Read by QxMD icon Read

Solid state NMR

Ulrich Sternberg, Raiker Witter, Ilya Kuprov, Jonathan M Lamley, Andres Oss, Józef R Lewandowski, Ago Samoson
Recent developments in magic angle spinning (MAS) technology permit spinning frequencies of ≥100 kHz. We examine the effect of such fast MAS rates upon nuclear magnetic resonance proton line widths in the multi-spin system of β-Asp-Ala crystal. We perform powder pattern simulations employing Fokker-Plank approach with periodic boundary conditions and 1 H-chemical shift tensors calculated using the bond polarization theory. The theoretical predictions mirror well the experimental results. Both approaches demonstrate that homogeneous broadening has a linear-quadratic dependency on the inverse of the MAS spinning frequency and that, at the faster end of the spinning frequencies, the residual spectral line broadening becomes dominated by chemical shift distributions and susceptibility effects even for crystalline systems...
April 7, 2018: Journal of Magnetic Resonance
Darryl Aucoin, Yongjie Xia, Theint Theint, Philippe S Nadaud, Krystyna Surewicz, Witold K Surewicz, Christopher P Jaroniec
The C-terminally truncated Y145Stop variant of prion protein (PrP23-144), which is associated with heritable PrP cerebral amyloid angiopathy in humans and also capable of triggering a transmissible prion disease in mice, serves as a useful in vitro model for investigating the molecular and structural basis of amyloid strains and cross-seeding specificities. Here, we determine the protein-solvent interfaces in human PrP23-144 amyloid fibrils generated from recombinant 13 C,15 N-enriched protein and incubated in aqueous solution containing paramagnetic Cu(II)-EDTA, by measuring residue-specific 15 N longitudinal paramagnetic relaxation enhancements using two-dimensional magic-angle spinning solid-state NMR spectroscopy...
April 18, 2018: Journal of Structural Biology
Songhwan Hwang, Pascal Fricke, Maximilian Zinke, Karin Giller, Joseph S Wall, Dietmar Riedel, Stefan Becker, Adam Lange
Intra-neuronal aggregation of α-synuclein into fibrils is the molecular basis for α -synucleinopathies, such as Parkinson's disease. The atomic structure of human α -synuclein (hAS) fibrils was recently determined by Tuttle et al. using solid-state NMR (ssNMR). The previous study found that hAS fibrils are composed of a single protofilament. Here, we have investigated the structure of mouse α -synuclein (mAS) fibrils by STEM and isotope-dilution ssNMR experiments. We found that in contrast to hAS, mAS fibrils consist of two or even three protofilaments which are connected by rather weak interactions in between them...
April 17, 2018: Journal of Structural Biology
Fabian Spitzer, Gabor Balazs, Christian Graßl, Martin Keilwerth, Karsten Meyer, Manfred Scheer
A first systematic study of the activation of As4 by Co complexes is presented. Three different low-valent [LCo(tol)] (L = β-diiminato) complexes reveal different steric influences as well as the electronic influence of their adjacent substituents. Dipp (2,6-diisopropylphenyl) and dmp (2,6-dimethylphenyl) flanking groups were applied, one of the ligands with H backbone substituents (β-dialdiminate L0) and two with Me substituents (β-diketiminates L3 and L1). In the reaction with As4, different dinuclear products [(LCo)2As4] (LM = L0 (1), L1 (2), L3 (3)) were isolated, each of them representing an individually shaped [Co2As4] core in the solid state: octahedral in 1, prismatic in 2 and asterane-like in 3...
April 20, 2018: Angewandte Chemie
Christopher P Gordon, Keishi Yamamoto, Keith Searles, Satoru Shirase, Richard A Andersen, Odile Eisenstein, Christophe Copéret
Metal alkylidenes, which are key organometallic intermediates in reactions such as olefination or alkene and alkane metathesis, are typically generated from metal dialkyl compounds [M](CH2 R)2 that show distinctively deshielded chemical shifts for their α-carbons. Experimental solid-state NMR measurements combined with DFT/ZORA calculations and a chemical shift tensor analysis reveal that this remarkable deshielding originates from an empty metal d-orbital oriented in the M-Cα -Cα' plane, interacting with the Cα p-orbital lying in the same plane...
February 21, 2018: Chemical Science
Francesco Manzoni, Johan Wallerstein, Tobias E Schrader, Andreas Ostermann, Leighton Coates, Mikael Akke, Matthew P Blakeley, Esko Oksanen, Derek Thomas Logan
The medically important drug target galectin-3 binds galactose-containing moieties on glycoproteins through an intricate pattern of hydrogen bonds to a largely polar surface-exposed binding site. All successful inhibitors of galectin-3 to date have been based on mono- or disaccharide cores closely resembling natural ligands. A detailed understanding of the H-bonding networks in these natural ligands will provide an improved foundation for the design of novel inhibitors. Neutron crystallography is an ideal technique to reveal the geometry of hydrogen bonds, because the positions of hydrogen atoms are directly detected rather than being inferred from the positions of heavier atoms as in X-ray crystallography...
April 19, 2018: Journal of Medicinal Chemistry
Jing Xie, Harrison A Neal, Jennifer Szymanowski, Peter C Burns, Todd M Alam, May Nyman, Laura Gagliardi
We obtained a kerosene-soluble form of the lithium salt [UO2 (O2 )(OH)2 ]24 phase (Li-U24 ), by adding cetyltrimethylammonium bromide surfactant to aqueous Li-U24 . Interestingly, its variable-temperature solution 7 Li NMR spectroscopy resolves two narrowly spaced resonances down to -10 °C, which shift upfield with increasing temperature, and finally coalesce at temperatures > 85 °C. Comparison with solid-state NMR demonstrates that the Li dynamics in the Li-U24 -CTA phase involves only exchange between different local encapsulated environments...
April 18, 2018: Inorganic Chemistry
Valerie Seymour, Stephen Day, Gudrun Scholz, Kerstin Scheurell, Dinu Iuga, John Griffin, Erhard Kemnitz, John Hanna, Mark E Smith
Multinuclear (1H, 13C, 25Mg) solid-state NMR data is reported for a series of magnesium acetate phases Mg(CH3COO)2.nH2O (n = 0 (two polymorphs), 1, 4). The central focus here is 25Mg as this set of compounds provides an expanded range of local magnesium coordinations compared to what has previously been reported in the literature using NMR. These four compounds provide 10 distinct magnesium sites with varying NMR interaction parameters. One of the anhydrous crystal structures (α) has an MgO7 site which is reported, to the best of our knowledge, for the first time...
April 18, 2018: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
Shixin Fang, Guangjian Wang, Pengcheng Li, Ronge Xing, Song Liu, Yukun Qin, Huahua Yu, Xiaolin Chen, Kecheng Li
A new superabsorbent polymer was synthesized using amino ethyl chitosan and an acrylic acid by a free radical polymerization. The chemical structure of the superabsorbent polymer was characterized using FTIR, TGA, XRD and solid-state 13 C NMR. The results revealed that the acrylic acid was successfully grafted onto the amino ethyl chitosan backbone. As revealed by SEM, a surface with homogeneous and interconnected pore structure was obtained. The influences of different factors (e.g., the initiator, cross-linker and monomer) on the water absorbency of the superabsorbent polymers were investigated...
April 14, 2018: International Journal of Biological Macromolecules
Tomaz Cendak, Lisa Sequeira, Mariana Sardo, Anabela Valente, Moisés Pinto, Luís Mafra
The wealth of site-selective structural information on CO2 speciation, obtained by spectroscopic techniques, is often hampered by the lack of easy-to-control synthetic routes. Herein, an alternative experimental protocol that relies on the high sensitivity of 13C chemical shift anisotropy (CSA) tensors to proton-transfer, is presented to unambiguously distinguish between ionic/charged and neutral CO2 species, formed upon adsorption of 13CO2 in amine-modified porous materials. Control of the surface amine spacing was achieved through the use of amine protecting groups during functionalization prior to CO2 adsorption...
April 16, 2018: Chemistry: a European Journal
Sumit S Lal, Shashank T Mhaske
Present work covers the state-of-art progress in the advanced nanoarchitecture of organic-inorganic hybrid material; a starting material for the antimicrobial filter. TEMPO-mediated oxidation of microfiber cellulose was carried out to introduce the surface active carboxyl groups. Accordingly, qualitative and quantitative substitution of a functional group was investigated using FTIR, Solid state 13 C CP/MAS NMR, and potentiometric titration; the reaction resulted to about 21.06% increase in carboxylate content...
July 1, 2018: Carbohydrate Polymers
Qianqian Shang, Chengguo Liu, Yun Hu, Puyou Jia, Lihong Hu, Yonghong Zhou
This work presents an efficient and environmentally friendly approach to generate hydrophobic cellulose nanocrystals (CNC) using thiol-containing castor oil (CO-SH) as a renewable hydrophobe with the assist of bio-inspired dopamine at room temperature. The modification process included the formation of the polydopamine (PDA) buffer layer on CNC surfaces and the Michael addition reaction between the catechol moieties of PDA coating and thiol groups of CO-SH. The morphology, crystalline structure, surface chemistry, thermal stability and hydrophobicity of the modified CNC were charactered by TEM, XRD, FT-IR, solid-state 13 C NMR, XPS, TGA and contact angle analysis...
July 1, 2018: Carbohydrate Polymers
Motoki Takeda, Satoru Hiroto, Hiroki Yokoi, Sangsu Lee, Dongho Kim, Hiroshi Shinokubo
We designed and synthesized molecular tweezers consisted of nitrogen-embedded buckybowl subunits. The judicious choice of the covalent linkers modulated their binding strength with C60 or C70 in solution. Titration studies by optical and 1 H NMR analysis revealed a 1:1 composition of the resulting complexes. X-Ray diffraction analysis elucidated their solid-state structures in which two azabuckybowl units surround one molecule of fullerenes. The large association constants stabilize the complexes under redox reactions and purification process on silica-gel column chromatography...
April 17, 2018: Journal of the American Chemical Society
Benjamin C Hudson, Alessia Battigelli, Michael D Connolly, John Edison, Ryan K Spencer, Stephen Whitelam, Ronald N Zuckermann, Anant K Paravastu
Peptoid nanosheets are supramolecular protein-mimetic materials that form from amphiphilic polypeptoids with aromatic and ionic sidechains. Nanosheets have been studied at the nanometer scale, but molecular structure has been difficult to probe. We report the use of 13 C-13 C dipolar recoupling solid-state NMR measurements to reveal the configuration of backbone amide bonds selected by 13 C isotopic labeling of adjacent α-carbons. Measurements on the same molecules in the amorphous state and in nanosheets revealed that amide bonds in the center of the amino block of peptoid (NaeNpe)7 -(NceNpe)7 (B28) favor the trans configuration in the amorphous state and the cis configuration in the nanosheet...
April 16, 2018: Journal of Physical Chemistry Letters
Sebastian Vogel, Dominik Baumann, Robin Niklaus, Elena Bykova, Maxim Bykov, Natalia Dubrovinskaia, Leonid Dubrovinsky, Wolfgang Schnick
Phosphorus oxonitride PON is isoelectronic with SiO2 and may exhibit a similar broad spectrum of intriguing properties as silica. However, PON has only been sparsely investigated at high-pressure conditions and there has been no evidence on a PON polymorph with an increased coordination number of P (CN > 4). Herein, we report on a post-coesite (pc) PON polymorph exhibiting a stishovite-related structure with P in a (5+1) coordination. The pc-PON was synthesized using the multianvil technique and characterized by powder X-ray diffraction, solid-state NMR, TEM measurements and in situ synchrotron X-ray diffraction in diamond anvil cells...
April 14, 2018: Angewandte Chemie
Alexander Marchanka, Christoph Kreutz, Teresa Carlomagno
Nucleic acids play key roles in most biological processes, either in isolation or in complex with proteins. Often they are difficult targets for structural studies, due to their dynamic behavior and high molecular weight. Solid-state nuclear magnetic resonance spectroscopy (ssNMR) provides a unique opportunity to study large biomolecules in a non-crystalline state at atomic resolution. Application of ssNMR to RNA, however, is still at an early stage of development and presents considerable challenges due to broad resonances and poor dispersion...
April 12, 2018: Journal of Biomolecular NMR
Oleksandr Shyshov, Kevin Andre Siewerth, Max von Delius
We report a solution NMR and X-ray crystallographic study on the anion affinity of all-cis 1,2,3,4,5,6-hexafluorocyclohexane, which has only recently become synthetically accessible. Our results suggest that the interaction exhibits preferential 1 : 1 stoichiometry, while its strength is only moderate (e.g. Ka = 400 M-1 in acetone for Cl-) and depends mainly on the size of the anion and the dielectric constant of the solvent.
April 12, 2018: Chemical Communications: Chem Comm
Johannes J Wittmann, Michael Eckardt, Wolfgang Harneit, Björn Corzilius
Dynamic nuclear polarization (DNP) can be applied to enhance the sensitivity of solid-state NMR experiments by several orders of magnitude due to microwave-driven transfer of spin polarization from unpaired electrons to nuclei. While the underlying quantum mechanical aspects are sufficiently well understood on a microscopic level, the exact description of the large-scale spin dynamics, usually involving hundreds to thousands of nuclear spins per electron, is still lacking consensus. Generally, it is assumed that nuclear hyperpolarization can only be observed on nuclei which do not experience strong influence of the unpaired electrons and thus being significantly removed from the paramagnetic polarizing agents...
April 12, 2018: Physical Chemistry Chemical Physics: PCCP
Vincent P Swamy, Hirekodathakallu V Thulasiram, Federico Rastrelli, Giacomo Saielli
We present the 1H, 13C and 15N NMR chemical shifts of bulk ionic liquids based on 1-butyl-3-methylimidazolium (the cation also known as 1-butyl-3-picolinium) halides (Cl-, Br- and I-) and tribromide (Br3-) salts. A characterization in solution of the analogous ICl2- and I3- salts is also reported. A series of DFT calculations has been run to predict the features of the NMR spectra of the pure ILs based on a few selected supramolecular ionic aggregates. To test the effect of temperature, and vibrational and conformational motions, only for the chloride salt, we also run first-principles molecular dynamics simulations of the ion pair in the gas phase, using the ADMP scheme (Atom Centered Density Matrix Propagation molecular dynamics model)...
April 12, 2018: Physical Chemistry Chemical Physics: PCCP
Steve Ullmann, René Schnorr, Christian Laube, Bernd Abel, Berthold Kersting
The synthesis and photophysical properties of four new hybrid salicylaldiminato-calix[4]arene ligands and their corresponding zinc(ii) complexes are described. The Schiff bases were obtained from condensation reactions between cone-25,27-di(aminoethoxy)-26,28-dihydroxy-calix[4]arene and salicylaldehyde (H2L1) or o-vanillin (H2L2) and 1,3-alt-25,27-di(aminoethoxy)-26,28-di(n-propyloxy)-calix[4]arene and 3,5-di-tert-butyl-salicylaldehyde (H2L3) or o-vanillin (H2L4). Complexation reactions were investigated by ESI-MS, IR, NMR, UV-vis absorption and steady-state and time resolved fluorescence spectroscopy, and X-ray crystallography...
April 12, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Fetch more papers »
Fetching more papers... Fetching...
Read by QxMD. Sign in or create an account to discover new knowledge that matter to you.
Remove bar
Read by QxMD icon Read

Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"