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Magnetic Resonance in Chemistry: MRC

Akhnef A Fatykhov, Elvira A Sedova, Aleksander Е Egorov, Sergey N Salazkin, Vladimir A Kraikin
All (1) H and (13) C NMR signals of the four poly(phenylenephthalides): polydiphenylenephthalide (P(DPh)-1), polyterphenylenephthalide (P(TPh)-2) and two sequentially ordered polymers with different ratios of alternating diphenylenephthalide and terphenylenephthalide units (P(DTPh)-3, P(DDTPh)-4) were assigned unequivocally with two-dimensional NMR techniques ((1) H-(1) H COSY and NOESY; (1) H-(13) C HSQC and HMBC). There are four types of polyphenylene fragments: not symmetrical end, symmetrical inner, symmetrical pre-end, and formally symmetric pre-end...
May 18, 2017: Magnetic Resonance in Chemistry: MRC
Dongsoo Koh, Yearam Jung, Seunghyun Ahn, Kenneth Hun Mok, Soon Young Shin, Yoongho Lim
No abstract text is available yet for this article.
May 15, 2017: Magnetic Resonance in Chemistry: MRC
Sumit Kumar Panja, Satyen Saha
Existence of microheterogeinity of imidazolium and piperidinium cation based ILs containing PF6 and NTf2 anions havebeen investigated by 1D and 2D NMR spectroscopy. 2D NMR (especially NOESY and HOESY) has been employed for studying the interactions present between cation and anion as well as the intermolecular interaction among cations. HOESY spectrum shows that fluorine of anion ( PF6- and NTf2-) significantly interacts with proton of the cations. Combined results of HOESY and NOESY for imidazolium IL indicate that the PF6- and imidazolium cation are distributed in organized manner, resulting a heterogeneous environment in liquid state...
May 15, 2017: Magnetic Resonance in Chemistry: MRC
Tzi-Yi Wu, Shyh-Gang Su, Chuen-Lin Chiu, Chung-Wen Kuo, Yi-Hsuan Tung
We conduct a comparative study of conductivity and diffusion coefficient of two dicationic ionic liquids (3,3'-(octane-1,8-diyl)bis(1-ethyl-3-imidazolium) bis(trifluoromethylsulfonyl)amide ([IMCI][TFSI], S1) and 3,3'-(2,2'-(ethane-1,2-diylbis(oxy))bis(ethane-2,1-diyl))bis(1-ethyl-3-imidazolium) bis(trifluoromethylsulfonyl)amide ([IMOI][TFSI], S2)) at various temperatures. The diffusion coefficients of cation and anion in ionic liquids (ILs) are determined using pulse gradient spin-echo nuclear magnetic resonance (PGSE-NMR) method...
May 12, 2017: Magnetic Resonance in Chemistry: MRC
Marianna Fekete, Peter J Rayner, Gary G R Green, Simon B Duckett
The Signal Amplification by Reversible Exchange (SABRE) approach has been used to hyperpolarize the substrates indazole and imidazole in the presence of the co-ligand acetonitrile through the action of the precataysts [IrCl(COD)(IMes)] and [IrCl(COD)(SIMes)]. (2) H-labelled forms of these catalysts were also examined. Our comparison of the two pre-catalysts [IrCl(COD)(IMes)] and [IrCl(COD)(SIMes)], coupled with (2) H-labelling of the N-heterocyclic carbene and associated relaxation and polarisation field variation studies demonstrate the critical and collective role these parameters play in controlling the efficiency of SABRE...
May 11, 2017: Magnetic Resonance in Chemistry: MRC
Yves Lingscheid, Mathias Paul, Andreas Bröhl, Jörg-Martin Neudörfl, Ralf Giernoth
We report the very first application of a Transient 1D (1) H{(19) F} NOE NMR experiment in neat ionic liquids. In comparison to classical 2D HOESY NMR spectroscopy,([1,2]) a substantial reduction in measurement time is gained with comparable quality and information content of the spectra. In combination with classical X-ray crystallography, we have applied this technique for the determination of inter-ionic distances (i.e. probabilities of presence) utilizing an ionic liquid containing a monofluorinated imidazilium cation...
May 11, 2017: Magnetic Resonance in Chemistry: MRC
Jorge Costa Pereira, Ivana Jarak, Rui Albuquerque Carvalho
Nuclear Magnetic Resonance (NMR) is a very powerful instrumental technique suited to identify and characterize organic compounds. NMR has been successfully used in the analysis of complex biological and environmental samples, however these applications are still rather limited. In this work we describe Unsupervised Component Analysis (UCA) as a multivariate unsupervised method suited to identify the number of relevant NMR signal contributions and to deconvolve mixed signals into signal individual sources and respective contributions...
May 8, 2017: Magnetic Resonance in Chemistry: MRC
Jessi A Baughman, G Joseph Ray, Christina M Szabo, Jane O Werling, Peter L Rinaldi
High-field (1) H NMR T2 relaxation studies were used to characterize the changes in the physical phases of water, NaCl, and dextrose solutions over a temperature range of -65 to 15 °C. The data were analyzed with the inverse Laplace transform and with a linear fit to the logarithm of the time domain signal. Two liquid phases were detected for the NaCl and dextrose solutions at lower temperatures, and assigned to low and high concentrated solution domains. The high concentrated solution domain was found to be present between -30 and -5 °C in the NaCl solution and between -55 and -5 °C in the dextrose solution...
May 4, 2017: Magnetic Resonance in Chemistry: MRC
Harri Koskela, Boban Anđelković
The spectral parameters of selected nerve agent degradation products relevant to the Chemical Weapons Convention, namely ethyl methylphosphonate, isopropyl methylphosphonate, pinacolyl methylphosphonate, and methylphosphonic acid, were studied in wide range of pH conditions and selected temperatures. The pH and temperature dependence of chemical shifts and J couplings was parameterized using Henderson-Hasselbalch -based functions. The obtained parameters allowed calculation of precise chemical shifts and J coupling constants in arbitrary pH conditions and typical measurement temperatures, thus facilitating quantum mechanical simulation of reference spectra in chosen magnetic field strength for chemical verification...
April 28, 2017: Magnetic Resonance in Chemistry: MRC
Dongsoo Koh, Soon Young Shin, Jiha Sung, Seunghyun Ahn, Yoongho Lim
No abstract text is available yet for this article.
April 28, 2017: 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 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. In this paper, we report on the development and (13) C hyperpolarization efficiency of a homebuilt 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. 2015, 53, 886-893), 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
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