaging of altered cerebral metabolism and protein oxidation at hemorrhage sites
    (American Association for the Advancement of Science, 2015-12-18) Hackett, MJ; Aitken, JB; El-Assaad, F; McQuillan, JA; Carter, EA; Ball, HJ; Tobin, MJ; Paterson, DJ; de Jonge, MD; Siegele, R; Cohen, DD; Vogt, S; Grau, GE; Hunt, NH; Lay, PA
    Using a multimodal biospectroscopic approach, we settle several long-standing controversies over the molecular mechanisms that lead to brain damage in cerebral malaria, which is a major health concern in developing countries because of high levels of mortality and permanent brain damage. Our results provide the first conclusive evidence that important components of the pathology of cerebral malaria include peroxidative stress and protein oxidation within cerebellar gray matter, which are colocalized with elevated nonheme iron at the site of microhemorrhage. Such information could not be obtained previously from routine imaging methods, such as electron microscopy, fluorescence, and optical microscopy in combination with immunocytochemistry, or from bulk assays, where the level of spatial information is restricted to the minimum size of tissue that can be dissected. We describe the novel combination of chemical probe–free, multimodal imaging to quantify molecular markers of disturbed energy metabolism and peroxidative stress, which were used to provide new insights into understanding the pathogenesis of cerebral malaria. In addition to these mechanistic insights, the approach described acts as a template for the future use of multimodal biospectroscopy for understanding the molecular processes involved in a range of clinically important acute and chronic (neurodegenerative) brain diseases to improve treatment strategies. 2015 © The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. Distributed under a Creative Commons Attribution Non Commercial Licence 4.0 (CC BY-NC).
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    Synthesis, structural and magnetic studies of the double perovskites Ba2CeMO6 (M = Ta, Nb)
    (American Chemical Society, 2012-07-16) Zhou, QD; Blanchard, PER; Kennedy, BJ; Reynolds, EM; Zhang, Z; Miiller, W; Aitken, JB; Avdeev, M; Jang, LY; Kimpton, JA
    Two Ce(3+) containing double perovskites Ba(2)CeMO(6) (M = Nb and Ta) have been prepared through the use of mildly reducing conditions, and the Ce valence state has been shown to be +3 through Ce L-edge X-ray absorption measurements. Both oxides adopt a monoclinic structure in I2/m at room temperature and undergo two phase transitions upon heating, a discontinuous I2/m -> R (3) over bar and a continuous R (3) over bar -> Fm (3) over barm transition. Analysis of the first order I2/m -> R (3) over bar transitions is impeded by the complex peak shapes and diffuse scattering evident in the synchrotron powder diffraction data because of domain wall effects. © 2012, American Chemical Society.
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    X-ray absorption near edge structure and crystallographic studies of the mixed valence oxides CaRu1-xMnxO3
    (American Chemical Society, 2009-09-22) Zhou, QD; Kennedy, BJ; Zhang, Z; Jang, LY; Aitken, JB
    Eleven members of the series CaRu1-xMnxO3 With 0 <= x <= 1 have been prepared and characterized using a combination of Mn K-edge and Ru L-3,L-2-edge X-ray absorption near edge structure spectroscopy and high resolution synchrotron X-ray powder diffraction. A complex distribution of four Mn3+/4+ and Ru4+/5+ oxidation states was observed and quantified. When incorporated into CaRuO3 at low doping levels, the Mn is present as Mn3+ and Mn4+ with the nominal Mn oxidation state increasing with x (from 3.6 at x = 0.1 to 4 at x = 1). The Ru exists predominantly as Ru5+ in CaMnO3 with the nominal Ru valency as 4.8 at x = 0.9. The formation of Mn3+/4+-Ru4+/5+ redox pairs accounts for the unusual chemical composition dependence of the cell volume, evident from the diffraction studies. The coexistence of mixed valence redox pairs is also believed to contribute to the phase separation observed at 0.1 <= x <= 0.6. © 2009, American Chemical Society