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Magnetic Resonance in Chemistry: MRC

Robert P Young, Corbin R Lewis, Chen Yang, Luther Wang, James K Harper, Leonard J Mueller
The representation of NMR tensors as surfaces on three-dimensional molecular models is an information-rich presentation that highlights the geometric relationship between the tensor principal components and the underlying molecular and electronic structure. Here we describe a new computational tool, TensorView, for depicting NMR tensors on the molecular framework. This package makes use of the graphical interface and built-in molecular display functionality present within the Mathematica programming environment and is robust for displaying tensor properties from a broad range of commercial and user-specific computational chemistry packages...
September 19, 2018: Magnetic Resonance in Chemistry: MRC
Miri Zilka, Jonathan R Yates, Steven P Brown
This paper presents an NMR crystallography study of three polymorphs of furosemide. Experimental magic-angle spinning (MAS) solid-state NMR spectra are reported for form of furosemide, and these are assigned using DFT-based GIPAW calculations. Focusing on the three known polymorphs we examine the changes to the NMR parameters due to crystal packing effects. We use a recently developed formalism to visualise which regions are responsible for the chemical shielding of particular sites, and hence understand the variation in NMR parameters between the three polymorphs...
August 23, 2018: Magnetic Resonance in Chemistry: MRC
Keunhong Jeong, Sein Min, Heelim Chae, Sung Keon Namgoong
No abstract text is available yet for this article.
August 17, 2018: Magnetic Resonance in Chemistry: MRC
Kavoos Kolahdouzan, O Maduka Ogba, Daniel J O'Leary
No abstract text is available yet for this article.
August 17, 2018: Magnetic Resonance in Chemistry: MRC
César Leroy, Patrick M J Szell, David L Bryce
No abstract text is available yet for this article.
August 16, 2018: Magnetic Resonance in Chemistry: MRC
Tiago Venâncio, Lyege Magalhaes Oliveira, Tomasz Pawlak, Javier Ellena, Nubia Boechat, Steven P Brown
Experimental 13 C solid-state magic-angle spinning (MAS) NMR as well as DFT (gauge-including projector augmented wave) GIPAW calculations were used to probe disorder and local mobility in diethylcarbamazine citrate, (DEC)+ (citrate)- . This compound has been used as the first option drug for the treatment of filariasis, a disease endemic in tropical countries and caused by adult worms of Wuchereria bancrofti, which is transmitted by mosquitoes. We firstly present 2D 13 C-1 H dipolar-coupling mediated heteronuclear correlation spectra recorded at moderate spinning frequency, to explore the intermolecular interaction between DEC and citrate molecules...
August 16, 2018: Magnetic Resonance in Chemistry: MRC
Daniel M Dawson, Robert F Moran, Scott Sneddon, Sharon E Ashbrook
The 31 P chemical shift anisotropy (CSA) offers a potential source of new information to help determine the structures of aluminophosphate (AlPO) framework materials. We investigate how to measure the CSAs, which are small (span of ~20-30 ppm) for AlPOs, demonstrating the need for CSA-amplification experiments (often in conjunction with 27 Al and/or 1 H decoupling) at high magnetic field (20.0 T) to obtain accurate values. We show that the most shielded component of the chemical shift tensor, δ33 , is related to the length of the shortest P─O bond, whereas the more deshielded components, δ11 and δ22 can be related more readily to the mean P─O bond lengths and P─O─Al angles...
August 13, 2018: Magnetic Resonance in Chemistry: MRC
T Niklas, P Schulze, C Farès
In this study, aqueous blends of cromolyn and gelatin ("cromogels") are introduced as anisotropic media. The addition of gelatin enables an advantageous adjustability of the strength, the homogeneity and the stability of the cromolyn alignment. The mechanical stability of these polymer-dispersed liquid crystals is further utilized by stacking layers of D2 O/cromolyn/gelatin with varying component ratio. The resulting distinct phases with correspondingly different degrees of alignment can be targeted by spatially resolved NMR techniques...
August 9, 2018: Magnetic Resonance in Chemistry: MRC
Benjamin Görling, Wolfgang Bermel, Stefan Bräse, Burkhard Luy
Similar to J-resolved spectroscopy, also, heteronuclear multiple bond correlation (HMBC), heteronuclear single bond correlation (HSBC), and heteronuclear multiple quantum coherence (HMQC) types of correlation experiments result in homonuclear tilted multiplet patterns. On the example of the high-resolution heteronuclear single bond correlation (HR-HSBC) pulse sequence, it is shown how the tilt angle can be varied within a wide range of positive and negative values. Projection along the tilt angles in all cases results in homonuclear decoupling...
July 29, 2018: Magnetic Resonance in Chemistry: MRC
Meike Hahn, Eric von Elert, Laurent Bigler, M Dolores Díaz Hernández, Nils E Schloerer
No abstract text is available yet for this article.
July 13, 2018: Magnetic Resonance in Chemistry: MRC
Kazuo Furihata, Mitsuru Tashiro
Natural products such as polyketides often possess various spin systems, consisting of a methine group directly bonded to a methyl group (e.g., ─CHA ─CHB (CH3 )─CHC ─). The methine proton HB splits into a broadened multiplet by coupling with several vicinal protons, rendering analysis difficult of n JH-H with respect to HB in double-quantum filtered COSY or exclusive COSY. For the purpose of measuring n JH-H in the aforesaid spin system, we have developed new techniques, named multifrequency homo-decoupling (MDEC)-J-resolved COSY and DPFGSE-MDEC-J-resolved COSY...
July 11, 2018: Magnetic Resonance in Chemistry: MRC
Luca Fusaro
17 O-enriched complexes between oxydiacetate ligand and several diamagnetic and paramagnetic lanthanide(III) metal ions (Ln) were investigated by solution-state 17 O NMR spectroscopy. The bound-state signals of chelating (Oin ) and nonchelating (Oout ) oxygen atoms of the carboxylate groups were observed for all the samples investigated. The data indicate that the 17 O line width is dominated by contributions from both quadrupole relaxation and chemical exchange in the case of Pr and Nd complexes. Dissection of the chemical shift induced by metal ions on Oin  into Fermi contact and pseudocontact contributions was performed , and the hyperfine coupling constant (A/ℏ) was estimated...
July 10, 2018: Magnetic Resonance in Chemistry: MRC
Bin-Bin Gu, Yu-Han Gui, Li Liu, Zhi-You Su, Wei-Hua Jiao, Lei Li, Fan Sun, Shu-Ping Wang, Fan Yang, Hou-Wen Lin
No abstract text is available yet for this article.
July 7, 2018: Magnetic Resonance in Chemistry: MRC
Aida R Contreras, Vladimir I Bakhmutov, Douglas W Elliott, Abraham Clearfield
For the first time, pore spaces in the Zr (IV) phosphonate (1) as a representative of layered metal (IV) phosphonate materials have been investigated by studying mobility of guest molecules, benzene-d6 , and toluene-d8 . Guest molecules located in micropores of 1 have been characterized by solid-state 13 C{1 H} and 2 H NMR spectra in static samples with varying temperatures. At moderately low temperatures, the benzene and toluene molecules experience fast isotropic reorientations and show the motionally averaged liquid-like carbon and deuterium line shapes in the NMR spectra...
July 5, 2018: Magnetic Resonance in Chemistry: MRC
Youngshim Lee, Dongsoo Koh, Yoongho Lim
No abstract text is available yet for this article.
June 27, 2018: Magnetic Resonance in Chemistry: MRC
Paolo Sabatino, Min Gao, Jianbo Hou
13 C nuclear magnetic resonance (NMR) is a powerful tool for the detailed characterization and structure elucidation of polymeric samples. The low natural abundance and sensitivity of the 13 C isotope, however, lead to very long acquisition time, therefore limiting the use of such technique. We report here the implementation of a quantitative method, quantitative adiabatic-refocused insensitive nuclei enhanced by polarization transfer (QA-RINEPT), for the characterization of polyol samples. The method, based on the well-known insensitive nuclei enhanced by polarization transfer sequence, allows the boost in sensitivity of the carbon resonances without sacrificing the quantitative aspects of the analysis...
June 27, 2018: Magnetic Resonance in Chemistry: MRC
Laura Castañar
No abstract text is available yet for this article.
October 2018: Magnetic Resonance in Chemistry: MRC
Julian Ilgen, Lukas Kaltschnee, Christina M Thiele
Band selective techniques offer the highest sensitivity of all pure shift approaches and thus are the best choice for decoupling well-separated 1 H-frequency regions, such as the amide- or the α-proton region of α-peptides. They are inept to fully decouple the amide- and the α-proton region simultaneously, though. Herein, we present a new homonuclear decoupling technique, which extends the capabilities of band selective decoupling using the perfect echo principle. This modification allows a complete backbone decoupling (amide- and α-protons) in peptides and opens band selective homonuclear decoupling to substances with two mutually coupled protons in the spectral range of interest...
October 2018: Magnetic Resonance in Chemistry: MRC
Josep Saurí, Wolfgang Bermel, Teodor Parella, R Thomas Williamson, Gary E Martin
1,n-ADEQUATE is a powerful NMR technique for elucidating the structure of proton-deficient small molecules that can help establish the carbon skeleton of a given molecule by providing long-range three-bond 13 C─13 C correlations. Care must be taken when using the experiment to identify the simultaneous presence of one-bond 13 C─13 C correlations that are not filtered out, unlike the HMBC experiment that has a low-pass J-filter to filter 1 JCH responses out. Dual-optimized, inverted 1 JCC 1,n-ADEQUATE is an improved variant of the experiment that affords broadband inversion of direct responses, obviating the need to take additional steps to identify these correlations...
October 2018: Magnetic Resonance in Chemistry: MRC
Juan A Aguilar, Raquel Belda, Benjamin R Gaunt, Alan M Kenwright, Ilya Kuprov
Recent developments in data sampling and processing techniques have made it possible to acquire 2-dimensional NMR spectra of small molecules at digital resolutions in both dimensions approaching the intrinsic limitations of the equipment and sample on a realistic timescale. These developments offer the possibility of enormously increased effective resolution (peak dispersion) and the ability to effectively study samples where peak overlap was previously a limiting factor. Examples of such spectra have been produced for a number of 2-dimensional techniques including TOCSY and HSQC...
October 2018: Magnetic Resonance in Chemistry: MRC
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