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Solid-state NMR

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https://www.readbyqxmd.com/read/28812886/room-temperature-ring-opening-of-quinoline-isoquinoline-and-pyridine-with-low-valent-titanium
#1
Seung-Yeol Baek, Takashi Kurogi, Dahye Kang, Masahiro Kamitani, Seongyeon Kwon, Douglas Solowey, Chun-Hsing Chen, Maren Pink, Patrick J Carroll, Daniel J Mindiola, Mu-Hyun Baik
The complex (PNP)Ti=CHtBu(CH2tBu) (PNP = N[2-PiPr2-4-methylphenyl]2-) dehydrogenates cyclohexane to cyclohexene by forming a transient low-valent titanium-alkyl species, [(PNP)Ti(CH2tBu)], which reacts with two equivalents of quinoline (Q) at room temperature to form H3CtBu and a Ti(IV) species where the less hindered C2=N1 bond of Q is ruptured and coupled to another equivalent of Q. The product isolated from this reaction is an imide with a tethered cycloamide group, (PNP)Ti=N[C18H13N] (1). Under photolytic conditions, intramolecular C-H bond activation across the imide-moiety in 1 occurs to form 2, and thermolysis reverses this process...
August 16, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28812758/a-metalloporphyrin-based-porous-organic-polymer-as-an-efficient-catalyst-for-the-catalytic-oxidation-of-olefins-and-arylalkanes
#2
Zheng-Dong Ding, Wei Zhu, Tao Li, Rui Shen, Yunxing Li, Zaijun Li, Xuehong Ren, Zhi-Guo Gu
A metalloporphyrin-based porous organic polymer, Mn-PPOP-1, was constructed in high yield via the ketoenamine condensation of robust porphyrin tetraamines (TBPP) with 1,3,5-triformylphloroglucinol. The stable keto-enamine form in the synthesized polymer was unambiguously confirmed by (13)C CP-MAS solid state NMR. Noticeably, besides the high thermal and chemical stability, this material contains both micropores and mesopores, which are favorable for mass transfer in the catalytic application. Mn-PPOP-1 exhibits significantly high catalytic oxidation of olefins and arylalkanes at room temperature...
August 16, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28812063/self-organization-of-amino-acid-derived-ndi-assemblies-into-a-nanofibrillar-superstructure-with-humidity-sensitive-n-type-semiconducting-properties
#3
Marco A Squillaci, Grzegorz Markiewicz, Anna Walczak, Artur Ciesielski, Artur R Stefankiewicz, Paolo Samorì
The hierarchical self-assembly of l-tyrosine substituted naphthalenediimide has been explored in solution by NMR spectroscopy and in the solid-state by atomic force microscopy. Spontaneous non-covalent polymerisation led to the formation of a three-dimensional fibre-like supramolecular polymer with n-type semiconducting properties.
August 16, 2017: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/28809493/macroscopic-structural-compositions-of-%C3%AF-conjugated-polymers-combined-insights-from-solid-state-nmr-and-molecular-dynamics-simulations
#4
Anton Melnyk, Matthias Junk, Michael D McGehee, Bradley F Chmelka, Michael Ryan Hansen, Denis Andrienko
Molecular dynamics simulations are combined with solid-state NMR measurements to gain insight into the macroscopic structural composition of the π-conjugated polymer poly(2,5-bis(3-tetradecyl-thiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT). The structural and dynamical properties, as established by the NMR analyses, were used to test the local structure of three constitutient mesophases with: (i) crystalline backbones and side chains, (ii) lamellar backbones and disordered side chains, or (iii) amorphous backbones and side chains...
August 15, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28809485/dispersion-and-halogen-bonding-interactions-binding-of-the-axial-conformers-of-monohalo-and-%C3%A2-trans-1-2-dihalocyclohexanes-in-enantiopure-alleno-acetylenic-cages
#5
Cornelius Gropp, Tamara Husch, Nils Trapp, Markus Reiher, François Diederich
Enantiopure alleno-acetylenic cage (AAC) receptors with a resorcin[4]arene scaffold, from which four homochiral alleno-acetylenes converge to shape a cavity closed by a four-fold OH-hydrogen-bonding array, form a highly ordered porous network in the solid state. They enable the complexation and co-crystallization of otherwise non-crystalline small molecules. This paper analyzes the axial conformers of monohalo- and (±)-trans-1,2-dihalocyclohexanes, bound in the interior cavity of the AACs, on the atomic level in the solid state and in solution, accompanied by accurate calculations...
August 15, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28809415/stimuli-responsive-emissive-behavior-of-1-and-1-3-connectivities-in-azulene-based-imine-ligands-cycloplatination-and-pt-tl-dative-bond-formation
#6
Sirous Jamali, Narges-Alsadat Mousavi, Mojtaba Bagherzadeh, Reza Kia, Hamidreza Samouei
The preparation of two new azulene-based imine ligands N-(2,6-diisopropylphenyl)-6-(t)Bu-1-azulenylmethaneimine, 3, and N-(2,6-diisopropylphenyl)-6-(t)Bu-3-(2,6-diisopropylphenyliminomethyl)-1-azulenylmethaneimine, 4, is described. These imine ligands display stimuli responsive emissive behavior and their fluorescence can be switched on and off by protonation and neutralization with trifluoroacetic acid and trimethylamine, respectively. The cyclometalation of the monoimine ligand by platinum gave the cyclometalated complex [PtMe(SMe2)(3')], 5, (where the prime denotes the cyclometalated ligand 3)...
August 15, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28806512/painkiller-isoxicam-and-its-copper-complex-can-form-inclusion-complexes-with-different-cyclodextrins-a-fluorescence-fourier-transform-infra-red-spectroscopy-and-nuclear-magnetic-resonance-study
#7
Sathi Goswami, Anupa Majumdar, Munna Sarkar
The interaction of a painkiller Isoxicam, belonging to the oxicam group of Non Steroidal Anti-Inflammatory Drugs (NSAIDs) and its copper complex with different cyclodextrins (β-CD, γ-CD, HPβCD and HPγCD ) has been investigated in both solution and the solid state. Steady state and time resolved fluorescence spectroscopy, fluorescence anisotropy, 1H NMR and FTIR spectroscopy are used. Both the drug and its copper complex form host-guest inclusion complex with all CDs. Fluorescence spectroscopy is used to determine binding constants and stoichiometries of the host-guest complex...
August 14, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/28805700/bilp-19-an-ultramicroporous-organic-network-with-exceptional-carbon-dioxide-uptake
#8
Christoph Klumpen, Florian Radakovitsch, Andreas Jess, Jürgen Senker
Porous benzimidazole-based polymers (BILPs) have proven to be promising for carbon dioxide capture and storage. The polarity of their chemical structure in combination with an inherent porosity allows for adsorbing large amounts of carbon dioxide in combination with high selectivities over unpolar guest molecules such as methane and nitrogen. For this reason, among purely organic polymers, BILPs contain some of the most effective networks to date. Nevertheless, they are still outperformed by competitive materials such as metal-organic frameworks (MOFs) or metal doped porous polymers...
August 12, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
https://www.readbyqxmd.com/read/28803476/rationally-turning-the-interface-activity-of-mesoporous-silicas-for-preparing-pickering-foam-and-dry-water
#9
Xia Rong, Hengquan Yang, Ning Zhao
We develop a novel protocol to prepare smart, gas/water interface-active, mesoporous silica particles. This protocol involves modification of highly mesoporous silicas with a mixture of hydrophobic octyl organosilane and hydrophilic triamine organosilane. Their structure and compositions are characterized by transmission electron microscopy (TEM), N2 sorption, solid state NMR, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FT-IR), Thermogravimetric analysis (TGA) and elemental analysis...
August 13, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
https://www.readbyqxmd.com/read/28802890/is-protein-deuteration-beneficial-for-proton-detected-solid-state-nmr-at-and-above-100%C3%A2-khz-magic-angle-spinning
#10
Diane Cala-De Paepe, Jan Stanek, Kristaps Jaudzems, Kaspars Tars, Loren B Andreas, Guido Pintacuda
(1)H-detection in solid-state NMR of proteins has been traditionally combined with deuteration for both resolution and sensitivity reasons, with the optimal level of proton dilution being dependent on MAS rate. Here we present (1)H-detected (15)N and (13)C CP-HSQC spectra on two microcrystalline samples acquired at 60 and 111 kHz MAS and at ultra-high field. We critically compare the benefits of three labeling schemes yielding different levels of proton content in terms of resolution, coherence lifetimes and feasibility of scalar-based 2D correlations under these experimental conditions...
July 25, 2017: Solid State Nuclear Magnetic Resonance
https://www.readbyqxmd.com/read/28801573/a-structural-and-mechanistic-study-of-%C3%AF-clamp-mediated-cysteine-perfluoroarylation
#11
Peng Dai, Jonathan K Williams, Chi Zhang, Matthew Welborn, James J Shepherd, Tianyu Zhu, Troy Van Voorhis, Mei Hong, Bradley L Pentelute
Natural enzymes use local environments to tune the reactivity of amino acid side chains. In searching for small peptides with similar properties, we discovered a four-residue π-clamp motif (Phe-Cys-Pro-Phe) for regio- and chemoselective arylation of cysteine in ribosomally produced proteins. Here we report mutational, computational, and structural findings directed toward elucidating the molecular factors that drive π-clamp-mediated arylation. We show the significance of a trans conformation prolyl amide bond for the π-clamp reactivity...
August 11, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28799601/on-the-use-of-solid-state-45-sc-nmr-for-structural-investigations-of-molecular-and-silica-supported-scandium-amide-catalysts
#12
T Vancompernolle, X Trivelli, L Delevoye, F Pourpoint, R M Gauvin
Tris- and tetra-coordinated scandium amides were grafted onto silica and probed as catalysts for alkyne dimerization. (45)Sc NMR was carried out, providing information about the metal coordination sphere. The increasing number of coordinated ligands was correlated with decreased catalytic activity.
August 11, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28797926/accurate-determination-of-chemical-shift-tensor-orientations-of-single-crystals-by-solid-state-magic-angle-spinning-nmr
#13
Yamini S Avadhut, Johannes Weber, Jörn Schmedt Auf der Günne
An improved implementation of single-crystal magic-angle-spinning (MAS) NMR is presented which gives access to chemical shift tensors both in orientation (relative to the crystal axis system) and principal axis values. For mounting arbitrary crystals inside ordinary MAS rotors, a mounting tool is described which allows to relate the crystal orientation determined by diffraction techniques to the rotor coordinate system. The crystal is finally mounted into a MAS rotor equipped with a special insert which allows a defined reorientation of the single-crystal by 90°...
July 24, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28793213/critical-influence-of-cosolutes-and-surfaces-on-the-assembly-of-serpin-derived-amyloid-fibrils
#14
Michael W Risør, Dennis W Juhl, Morten Bjerring, Joachim Mathiesen, Jan J Enghild, Niels C Nielsen, Daniel E Otzen
Many proteins and peptides self-associate into highly ordered and structurally similar amyloid cross-β aggregates. This fibrillation is critically dependent on properties of the protein and the surrounding environment that alter kinetic and thermodynamic equilibria. Here, we report on dominating surface and solution effects on the fibrillogenic behavior and amyloid assembly of the C-36 peptide, a circulating bioactive peptide from the α1-antitrypsin serine protease inhibitor. C-36 converts from an unstructured peptide to mature amyloid twisted-ribbon fibrils over a few hours when incubated on polystyrene plates under physiological conditions through a pathway dominated by surface-enhanced nucleation...
August 8, 2017: Biophysical Journal
https://www.readbyqxmd.com/read/28792111/solid-state-nmr-h-n-c-h-and-h-n-c-c-3d-4d-correlation-experiments-for-resonance-assignment-of-large-proteins
#15
Hugo Fraga, Charles-Adrien Arnaud, Diego F Gauto, Maxime J C Audin, Vilius Kurauskas, Pavel Macek, Carsten Krichel, Jia-Ying Guan, Jérôme Boisbouvier, Remco Sprangers, Cécile Breyton, Paul Schanda
Solid-state NMR can provide insight into protein structure and dynamics at the atomic level without inherent protein size limitations. However, a major hurdle to studying large proteins by solid-state NMR spectroscopy is related to spectral complexity and resonance overlap, which increase with molecular weight and severely hamper the assignment process. Here we show the use of two sets of experiments that expand the tool kit of 1H-detected assignment approaches, and which correlate a given amide pair either to the two adjacent CO-CA pairs (4D hCOCANH/hCOCAcoNH), or to the amide 1H of the neighboring residue (3D HcocaNH/HcacoNH, which can be extended to up to 5D)...
August 9, 2017: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
https://www.readbyqxmd.com/read/28791761/biomimicry-of-artificial-spider-silk-spinning-assessed-by-nmr
#16
Martins Otikovs, Marlene Andersson, Qiupin Jia, Kerstin Nordling, Qing Meng, Loren B Andreas, Guido Pintacuda, Jan Johansson, Anna Rising, Kristaps Jaudzems
Biomimetic spinning of artificial spider silk requires that the terminal domains of designed minispidroins undergo specific structural changes in concert with the β-sheet conversion of the repetitive region. Here, we combine solution and solid state NMR methods to probe domain-specific structural changes in the NT2RepCT minispidroin, which allows us to assess the degree of biomimicry of artificial silk spinning. In addition, we show that the structural effects of post-spinning procedures can be examined. By studying the impact of NT2RepCT fiber drying we observed a reversible beta-to-alpha conversion...
August 9, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28783328/single-crystal-time-of-flight-neutron-diffraction-and-magic-angle-spinning-nmr-spectroscopy-resolve-the-structure-and-1-h-and-7-li-dynamics-of-the-uranyl-peroxide-nanocluster-u60
#17
Travis A Olds, Mateusz Dembowski, Xiaoping Wang, Christina Hoffman, Todd M Alam, Sarah Hickam, Kristi L Pellegrini, Junhong He, Peter C Burns
Single-crystal time-of-flight neutron diffraction has provided atomic resolution of H atoms of H2O molecules and hydroxyl groups, as well as Li cations in the uranyl peroxide nanocluster U60. Solid-state magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy was used to confirm the dynamics of these constituents, revealing the transportation of Li atoms and H2O through cluster walls. H atoms of hydroxyl units that are located on the cluster surface are involved in the transfer of H2O and Li cations from inside to outside and vice versa...
August 7, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/28783321/effects-of-pectin-molecular-weight-changes-on-the-structure-dynamics-and-polysaccharide-interactions-of-primary-cell-walls-of-arabidopsis-thaliana-insights-from-solid-state-nmr
#18
Pyae Phyo, Tuo Wang, Chaowen Xiao, Charles Thomas Anderson, Mei Hong
Significant cellulose-pectin interactions in plant cell walls have been reported recently based on 2D 13C solid-state NMR spectra of intact cell walls, but how these interactions affect cell growth has not been probed. Here, we characterize two Arabidopsis thaliana lines with altered expression of a PGX1 (POLYGALACTURONASE INVOLVED IN EXPANSION1) gene, which encodes a polygalacturonase that cleaves homogalacturonan (HG). PGX1AT plants overexpress PGX1, have HG with lower molecular weight and grow larger, whereas pgx1-2 knockout plants have HG with higher molecular weight and grow smaller...
August 7, 2017: Biomacromolecules
https://www.readbyqxmd.com/read/28782953/revealing-the-local-proton-network-through-three-dimensional-13-c-1-h-double-quantum-1-h-single-quantum-and-1-h-double-quantum-13-c-1-h-single-quantum-correlations-fast-mas-solid-state-nmr-spectroscopy-at-natural-abundance
#19
Michal Malon, Manoj Kumar Pandey, Yusuke Nishiyama
1H double quantum (DQ)/1H single quantum (SQ) correlation solid-state NMR spectroscopy is widely used to obtain internuclear 1H-1H proximities, especially at fast magic angle spinning (MAS) rate > 60 kHz. However, 1H signals are not well-resolved due to intense 1H-1H homonuclear dipolar interactions even at the attainable maximum MAS frequencies of ~100 kHz to date and/or under 1H-1H homonuclear dipolar decoupling irradiations. Here we introduce novel three-dimensional (3D) experiments to resolve the 1H DQ/1H SQ correlation peaks using the additional 13C dimension...
August 7, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/28782188/a-simple-route-to-calcium-and-strontium-hydride-clusters
#20
Sjoerd Harder, Brant Maitland, Michael Wiesinger, Jens Langer, Gerd Ballmann, Jürgen Pahl, Holger Elsen, Christian Färber
The first Sr hydride complex has been obtained by simply reacting Sr[N(SiMe3)2]2 with PhSiH3 in the presence of PMDTA. The Sr complex Sr6[N(SiMe3)2]3H9∙(PMDTA)3 crystallizes as an "inverse cryptand": an interstitial H- is surrounded by a Sr6H84+ cage decorated with amide and PMDTA ligands. The analogue Ca complex could also be obtained and both retain their solid state structures in solution: 1H NMR spectra in C6D6 show two doublets and one nonet (4:4:1). Up till 90 °C, no coalescence is observed. The Ca cluster was investigated by DFT calculations and shows atypically low charges on Ca (+1...
August 6, 2017: Angewandte Chemie
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