142 results on '"Ray Dupree"'
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2. Hemocyanin facilitates lignocellulose digestion by wood-boring marine crustaceans
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Katrin Besser, Graham P. Malyon, William S. Eborall, Giovanni Paro da Cunha, Jefferson G. Filgueiras, Adam Dowle, Lourdes Cruz Garcia, Samuel J. Page, Ray Dupree, Marcelo Kern, Leonardo D. Gomez, Yi Li, Luisa Elias, Federico Sabbadin, Shaza E. Mohamad, Giovanna Pesante, Clare Steele-King, Eduardo Ribeiro de Azevedo, Igor Polikarpov, Paul Dupree, Simon M. Cragg, Neil C. Bruce, and Simon J. McQueen-Mason
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Science - Abstract
Marine woodborers can digest woody biomass without the help of gut microbiota but the mechanism has remained unclear. Here, the authors provide evidence that the woodborer’s respiratory protein hemocyanin plays a central role in wood digestion and may offer a route toward biorefining of woody plant biomass.
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- 2018
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3. Folding of xylan onto cellulose fibrils in plant cell walls revealed by solid-state NMR
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Thomas J. Simmons, Jenny C. Mortimer, Oigres D. Bernardinelli, Ann-Christin Pöppler, Steven P. Brown, Eduardo R. deAzevedo, Ray Dupree, and Paul Dupree
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Science - Abstract
The polysaccharide xylan binds to cellulose microfibrils in the plant cell wall, but the nature of this interaction remains unclear. Here Simmonset al. show that while xylan forms a threefold helical screw in solution it forms a twofold screw to bind cellulose microfibrils in the plant cell wall.
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- 2016
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4. Golgi-localized STELLO proteins regulate the assembly and trafficking of cellulose synthase complexes in Arabidopsis
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Yi Zhang, Nino Nikolovski, Mathias Sorieul, Tamara Vellosillo, Heather E. McFarlane, Ray Dupree, Christopher Kesten, René Schneider, Carlos Driemeier, Rahul Lathe, Edwin Lampugnani, Xiaolan Yu, Alexander Ivakov, Monika S. Doblin, Jenny C. Mortimer, Steven P. Brown, Staffan Persson, and Paul Dupree
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Science - Abstract
Cellulose is produced in plants by cellulose synthase complexes (CSCs) that are assembled in the endomembrane system and then trafficked to the plasma membrane. Here Zhang et al. show that the Golgi-localized STELLO1 and 2 proteins are required for the proper assembly and distribution of CSCs in plant cells.
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- 2016
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5. Synthesis and structural characterisation of solid titanium(<scp>iv</scp>) phosphate materials by means of X-ray absorption and NMR spectroscopy
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Daniela Rusanova-Naydenova, Mylène Trublet, Wantana Klysubun, Chanakan Cholsuk, Dinu Iuga, Ray Dupree, Oleg N. Antzutkin, and Ingmar Persson
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TP ,Inorganic Chemistry ,QD - Abstract
Solid titanium phosphate, TiP, materials hold great promise for wastewater treatment for removal of metal ions and complexes. A series of TiP materials, synthesised at mild conditions and short reaction times, have been structurally characterised using solid-state X-ray absorption spectroscopy, phosphorus and titanium K edge XANES and EXAFS, and P-31 and Ti-47/49 NMR spectroscopy. The titanium K edge EXAFS data of alpha-Ti(HPO4)(2)center dot H2O (alpha-TiP) revealed octahedral coordination of oxygens around titanium. Repeated washing of primary beta-/gamma-TiP with hydrochloric acid results in formation of a weakly ordered solid, TiO(OH)(H2PO4)center dot H2O, TiP1-H. The structure of TiP1-H is shown by Ti EXAFS to be a titanyl compound, containing a short Ti=O bond. The analogous data for linked titanium phosphate compounds (LTP) disclosed that inter-linkage occurs between alpha-TiP and titanyl phosphate units, supported by P-31-P-31 NOESY NMR data. Ti-47/49 NMR and Ti pre-edge XANES show evidence of two different titanium environments in LTP, one very similar to that observed in TiP1-H and a second more symmetric octahedral environment. Data are discussed in terms of induced acidic hydrolyses of titanium(IV) and phosphate counterpart during washings with hydrochloric acid and water. A straightforward relation between synthesis parameters/post synthetic treatment and structural re-arrangement in the materials is established.
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- 2022
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6. Importance of Water in Maintaining Softwood Secondary Cell Wall Nanostructure
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Ray Dupree, Caroline S. Pereira, Mathias Sorieul, Rosalie Cresswell, Stefan J. Hill, Paul Dupree, Munir S. Skaf, Steven P. Brown, Brown, Steven P [0000-0003-2069-8496], Skaf, Munir S [0000-0001-7485-1228], Sorieul, Mathias [0000-0001-7326-3707], Dupree, Paul [0000-0001-9270-6286], Hill, Stefan [0000-0003-4452-9152], and Apollo - University of Cambridge Repository
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Softwood ,Nanostructure ,Polymers and Plastics ,Bioengineering ,02 engineering and technology ,010402 general chemistry ,TS ,7. Clean energy ,01 natural sciences ,Article ,Biomaterials ,Cell wall ,chemistry.chemical_compound ,Cell Wall ,Materials Chemistry ,medicine ,Dehydration ,Cellulose ,chemistry.chemical_classification ,QK ,Water ,Polymer ,021001 nanoscience & nanotechnology ,medicine.disease ,Xylan ,Nanostructures ,0104 chemical sciences ,TA ,chemistry ,Biophysics ,Xylans ,0210 nano-technology ,Secondary cell wall - Abstract
Water is one of the principal constituents by mass of living plant cell walls. However, its role and interactions with secondary cell wall polysaccharides and the impact of dehydration and subsequent rehydration on the molecular architecture are still to be elucidated. This work combines multidimensional solid-state 13C magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) with molecular dynamics modeling to decipher the role of water in the molecular architecture of softwood secondary cell walls. The proximities between all main polymers, their molecular conformations, and interaction energies are compared in never-dried, oven-dried, and rehydrated states. Water is shown to play a critical role at the hemicellulose–cellulose interface. After significant molecular shrinkage caused by dehydration, the original molecular conformation is not fully recovered after rehydration. The changes include xylan becoming more closely and irreversibly associated with cellulose and some mannan becoming more mobile and changing conformation. These irreversible nanostructural changes provide a basis for explaining and improving the properties of wood-based materials.
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- 2021
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7. Lead silicate glass structure: New insights from diffraction and modeling of probable lone pair locations
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Steve Feller, O. L. G. Alderman, Ray Dupree, Alex C. Hannon, Adam J. Vitale, Gloria J. Lehr, and Diane Holland
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Materials science ,Neutron diffraction ,Square pyramidal molecular geometry ,Silicate ,Amorphous solid ,law.invention ,Bond length ,Crystallography ,chemistry.chemical_compound ,chemistry ,law ,Covalent bond ,Materials Chemistry ,Ceramics and Composites ,QD ,Crystallization ,Lone pair - Abstract
Structures of binary PbO‐SiO2 glasses have been studied in detail over the compositional range 35 to 80 mol% PbO using high‐resolution neutron diffraction, high‐energy X‐ray diffraction, static 207Pb NMR, and structural modeling. The changes in the local environment of Pb(II) are subtle; it has a low coordination to oxygen (∼3 to 4) plus a stereochemically active electron lone pair and, thus, behaves as a glass network forming (or intermediate) cation over the entire composition range. This conclusion contradicts previous reports that Pb(II) is a network modifier at low concentrations, and is supported by an analysis of lead and alkaline earth silicate glass molar volumes. The Pb‐O peak bond length shortens by 0.04 Å with increasing PbO content, indicating stronger, more covalent bonding, and consistent with an increase in the number of short (≤ 2.70 Å) Pb‐O bonds, from 3.3 to 3.6. This is accompanied by increased axial symmetry of the Pb(II) sites, and is interpreted as a gradual transition toward square pyramidal [PbO4] sites such as those found in crystalline PbO polymorphs. An attendant decrease in the periodicity associated with the first sharp diffraction peak (FSDP) toward that of β‐PbO, accompanied by increases in the correlation lengths associated with the plumbite network (FSDP) and silicate anions (neutron prepeak), provides evidence of increased intermediate‐range order and has implications for the glass forming limit imposed by crystallization. Pb(II) electron lone pairs occupy the natural voids within the silicate network at low PbO contents, while at high PbO contents they aggregate to create voids that form part of the plumbite network, analogous to the open channels in Pb11Si3O17 and the layered structures of α‐ and β‐PbO. Si‐O and Pb‐O bond lengths have been correlated with 29Si and 207Pb NMR chemical shifts, respectively. This is the first time that such correlations have been demonstrated for glasses and attests to the accuracy with which pulsed neutron total scattering can measure average bond lengths.
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- 2021
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8. Golgi-localized putative S-adenosyl methionine transporters required for plant cell wall polysaccharide methylation
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Henry Temple, Pyae Phyo, Weibing Yang, Jan J. Lyczakowski, Alberto Echevarría-Poza, Igor Yakunin, Juan Pablo Parra-Rojas, Oliver M. Terrett, Susana Saez-Aguayo, Ray Dupree, Ariel Orellana, Mei Hong, Paul Dupree, Temple, Henry [0000-0002-0415-6403], Yakunin, Igor [0000-0002-9705-6312], Hong, Mei [0000-0001-5255-5858], Dupree, Paul [0000-0001-9270-6286], and Apollo - University of Cambridge Repository
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Arabidopsis Proteins ,plant transporters ,QH ,QK ,Arabidopsis ,Golgi Apparatus ,Membrane Transport Proteins ,Plant Science ,Methylation ,QP ,Methionine ,Cell Wall ,Polysaccharides ,cell wall ,Pectins ,QD - Abstract
Polysaccharide methylation, especially that of pectin, is a common and important feature of land plant cell walls. Polysaccharide methylation takes place in the Golgi apparatus and therefore relies on the import of S-adenosyl methionine (SAM) from the cytosol into the Golgi. However, so far, no Golgi SAM transporter has been identified in plants. Here we studied major facilitator superfamily members in Arabidopsis that we identified as putative Golgi SAM transporters (GoSAMTs). Knockout of the two most highly expressed GoSAMTs led to a strong reduction in Golgi-synthesized polysaccharide methylation. Furthermore, solid-state NMR experiments revealed that reduced methylation changed cell wall polysaccharide conformations, interactions and mobilities. Notably, NMR revealed the existence of pectin 'egg-box' structures in intact cell walls and showed that their formation is enhanced by reduced methyl esterification. These changes in wall architecture were linked to substantial growth and developmental phenotypes. In particular, anisotropic growth was strongly impaired in the double mutant. The identification of putative transporters involved in import of SAM into the Golgi lumen in plants provides new insights into the paramount importance of polysaccharide methylation for plant cell wall structure and function.
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- 2022
9. Eudicot primary cell wall glucomannan is related in synthesis, structure and function to xyloglucani
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Li Yu, Yoshihisa Yoshimi, Rosalie Cresswell, Raymond Wightman, Jan J. Lyczakowski, Louis F.L. Wilson, Konan Ishida, Katherine Stott, Xiaolan Yu, Stephan Charalambous, Joel Wurman-Rodrich, Ray Dupree, Oliver M. Terrett, Steven P. Brown, Henry Temple, Kristian B.R.M. Krogh, and Paul Dupree
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The functional differences between plant cell wall hemicelluloses such as glucomannan, xylan and xyloglucan (XyG) remain unclear. These polysaccharides influence assembly and properties of the wall, perhaps by interacting with cellulose to affect the deposition and bundling of the fibrils. As the most abundant hemicellulose, XyG is considered important in eudicot primary cell walls (PCWs), but plants devoid of XyG show relatively mild phenotypes. We report here that a patterned β-galactoglucomannan (β-GGM) is widespread in PCW of eudicots and shows remarkable similarities to XyG. The sugar linkages forming the backbone and side chains of β-GGM are analogous to those that make up XyG, and moreover, these linkages are formed by glycosyltransferases from the same CAZy families. Solid-state NMR indicated that β-GGM shows low mobility in the cell wall, consistent with interaction with cellulose. Although Arabidopsis β-GGM synthesis mutants show no obvious growth defects, genetic crosses between β-GGM and XyG mutants produce exacerbated phenotypes compared to XyG mutants. These findings demonstrate a related role of these two similar but distinct classes of hemicelluloses in PCWs. This work will provide new avenues to study the roles of both β-GGM and XyG in PCWs.One sentence summaryPatterned β-GGM resembles xyloglucan in structure, biosynthesis and function.
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- 2022
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10. Discovery of putative Golgi S-Adenosyl methionine transporters reveals the importance of plant cell wall polysaccharide methylation
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Mei Hong, Pyae Phyo, Oliver M. Terrett, Henry Temple, Ray Dupree, Paul Dupree, Ariel Orellana, Susana Saez-Aguayo, Yakunin I, Jan J. Lyczakowski, Weibing Yang, Echevarria-Poza A, and Juan Pablo Parra-Rojas
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Methionine ,biology ,Methylation ,Golgi apparatus ,biology.organism_classification ,Golgi lumen ,Major facilitator superfamily ,Cell wall ,chemistry.chemical_compound ,symbols.namesake ,Biochemistry ,chemistry ,Arabidopsis ,symbols ,S-Adenosyl methionine - Abstract
Polysaccharide methylation, especially that of pectin, is a common and important feature of land plant cell walls. Polysaccharide methylation takes place in the Golgi apparatus and therefore relies on the import of S-adenosyl methionine (SAM) from the cytosol into the Golgi. However, to date, no Golgi SAM transporter has been identified in plants. In this work, we studied major facilitator superfamily members in Arabidopsis that we identified as putative Golgi SAM transporters (GoSAMTs). Knock-out of the two most highly expressed GoSAMTs led to a strong reduction in Golgi-synthesised polysaccharide methylation. Furthermore, solid-state NMR experiments revealed that reduced methylation changed cell wall polysaccharide conformations, interactions and mobilities. Notably, the NMR revealed the existence of pectin ‘egg-box’ structures in intact cell walls, and showed that their formation is enhanced by reduced methyl-esterification. These changes in wall architecture were linked to substantial growth and developmental phenotypes. In particular, anisotropic growth was strongly impaired in the double mutant. The identification of putative transporters that import SAM into the Golgi lumen in plants provides new insights into the paramount importance of polysaccharide methylation for plant cell wall structure and function.
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- 2021
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11. Toward a Structural Model for the Aluminum Tellurite Glass System
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Ray Dupree, Dinu Iuga, Thomas F. Kemp, Diane Holland, Faizani Mohd-Noor, Emma R. Barney, and Nattapol Laorodphan
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Uniform distribution (continuous) ,Materials science ,Scattering ,Coordination number ,Neutron diffraction ,TN ,chemistry.chemical_element ,Charge (physics) ,Electron ,Electronic, Optical and Magnetic Materials ,Surfaces, Coatings and Films ,Crystallography ,General Energy ,chemistry ,QD ,Physical and Theoretical Chemistry ,Tellurium ,Boron ,QC - Abstract
Neutron diffraction, 27Al MAS NMR, and 27Al Double Quantum MAS NMR results are presented and analyzed to determine the local environments of the cations in a series of aluminum tellurite glasses. Total scattering results show that, within a maximum Te–O distance of 2.36 Å, tellurium exhibits a mix of [TeO3E] and [TeO4E] environments (E = electron lone-pair), with a linear reduction in the average tellurium–oxygen coordination number as Al2O3 is added to the glass. This is accompanied by a linear decrease in the average aluminum–oxygen coordination number as [AlO4] units form at the expense of [AlO6] units, while the fraction of [AlO5] units remains roughly constant. A consideration of the bonding requirements of the five structural units in the glass, [TeO3E], [TeO4E], [AlO4], [AlO5], and [AlO6], has allowed a direct quantitative relationship between tellurium–oxygen and aluminum–oxygen coordination numbers to be derived for the first time, and this has been successfully extended to the boron tellurite system. Double Quantum 27Al MAS NMR indicates that, in contrast to previous reports, the shortest Al...Al separations are significantly smaller (∼3.2 Å) than expected for a uniform distribution and there is a preference for [AlO6]–[AlO6] and [AlO4]–[AlO4] corner sharing polyhedra. These associations support a new structural model which successfully applies the principle of charge balance to describe the interaction of tellurium and aluminum and identifies and explains the clustering of [AlOn] polyhedra in the glass and their preferred associations. [AlO6] and [TeO4E] units dominate the network in TeO2-rich glasses and [AlO4]− units form to stabilize the [TeO3E]+ units as alumina is added to the glass.\ud \ud
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- 2020
12. Molecular architecture of softwood revealed by solid-state NMR
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Dinu Iuga, Steven P. Brown, Paul Dupree, Ray Dupree, Oliver M. Terrett, W. Trent Franks, Jan J. Lyczakowski, Li Yu, Terrett, Oliver M. [0000-0002-3796-2858], Lyczakowski, Jan J. [0000-0002-7694-8629], Yu, Li [0000-0001-8820-6705], Franks, W. Trent [0000-0003-4111-8868], Brown, Steven P. [0000-0003-2069-8496], Dupree, Paul [0000-0001-9270-6286], Apollo - University of Cambridge Repository, Terrett, Oliver M [0000-0002-3796-2858], Lyczakowski, Jan J [0000-0002-7694-8629], Franks, W Trent [0000-0003-4111-8868], and Brown, Steven P [0000-0003-2069-8496]
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HD ,0301 basic medicine ,631/449/448/1365 ,Softwood ,Science ,639/638/45 ,101/6 ,General Physics and Astronomy ,Plant cell biology ,02 engineering and technology ,Polysaccharide ,Biochemistry ,General Biochemistry, Genetics and Molecular Biology ,631/449 ,Cell wall ,631/45/72/1205 ,03 medical and health sciences ,chemistry.chemical_compound ,Polysaccharides ,631/449/448 ,Lignin ,128 ,QD ,Biorefining ,Cellulose ,lcsh:Science ,Galactoglucomannan ,SD ,chemistry.chemical_classification ,3403 Macromolecular and Materials Chemistry ,Multidisciplinary ,34 Chemical Sciences ,Polymer science ,article ,technology, industry, and agriculture ,General Chemistry ,15. Life on land ,021001 nanoscience & nanotechnology ,QP ,Xylan ,030104 developmental biology ,chemistry ,140/131 ,lcsh:Q ,Plant sciences ,0210 nano-technology - Abstract
Economically important softwood from conifers is mainly composed of the polysaccharides cellulose, galactoglucomannan and xylan, and the phenolic polymer, lignin. The interactions between these polymers lead to wood mechanical strength and must be overcome in biorefining. Here, we use 13C multidimensional solid-state NMR to analyse the polymer interactions in never-dried cell walls of the softwood, spruce. In contrast to some earlier softwood cell wall models, most of the xylan binds to cellulose in the two-fold screw conformation. Moreover, galactoglucomannan alters its conformation by intimately binding to the surface of cellulose microfibrils in a semi-crystalline fashion. Some galactoglucomannan and xylan bind to the same cellulose microfibrils, and lignin is associated with both of these cellulose-bound polysaccharides. We propose a model of softwood molecular architecture which explains the origin of the different cellulose environments observed in the NMR experiments. Our model will assist strategies for improving wood usage in a sustainable bioeconomy., Understanding the interactions between the constituents of the cell walls in wood is important for understanding the mechanical properties. Here, the authors report on a solid-state NMR study of never-dried softwood, noticing differences to previous reports and develop a model of softwood architecture.
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- 2019
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13. Vitrification of β-tricalcium phosphate in sodium aluminoborophosphate glass and the effect of Ga3+ substitution
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Martin Mee, Phillip M. Mallinson, Alexander J. Marsden, Diane Holland, Andrew T. Grigg, Shirley K. Fong, Ray Dupree, and Steve Feller
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chemistry.chemical_classification ,Base (chemistry) ,Sodium ,chemistry.chemical_element ,Mineralogy ,Condensed Matter Physics ,Phosphate ,Electronic, Optical and Magnetic Materials ,Inorganic Chemistry ,Crystal ,symbols.namesake ,Crystallography ,chemistry.chemical_compound ,Devitrification ,chemistry ,Materials Chemistry ,Ceramics and Composites ,symbols ,Physical and Theoretical Chemistry ,Gallium ,Boron ,Raman spectroscopy - Abstract
Sodium calcium aluminoborophosphate glasses (some containing Ga 3+ ) simulate interactions at the interface between β-tricalcium phosphate crystal waste hosts (β-TCP and β-TC(Ga)P) and sodium aluminoborophosphate (NABP) glass encapsulant. 31 P NMR and Raman spectroscopies show progression from Na + charge-balanced, mixed Q Al P = Q 2 1 + Q 3 0 in the NABP base glass, to Ca 2+ charge-balanced, Q 0 0 dominated structure, eventually inhibiting vitrification above 80 wt% addition of β-TCP or β-TC(Ga)P. 27 Al NMR shows [Al(PO 4 ) n ] species with dominant n =4 and 11 B NMR shows the 4-coordinated boron fraction in NABP falls from 0.7 to 0.1 on addition of the crystal hosts. Devitrification of glasses with 60–70 wt% crystal additions shows that Na + and Al 3+ from the encapsulant substitute for ∼20% of Ca 2+ in the β-TCP phase formed from the β-TCP:NABP glasses whilst ∼85% of Ga 3+ resubstitutes into β-TCP from the β-TC(Ga)P:NABP glasses. This demonstrates the preference for Ga 3+ substitution over Al 3+ in the Ca(5) site.
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- 2015
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14. An even pattern of xylan substitution is critical for interaction with cellulose in plant cell walls
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Jan J. Lyczakowski, Oliver M. Terrett, Paul Dupree, Dinu Iuga, Ray Dupree, Katherine Stott, Mylene Durand-Tardif, Steven P. Brown, Marta Busse-Wicher, Nicholas J. Grantham, Joel Wurman-Rodrich, Thomas J. Simmons, Terrett, Oliver [0000-0002-3796-2858], Lyczakowski, Jan [0000-0002-7694-8629], Stott, Katherine [0000-0002-4014-1188], Dupree, Paul [0000-0001-9270-6286], Apollo - University of Cambridge Repository, Department of Biochemistry, University of Cambridge [UK] (CAM), University of Warwick, Institut Jean-Pierre Bourgin (IJPB), Institut National de la Recherche Agronomique (INRA)-AgroParisTech, Centre National de la Recherche Scientifique (CNRS), Université Paris Saclay (COmUE), Leverhulme Trust, Conicyt Chile, Cambridge Trusts, BBSRC [BB/J014540/1, PR140003], BBSRC Novozymes iCASE award [BB/M015432/1], EPSRC, University of Warwick through Advantage West Midlands (AWM), and European Regional Development Fund (ERDF)
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0106 biological sciences ,0301 basic medicine ,Cell biology ,animal structures ,Plant physiology ,European Regional Development Fund ,Arabidopsis ,Library science ,Plant Science ,macromolecular substances ,Advanced materials ,01 natural sciences ,Mass Spectrometry ,03 medical and health sciences ,Acetyltransferases ,Cell Wall ,Political science ,Plant Cells ,Botany ,[SDV.BV]Life Sciences [q-bio]/Vegetal Biology ,Cellulose ,Natural materials ,West midlands ,Arabidopsis Proteins ,QK ,technology, industry, and agriculture ,food and beverages ,Glycosyltransferases ,Membrane Proteins ,Acetylation ,carbohydrates (lipids) ,030104 developmental biology ,Biofuels ,Xylans ,010606 plant biology & botany - Abstract
International audience; Xylan and cellulose are abundant polysaccharides in vascular plants and essential for secondary cell wall strength. Acetate or glucuronic acid decorations are exclusively found on even-numbered residues in most of the glucuronoxylan polymer. It has been proposed that this even-specific positioning of the decorations might permit docking of xylan onto the hydrophilic face of a cellulose microfibril(1-3). Consequently, xylan adopts a flattened ribbon-like twofold screw conformation when bound to cellulose in the cell wall(4). Here we show that ESKIMO1/XOAT1/TBL29, a xylan-specific O-acetyltransferase, is necessary for generation of the even pattern of acetyl esters on xylan in Arabidopsis. The reduced acetylation in the esk1 mutant deregulates the position-specific activity of the xylan glucuronosyltransferase GUX1, and so the even pattern of glucuronic acid on the xylan is lost. Solid-state NMR of intact cell walls shows that, without the even-patterned xylan decorations, xylan does not interact normally with cellulose fibrils. We conclude that the even pattern of xylan substitutions seen across vascular plants enables the interaction of xylan with hydrophilic faces of cellulose fibrils, and is essential for development of normal plant secondary cell walls.
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- 2017
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15. A 3D experiment that provides isotropic homonuclear correlations of half-integer quadrupolar nuclei
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Ray Dupree, Dinu Iuga, and Diane Holland
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Nuclear and High Energy Physics ,Magnetic Resonance Spectroscopy ,Chemistry ,Statistics as Topic ,Isotropy ,Biophysics ,Spin–lattice relaxation ,Reproducibility of Results ,Condensed Matter Physics ,Sensitivity and Specificity ,Biochemistry ,Homonuclear molecule ,Dipole ,Isotopes ,Anisotropy ,Half-integer ,Atomic physics ,Rubidium Radioisotopes ,Quantum ,Excitation ,Boron ,Coherence (physics) - Abstract
Two 3D experiments, capable of producing enhanced resolution two-spin double-quantum (DQ) homonuclear correlations for half-integer quadrupolar nuclei, are described. The first uses a split-t1 MQMAS sequence followed by a sandwiched oR3 symmetry-based dipolar recoupling sequence to directly excite DQ coherences. In this case an isotropic single-quantum (SQ) coherence starts the homonuclear DQ excitation. In the second experiment a single strong pulse is used to create triple quantum (TQ) coherence followed by a further single pulse conversion to zero-order before a non-sandwiched oR3 DQ sequence. The first experiment is demonstrated using 87Rb in RbNO3, with three Rb sites in a ∼5 ppm range, and the second to 11B in caesium triborate, CsB3O5, with two three-coordinated sites separated by ∼2 ppm and one four-coordinated boron site. In both cases, all sites are clearly resolved and their connections observed. The second experiment has higher sensitivity and a good signal to noise is obtained in a reasonable time despite the long T1 relaxation time of 11B in this material.
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- 2014
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16. Constraints on the incorporation mechanism of chlorine in peralkaline and peraluminous Na2O-CaO-Al2O3-SiO2 glasses
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Sharon L. Webb, Ray Dupree, Thomas F. Kemp, Ivan Hung, A. Baasner, and Burkhard C. Schmidt
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010504 meteorology & atmospheric sciences ,Chemistry ,Analytical chemistry ,Mineralogy ,010502 geochemistry & geophysics ,01 natural sciences ,Peralkaline rock ,Spectral line ,Geophysics ,13. Climate action ,Geochemistry and Petrology ,Aluminosilicate ,Quadrupole ,Magic angle spinning ,Dispersion (chemistry) ,Spectroscopy ,Electric field gradient ,0105 earth and related environmental sciences - Abstract
Incorporation mechanisms of Cl in peralkaline and peraluminous Na2O-CaO-Al2O3-SiO2 glasses as a model system for phonolitic melts were investigated using 35Cl, 23Na, 27Al, and 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The size and large distribution of electric field gradients for 35Cl causes loss of signal in the MAS NMR experiment and this, in combination with the low concentration of Cl and the large chemical shift dispersion, means that even at the highest available fields we are at the limits of MAS NMR. Nevertheless clear differences in the Cl environment in peralkaline and peraluminous glasses can readily be seen. In both glass types Cl exists in relatively symmetric Na-Ca-Cl environments. The 35Cl chemical shift indicates that the Cl environment is dominated by the presence of Na cations, consistent with the Na/Ca ratio of 5/1 in the glasses. 35Cl MAS NMR spectra of the peraluminous glasses show a larger chemical shift distribution and a more positive isotropic chemical shift, ~−75 ppm, than the peralkaline glasses, ~−100 ppm. They also have a larger quadrupole coupling constant with a larger distribution, indicating greater disorder in the peraluminous glasses. It is likely that there are more Ca cations present in the Cl environments in the peraluminous glasses than in the peralkaline glasses despite their having the same Na/Ca ratio. In the peralkaline glasses the formation of Na-Ca-Cl environments leads to a decrease in the number of network-modifying cations, which causes a polymerization of the glass network. No effect on the glass polymerization was observed in the peraluminous glasses. Some 35Cl signal is also lost in the static spectra indicating that ~20% of Cl for a peralkaline glass and more than ~70% for a peraluminous glass must be in environments where there is a large enough electric field gradient that the resulting very broad line is unobservable. These environments could be simply Na-Ca-Cl with higher electric field gradients than those producing the observed 35Cl signal or non-bridging Cl environments like for example Al-Cl. The Cl environment in the present mixed Na2O-CaO aluminosilicate glasses appears to be more disordered than was to be expected from previous NMR spectroscopic studies on simpler glass compositions.
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- 2014
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17. Fluorine speciation as a function of composition in peralkaline and peraluminous Na2O–CaO–Al2O3–SiO2 glasses: A multinuclear NMR study
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Sharon L. Webb, Burkhard C. Schmidt, Ray Dupree, and A. Baasner
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media_common.quotation_subject ,Analytical chemistry ,chemistry.chemical_element ,Peralkaline rock ,Spectral line ,Speciation ,chemistry ,Geochemistry and Petrology ,Aluminosilicate ,Magic angle spinning ,Fluorine ,Composition (visual arts) ,Spectroscopy ,media_common - Abstract
The incorporation mechanisms of fluorine (F) into peralkaline and peraluminous Na2O–CaO aluminosilicate glasses with ∼65 mol% SiO2 (model system for phonolites) were investigated by magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. In 19F MAS NMR spectra of the fluorine-bearing peralkaline glasses at least five F sites could be distinguished, while only three of these sites could be found in the corresponding peraluminous glasses, which shows that there are more F incorporation mechanisms in peralkaline than in peraluminous glasses. In the peralkaline glasses containing up to 6.2 mol% F the following F environments were identified: F–Ca(n) at ∼−113 ppm, Si–F–Na(n) or Al–F–Ca(n) at ∼−146 ppm, Al–F–Al at ∼−168 ppm, Al–F–Na(n) at ∼−188 ppm and F–Na(n) at ∼−225 ppm (“n” indicates that the number of atoms is variable or uncertain). F–Ca(n) is the most abundant site which is surprising as Ca is the least common cation in the glasses. The fraction of F–Ca(n) sites increases from 42% to 53% as the F content increases from 1.2 to 6.2 mol%. The addition of up to 16.5 mol% (5.3 wt%) water strongly affects F speciation in peralkaline glasses and results in a decrease in the fraction of F–Al sites compared to F–Ca(n) sites. It seems that hydroxyl groups (OH) and F occupy similar Al environments and that F cannot compete with OH. In the peraluminous glasses containing up to 18.3 mol% F only three F environments Si–F–Na(n) or Al–F–Ca(n) at ∼−149 ppm, Al–F–Al at ∼−170 ppm and Al–F–Na(n) at ∼−190 ppm are observed. Al–F–Na(n) is the most abundant site with a fraction of 54–61%. The F speciation also changes with the F concentration, with a minimum in Al–F–Na(n) sites between 3.5 and 9.7 mol% F. Fluorine has only a small effect on the 23Na and 29Si MAS NMR spectra. 27Al MAS NMR spectra of the peralkaline glasses show only four-coordinated Al while in the peraluminous glasses ∼5% of the Al was found to be five-coordinated. The amount of five-coordinate Al does not change with increasing F content, but the environment of the five-coordinate Al becomes more symmetric with increasing F.
- Published
- 2014
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18. Cation substitution in β-tricalcium phosphate investigated using multi-nuclear, solid-state NMR
- Author
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Zhehong Gan, Diane Holland, Ray Dupree, Martin Mee, Phillip M. Mallinson, Andrew T. Grigg, and Shirley K. Fong
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Sodium ,chemistry.chemical_element ,Condensed Matter Physics ,Phosphate ,Electronic, Optical and Magnetic Materials ,Inorganic Chemistry ,chemistry.chemical_compound ,Crystallography ,Solid-state nuclear magnetic resonance ,Heteronuclear molecule ,chemistry ,Aluminium ,Phase (matter) ,Materials Chemistry ,Ceramics and Composites ,Qualitative inorganic analysis ,Physical and Theoretical Chemistry ,Gallium ,Nuclear chemistry - Abstract
The substitution of aluminium, gallium and sodium cations into β-tricalcium phosphate (β-TCP; Ca3(PO4)2) has been investigated, and the Ca sites involved successfully determined, using a combination of 1D 31P, 27Al, 71Ga, 23Na and 43Ca (natural abundance) NMR and 2D 27Al{31P}, 71Ga{31P} and 23Na{31P} rotary-resonance-recoupled heteronuclear multiple-quantum correlation (R3-HMQC) NMR. Over the compositional range studied, substitution of Ca2+ by Al3+ or Ga3+ was observed only on the Ca(5) site, whilst substitution by Na+ was confined to the Ca(4) site. Some AlPO4 or GaPO4 second phase was observed at the highest doping levels in the Al3+ and Ga3+ substituted samples.
- Published
- 2014
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19. Solid-state 17O NMR as a probe for structural studies of proteins in biomembranes
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Ray Dupree,§ and, Maurits R.R. de Planque, Anthony Watts, Vincent Lemaître, Andy P. Howes, and Mark E. Smith
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Oxygen-17 ,Models, Molecular ,Chemistry ,Cell Membrane ,Solid-state ,Analytical chemistry ,Membrane Proteins ,Sequence (biology) ,Biological membrane ,General Chemistry ,Oxygen Isotopes ,Biochemistry ,Catalysis ,Transmembrane protein ,Crystallography ,Colloid and Surface Chemistry ,WALP peptide ,Molecule ,Peptides ,Transmembrane peptide ,Nuclear Magnetic Resonance, Biomolecular - Abstract
We report the first example of 17O NMR spectra from a selectively labeled transmembrane peptide, 17O-[Ala12]-WALP23, as a lyophilized powder and incorporated in hydrated phospholipid vesicles. It is shown that at high magnetic field it is feasible to apply 17O NMR to the study of membrane-incorporated peptides. Furthermore, we were able to estimate distances within the selectively labeled WALP peptide, which represents a consensus transmembrane protein sequence. This work opens up new applications of 17O solid-state NMR on biological systems.
- Published
- 2016
20. Ultra-high resolution 17O solid-state NMR spectroscopy of biomolecules: a comprehensive spectral analysis of monosodium L-glutamate·monohydrate
- Author
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Alan Wong, Anthony Watts, Ago Samoson, Andrew P. Howes, Ray Dupree, Tiit Anupõld, Jaan Past, Jonathan R. Yates, and Mark E. Smith
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Models, Molecular ,Deuterium NMR ,Magnetic Resonance Spectroscopy ,010405 organic chemistry ,Chemistry ,Carbon-13 NMR satellite ,Analytical chemistry ,General Physics and Astronomy ,Hydrogen Bonding ,Fluorine-19 NMR ,Nuclear magnetic resonance crystallography ,Nuclear magnetic resonance spectroscopy ,Oxygen Isotopes ,Carbon-13 NMR ,010402 general chemistry ,Sensitivity and Specificity ,01 natural sciences ,0104 chemical sciences ,Sodium Glutamate ,Quantum Theory ,Phosphorus-31 NMR spectroscopy ,Transverse relaxation-optimized spectroscopy ,Physical and Theoretical Chemistry ,QC - Abstract
Monosodium L-glutamate monohydrate, a multiple oxygen site (eight) compound, is used to demonstrate that a combination of high-resolution solid-state NMR spectroscopic techniques opens up new possibilities for (17)O as a nuclear probe of biomolecules. Eight oxygen sites have been resolved by double rotation (DOR) and multiple quantum (MQ) NMR experiments, despite the (17)O chemical shifts lying within a narrow shift range of
- Published
- 2016
21. Enhancing resolution and sensitivity of O-17 solid-state NMR through combining double rotation, H-1 decoupling and satellite modulation for biomolecular applications
- Author
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Tiit Anupõld, Ray Dupree, V. Lemaitre, Anthony Watts, Andrew P. Howes, Andreas Kukol, Ago Samoson, and Mark E. Smith
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Double rotation ,Solid-state nuclear magnetic resonance ,Chemistry ,General Physics and Astronomy ,Nanotechnology ,Decoupling (cosmology) ,Physical and Theoretical Chemistry ,Computational physics - Abstract
17O solid-state NMR is a highly sensitive probe of structural detail of organic solids but improvements in sensitivity and resolution are crucial for it to be applied to larger biological molecules. Here it is shown that high resolution (∼1 ppm) and significant signal enhancement can be achieved by combining 1H decoupled double rotation (DOR), which narrows the lines by a factor of ∼100 compared to conventional magic angle spinning, and manipulation of the satellite transition populations to transfer magnetisation to the central transition, which produces a signal enhancement of ∼2. © 2006 Elsevier B.V. All rights reserved.
- Published
- 2016
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22. Amyloid hydrogen bonding polymorphism evaluated by15N{17O}REAPDOR solid-state NMR and ultra-high resolution fourier transform ion cyclotron resonance mass spectrometry
- Author
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Andrei Filippov, Steven P. Brown, Juan Wei, Mark P. Barrow, Pui Yiu Lam, Dinu Iuga, Peter B. O’Connor, Oleg N. Antzutkin, and Ray Dupree
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Models, Molecular ,Amyloid ,Protein Folding ,Analytical chemistry ,Peptide ,Oxygen Isotopes ,010402 general chemistry ,Tandem mass spectrometry ,Mass spectrometry ,01 natural sciences ,Biochemistry ,Mass Spectrometry ,Fourier transform ion cyclotron resonance ,Alzheimer Disease ,Tandem Mass Spectrometry ,Humans ,Molecule ,Nuclear Magnetic Resonance, Biomolecular ,chemistry.chemical_classification ,Amyloid beta-Peptides ,Fourier Analysis ,Nitrogen Isotopes ,Protein Stability ,010405 organic chemistry ,Chemistry ,Hydrogen bond ,Hydrogen Bonding ,Cyclotrons ,QP ,Peptide Fragments ,0104 chemical sciences ,Crystallography ,Solid-state nuclear magnetic resonance ,Isotope Labeling ,Protein folding ,Oligopeptides - Abstract
A combined approach, using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and solid-state NMR (Nuclear Magnetic Resonance), shows a high degree of polymorphism exhibited by Aβ species in forming hydrogen-bonded networks. Two Alzheimer's Aβ peptides, Ac-Aβ(16-22)-NH2 and Aβ(11-25), selectively labeled with (17)O and (15)N at specific amino acid residues were investigated. The total amount of peptides labeled with (17)O as measured by FTICR-MS enabled the interpretation of dephasing observed in (15)N{(17)O}REAPDOR solid-state NMR experiments. Specifically, about one-third of the Aβ peptides were found to be involved in the formation of a specificC═(17)O···H-(15)N hydrogen bond with their neighbor peptide molecules, and we hypothesize that the rest of the molecules undergo ± n off-registry shifts in their hydrogen bonding networks.
- Published
- 2016
23. Hydrogen Bonding in Alzheimer’s Amyloid-β Fibrils Probed by15N{17O} REAPDOR Solid-State NMR Spectroscopy
- Author
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Oleg N. Antzutkin, Dinu Iuga, Andrei V. Filippov, Robert T. Kelly, Johanna Becker-Baldus, Steven P. Brown, and Ray Dupree
- Subjects
General Medicine - Published
- 2012
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24. A neutron diffraction and 205Tl NMR study of the thallium germanate glass system
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Alex C. Hannon, Ray Dupree, Nattapol Laorodphan, Emma R. Barney, and Diane Holland
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Coordination number ,Neutron diffraction ,Analytical chemistry ,chemistry.chemical_element ,Germanium ,Condensed Matter Physics ,Alkali metal ,Electronic, Optical and Magnetic Materials ,chemistry ,Caesium ,Materials Chemistry ,Ceramics and Composites ,Thallium ,Germanate ,Lone pair ,Nuclear chemistry - Abstract
Neutron diffraction data, measured for two thallium germanate glass compositions, are presented and compared with previously published data for caesium germanate glasses. The measured coordination number, n(Ge-O), for the 10 mol%Tl2O thallium germanate glass is in good agreement with the average coordination number measured for the equivalent caesium germanate. However, while n(Ge-O) declines for caesium germanate glasses as the amount of modifier increases above 18 mol% Cs2O, n(Ge-O) for the 30 mol% Tl2O thallium germanate glass remains high with, on average, 4.40 +/- 0.03 oxygen neighbours per germanium. The difference in behaviour of the germanium coordination, compared to caesium germanate glasses, arises from a change in the average thallium environment, as the role of the thallium changes from that of a modifier (similar to an alkali), to a role where some of the thallium atoms act as network formers. This is supported by Tl-205 NMR measurements which indicate the presence of two thallium environments. (C) 2010 Elsevier B.V. All rights reserved.
- Published
- 2010
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25. Gyrotron FU CW VII for 300 MHz and 600 MHz DNP-NMR Spectroscopy
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Mark E. Smith, Isamu Ogawa, Ray Dupree, Hiroki Takahashi, La Agusu, Toshitaka Idehara, and Kosuke Kosuga
- Subjects
Physics ,Radiation ,Cyclotron ,Nuclear magnetic resonance spectroscopy ,Condensed Matter Physics ,law.invention ,Nuclear magnetic resonance ,Far infrared ,law ,Harmonics ,Gyrotron ,Electrical and Electronic Engineering ,Atomic physics ,Instrumentation - Abstract
Gyrotron FU CW VII, one of the FU CW Series Gyrotrons, has been designed, constructed and completed operational tests successfully in the Research Center for Development of Far Infrared Region, University of Fukui (FIR FU). The gyrotron operates at around 200 GHz for the fundamental cyclotron resonances and at around 400 GHz for the second harmonics. These radiation frequencies will be applied to 300 MHz and 600 MHz DNP enhanced NMR spectroscopy.
- Published
- 2010
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26. Determination of the bond-angle distribution in vitreous B2O3 by 11B double rotation (DOR) NMR spectroscopy
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Tiit Anupõld, Ray Dupree, Diane Holland, P. F. Harrison, Steven P. Brown, Ivan Hung, Andrew P. Howes, Ago Samoson, and B. G. Parkinson
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Analytical chemistry ,chemistry.chemical_element ,Nuclear magnetic resonance spectroscopy ,Condensed Matter Physics ,Resonance (chemistry) ,Ring (chemistry) ,Spectral line ,Electronic, Optical and Magnetic Materials ,Inorganic Chemistry ,NMR spectra database ,Molecular geometry ,chemistry ,Materials Chemistry ,Ceramics and Composites ,Spin diffusion ,Physical and Theoretical Chemistry ,Boron - Abstract
The B-O-B bond angle distributions for both ring and non-ring boron sites in vitreous B2O3 have been determined by B-11 double rotation (DOR) NMR and multiple-quantum (MQ) DOR NMR. The [B3O6] boroxol rings are observed to have a mean internal B-O-B angle of 120.0+/-0.7 degrees with a small standard deviation, sigma(R) = 3.2+/-0.4 degrees, indicating that the rings are near-perfect planar, hexagonal structures. The rings are linked predominantly by non-ring [BO3] units, which share oxygens with the boroxol ring, with a mean B-ring-O-Bnon-ring angle of 135.1+/-0.6 degrees and sigma(NR) = 6.7+/-0.4 degrees. In addition, the fraction of boron atoms, f, which reside in the boroxol rings has been measured for this sample as f = 0.73+/-0.01. (C) 2009 Elsevier Inc. All rights reserved.
- Published
- 2009
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27. Two-dimensional 43Ca–1H correlation solid-state NMR spectroscopy
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Ray Dupree, Danielle Laurencin, Mark E. Smith, Alan Wong, Solid State NMR Group, University of Warwick, University of Warwick [Coventry], and Bourse Marie Curie Intra-European Fellowship
- Subjects
Calcium Isotopes ,Nuclear and High Energy Physics ,Magnetic Resonance Spectroscopy ,dipolar interaction ,Carbon-13 NMR satellite ,Nuclear magnetic resonance spectroscopy of nucleic acids ,02 engineering and technology ,Fluorine-19 NMR ,Nuclear magnetic resonance crystallography ,[CHIM.INOR]Chemical Sciences/Inorganic chemistry ,010402 general chemistry ,Sensitivity and Specificity ,01 natural sciences ,Nuclear magnetic resonance ,low-gamma ,Magnetization transfer ,oxyhydroxyapatite ,Instrumentation ,43Ca NMR ,Radiation ,Chemistry ,hydroxyapatite ,[CHIM.MATE]Chemical Sciences/Material chemistry ,General Chemistry ,021001 nanoscience & nanotechnology ,R3-HMQC ,0104 chemical sciences ,Durapatite ,Solid-state nuclear magnetic resonance ,Chemical physics ,Residual dipolar coupling ,Spin Labels ,hetero-nuclear correlation NMR spectroscopy ,Protons ,0210 nano-technology ,Algorithms ,Magnetic dipole–dipole interaction - Abstract
Calcium-43 (nuclear spin, S = 7/2) is an NMR insensitive low-gamma quadrupolar nucleus and up until recently only one-dimensional solid-state Ca-43 NMR spectra have been reported. Through-space correlation experiments are challenging between spin-1/2 and low-gamma quadrupolar nuclei because of the intrinsically weak dipolar interaction and the often-low natural abundance of the quadrupolar nucleus. Rotary-resonance recoupling (R-3) has recently been used to re-introduce hetero-nuclear dipolar interactions for sensitive high-gamma quadrupolar nuclei, but has not yet been applied in the case of low-gamma half-integer quadrupolar nuclei. Here an effective and robust 2D H-1-Ca-43 NMR correlation experiment combining the R-3 dipole-recoupling scheme with 2D HMQC is presented. It is demonstrated that the weak Ca-43-H-1 dipolar coupling in hydroxyapatite and oxy-hydroxyapatite can be readily re-introduced and that this recoupling scheme is more efficient than conventional cross-polarization transfer. Moreover, three Ca-43-H-1 dipolar coupled calcium environments are clearly resolved in the structurally unknown oxy-hydroxyapatite. This local information is not readily available from other techniques such as powder XRD and high resolution electron microscopy. R-3-HMQC is also a desirable experiment because the set-up is simple and it can be applied using conventional multi-resonance probes. (C) 2008 Elsevier Inc. All rights reserved.
- Published
- 2009
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28. Water speciation in sodium silicate glasses based on NIR and NMR spectroscopy
- Author
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Shigeru Yamashita, Harald Behrens, Burkhard C. Schmidt, and Ray Dupree
- Subjects
010504 meteorology & atmospheric sciences ,Chemistry ,Sodium ,Near-infrared spectroscopy ,Analytical chemistry ,chemistry.chemical_element ,Geology ,Sodium silicate ,Nuclear magnetic resonance spectroscopy ,Molar absorptivity ,010502 geochemistry & geophysics ,01 natural sciences ,chemistry.chemical_compound ,13. Climate action ,Geochemistry and Petrology ,Absorption (chemistry) ,Spectroscopy ,Water content ,0105 earth and related environmental sciences - Abstract
Water speciation in hydrated Na2O·2SiO2 (NS2), Na2O·4SiO2 (NS4), and Na2O·6SiO2 (NS6) glasses was analyzed by near-infrared (NIR) spectroscopy and low temperature static 1H nuclear magnetic resonance (NMR) spectroscopy. For each composition 6–9 glasses containing between 0.5 and 7.0 wt.% total water (measured by Karl–Fischer titration) were used to calibrate the molar absorption coefficients for the NIR combination bands near 4500 cm− 1 (OH groups) and near 5200 cm− 1 (H2O molecules). Noticeable disagreement was found between the water speciation derived from NIR spectra using an internally consistent calibration based on total water content and the water speciation determined by 1H NMR spectroscopy. The discrepancies are more pronounced for the evaluation of NIR peak areas (differences up to 55% in OH group content) than for the evaluation of peak heights (differences up to 35% in OH group content). Based on the NMR data we performed a new calibration for the NIR combination bands of the hydrous sodium silicate glasses. The molar absorption coefficients for the 4500 cm− 1 band (e4500) and the 5200 cm− 1 band (e5200) noticeably decrease with increasing Na2O content of the glasses from NS6 to NS2. The e values for both bands also decrease with total water content in NS4 and NS6 glasses. The variation of e values may be due to changes in the relative abundance of water subspecies, i.e. species exposed to strong or weak hydrogen bonding. Another explanation could be an incomplete separation of the combination bands from the tail of the fundamental OH stretching vibration bands and from the unassigned water-related band at 4000 cm− 1. Using the NMR-supported NIR calibration we calculated water species concentrations in the sodium silicate glasses as a function of total water content. At a total water content of 6.0 wt.%, the amount of water dissolved as OH groups is noticeably higher in the depolymerized glasses NS2 and NS4 (∼ 3.0 wt.%) than in the less depolymerized NS6 (∼ 2.5 wt.%). This observation implies that non-bridging oxygen, charge-compensated by sodium, promotes the formation of OH groups. No significant difference in water speciation was found between rapidly quenched glasses (∼ 150 K/s) and more slowly cooled glasses (∼ 2 K/s).
- Published
- 2008
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29. Disproportionation of Qm (0 ≤ m ≤ 4) species in partially devitrified Li2Si2O5 glasses with small amounts of P2O5
- Author
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Ray Dupree, M. R. Ahsan, Diane Holland, and M. G. Mortuza
- Subjects
chemistry.chemical_classification ,Base (chemistry) ,Mechanical Engineering ,Inorganic chemistry ,Disproportionation ,Phosphate ,Silicate ,Amorphous solid ,law.invention ,chemistry.chemical_compound ,chemistry ,Mechanics of Materials ,law ,General Materials Science ,Phosphorus-31 NMR spectroscopy ,Crystallization ,Scavenging - Abstract
The effect of addition of small amounts of P2O5 in the lithium disilicate glasses results in the scavenging of lithium metal ions by a phosphate group, Li3PO4. As a consequence of the scavenging, the silicate network partially repolymerises. The phosphate group remains intact during heat treatment of the optically clear, X-ray amorphous and slightly nucleated base glasses. However, the relative amounts of the silicate species, Qm (0 ≤ m ≤ 4), are dependent on the state of the glasses. These amounts, in the optically clear and X-ray amorphous, do not change with heat treatment but they do change, i.e. disproportionation occurs in the slightly nucleated and milky coloured glasses. The disproportionation follows the relation 2Q3 → Q2 + Q4 which is evident from the relative intensity of the different peaks.
- Published
- 2007
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30. A first-principles computational 17O NMR investigation of metal ion–oxygen interactions in carboxylate oxygens of alkali oxalates
- Author
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Ray Dupree, Mark E. Smith, Gary Thurgood, and Alan Wong
- Subjects
Oxygen-17 ,Bond strength ,Inorganic chemistry ,General Physics and Astronomy ,Alkali metal ,Resonance (chemistry) ,Oxalate ,Ion ,Metal ,chemistry.chemical_compound ,chemistry ,visual_art ,visual_art.visual_art_medium ,Physical chemistry ,Carboxylate ,Physical and Theoretical Chemistry - Abstract
O-17 NMR parameters, including chemical shift (CS) and electrical-field gradient (EFG) tensors, are calculated for oxalate compounds containing various different alkali ions using a DFT infinite periodic solid approach. This DFT study allows correlations to be found between the metal ion and oxygen interaction and the O-17 NMR interaction parameters. The O-17 CS shows greater sensitivity to the local alkali ions than that shown by the C-13 CS in the same compounds. It is found that the combination of metal ion-oxygen bond strength and cation size induce a deshielding shift up to similar to 70 ppm of O-17 delta(iso). The results also show the effects of different M-O interactions and C-O bond characteristics on the orientation of O-17 CS tensor components, and suggest that the O-17 quadrupolar parameters are systematically sensitive to the local cation environments around the carboxylate oxygen.
- Published
- 2007
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31. Probing the molecular architecture of Arabidopsis thaliana\ud secondary cell walls using two- and three-dimensional 13C solid\ud state nuclear magnetic resonance spectroscopy
- Author
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Jennifer C. Mortimer, Ray Dupree, Paul Dupree, Dharmesh Patel, Thomas J. Simmons, Steven P. Brown, and Dinu Iuga
- Subjects
Magnetic Resonance Spectroscopy ,Arabidopsis ,Analytical chemistry ,chemistry.chemical_element ,010402 general chemistry ,Lignin ,01 natural sciences ,7. Clean energy ,Biochemistry ,03 medical and health sciences ,chemistry.chemical_compound ,Cell Wall ,Magic angle spinning ,Arabidopsis thaliana ,QD ,Cellulose ,QC ,030304 developmental biology ,chemistry.chemical_classification ,0303 health sciences ,Plant Stems ,biology ,Arabidopsis Proteins ,QK ,Polymer ,15. Life on land ,biology.organism_classification ,0104 chemical sciences ,chemistry ,Solid-state nuclear magnetic resonance ,Biophysics ,Pectins ,Xylans ,Microfibril ,Carbon ,Secondary cell wall - Abstract
The plant secondary cell wall is a thickened polysaccharide and phenolic structure, providing mechanical strength to cells, particularly in woody tissues. It is the main feedstock for the developing bioenergy and green chemistry industries. Despite the role that molecular architecture (the arrangement of biopolymers relative to each other, and their conformations) plays in dictating biomass properties, such as recalcitrance to breakdown, it is poorly understood. Here, unprocessed dry 13C-labeled stems from the model plant Arabidopsis thaliana were analyzed by a variety of 13C solid state magic angle spinning nuclear magnetic resonance methods, such as one-dimensional cross-polarization and direct polarization, two-dimensional refocused INADEQUATE, RFDR, PDSD, and three-dimensional DARR, demonstrating their viability for the study of native polymer arrangements in intact secondary cell walls. All carbon sites of the two main glucose environments in cellulose (previously assigned to microfibril surface and interior residues) are clearly resolved, as are carbon sites of the other major components of the secondary cell wall: xylan and lignin. The xylan carbon 4 chemical shift is markedly different from that reported previously for solution or primary cell wall xylan, indicating significant changes in the helical conformation in these dried stems. Furthermore, the shift span indicates that xylan adopts a wide range of conformations in this material, with very little in the 31 conformation typical of xylan in solution. Additionally, spatial connections of noncarbohydrate species were observed with both cellulose peaks conventionally assigned as “surface” and as “interior” cellulose environments, raising questions about the origin of these two cellulose signals. In woody plant tissues, a secondary cell wall is laid down on the interior of the thin, extensible, and biochemically and functionally distinct primary cell wall during cellular differentiation. The secondary wall is crucial to many aspects of plant physiology, including mechanical strength. It also comprises the vast majority of the material of mature plant tissues and lignocellulosic biomass and is therefore an invaluable resource for renewable materials and for bioenergy feedstocks.1,2 The polysaccharide components of the cell wall, which constitute more than 60% of its dry weight, are commonly categorized into three constituent types: cellulose, hemicellulose, and pectin.3,4 Cellulose is thought to be the main load-bearing structure of the cell wall and is the most abundant polymer in both primary and secondary walls.5 Cellulose chains are composed of β-(1→4)-D-glucosyl residues (Figure 1) that are partly assembled into layers in a microfibril by inter- and intrachain hydrogen bonding and hydrophobic interactions. Within crystalline regions of cellulose microfibrils (known as crystallites), glucan chains are found in a 2-fold (21) helical conformation.
- Published
- 2015
32. Solid-state static 65Cu and 31P CP/MAS NMR, and liquid-state EXAFS studies on copper(I) O,O′-dialkyldithiophosphate cluster compounds: Formation of the copper(I) O,O′-di-iso-amyldithiophosphate cluster compound on the surface of synthetic chalcocite
- Author
-
Ray Dupree, Kevin J. Pike, Mats Lindberg, Oleg N. Antzutkin, John V. Hanna, Willis Forsling, Daniela Rusanova, and Ingniar Persson
- Subjects
Chalcocite ,Extended X-ray absorption fine structure ,Inorganic chemistry ,chemistry.chemical_element ,Nuclear magnetic resonance spectroscopy ,engineering.material ,Copper ,Inorganic Chemistry ,Crystallography ,Adsorption ,chemistry ,Materials Chemistry ,engineering ,Cluster (physics) ,Crystallite ,Physical and Theoretical Chemistry ,Anisotropy - Abstract
Polycrystalline octa-nuclear copper(I) O , O ′-di- i -propyl- and O , O ′-di- i -amyldithiophosphate cluster compounds, {Cu 8 [S 2 P(OR) 2 ] 6 (μ 8 -S)} where R = i Pr and i Am, were synthesized and characterized by 31 P CP/MAS NMR at 8.46 T and static 65 Cu NMR at multiple magnetic field strengths (7.05, 9.4 and 14.1 T). The symmetries of the electronic environments around the P sites were estimated from the 31 P chemical shift anisotropy (CSA) parameters, δ aniso and η . Analyses of the 65 Cu chemical shift and quadrupolar splitting parameters for these compounds are presented with the data being compared to those for the analogous octa-nuclear cluster compounds with R = n Bu and i Bu. The 65 Cu transverse relaxation for the copper sites in {Cu 8 [S 2 P(O i Pr) 2 ] 6 (μ 8 -S)} and {Cu 8 [S 2 P(O i Am) 2 ] 6 (μ 8 -S)} was found to be very different, with a relaxation time, T 2 , of 590 μs (Gaussian) and 90 μs (exponential), respectively. The structures of {Cu 4 [S 2 P(O i Pr) 2 ] 4 } and {Cu 8 [S 2 P(O i Pr) 2 ] 6 (μ 8 -S)} cluster compounds in the liquid- and the solid-state were studied by Cu K-edge EXAFS. The disulfide, [S 2 P(O i Am) 2 ] 2 , was obtained and characterized by 31 P{ 1 H} NMR. The interactions of the disulfide and of the potassium O , O ′-di- i -amyldithiophosphate salt with the surfaces of synthetic chalcocite (Cu 2 S) were probed using solid-state 31 P NMR spectroscopy and only the presence of copper(I) dithiophosphate species with the {Cu 8 [S 2 P(O i Am) 2 ] 6 (μ 8 -S)} structure was observed.
- Published
- 2006
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33. 27Al double rotation two-dimensional spin diffusion NMR: Complete unambiguous assignment of aluminium sites in 9Al2O3· 2B2O3
- Author
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Tiit Anupõld, Andrew P. Howes, Steven P. Brown, Ray Dupree, Dominique Massiot, Mark E. Smith, Ago Samoson, and Ivan Hung
- Subjects
Carbon-13 NMR satellite ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,NMR spectra database ,Double rotation ,chemistry ,Aluminium ,Tetrahedron ,Spin diffusion ,Physical and Theoretical Chemistry ,0210 nano-technology ,Mixing (physics) - Abstract
High-resolution two-dimensional Al-27 spin diffusion NMR spectra of 9Al(2)O(3) (.) 2B(2)O(3) recorded under double rotation for different mixing times are presented. The two crystallographically distinct pentahedral Al sites are distinguished by the presence or absence of correlation peaks with neighboring tetrahedral sites.
- Published
- 2006
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34. Spectroscopic characterization of the polycrystalline copper(I) di-n-butyldithiophosphate cluster – Cu8[S2P(O-n-Bu)2]6(μ8-S): Solid-state 31P CP/MAS and static 65Cu NMR studies
- Author
-
Ray Dupree, Ingmar Persson, Daniela Rusanova, Oleg N. Antzutkin, John V. Hanna, Kevin J. Pike, and Willis Forsling
- Subjects
Inorganic Chemistry ,Crystallography ,Chemistry ,Relaxation (NMR) ,Materials Chemistry ,Solid-state ,Cluster (physics) ,Analytical chemistry ,Physical and Theoretical Chemistry ,Polycrystalline copper - Abstract
A polycrystalline copper(I) O,O′-di-n-butyldithiophosphate cluster compound, Cu8[S2P(O-n-Bu)2]6(μ8-S), was synthesized and characterized by 31P CP/MAS NMR at 8.46 T and static 65Cu NMR at multiple ...
- Published
- 2006
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35. Natural abundance 43Ca NMR study of calcium-containing organic solids: A model study for Ca-binding biomaterials
- Author
-
Mark E. Smith, Ray Dupree, Alan Wong, and Andrew P. Howes
- Subjects
chemistry.chemical_classification ,Range (particle radiation) ,Abundance (chemistry) ,Biomolecule ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Nuclear magnetic resonance spectroscopy ,Calcium ,Carbon-13 NMR ,Solid material ,chemistry ,Electric field ,Physical and Theoretical Chemistry - Abstract
As a first step for probing Ca sites in biomolecules using solid-state Ca-43 NMR spectroscopy, natural abundance Ca-43 NMR data of calcium-containing organic solids is reported. The Ca-43 NMR interaction parameters indicate small electric field gradients and a relatively small chemical shift range for the calcium sites in these bio-related model compounds. A correlation of the Ca-43 isotropic chemical shift with Ca-O distance is found: the Ca-43 shift increases as the mean Ca-O distance decreases, with a strong deshielding being observed for calcium with strong Ca-O bonds (distance < 2.4,angstrom) in both organic and inorganic materials.
- Published
- 2006
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36. Solid-State NMR and EXAFS Spectroscopic Characterization of Polycrystalline Copper(I)O,O′-Dialkyldithiophosphate Cluster Compounds: Formation of Copper(I)O,O′-Diisobutyldithiophosphate Compounds on the Surface of Synthetic Chalcocite
- Author
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Ingmar Persson, Kevin J. Pike, Ray Dupree, Willis Forsling, Daniela Rusanova, Oleg N. Antzutkin, and John V. Hanna
- Subjects
Chalcocite ,Extended X-ray absorption fine structure ,Organic Chemistry ,Analytical chemistry ,chemistry.chemical_element ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,engineering.material ,Resonance (chemistry) ,Copper ,Catalysis ,NMR spectra database ,Crystallography ,Solid-state nuclear magnetic resonance ,chemistry ,engineering ,Spectroscopy - Abstract
A number of polycrystalline copper(I) O,O'-dialkyldithiophosphate cluster compounds with Cu-4, Cu-6, and Cu-8 cores were synthesized and characterized by using extended X-ray absorption fine-structure (EXAFS) spectroscopy. The structural relationship of these compounds is discussed. The polycrystalline copper(i) O,O'-diisobutyldithiophosphate cluster compounds, [Cu-8{S2P(OiBu)(2),}(6)(S)] and [CU6{S2P(OiBU)(2)}(6)], were also characterized by using P-31 CP/MAS NMR (CP = cross polarization, MAS = magic-angle spinning) and static Cu-65 NMR spectroscopies (at different magnetic fields) and powder X-ray diffraction (XRD) analysis. Comparative analyses of the P-31 chemical-shift tensor, and the Cu-65 chemical shift and quadrupolar-splitting parameters, estimated from the experimental NMR spectra of the polycrystalline copper(I) cluster compounds, are presented. The adsorption mechanism of the potassium O,O'-diisobutyldithiophosphate collector, K[S2P(OiBu)(2)], at the surface of synthetic chalcocite (Cu2S) was studied by means of solid-state P-31 CP/MAS NMR spectroscopy and scanning electron microscopy (SEM). P-31 NMR resonance lines from collector-treated chalcocite surfaces were assigned to a mixture of [Cu-8{S2P(OiBu)(2)}(6)(S)] and [Cu-6- {S2P(OiBu)(2)}(6)] compounds.
- Published
- 2006
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37. Solid-state 31P CP/MAS and static 65Cu NMR characterization of polycrystalline copper(I) dialkyldithiophosphate clusters
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Oleg N. Antzutkin, Daniela Rusanova, Willis Forsling, Kevin J. Pike, and Ray Dupree
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Nuclear and High Energy Physics ,Carbon-13 NMR satellite ,Chemistry ,Biophysics ,Nuclear magnetic resonance spectroscopy ,Nuclear magnetic resonance crystallography ,Fluorine-19 NMR ,Carbon-13 NMR ,Condensed Matter Physics ,Biochemistry ,NMR spectra database ,Crystallography ,Transverse relaxation-optimized spectroscopy ,Crystallite - Abstract
Polycrystalline tetra-nuclear Cu 4 [S 2 P(O- i -C 3 H 7 ) 2 ] 4 , hexa-nuclear Cu 6 [S 2 P(OC 2 H 5 ) 2 ] 6 , and octa-nuclear Cu 8 [S 2 P(O- i -C 4 H 9 ) 2 ] 6 (S) complexes were synthesized and analyzed by means of solid-state 31 P CP/MAS and 65 Cu static NMR spectroscopy. The symmetries of the electronic environments around each P-site were estimated from the 31 P chemical shift anisotropy (CSA) parameters, Δ aniso and η . The 65 Cu chemical shift and quadrupolar splitting parameters obtained from the experimental 65 Cu NMR spectra of the polycrystalline Cu I -complexes are presented. A solid-state NMR approach for the elucidation of the stereochemistry of poly-nuclear Cu(I) dithiophosphate complexes, when the structural analysis of the systems by single-crystal X-ray diffraction is not readily available, is proposed.
- Published
- 2006
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38. Symmetry-based recoupling of 17O–1H spin pairs in magic-angle spinning NMR
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Ray Dupree, Malcolm H. Levitt, and Jacco D. van Beek
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Oxygen-17 ,Larmor precession ,Nuclear and High Energy Physics ,Proton ,Chemistry ,Biophysics ,Condensed Matter Physics ,Biochemistry ,Molecular physics ,Nuclear magnetic resonance ,Heteronuclear molecule ,Solid-state nuclear magnetic resonance ,Magic angle spinning ,Physics::Atomic Physics ,Physics::Chemical Physics ,Two-dimensional nuclear magnetic resonance spectroscopy ,Electric field gradient - Abstract
We have performed magic-angle-spinning solid-state NMR experiments in which protons are recoupled to oxygen-17 nuclei by applying a symmetry-based recoupling sequence at the proton Larmor frequency. Two-dimensional quadrupole-dipole correlation spectra are produced, in which the second-order quadrupolar shift of the oxygen-17 central transition is correlated with the recoupled heteronuclear dipole–dipole interaction. These spectra are sensitive to the relative orientation of the electric field gradient at the site of the oxygen-17 nucleus and the O–H internuclear vector. We also demonstrate experiments in which polarization is transferred from protons to oxygen-17, and show that oxygen-17 signals may be selected according to the protonation state of the oxygen site. We discuss the small observed value of the heteronuclear dipolar splitting in the central-transition oxygen-17 spectra.
- Published
- 2006
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39. Experimental and Theoretical 17O NMR Study of the Influence of Hydrogen-Bonding on CO and O−H Oxygens in Carboxylic Solids
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Kevin J. Pike, Alan Wong, Guy J. Clarkson, Ray Dupree, Tiit Anupõld, Andrew P. Howes, Ago Samoson, Mark E. Smith, Robert Jenkins, and David H. G. Crout
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Deuterium NMR ,Magnetic Resonance Spectroscopy ,Maleic acid ,Hydrogen bond ,Carbon-13 NMR satellite ,Carboxylic Acids ,chemistry.chemical_element ,Hydrogen Bonding ,Oxygen Isotopes ,Oxygen ,Spectral line ,chemistry.chemical_compound ,chemistry ,Yield (chemistry) ,Physical chemistry ,Organic chemistry ,Physical and Theoretical Chemistry ,Spectroscopy - Abstract
A systematic solid-state 17O NMR study of a series of carboxylic compounds, maleic acid, chloromaleic acid, KH maleate, KH chloromaleate, K2 chloromaleate, and LiH phthalate.MeOH, is reported. Magic-angle spinning (MAS), triple-quantum (3Q) MAS, and double angle rotation (DOR) 17O NMR spectra were recorded at high magnetic fields (14.1 and 18.8 T). 17O MAS NMR for metal-free carboxylic acids and metal-containing carboxylic salts show featured spectra and demonstrate that this combined, where necessary, with DOR and 3QMAS, can yield site-specific information for samples containing multiple oxygen sites. In addition to 17O NMR spectroscopy, extensive quantum mechanical calculations were carried out to explore the influence of hydrogen bonding at these oxygen sites. B3LYP/6-311G++(d,p) calculations of 17O NMR parameters yielded good agreement with the experimental values. Linear correlations are observed between the calculated 17O NMR parameters and the hydrogen bond strengths, suggesting the possibility of estimating H-bonding information from 17O NMR data. The calculations also revealed intermolecular H-bond effects on the 17O NMR shielding tensors. It is found that the delta11 and delta22 components of the chemical shift tensor at O-H and C=O, respectively, are aligned nearly parallel with the strong H-bond and shift away from this direction as the H-bond interaction weakens.
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- 2006
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40. Formation of {Cu6[S2P(OC2H5)2]6} on Cu2S Surfaces from Aqueous Solutions of the KS2P(OC2H5)2 Collector: Scanning Electron Microscopy and Solid-State 31P Cross-Polarization/Magic Angle Spinning and Static 65Cu NMR Studies
- Author
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Willis Forsling, Oleg N. Antzutkin, Kevin J. Pike, Ray Dupree, and Daniela Rusanova
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Magic angle ,Chemistry ,Scanning electron microscope ,Analytical chemistry ,Surfaces and Interfaces ,Nuclear magnetic resonance spectroscopy ,Flory–Huggins solution theory ,Condensed Matter Physics ,X-ray crystallography ,Electrochemistry ,Magic angle spinning ,General Materials Science ,Crystallite ,Anisotropy ,Spectroscopy - Abstract
The interactions of synthetic chalcocite surfaces with diethyldithiophosphate, potassium salt, K[S2P(OC2H5)2], were studied by means of 31P cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopy and scanning electron microscopy (SEM). To identify the species formed on the Cu2S surfaces, a polycrystalline {CuI6[S2P(OC2H5)2]6} cluster was synthesized and analyzed by SEM, powder X-ray diffraction techniques and solid-state 31P CP/MAS NMR and static 65Cu NMR spectroscopy. 31P chemical shift anisotropy (CSA) parameters, delta(cs) and eta(cs), were estimated and used for assigning the bridging type of diethyldithiophosphate ligands in the {CuI6[S2P(OC2H5)2]6} cluster. The latter data were compared to 31P CSA parameters estimated from the spinning sideband patterns in 31P NMR spectra of the collector-treated mineral surfaces: formation of polycrystalline {CuI6[S2P(OC2H5)2]6} on the Cu2S surfaces is suggested. The second-order quadrupolar line shape of 65Cu was simulated, and the NMR interaction parameters, CQ and etaQ, for the copper(I) diethyldithiophosphate cluster were obtained.
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- 2005
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41. Structural implications of water and boron dissolution in albite glass
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Ray Dupree, Nikolay Zotov, and Burkhard C. Schmidt
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chemistry.chemical_classification ,Base (chemistry) ,Chemistry ,Inorganic chemistry ,Infrared spectroscopy ,chemistry.chemical_element ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Albite ,symbols.namesake ,Aluminosilicate ,Materials Chemistry ,Ceramics and Composites ,Anhydrous ,symbols ,Raman spectroscopy ,Boron ,Dissolution - Abstract
A combined nuclear magnetic resonance, infrared and Raman spectroscopic study on the effect of water dissolution on the structure of B-bearing aluminosilicate glasses is presented. The base composition was albite (NaAlSi3O8) to which different amounts of B2O3 (4.8, 9.1, 16.7 wt%) were added. Hydrous glasses containing 4.4 ± 0.1 wt% water were synthesized at pressures of 2000 bar. The results show that B dissolves in both dry and hydrous glasses by forming predominantly trigonal BO3 groups although some tetrahedral BO4 is also present. In anhydrous glasses prepared at high pressures (above 10 kbar) the fraction of BO4 increased. The hydrous glasses contain more BO4 groups compared to the dry counterparts, suggesting that this species is stabilized by water. The Raman and NMR (17O, 27Al, 29Si) spectra show that B interacts with the aluminosilicate network by formation of Si–O–B and probably Al–O–B units. In the hydrous glasses the water speciation changes significantly towards higher hydroxyl concentrations with increasing B-content. The NIR peaks, which are related to OH groups and molecular H2O, develop additional shoulders, suggesting that possibly B–OH complexes are formed.
- Published
- 2004
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42. Synthesis, structure and superconducting properties of the (Hg0.65V0.35)Sr2(Nd1−ySry)Cu2O6+δ system
- Author
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Neil C. Hyatt, Ray Dupree, Kelly L. Moran, and Ian Gameson
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Materials science ,Annealing (metallurgy) ,Neutron diffraction ,Analytical chemistry ,Energy Engineering and Power Technology ,Crystal structure ,Condensed Matter Physics ,Microstructure ,Magnetic susceptibility ,Electronic, Optical and Magnetic Materials ,Molecular geometry ,X-ray crystallography ,Electrical and Electronic Engineering ,Powder diffraction - Abstract
Near single-phase compositions in the (Hg 0.65 V 0.35 )Sr 2 (Nd 1− y Sr y )Cu 2 O 6+ δ system have been prepared in the narrow composition range 0.3⩽ y ⩽0.5, with a maximum T c =82 K observed for y =0.5. The crystal structure of a phase with the refined composition (Hg 0.60 V 0.40 )Sr 2 (Nd 0.53 Sr 0.47 )Cu 2 O 6.94 was determined from a combination of 51 V solid state NMR and (X-ray and neutron) powder diffraction data. In this material, linear HgO 2 2− units are partially substituted by tetrahedral VO 4 3− oxyanions, resulting in a significant distortion of the neighbouring CuO 5 and SrO 8+ δ polyhedra. Annealing (Hg 0.60 V 0.40 )Sr 2 (Nd 0.53 Sr 0.47 )Cu 2 O 6.94 under flowing argon reduces T c from 67 K in the as prepared material to 54 K in the annealed product; in contrast, annealing the as-prepared material under flowing oxygen does not change T c significantly.
- Published
- 2003
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43. Application of amplitude-modulated radiofrequency fields to the magic-angle spinning NMR of spin- nuclei
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Perunthiruthy K. Madhu, Malcolm H. Levitt, Mark E. Smith, Kevin J. Pike, Ray Dupree, and Ole G. Johannessen
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Physics ,Nuclear and High Energy Physics ,Pulse (signal processing) ,Biophysics ,Condensed Matter Physics ,Biochemistry ,Signal ,Spectral line ,Amplitude ,Nuclear magnetic resonance ,Magic angle spinning ,Atomic physics ,Spin (physics) ,Spinning ,Excitation - Abstract
We report pulse sequences for the sensitivity enhancement of magic-angle spinning and multiple-quantum magic-angle spinning spectra of spin-(7)/(2) systems. Sensitivity enhancement is obtained with the use of fast amplitude-modulated (FAM) radiofrequency pulses. In one-dimensional magic-angle spinning experiments, signal enhancement of 3 is obtained by a FAM pulse followed by a soft 90 pulse. In two-dimensional multiple-quantum magic-angle spinning experiments, FAM pulses are used for both the excitation of multiple-quantum coherences and for their conversion into observable single-quantum coherences. The observed signal enhancements are 2.2 in 3Q experiments, 3.1 in 5Q experiments, and 4.1 in 7Q experiments, compared to the conventional two-pulse scheme. The pulse schemes are demonstrated on the Sc-45 NMR of Sc-2(SO4)(3) (.) 5H(2)O and the La-139 NMR of LaAlO3. We also demonstrate the generation of FAM pulses by double-frequency irradiation.
- Published
- 2003
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44. A High-Resolution 17O and 29Si NMR Study of Zeolite Siliceous Ferrierite and ab Initio Calculations of NMR Parameters
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Ray Dupree, B. Bussemer, Andres Reinhold, and A. K. Cheetham, Ago Samoson, J. Sauer, Tiit Anupõld, and L. M. Bull
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Coupling constant ,Chemistry ,Carbon-13 NMR satellite ,Chemical shift ,Resolution (electron density) ,Analytical chemistry ,General Chemistry ,Biochemistry ,Catalysis ,Spectral line ,Colloid and Surface Chemistry ,Ferrierite ,Ab initio quantum chemistry methods ,Magic angle spinning - Abstract
High resolution 17O NMR spectra of siliceous ferrierite (Sil-FER) have been collected and the 29Si and 17O isotropic chemical shifts and the electric field gradients of oxygen have been calculated from first principles. The theoretical 29Si MAS NMR spectrum is found to be in excellent quantitative agreement with the experimentally determined spectrum, and is extremely sensitive to the accuracy of the structure used for the calculations, thus providing a method for assessing the quality of the structure determination. However, theoretical predictions of the chemical shifts, quadrupolar coupling constants and asymmetry parameters show only qualitative agreement with the experimental 17O NMR spectra obtained by Double Rotation (DOR) and multiple quantum magic angle spinning (MQMAS) as the spectra are much more complex (10 peaks within a shift range of less than 15 ppm, and the quadrupolar coupling constants only differ by 0.4 MHz) and hence higher accuracy is required from the shift calculations (>0.5 ppm), ...
- Published
- 2000
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45. NMR Evidence for ad-Wave Normal-State Pseudogap
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E. M. Haines, Ray Dupree, J. L. Tallon, R. Michalak, and Grant V. M. Williams
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Physics ,Superconductivity ,Condensed matter physics ,Band gap ,Condensed Matter::Superconductivity ,General Physics and Astronomy ,Condensed Matter::Strongly Correlated Electrons ,Cuprate ,Charge (physics) ,Knight shift ,Pseudogap ,Magnetic susceptibility ,Energy (signal processing) - Abstract
NMR data from high- ${T}_{c}$ superconducting cuprates having widely different ${T}_{c,\mathrm{max}}$ values and different hole concentrations, $p$, are shown to implicate a $d$-wave-like pseudogap. The deduced pseudogap energies agree well with the gap in the charge excitations determined from photoemission measurements, and the gap energies scale with ${T}_{c,\mathrm{max}}$. The pseudogap and superconducting gap thus have the same energy scale and for different cuprates have a universal $p$ dependence.
- Published
- 1997
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46. Transport and NMR studies of the effect of Ni substitution on superconductivity and the normal-state pseudogap inYBa2Cu4O8
- Author
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Ray Dupree, J. L. Tallon, R. Michalak, and Grant V. M. Williams
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Physics ,Superconductivity ,Condensed matter physics ,chemistry.chemical_element ,Substitution (algebra) ,NMR spectra database ,Crystallography ,Nickel ,chemistry ,Impurity ,Condensed Matter::Superconductivity ,Seebeck coefficient ,Condensed Matter::Strongly Correlated Electrons ,Pseudogap ,Energy (signal processing) - Abstract
Resistance, thermopower, and $^{89}\mathrm{Y}$ nuclear magnetic resonance (NMR) measurements have been carried out on ${\mathrm{YBa}}_{2}$(${\mathrm{Cu}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ni}}_{\mathit{x}}$${)}_{4}$${\mathrm{O}}_{8}$ superconductors. Nickel substitution reduces both ${\mathit{T}}_{\mathit{c}}$ and the pseudogap energy at almost the same rate as does Zn substitution, but unlike Zn substitution, there is no second peak in the $^{89}\mathrm{Y}$ NMR spectra that can be attributed to Y atoms sited near a local moment. We show that this discrepancy is consistent with there being no local suppression of the normal-state pseudogap about the Ni impurity contrary to the case for Zn. \textcopyright{} 1996 The American Physical Society.
- Published
- 1996
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47. In situ29Si MAS NMR studies of structural phase transitions of tridymite
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Kuniaki Kihara, Simon J. Kitchin, C. Michael B. Henderson, Ray Dupree, and Simon C. Kohn
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In situ ,Structural phase ,Crystallography ,Geophysics ,Materials science ,Tridymite ,Geochemistry and Petrology - Published
- 1996
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48. Structural Studies of ZrV2-xPxO7 Solid Solutions Using 31P−{51V} and 51V−{31P} Rotational Echo Double Resonance NMR
- Author
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Ray Dupree, Hellmut Eckert, and Christopher Hudalla
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Solid-state nuclear magnetic resonance ,Negative thermal expansion ,Chemistry ,Echo (computing) ,General Engineering ,Analytical chemistry ,Linear molecular geometry ,Physical and Theoretical Chemistry ,Space (mathematics) ,Spin (physics) ,Resonance (particle physics) ,Molecular physics ,Solid solution - Abstract
The negative thermal expansion coefficients of ZrV2-xPxO7 solid solutions are attributed to the structural flexibility of M−O−M‘ dimers (M, M‘ = P, V), upon which the structure of these materials is based. The local environments of these M species have been probed by high-resolution 31P and 51V solid state NMR experiments, assisted by 51V−{31P} and 31P−{51V} rotational echo double resonance (REDOR) studies for assignment purposes. At all of the compositions studied, formation of mixed P−O−V dimers is distinctly preferred over the symmetric P−O−P and V−O−V species, indicative of chemical ordering. Analysis of the REDOR experiments, assuming simple spin 1/2 behavior of the 51V nuclei, yields an estimate of the P···V internuclear distance in the mixed dimers of 3.42 A, consistent with a linear geometry of the P−O−V units as required by the space group symmetry. This result is subject to the important caveat that a precise theoretical description of REDOR behavior involving quadrupolar nuclei is not yet avail...
- Published
- 1996
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49. NMR investigation of the structure of some bioactive and related glasses
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M.W.G. Lockyer, Ray Dupree, and Diane Holland
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Silicon ,Chemistry ,Chemical shift ,Inorganic chemistry ,chemistry.chemical_element ,Condensed Matter Physics ,Condensation reaction ,Electronic, Optical and Magnetic Materials ,Crystallography ,Hydrolysis ,Materials Chemistry ,Ceramics and Composites ,Magic angle spinning ,Dissolution - Abstract
A magic angle spinning nuclear magnetic resonance (MAS-NMR) investigation of the environments of 29 Si, 31 P and 23 Na, in glasses from the Na 2 OCaOSiO 2 (6 wt% P 2 O 5 ) system, has shown that the distribution of non-bridging oxygens can be described by a binary distribution of Q 2 and Q 3 silicon species. The changes in the chemical shifts of these two species with composition are interpreted as resulting from the preferential association of Na + with Q 3 and Ca 2+ with Q 2 . It is suggested that it is this partitioning that determines bioactivity by controlling the dissolution, hydrolysis and condensation reactions which occur at the interface between the glass and the physiological environment.
- Published
- 1995
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50. Si-Al order in leucite revisited; new information from an analcite-derived analogue
- Author
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Ray Dupree, C. Michael B. Henderson, and Simon C. Kohn
- Subjects
Crystallography ,Geophysics ,Ion exchange ,Geochemistry and Petrology ,Chemistry ,Analytical chemistry ,Order (group theory) ,Neutron ,Remainder ,Leucite ,Spectral line - Abstract
The Si-AI ordering in t\VOcontrasting samples of leucite was studied using MAS NMR. One sample was synthesized by performing an ion exchange, in molten KCl, on a natural analcite specimen that had a small distribution of Al next-nearest neighbors (NNN). The other leucite sample was a typical natural specimen from the Alban Hills. In the specimen derived by ion exchange, 45-50% of the Al is on T2 sites with the remainder distributed approximately equally bet\veen the T 1 and T3 sites. The 29Sipeak positions in this sample resolve a debate in the literature over assignment of the more complex 29Si spectra of naturalleucite specimens. It is possible to simulate the 29Sispectrum of Alban Hills leucite with a wide variety of Al distributions, including either Al ordering onto T2 or Al ordering onto Tl + T3. By analogy with the analcite-derived sample and considering previous neutron and X-ray data, Al ordering onto T2 is considered somewhat more probable than the alternative schemes. ~ite-ordering information obtained from
- Published
- 1995
- Full Text
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