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Yi-Jung Tu, Zhijin Lin, Matthew J Allen, G Andrés Cisneros
We report a kinetic study of the water exchange on lanthanide ions in water/[1-ethyl-3-methylimidazolium][trifluoromethylsufate] (water/[EMIm][OTf]). The results from 17O-NMR measurements show that the water-exchange rates in water/[EMIm][OTf] increase with decreasing size of the lanthanide ions. This trend for water-exchange is similar to the previously reported trend in water/1-ethyl-3-methylimidazolium ethyl sulfate (water/[EMIm][EtSO4]) but opposite to that in water. To gain atomic-level insight into these water-exchange reactions, molecular dynamics simulations for lanthanide ions in water/[EMIm][OTf] have been performed using the atomic-multipole-optimized-energetics-for-biomolecular-application polarizable force field...
January 14, 2018: Journal of Chemical Physics
Balamurugan Kandasamy, Peter G Bruce, William Clegg, Ross W Harrington, Antonio Rodriguez Fortea, Magda Pascual Borras, John Errington
Incorporation of {MX}n+ groups into polyoxometalates (POMs) provides the means not only to introduce reactivity and functionality but also to tune the electronic properties of the oxide framework by varying M, X and n. In order to elucidate the factors responsible for differences in reactivity between {TiW5} and {SnW5} Lindqvist-type hexametalates, a series of alkoxido- and aryloxido-tin substituted POMs (nBu4N)3[(RO)SnW5O18] (R = Me, Et, iPr and tBu) and (nBu4N)3[(ArO)SnW5O18] (Ar = C6H5, 4-MeC6H5, 4-tBuC6H5, 4-HOC6H4, 3-HOC6H4 and 2-CHOC6H4) has been structurally characterised and studied by multinuclear NMR (1H, 13C, 17O, 119Sn and 183W) and FTIR spectroscopy...
January 5, 2018: Chemistry: a European Journal
Stuart J Elliott, Christian Bengs, Karel Kouril, Benno Meier, Shamim Alom, Richard J Whitby, Malcolm Harris Levitt
The 17O isotopomer of the water-endofullerene H2O@C60 displays a remarkable proton NMR spectrum, with six well resolved peaks. These peaks are due to the J-coupling between the water protons and the 17O nucleus, which has spin-5/2. The resolution of these peaks is enabled by the suppression of water proton exchange by the fullerene cage. The six peaks display an unusual pattern of linewidths, which we model by a Liouville-space treatment of scalar relaxation due to quadrupolar relaxation of the 17O nuclei. The data are consistent with rotational diffusion of the water molecule on the sub-picosecond timescale...
December 13, 2017: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
Pieter Geysens, Vijay Shankar Rangasamy, Savitha Thayumanasundaram, Koen Robeyns, Luc Van Meervelt, Jean-Pierre Locquet, Jan Fransaer, Koen Binnemans
Electrolytes consisting of sodium bis(fluorosulfonyl)imide (NaFSI) dissolved in glymes (monoglyme, diglyme and triglyme) were characterized by FT-Raman spectroscopy and 13C, 17O and 23Na NMR spectroscopy. The glyme:NaFSI molar ratio was varied from 50:1 to 1:1 and it was observed that in the dilute electrolytes, the sodium salt is completely dissociated into solvent separated ion pairs (SSIPs). However, contact ion pairs (CIPs) and aggregates (AGGs) become the predominant species in more concentrated solutions...
December 4, 2017: Journal of Physical Chemistry. B
Rui Zhou, Michihiro Hirata, Tao Wu, Igor Vinograd, Hadrien Mayaffre, Steffen Krämer, Arneil P Reyes, Philip L Kuhns, Ruixing Liang, W N Hardy, D A Bonn, Marc-Henri Julien
The value of the upper critical field Hc2, a fundamental characteristic of the superconducting state, has been subject to strong controversy in high-Tc copper oxides. Since the issue has been tackled almost exclusively by macroscopic techniques so far, there is a clear need for local-probe measurements. Here, we use 17O NMR to measure the spin susceptibility [Formula: see text] of the CuO2 planes at low temperature in charge-ordered YBa2Cu3O y We find that [Formula: see text] increases (most likely linearly) with magnetic field H and saturates above field values ranging from 20 T to 40 T...
November 28, 2017: Proceedings of the National Academy of Sciences of the United States of America
Nathan J Beal, Thomas A Corry, Patrick J O'Malley
A comparison between experimental and Broken Symmetry Density Functional Theory (BS-DFT) calculated hyperfine couplings for the S2 state of the oxygen evolving complex (OEC) has been performed. The effect of Ca substitution by Sr combined with the protonation state of two terminal hydroxo or water ligands, W1 and W2, on the calculated hyperfine couplings of 55Mn, 13C, 14N, 17O and 1H nuclei has been investigated. Our findings show best agreement for OEC models which contain a hydroxo group at the W2 position and a water molecule at W1...
November 27, 2017: Journal of Physical Chemistry. B
Eric G Keeler, Vladimir K Michaelis, Michael T Colvin, Ivan Hung, Peter L Gor'kov, Timothy A Cross, Zhehong Gan, Robert G Griffin
The structure of two protected amino acids, FMOC-L-leucine and FMOC-L-valine, and a dipeptide, N-acetyl-L-valyl-L-leucine (N-Ac-VL), were studied via one- and two-dimensional solid-state nuclear magnetic resonance (NMR) spectroscopy. Utilizing 17O magic-angle spinning (MAS) NMR at multiple magnetic fields (17.6-35.2 T/750-1500 MHz for 1H) the 17O quadrupolar and chemical shift parameters were determined for the two oxygen sites of each FMOC-protected amino acids and the three distinct oxygen environments of the dipeptide...
November 7, 2017: Journal of the American Chemical Society
Caroline A Yao, Thomas Imahiyerobo, Jordan Swanson, Allyn Auslander, Diego De Cardenas, Jane C Figueiredo, Meghan McCullough, Melinda Costa, Richard Vanderburg, William P Magee
BACKGROUND: Unilateral cleft lip has a spectrum of disease morphology but severity assessments are difficult given the absence of an accessible, objective assessment tools or reference data. We characterize the spectrum of cleft morphology before and after surgical repair for a large, multi-ethnic population using easily identifiable facial landmarks collected through a novel smart phone-based application. METHODS: Anthropometric measurements and standardized photographs were prospectively collected in Morocco, Bolivia, Vietnam and Madagascar during medical missions in 2015 utilizing an application designed specifically for the study...
September 14, 2017: Plastic and Reconstructive Surgery
Tomáš Magna, Karel Žák, Andreas Pack, Frédéric Moynier, Bérengère Mougel, Stefan Peters, Roman Skála, Šárka Jonášová, Jiří Mizera, Zdeněk Řanda
Chemical fingerprints of impacts are usually compromised by extreme conditions in the impact plume, and the contribution of projectile matter to impactites does not often exceed a fraction of per cent. Here we use chromium and oxygen isotopes to identify the impactor and impact-plume processes for Zhamanshin astrobleme, Kazakhstan. ε(54)Cr values up to 1.54 in irghizites, part of the fallback ejecta, represent the (54)Cr-rich extremity of the Solar System range and suggest a CI-like chondrite impactor. Δ(17)O values as low as -0...
August 9, 2017: Nature Communications
Philipp Roesch, Ulrike Warzok, Martin Enke, Robert Müller, Caspar Schattenberg, Christoph A Schalley, Martin Kaupp, Thomas Braun, Philipp Wittwer
A series of isotopologues of the siloxanediol Mes2 Si(OH)(μ-O)Si(OH)Mes2 (3 a) (Mes=2,4,6-trimethylphenyl) were synthesized by reactions of the corresponding disiloxane precursors Mes2 Si(μ-O)2 SiMes2 (2 a), Mes2 Si(μ-(17) O)2 SiMes2 (2 b) or Mes2 Si(μ-(18) O)2 SiMes2 (2 c) with an excess of H2 O, H2(17) O or H2(18) O. NMR and IR signal assignments for the siloxanediols in benzene are supported by quantum-chemical calculations, which indicate small energy differences between trans and cis conformers, the latter of which exhibits an intramolecular hydrogen bond...
July 29, 2017: Chemistry: a European Journal
Chamika U Lenora, Fabio Carniato, Yimin Shen, Zahid Latif, E Mark Haacke, Philip D Martin, Mauro Botta, Matthew J Allen
Eu(II) -containing complexes were studied with respect to properties relevant to their use as contrast agents for magnetic resonance imaging. The influences of molecular parameters and field strength on relaxivity were studied for a series of Eu(II) -containing cryptates and their adducts with β-cyclodextrins, poly-β-cyclodextrins, and human serum albumin. Solid- and solution-phase characterization of Eu(II) -containing complexes is presented that demonstrates the presence of inner-sphere molecules of water...
November 2, 2017: Chemistry: a European Journal
Yin Gao, Yizhe Dai, Gang Wu
We report a solid-state (15)N and (17)O NMR study of two representative S-nitrosothiols (RSNO): S-nitroso N-acetylpenicillamine (SNAP) and S-nitrosoglutathione (GSNO). The (15)N and (17)O NMR tensors are experimentally determined for the first time for this important class of nitric-oxide (NO)-related compounds. The observed NMR characteristics for RSNO include large (15)N and (17)O chemical shift anisotropies and large (17)O quadrupole coupling constants. Quantum chemical calculations are also performed for the (15)N and (17)O NMR tensors in two simple RSNO models: t-BuSNO and MeSNO...
July 20, 2017: Journal of Physical Chemistry. B
Keith M Haynes, Narges Abdali, Varsha Jhawar, Helen I Zgurskaya, Jerry M Parks, Adam T Green, Jerome Baudry, Valentin V Rybenkov, Jeremy C Smith, John K Walker
In Gram-negative bacteria, efflux pumps are able to prevent effective cellular concentrations from being achieved for a number of antibiotics. Small molecule adjuvants that act as efflux pump inhibitors (EPIs) have the potential to reinvigorate existing antibiotics that are currently ineffective due to efflux mechanisms. Through a combination of rigorous experimental screening and in silico virtual screening, we recently identified novel classes of EPIs that interact with the membrane fusion protein AcrA, a critical component of the AcrAB-TolC efflux pump in Escherichia coli...
July 27, 2017: Journal of Medicinal Chemistry
Frédéric A Perras, Zhuoran Wang, Pranjali Naik, Igor I Slowing, Marek Pruski
Heterogeneous Brønsted acid catalysts are tremendously important in industry, particularly in catalytic cracking processes. Here we show that these Brønsted acid sites can be directly observed at natural abundance by (17) O DNP surface-enhanced NMR spectroscopy (SENS). We additionally show that the O-H bond length in these catalysts can be measured with sub-picometer precision, to enable a direct structural gauge of the lability of protons in a given material, which is correlated with the pH of the zero point of charge of the material...
May 12, 2017: Angewandte Chemie
Sohei Sukenaga, Pierre Florian, Koji Kanehashi, Hiroyuki Shibata, Noritaka Saito, Kunihiko Nakashima, Dominique Massiot
The description of the structure of aluminosilicate glasses is more often centered on its cationic constituents, and oxygen ions determine their connectivity, directly impacting the physical properties of those disordered materials. A very powerful approach to ascertain this short- to medium-range order is to use (17)O NMR, but up to now the speciation of the chemical bonds was only ambiguously achieved for multicomponent glasses. Here, we propose to directly probe the very scarcely explored through-bond correlations using (17)O{(27)Al} and (17)O{(23)Na} solid-state nuclear magnetic resonance (NMR) double-resonance experiments...
May 8, 2017: Journal of Physical Chemistry Letters
Giulia P M Bignami, Daniel M Dawson, Valerie R Seymour, Paul S Wheatley, Russell E Morris, Sharon E Ashbrook
The great utility and importance of zeolites in fields as diverse as industrial catalysis and medicine has driven considerable interest in the ability to target new framework types with novel properties and applications. The recently introduced and unconventional assembly, disassembly, organization, reassembly (ADOR) method represents one exciting new approach to obtain solids with targeted structures by selectively disassembling preprepared hydrolytically unstable frameworks and then reassembling the resulting products to form materials with new topologies...
April 12, 2017: Journal of the American Chemical Society
Xianqi Kong, Andreas Brinkmann, Victor Terskikh, Roderick E Wasylishen, Guy M Bernard, Zhuang Duan, Qichao Wu, Gang Wu
We report a combined solid-state ((1)H, (2)H, (13)C, (17)O) NMR and plane-wave density functional theory (DFT) computational study of the O···H···O low-barrier hydrogen bonds (LBHBs) in two 1,3-diketone compounds: dibenzoylmethane (1) and curcumin (2). In the solid state, both 1 and 2 exist in the cis-keto-enol tautomeric form, each exhibiting an intramolecular LBHB with a short O···O distance (2.435 Å in 1 and 2.455 Å in 2). Whereas numerous experimental (structural and spectroscopic) and computational studies have been reported for the enol isomers of 1,3-diketones, a unified picture about the proton location within an LBHB is still lacking...
November 17, 2016: Journal of Physical Chemistry. B
Aaron W Tang, Xianqi Kong, Victor Terskikh, Gang Wu
We report preparation, trapping, and solid-state 17O NMR characterization of three unstable acyl-enzyme intermediates (≈ 26 kDa): p-N,N-dimethylamino-[17O]benzoyl-chymotrypsin, trans-o-methoxy-[17O]cinnamoyl-chymotrypsin, and trans-p-methoxy-[17O]cinnamoyl-chymotrypsin. We show that both the 17O chemical shifts and nuclear quadrupolar parameters obtained for these acyl-enzyme intermediates in the solid state are correlated with their deacylation rate constants measured in aqueous solution. With the aid of quantum mechanical calculations, the experimental 17O NMR parameters were interpreted as to reflect the hydrogen bonding interactions between the carbonyl (C=17O) functional group of the acyl moiety and the two NH groups from the protein backbone (Ser195 and Gly193) in the oxyanion hole, a general feature of all serine proteases...
October 12, 2016: Journal of Physical Chemistry. B
Frédéric Angeli, Patrick Jollivet, Thibault Charpentier, Maxime Fournier, Stéphane Gin
Silicate glasses containing lead, also called lead crystal glasses, are commonly used as food product containers, in particular for alcoholic beverages. Lead's health hazards require major attention, which can first be investigated through the understanding of Pb release mechanisms in solution. The behavior of a commercial crystal glass containing 10.6 mol % of PbO (28.3 wt %) was studied in a reference solution of 4% acetic acid at 22, 40, and 70 °C at early and advanced stages of reaction. High-resolution solid-state (17)O and (29)Si NMR was used to probe the local structure of the pristine and, for the first time, of the altered lead crystal glass...
November 1, 2016: Environmental Science & Technology
Gregoire Guillon, Pascal Honvault
We report full quantum integral and differential cross sections and rate constants for the 17O + 32O2 collision, possibly reactive, process. This constitutes the first quantum scattering study of the 17O16O16O system. We emphasize the comparison with the 18O + 32O2 collision in close connection to the mass independent fractionation (thereafter refered to as MIF) puzzle for ozone in atmospheric chemistry. We find similar general trends in the cross sections and rate constants for both rare isotopes, but we note some singular behaviors peculiar to the use of 17O isotope, particularly at the lowest collision energies...
October 7, 2016: Journal of Physical Chemistry. A
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