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https://www.readbyqxmd.com/read/28527462/low-power-broadband-solid-state-mas-nmr-of-14-n
#1
Andrew J Pell, Kevin J Sanders, Sebastian Wegner, Guido Pintacuda, Clare P Grey
We propose two broadband pulse schemes for (14)N solid-state magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) that achieves (i) complete population inversion and (ii) efficient excitation of the double-quantum spectrum using low-power single-sideband-selective pulses. We give a comprehensive theoretical description of both schemes using a common framework that is based on the jolting-frame formalism of Caravatti et al. [J. Magn. Reson. 55, 88 (1983)]. This formalism is used to determine for the first time that we can obtain complete population inversion of (14)N under low-power conditions, which we do here using single-sideband-selective adiabatic pulses...
May 21, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/28524206/co2-adsorption-on-different-organo-modified-sba-15-silicas-a-multidisciplinary-study-on-the-effects-of-basic-surface-groups
#2
G Gatti, D Costenaro, C Vittoni, G Paul, V Crocellà, E Mangano, S Brandani, S Bordiga, M Cossi, L Marchese, C Bisio
Hybrid organic-inorganic SBA-15 silicas functionalized with increasing amounts of amino groups were studied in this work aiming to evaluate the effects of their physico-chemical properties on CO2 capture ability. Three different amino-silane species were used: 3-aminopropyltriethoxysilane (APTS), 3-(2-aminoethyl)aminopropyltrimethoxysilane (EAPTS) and 3-[2-(2-aminoethyl)aminoethyl] aminopropyltrimethoxysilane (PAPTS). More specifically, samples were prepared by using two methods, following a post-synthesis grafting procedure and a one-pot preparation method...
May 19, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28521205/preparation-and-characterization-of-a-novel-macroporous-silica-bipyridine-asymmetric-multidentate-functional-adsorbent-and-its-application-for-heavy-metal-palladium-removal
#3
Lei Xu, Anyun Zhang, Fengmei Zhang, Jiyong Liu
The effective removal of heavy metal (107)Pd(II) from highly active liquid waste (HLW) is very valuable for reducing its hazardous and risk to public health and environment. For this purpose, a novel silica-bipyridine multidentate functional adsorbent was synthesized by vacuum infusing a new asymmetric N-donor ligand CA-MTBP (bipyridine derivative) into the macroporous SiO2-P support. SEM, N2 adsorption-desorption isotherms, TGA, XRD, FT-IR, (29)Si solid-state NMR and XPS spectroscopy were utilized to systematically characterize the physicochemical properties of the adsorbent...
April 19, 2017: Journal of Hazardous Materials
https://www.readbyqxmd.com/read/28514507/hydrogen-bond-involving-cavity-nh-protons-drives-supramolecular-oligomerization-of-amido-corroles
#4
Daniel T Gryko, Rafał Orłowski, Mariusz Tasior, Barbara Ventura, Olga Staszewska-Krajewska, Wojciech Schilf, Michał Cyrański, Łukasz Dobrzycki
Trans-A2B-Corroles with amide substituents at different positions versus the macrocyclic core have been synthesized. Their self-organizing properties have been comprehensively evaluated both in solid-state and in solution. The rigid arrangement of the amide functionality with the corrole ring led to the formation of strong intramolecular interactions and precluded intermolecular interactions. Replacement of sterically hindered C6F5 substituents at positions 5 and 15 with smaller electron-withdrawing CO2Me groups resulted in significant changes in the self-assembly pattern...
May 17, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28513727/self-assembled-air-stable-magnesium-hydride-embedded-in-3-d-activated-carbon-for-reversible-hydrogen-storage
#5
S S Shinde, Dong-Hyung Kim, Jin-Young Yu, Jung-Ho Lee
The rational design of stable, inexpensive catalysts with excellent hydrogen dynamics and sorption characteristics under realistic environments for reversible hydrogen storage remains a great challenge. Here, we present a simple and scalable strategy to fabricate a monodispersed, air-stable, magnesium hydride embedded in three-dimensional activated carbon with periodic synchronization of transition metals (MHCH). The high surface area, homogeneous distribution of MgH2 nanoparticles, excellent thermal stability, high energy density, steric confinement by carbon, and robust architecture of the catalyst resulted in a noticeable enhancement of the hydrogen storage performance...
May 17, 2017: Nanoscale
https://www.readbyqxmd.com/read/28509541/synthesis-characterization-and-variable-temperature-nmr-studies-of-silver-i-complexes-for-selective-nitrene-transfer
#6
Minxue Huang, Joshua R Corbin, Nicholas S Dolan, Charles G Fry, Anastasiya I Vinokur, Ilia A Guzei, Jennifer M Schomaker
An array of silver complexes supported by nitrogen-donor ligands catalyze the transformation of C═C and C-H bonds to valuable C-N bonds via nitrene transfer. The ability to achieve high chemoselectivity and site selectivity in an amination event requires an understanding of both the solid- and solution-state behavior of these catalysts. X-ray structural characterizations were helpful in determining ligand features that promote the formation of monomeric versus dimeric complexes. Variable-temperature (1)H and DOSY NMR experiments were especially useful for understanding how the ligand identity influences the nuclearity, coordination number, and fluxional behavior of silver(I) complexes in solution...
May 16, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/28507688/donor-acceptor-stacking-arrangements-in-bulk-and-thin-film-high-mobility-conjugated-polymers-characterized-using-molecular-modelling-and-mas-and-surface-enhanced-solid-state-nmr-spectroscopy
#7
Sachin R Chaudhari, John M Griffin, Katharina Broch, Anne Lesage, Vincent Lemaur, Dmytro Dudenko, Yoann Olivier, Henning Sirringhaus, Lyndon Emsley, Clare P Grey
Conjugated polymers show promising properties as cheap, sustainable and solution-processable semiconductors. A key challenge in the development of these materials is to determine the polymer chain structure, conformation and packing in both the bulk polymer and in thin films typically used in devices. However, many characterisation techniques are unable to provide atomic-level structural information owing to the presence of disorder. Here, we use molecular modelling, magic-angle spinning (MAS) and dynamic nuclear polarisation surface-enhanced NMR spectroscopy (DNP SENS) to characterise the polymer backbone group conformations and packing arrangement in the high-mobility donor-acceptor copolymer diketopyrrolo-pyrrole-dithienylthieno[3,2-b]thiophene (DPP-DTT)...
April 1, 2017: Chemical Science
https://www.readbyqxmd.com/read/28505425/a-refined-crystal-structure-of-samia-cynthia-ricini-silk-fibroin-revealed-by-solid-state-nmr-investigations
#8
Tetsuo Asakura, Akio Nishimura, Shunsuke Kametani, Shuto Kawanishi, Akihiro Aoki, Furitsu Suzuki, Hironori Kaji, Akira Naito
Samia cynthia ricini is one of the wild silkworms and its silk fibroin (SF) consists of alternatively repeating poly-L-alanine (PLA) sequences as crystalline domain and glycine-rich sequences as non-crystalline domain; the structure is similar to those of spider silk and other wild silkworm silks. In this paper, we proposed a new staggered model for the packing arrangement of the PLA sequence through the use of the Cambridge Serial Total Energy Package program and a comparison of the observed and calculated chemical shifts of the PLA sequence with the Gauge Including Projector Augmented Wave method...
May 15, 2017: Biomacromolecules
https://www.readbyqxmd.com/read/28503894/revaling-the-direct-mechanism-of-the-first-carbon-carbon-bond-formation-in-methanol-to-hydrocarbons-process
#9
Xinqiang Wu, Shutao Xu, Wenna Zhang, Jindou Huang, Jinzhe Li, Bowen Yu, Yingxu Wei, Zhongmin Liu
In the past two decades, the reaction mechanism of C-C bond formation from methanol or dimethyl ether (DME) has been intensively studied as the most critical problem of methanol to hydrocarbons (MTH) process, one of the most important reactions in C1 chemistry, but the first C-C bond generation during the very initial reaction stage remains a highly controversial issue. For the first time, a surface methyleneoxy-analogue, originated from the surface activated DME, was directly observed by in situ solid-state NMR and recognized to be the crucial intermediate for the first C-C bond formation in MTH process...
May 15, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28503206/inclusion-complexes-of-%C3%AE-cyclodextrin-with-tricyclic-drugs-an-x-ray-diffraction-nmr-and-molecular-dynamics-study
#10
Franca Castiglione, Fabio Ganazzoli, Luciana Malpezzi, Andrea Mele, Walter Panzeri, Giuseppina Raffaini
Tricyclic fused-ring cyclobenzaprine (1) and amitriptyline (2) form 1:1 inclusion complexes with β-cyclodextrin (β-CD) in the solid state and in water solution. Rotating frame NOE experiments (ROESY) showed the same geometry of inclusion for both 1/β-CD and 2/β-CD complexes, with the aromatic ring system entering the cavity from the large rim of the cyclodextrin and the alkylammonium chain protruding out of the cavity and facing the secondary OH rim. These features matched those found in the molecular dynamics (MD) simulations in solution and in the solid state from single-crystal X-ray diffraction of 1/β-CD and 2/β-CD complexes...
2017: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28502167/transient-porosity-in-densely-packed-crystalline-carbazole-p-diethynylphenylene-carbazole-rotors-co2-and-acetone-sorption-properties
#11
Andres Aguilar-Granda, Salvador Perez-Estrada, Elí Sánchez-González, J Raziel Álvarez, Joelis Rodriguez-Hernandez, Mario Rodriguez, Arian E Roa, Simón Hernandez-Ortega, Ilich A Ibarra, Braulio Rodríguez-Molina
We report for the first time the high sorption properties of a molecular rotor with no permanent voids or channels in its crystal structure. Such crystalline phase originates either from THF, DCM or by the irreversible desolvation of entrapped benzene molecules. From these, the benzene in its solvate form acts as rotation stopper, as supported by dynamic characterization using solid-state 2H NMR experiments. In the solvent free form, the diffusion of small quantities of iodine vapors caused a significant change in the intramolecular rotation, increasing the known activation energy to rotation from 8...
May 14, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28501859/molecular-insights-into-covalently-stained-carious-dentine-using-solid-state-nmr-and-tof-sims
#12
Ulrica S Almhöjd, Peter Lingström, Åke Nilsson, Jörgen G Norén, Sandra Siljeström, Åsa Östlund, Diana Bernin
Dyes currently used to stain carious dentine have a limited capacity to discriminate normal dentine from carious dentine, which may result in overexcavation. Consequently, finding a selective dye is still a challenge. However, there is evidence that hydrazine-based dyes, via covalent bonds to functional groups, bind specifically to carious dentine. The aim of this study was to investigate the possible formation of covalent bonds between carious dentine and 15N2-hydrazine and the hydrazine-based dye, 15N2-labelled Lucifer Yellow, respectively...
May 13, 2017: Caries Research
https://www.readbyqxmd.com/read/28501588/oligomeric-structure-of-anabaena-sensory-rhodopsin-in-a-lipid-bilayer-environment-by-combining-solid-state-nmr-and-long-range-deer-constraints
#13
Sergey Milikisiyants, Shenlin Wang, Rachel A Munro, Matthew Donohue, Meaghan E Ward, David Bolton, Leonid S Brown, Tatyana I Smirnova, Vladimir Ladizhansky, Alex I Smirnov
Oligomerization of membrane proteins is common in nature. Here, we combine spin-labeling Double Electron-Electron Resonance (DEER) and solid-state NMR (ssNMR) spectroscopy to refine the structure of an oligomeric integral membrane protein, Anabaena Sensory Rhodopsin (ASR), reconstituted in a lipid environment. An essential feature of such a combined approach is that it provides structural distance restraints spanning a range of ca. 3-60Å, while using the same sample preparation (i.e., mutations, paramagnetic labeling, and reconstitution in lipid bilayers) for both ssNMR and DEER...
May 10, 2017: Journal of Molecular Biology
https://www.readbyqxmd.com/read/28500715/crystal-effects-on-mesobilirubin-a-combined-nmr-spectroscopic-and-density-functional-theory-study
#14
Chen Song, Jörg Matysik, Franz Mark
We report solid-state NMR investigations of crystal effects in powdered mesobilirubin-IXα, an open-chain tetrapyrrole that is structurally related to bilirubin-IXα but hydrogenated at the 3- and 18-vinyl groups. (13) C and (15) N cross-polarization magic-angle spinning (CP/MAS) NMR experiments were performed on the compound at natural abundance. To facilitate the spectral analysis, density functional calculations were carried out at the B3LYP/6-311G(d,p) level of theory, using an enneameric cluster to simulate the solid...
May 2017: Photochemistry and Photobiology
https://www.readbyqxmd.com/read/28496061/application-of-electron-paramagnetic-resonance-and-solid-state-13-c-nuclear-magnetic-resonance-of-cross-polarization-magic-angle-spinning-to-study-enzymatic-degradation-of-silk-fabrics
#15
Yuan Zeng, Zhiqin Peng, Bing Wang, Zhiwen Hu, Junmin Wan, Yang Zhou
The enzymatic degradation of silk by protease XIV has been investigated by using scanning electron microscopy (SEM), Fourier transfer infrared spectroscopy (FTIR), solid-state (13)C nuclear magnetic resonance of cross-polarization/magic angle spinning ((13)C CP/MAS solid state NMR) and electron paramagnetic resonance (EPR). Micro-morphology of protease XIV aged samples showed that microfilaments were stripped out from the surface of silk fibers. The results of FTIR and (13)C CP/MAS solid-state NMR indicated that the enzymatic degradation process could be divided into two stages...
2017: Analytical Sciences: the International Journal of the Japan Society for Analytical Chemistry
https://www.readbyqxmd.com/read/28493689/a-bis-calix-4-pyrrole-enzyme-mimic-that-constrains-two-oxoanions-in-close-proximity
#16
Qing He, Michael Kelliher, Steffen Bähring, Vincent M Lynch, Jonathan L Sessler
Herein we describe a large capsule-like bis-calix[4]pyrrole 1, which is able to host concurrently two dihydrogen phosphate anions within a relatively large internal cavity. Evidence for the concurrent, dual recognition of the encapsulated anions came from (1)H NMR and UV-vis spectroscopies and ITC titrations carried out in CD2Cl2/CD3OD (9/1, v/v) or dichloroethane (DCE), as well as single crystal X-ray diffraction analyses. Receptor 1 was also found to bind two dianionic sulfate anions bridged by two water molecules in the solid state...
May 17, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28493380/post-synthesis-amine-borane-functionalization-of-metal-organic-framework-and-its-unusual-chemical-hydrogen-release-phenomenon
#17
Heinz Berke, Smair Barman, Arndt Remhof, Ralph Koitz, Marcella Iannuzzi, Olivier Blacque, Yigang Yan, Thomas Fox, Jürg Hutter, Andreas Züttel
We report a novel strategy for post-synthesis amine borane functionalization of MOFs under gas-solid phase transformation utilizing gaseous diborane. The covalently confined amine borane derivative decorated on the framework backbone is stable when preserved at low temperature, but spontaneously liberates soft chemical hydrogen at room temperature leading to the development of an unusual borenium type species (-NH=BH2+) ion-paired with hydroborate anion. Furthermore, the unsaturated amino borane (-NH=BH2) and the -iminodiborane ((--NHB2H5) were detected as final products...
May 11, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28492687/packing-arrangement-of-13-c-selectively-labeled-sequence-model-peptides-of-samia-cynthia-ricini-silk-fibroin-fibers-studied-by-solid-state-nmr
#18
Tetsuo Asakura, Kenta Miyazawa, Yugo Tasei, Shunsuke Kametani, Yasumoto Nakazawa, Akihiro Aoki, Akira Naito
Samia cynthia ricini (S. c. ricini) is one of the wild silkworms. Their silk fibroins have been paid attention as potentially valuable biomedical materials as well as Bombyx mori silk fibroins, but detailed information on the packing arrangement of the fibers is still not currently well understood at a molecular level. In this study, 34 mer model peptides, GGAGGGYGGDGG(A)12GGAGDGYGAG with different (13)C labeled positions have been synthesized as a typical sequence of the primary structure of S. c. ricini silk fibroins made up of tandemly repeated sequences of polyalanine as the crystalline region and glycin-rich sequences as the non-crystalline region...
May 11, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28492324/selective-1-h-1-h-distance-restraints-in-fully-protonated-proteins-by-very-fast-magic-angle-spinning-solid-state-nmr
#19
Mukul G Jain, Daniela Lalli, Jan Stanek, Chandrakala Gowda, Satya Prakash, Tom S Schwarzer, Tobias Schubeis, Kathrin Castiglione, Loren B Andreas, P K Madhu, Guido Pintacuda, Vipin Agarwal
Very fast magic-angle spinning (MAS > 80 kHz) NMR combined with high-field magnets has enabled the acquisition of proton-detected spectra in fully protonated solid samples with sufficient resolution and sensitivity. One of the primary challenges in structure determination of protein is observing long-range (1)H-(1)H contacts. Here we use band-selective spin-lock pulses to obtain selective (1)H-(1)H contacts (e.g., H(N)-H(N)) on the order of 5-6 Å in fully protonated proteins at 111 kHz MAS. This approach is a major advancement in structural characterization of proteins given that magnetization can be selectively transferred between protons that are 5-6 Å apart despite the presence of other protons at shorter distance...
May 15, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28489262/mechanochemical-friedel-crafts-alkylation-a-sustainable-pathway-towards-porous-organic-polymers
#20
Erik Troschke, Sven Grätz, Tilo Lübken, Lars Borchardt
This study elucidates an innovative mechanochemical approach applying Friedel-Crafts alkylation to synthesize porous covalent triazine frameworks (CTFs). Herein, we pursue a counterintuitive approach by utilizing a rather destructive method to synthesize well-defined materials with intrinsic porosity. Investigating a model system including carbazole as monomer and cyanuric chloride as triazine node, ball milling is shown to successfully yield porous polymers almost quantitatively. We verified the successful structure formation by an in-depth investigation applying XPS, solid-state NMR and FT-IR spectroscopy...
May 10, 2017: Angewandte Chemie
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