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https://www.readbyqxmd.com/read/28794408/zhamanshin-astrobleme-provides-evidence-for-carbonaceous-chondrite-and-post-impact-exchange-between-ejecta-and-earth-s-atmosphere
#1
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
https://www.readbyqxmd.com/read/28755523/reactivity-of-the-sterically-demanding-siloxanediol-mes2si-oh-%C3%A2%C2%B5-o-si-oh-mes2-towards-water-and-ether-molecules
#2
Thomas Braun, Philipp Roesch, Ulrike Warzok, Martin Enke, Robert Müller, Caspar Schattenberg, Christoph Schalley, Martin Kaupp, Philipp Wittwer
A series of isotopologues of the siloxanediol Mes2Si(OH)(µ-O)Si(OH)Mes2 (3a) (Mes = 1,3,5-trimethylphenyl) were synthesized by reactions of the corresponding disiloxane precursors Mes2Si(µ-O)2SiMes2 (2a), Mes2Si(µ-17O)2SiMes2 (2b) or Mes2Si(µ-18O)2SiMes2 (2c) with an excess of H2O, H217O or H218O. 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
https://www.readbyqxmd.com/read/28707809/structural-features-of-europium-ii-containing-cryptates-that-influence-relaxivity
#3
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...
July 14, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28692274/solid-state-15-n-and-17-o-nmr-studies-of-s-nitrosothiols
#4
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
https://www.readbyqxmd.com/read/28650638/identification-and-structure-activity-relationships-of-novel-compounds-that-potentiate-the-activities-of-antibiotics-in-escherichia-coli
#5
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
https://www.readbyqxmd.com/read/28499071/natural-abundance-17-o-dnp%C3%A2-nmr-provides-precise-o-h-distances-and-insights-into-the-br%C3%A3-nsted-acidity-of-heterogeneous-catalysts
#6
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
https://www.readbyqxmd.com/read/28475335/oxygen-speciation-in-multicomponent-silicate-glasses-using-through-bond-double-resonance-nmr-spectroscopy
#7
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
https://www.readbyqxmd.com/read/28319391/synthesis-isotopic-enrichment-and-solid-state-nmr-characterization-of-zeolites-derived-from-the-assembly-disassembly-organization-reassembly-process
#8
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
https://www.readbyqxmd.com/read/27782387/proton-probability-distribution-in-the-o%C3%A2-%C3%A2-%C3%A2-h%C3%A2-%C3%A2-%C3%A2-o-low-barrier-hydrogen-bond-a-combined-solid-state-nmr-and-quantum-chemical-computational-study-of-dibenzoylmethane-and-curcumin
#9
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
https://www.readbyqxmd.com/read/27731644/solid-state-17-o-nmr-of-unstable-acyl-enzyme-intermediates-a-direct-probe-of-hydrogen-bonding-interactions-in-the-oxyanion-hole-of-serine-proteases
#10
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
https://www.readbyqxmd.com/read/27723980/structure-and-chemical-durability-of-lead-crystal-glass
#11
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
https://www.readbyqxmd.com/read/27712065/quantum-dynamics-of-the-17-o-32-o2-collision-process
#12
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
https://www.readbyqxmd.com/read/27690222/identification-of-anthropogenic-co2-using-triple-oxygen-and-clumped-isotopes
#13
Amzad H Laskar, Sasadhar Mahata, Mao-Chang Liang
Quantification of contributions from various sources of CO2 is important for understanding the atmospheric CO2 budget. Considering the number and diversity of sources and sinks, the widely used proxies such as concentration and conventional isotopic compositions (δ(13)C and δ(18)O) are not always sufficient to fully constrain the CO2 budget. Additional constraints may help in understanding the mechanisms of CO2 production and consumption. The anomaly in triple oxygen isotopes or (17)O excess (denoted by Δ(17)O) and molecules containing two rare isotopes, called clumped isotopes, are two recently developed tracers with potentials to independently constrain some important processes that regulate CO2 in the atmosphere...
November 1, 2016: Environmental Science & Technology
https://www.readbyqxmd.com/read/27616442/effect-of-condensed-tannin-profile-on-wheat-flour-dough-rheology
#14
Audrey L Girard, M Elena Castell-Perez, Scott R Bean, Sherry L Adrianos, Joseph M Awika
Proanthocyanidins (PA) cross-link proteins and could expand wheat gluten functionality; however, how the PA MW or gluten profile affect these interactions is unknown. Effect of PA MW profile (sorghum versus grape seed PA) on dough rheology of high versus low insoluble polymeric protein (IPP) wheat flour was evaluated using mixograph, large (TA.XT2i) and small (HAAKE Rheostress 6000) deformation rheometry. Sorghum PA (93% polymeric) more effectively (p < 0.05) strengthened both glutens than grape seed PA (45% polymeric), without reducing gluten extensibility...
October 5, 2016: Journal of Agricultural and Food Chemistry
https://www.readbyqxmd.com/read/27538437/probing-oxide-ion-mobility-in-the-mixed-ionic-electronic-conductor-la2nio4-%C3%AE-by-solid-state-17-o-mas-nmr-spectroscopy
#15
David M Halat, Rıza Dervişoğlu, Gunwoo Kim, Matthew T Dunstan, Frédéric Blanc, Derek S Middlemiss, Clare P Grey
While solid-state NMR spectroscopic techniques have helped clarify the local structure and dynamics of ionic conductors, similar studies of mixed ionic-electronic conductors (MIECs) have been hampered by the paramagnetic behavior of these systems. Here we report high-resolution (17)O (I = 5/2) solid-state NMR spectra of the mixed-conducting solid oxide fuel cell (SOFC) cathode material La2NiO4+δ, a paramagnetic transition-metal oxide. Three distinct oxygen environments (equatorial, axial, and interstitial) can be assigned on the basis of hyperfine (Fermi contact) shifts and quadrupolar nutation behavior, aided by results from periodic DFT calculations...
September 14, 2016: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/27525537/observation-of-the-second-order-quadrupolar-interaction-as-a-dominating-nmr-relaxation-mechanism-in-liquids-the-ultraslow-regime-of-motion
#16
Jiahui Shen, Victor Terskikh, Gang Wu
We report variable-temperature (VT) (17)O NMR spectra of [5-(17)O]-d-glucose in an aqueous solution and in glycerol at 14.1 and 21.1 T. The VT (17)O NMR data cover a wide range of motion for which the molecular rotational correlation time (τc) of glucose changes more than 5 orders of magnitude. The observed line width of the (17)O NMR signal for [5-(17)O]-d-glucose displays a maximum at ω0τc ≈ 1 and a minimum at ω0τc ≈ 150, where ω0 is the angular Larmor frequency of (17)O. Under the ultraslow motion condition (i...
September 1, 2016: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/27525444/water-soluble-pentagonal-prismatic-titanium-oxo-clusters
#17
Guanyun Zhang, Caiyun Liu, De-Liang Long, Leroy Cronin, Chen-Ho Tung, Yifeng Wang
By using solubility control to crystallize the prenucleation clusters of hydrosol, a family of titanium-oxo clusters possessing the {Ti18O27} core in which the 18 Ti(IV)-ions are uniquely connected with μ-oxo ligands into a triple-decked pentagonal prism was obtained. The cluster cores are wrapped by external sulfate and aqua ligands, showing good solubilities and stabilities in a variety of solvents including acetonitrile and water and allowing their solution chemistry being studied by means of electrospray ionization mass spectroscopy, (17)O NMR, and vibrational spectroscopy...
September 7, 2016: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/27454747/-17-o-nmr-investigation-of-water-structure-and-dynamics
#18
Eric G Keeler, Vladimir K Michaelis, Robert G Griffin
The structure and dynamics of the bound water in barium chlorate monohydrate were studied with (17)O nuclear magnetic resonance (NMR) spectroscopy in samples that are stationary and spinning at the magic-angle in magnetic fields ranging from 14.1 to 21.1 T. (17)O NMR parameters of the water were determined, and the effects of torsional oscillations of the water molecule on the (17)O quadrupolar coupling constant (CQ) were delineated with variable temperature MAS NMR. With decreasing temperature and reduction of the librational motion, we observe an increase in the experimentally measured CQ explaining the discrepancy between experiments and predictions from density functional theory...
August 18, 2016: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/27443474/modified-limb-lead-ecg-system-effects-on-electrocardiographic-wave-amplitudes-and-frontal-plane-axis-in-sinus-rhythm-subjects
#19
Sivaraman Jayaraman, Venkatesan Sangareddi, R Periyasamy, Justin Joseph, Ravi Marimuthu Shanmugam
OBJECTIVE: Modified Limb Lead (MLL) ECG system may be used during rest or exercise ECG, or atrial activity enhancement. Because of modification in the limb electrode placement, changes are likely to happen in ECG wave amplitudes and frontal plane axis, which may alter the clinical limits of normality and ECG diagnostic criteria. The present study investigated the effects of the modified limb electrode position on the electrocardiographic waveforms, ST segment amplitudes (STa) and frontal plane axis...
January 2017: Anatolian Journal of Cardiology
https://www.readbyqxmd.com/read/27315634/paramagnetic-phospholipid-based-micelles-targeting-vcam-1-receptors-for-mri-visualization-of-inflammation
#20
Amerigo Pagoto, Rachele Stefania, Francesca Garello, Francesca Arena, Giuseppe Digilio, Silvio Aime, Enzo Terreno
Inflammation is signaled by the overexpression of epitopes on the vascular endothelium that primarily aim at recruiting immune cells into the inflamed area. The intravascular localization of these biomarkers makes them suitable targets for the MRI visualization of inflammation. Phospholipid-based nanosystems appear excellent candidates in virtue of their good biocompatibility, ability to deliver a high number of imaging units at the target site, and for the easy functionalization with targeting vectors. In this work, phospholipid-based micelles (hydrodynamic diameter of 20 nm) loaded with the amphiphilic Gd(III)-complex Gd-DOTAMA(C18)2 were vectorized with a small peptide able to specifically bind VCAM-1 receptors...
August 17, 2016: Bioconjugate Chemistry
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