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Magnetic Resonance in Chemistry: MRC

David Jebaraj D, Hideo Utsumi, Milton Franklin Benial A
Detailed dynamic nuclear polarization and electron spin resonance studies were carried out for 3-carbamoyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl, 3-carboxy-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl,3-methoxycarbonyl-2,2,5,5-tetramethy pyrolidine-1-oxyl nitroxyl radicals and their corresponding deuterated nitroxyl radicals, used in Overhauser-enhanced magnetic resonance imaging for the first time. The dynamic nuclear polarization parameters such as DNP factor, longitudinal relaxivity, saturation parameter, leakage factor and coupling factor were estimated for deuterated nitroxyl radicals...
April 26, 2017: Magnetic Resonance in Chemistry: MRC
Mohamed Haouas, Julien Trébosc, Catherine Roch-Marchal, Emmanuel Cadot, Francis Taulelle, Charlotte Martineau-Corcos
The potential of high-field NMR to measure solid-state (95) Mo and (183) W NMR in polyoxometalates (POMs) is explored using some archetypical structures like Lindqvist, Keggin, and Dawson as model compounds that are well characterized in solution. NMR spectra in static and under magic angle spinning (MAS) were obtained, and their analysis allowed extraction of the NMR parameters, including chemical shift anisotropy (CSA) and quadrupolar coupling parameters. Despite the inherent difficulties of measurement in solid state of these low-gamma NMR nuclei, due mainly to the low spectral resolution and poor signal-to-noise ratio, the observed global trends compare well with the solution state NMR data...
April 24, 2017: Magnetic Resonance in Chemistry: MRC
Xiaochen Tang, Yingjie Xu, Xiao Zhu, Yueqing Lu
In this work, changes in microstructure of two protic ionic liquids (PILs), namely n-butylammonium acetate (N4Ac) and n-butylammonium nitrate (N4NO3 ) are proved by in situ variable-temperature (1) H NMR spectroscopy at the temperature range from 25 °C to 115 °C, and the influence of the nature of anion is discussed accordingly. The results demonstrate that (1) H NMR chemical shifts of alkyl protons of both N4Ac and N4NO3 are almost not changed with the increasing of temperature, due to the absence of hydrogen bond interaction between alkyl protons with anions...
April 22, 2017: Magnetic Resonance in Chemistry: MRC
John S Lomas, Laurent Joubert
The idea that hydrogen bond cooperativity is responsible for the structure and reactivity of carbohydrates is examined. Density functional theory and gauge-including atomic orbital calculations on the known conformers of the α and β anomers of D-glucopyranose in the gas phase are used to compute proton NMR chemical shifts and interatomic distances, which are taken as criteria for probing intramolecular interactions. Atom-atom interaction energies are calculated by the interacting quantum atoms approach in the framework of the quantum theory of atoms in molecules...
April 22, 2017: Magnetic Resonance in Chemistry: MRC
Raymond J Abraham, M Ashley Cooper
Molecular mechanics calculations plus the application of a refined Karplus equation gave the conformations of 19 pinanes. These range from a Y-shaped geometry in the apopinene and α-pinene series to a pseudo chair conformation in β-pinene, nopinone and verbanone, a flattened chair in pinocarvone and the pinocarveols and a distorted Y shape for iso-verbanone. These structures were then used as input to predict the (1) H chemical shifts of these compounds by semi-empirical (HSPEC) and ab initio GIAO calculations, the latter at the B3LYP hybrid DFT level using 6-31++G** basis set...
April 19, 2017: Magnetic Resonance in Chemistry: MRC
Jonathan Farjon
Nuclear Magnetic Resonance (NMR) is one of the most widely used analytical techniques in numerous domains where molecules are objects of investigation. However, major limitations of multidimensional NMR experiments come from their low sensitivity and from the long times needed for their acquisition. In order to overcome such limitations, fast repetition NMR techniques allowed for the reduction of 2D experimental time and for the conversion of the gained time into a higher number of scans leading to a better sensitivity...
April 13, 2017: Magnetic Resonance in Chemistry: MRC
Andhika Kiswandhi, Peter Niedbalski, Christopher Parish, Sarah Ferguson, David Taylor, George McDonald, Lloyd Lumata
Dynamic nuclear polarization (DNP) via the dissolution method has become one of the rapidly emerging techniques to alleviate the low signal sensitivity in nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI). In this paper, we report on the development and (13) C hyperpolarization efficiency of a homebuilt dynamic nuclear polarization (DNP) system operating at 6.423 T and 1.4 K. The DNP hyperpolarizer system was assembled on a wide-bore superconducting magnet, equipped with a standard continuous-flow cryostat, and a 180 GHz microwave source with 120 mW power output and wide 4 GHz frequency tuning range...
April 13, 2017: Magnetic Resonance in Chemistry: MRC
Robert H Morris, Md Nur Mostafa, Steven T Parslow, Michael I Newton
No abstract text is available yet for this article.
March 29, 2017: Magnetic Resonance in Chemistry: MRC
Martin R M Koos, Hannes Feyrer, Burkhard Luy
Pulse sequences in NMR spectroscopy sometimes require the application of pulses with effective flip angles different from 90˚ and 180˚ Previously (Magn. Reson. Chem.), offset-compensated broadband excitation pulses with rf-amplitude-dependent effective flip angles (RADFA) were introduced that are applicable in such cases. However, especially rf-amplitude-restricted RADFA pulses turned out to perform not as good as desired in terms of achievable bandwidths. Here, a class of rf-amplitude-restricted RADFA pulses with linear phase slope is introduced that allows excitation over much larger bandwidths with better performance...
March 20, 2017: Magnetic Resonance in Chemistry: MRC
Bruno Guigas
SpecPad is a new device-independent software program for the visualization and processing of one- and two-dimensional NMR time domain (FID) and frequency domain (spectrum) data. It is the result of a project to investigate whether the novel programming language DART, in combination with Html5 Web technology, forms a suitable base to write an NMR data evaluation software which runs on modern computing devices such as Android, iOS, and Windows tablets as well as on Windows, Linux, and Mac OS X desktop PCs and notebooks...
March 12, 2017: Magnetic Resonance in Chemistry: MRC
Yulia B Monakhova, Bernd W K Diehl
Quantitative nuclear magnetic resonance (qNMR) is considered as a powerful tool for measuring the absolute amount of small molecules in complex mixtures. However, verification of the accuracy of such quantification is not a trivial task. In particular, preprocessing and integration steps are challenging and potentially erroneous. A script was developed in Matlab environment to automate qNMR analysis. Verification of the results is based on two evolving integration profiles. The analysis of binary mixtures of internal standards as well as pharmaceutical products has shown that all common artifacts (phase and baseline distortion, impurities) can be easily recognized in routine qNMR experiments...
March 10, 2017: Magnetic Resonance in Chemistry: MRC
Rongfu Zhang, Indra D Sahu, Raven G Comer, Sergey Maltsev, Carole Dabney-Smith, Gary A Lorigan
KCNE1 is known to modulate the voltage-gated potassium channel α subunit KCNQ1 to generate slowly activating potassium currents. This potassium channel is essential for the cardiac action potential that mediates a heartbeat as well as the potassium ion homeostasis in the inner ear. Therefore, it is important to know the structure and dynamics of KCNE1 to better understand its modulatory role. Previously, the Sanders group solved the three-dimensional structure of KCNE1 in LMPG micelles, which yielded a better understanding of this KCNQ1/KCNE1 channel activity...
February 23, 2017: Magnetic Resonance in Chemistry: MRC
Esa Haapaniemi
The (1) H, (13) C{(1) H}, and (31) P NMR spectral parameters of some pyrophosphates were determined in CDCl3 . The most complicated (1) H spectrum can be solved fully only as (A3 MN)R6 XX'R6 '(MNA3 )', where R6 (= -N(CH3 )2 ) is coupled only to phosphorus (X). Second order coupling between phosphorus was found and solved with iterative analysis. A signal shape of one of the carbon resonance cannot be explained only with couplings. Explanation for exceptional shape was searched from molecular modeling results...
February 22, 2017: Magnetic Resonance in Chemistry: MRC
Jaspal Singh, Vineeta Rustagi, Shanrong Zhang, A Dean Sherry, D Gomika Udugamasooriya
The rate of water exchange between the inner sphere of a paramagnetic ion and bulk water is an important parameter in determining the magnitude of the chemical exchange saturation transfer signal from paramagnetic CEST agents (paraCEST). This is governed by various geometric, steric and ligand field factors created by macrocyclic ligands surrounding the paramagnetic metal ion. Our previous on-bead combinatorial studies of di-peptoid-europium(III)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-tetraamide complexes revealed that negatively charged groups in the immediate vicinity of the metal center strongly enhances the CEST signal...
February 21, 2017: Magnetic Resonance in Chemistry: MRC
Indrek Reile, Ruud L E G Aspers, Martin C Feiters, Floris P J T Rutjes, Marco Tessari
DOSY analysis can resolve analytes according to their molecular size, offering a complementary way to traditional 2D NMR spectroscopy in the study of chemical mixtures. Applications are, however, limited if analytes have similar shape and size, as is the case in isomer mixtures. Herein we show how solvent effects in methanol-d4 , a common solvent in NMR laboratories, allow to overcome this limitation and provide increased separation of isomeric compounds. Clear NMR signal separation of eight structurally related analytes within a molecular weight (MW) range of three units is demonstrated, allowing unambiguous analysis of a mixture that would have otherwise been unsuitable for DOSY...
February 20, 2017: Magnetic Resonance in Chemistry: MRC
Vadim Zorin, Michael A Bernstein, Carlos Cobas
The trends towards rapid NMR data acquisition, automated NMR spectrum analysis, and data processing and analysis by more naïve users combine to place a higher burden on data processing software to automatically process these data. Downstream data analysis is compromised by poor processing, and the automated processing algorithms must therefore be robust and accurate. We describe a new algorithm for automatic phase correction of frequency-domain, high-resolution NMR spectra. We show this to be reliable for data derived from a wide variety of typical NMR usages...
February 20, 2017: Magnetic Resonance in Chemistry: MRC
Aikaterini Koutsaviti, Efstathia Ioannou, Maria Couladis, Olga Tzakou, Vassilios Roussis
No abstract text is available yet for this article.
February 16, 2017: Magnetic Resonance in Chemistry: MRC
Ēriks Kupče, Ole W Sørensen
Two new related methods for tracking out the backbone of protonated (13) C nuclei are presented. 2BOB extracts an H2BC and an HSQC-type spectrum from one and the same data set, and the combined information of these two spectra tracks out the molecular backbone. The faster method, H2OBC, typically requiring only a few minutes of instrument time, yields a single spectrum with distinct and different phases imposed on the H2BC and one-bond peaks thus obviating the need to separate them in the absence of complicating spectral overlap...
February 16, 2017: Magnetic Resonance in Chemistry: MRC
David Soulsby, Jeryl A M Chica
We have developed a simple, direct and novel method for the determination of partition coefficients and partitioning behavior using (1) H NMR spectroscopy combined with time domain complete reduction to amplitude-frequency tables (CRAFT). After partitioning into water and 1-octanol using standard methods, aliquots from each layer are directly analyzed using either proton or selective excitation NMR experiments. Signal amplitudes for each compound from each layer are then extracted directly from the time domain data in an automated fashion and analyzed using the CRAFT software...
February 9, 2017: Magnetic Resonance in Chemistry: MRC
Alexander K Osipov, Alexander A Aniskov, Vyacheslav S Grinev, Alevtina Yu Yegorova
The structure and configuration of the series of previously unknown arylaminomethylidenefuran-2(3H)-ones have been determined in solution by (1) H, (13) C, (15) N NMR spectroscopy including two-dimensional experiments such as (1) H-(1) H COSY, dqCOSY, (1) H-(13) C HSQC, (1) H-(13) C HMBC. It was found, that synthesized substances exist as an equilibrium mixture of E- and Z-enamines in solution. It was established on the basis of DFT calculations, that the exchange between the two push-pull enamines is a simple rotation around exocyclic partial double bond which depends on the effect of the solvents...
February 8, 2017: Magnetic Resonance in Chemistry: MRC
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