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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 to establish the carbon skeleton of a given molecule by providing long-range three-bond13 C-13 C correlations. Care must be taken when using the experiment to identify the simultaneous presence of one-bond13 C-13 C correlations that are not filtered out, unlike the HMBC experiment that has a low-pass J-filter to filter1 JCH responses out. Dual-optimized, inverted1 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...
March 13, 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 two-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 two-dimensional techniques including TOCSY and HSQC...
March 8, 2018: Magnetic Resonance in Chemistry: MRC
Valentin A Semenov, Dmitry O Samultsev, Leonid B Krivdin
A systematic study of the accuracy factors for the computation of15 N NMR chemical shifts in comparison with available experiment in the series of 72 diverse heterocyclic azines substituted with a classical series of substituents (CH3 , F, Cl, Br, NH2 , OCH3 , SCH3 , COCH3 , CONH2 , COOH and CN) providing marked electronic σ- and π-electronic effects and strongly affecting15 N NMR chemical shifts is performed. The best computational scheme for heterocyclic azines at the DFT level was found to be KT3/pcS-3//pc-2 (IEF-PCM)...
March 5, 2018: Magnetic Resonance in Chemistry: MRC
John S Lomas
Density functional theory calculations are used to compute proton NMR chemical shifts, interatomic distances, atom-atom interaction energies and atomic charges for partial structures and conformers of α-D-glucopyranose, β-D-glucopyranose and α-D-galactopyranose built up by introducing OH groups into 2-methyltetrahydropyran stepwisely. For the counter-clockwise conformers the most marked effects on the NMR shift and the charge on the OH1 proton are produced by OH2, those of OH3 and OH4 being somewhat smaller...
March 1, 2018: Magnetic Resonance in Chemistry: MRC
Veera Mohana Rao Kakita, Kanaka Mahalakshmi Jerripothula, Sahithya Phani Babu Vemulapalli, Jagadeesh Bharatam
JHH scalar couplings carry rich structural information and their measurements are fundamental in the1 H NMR based elucidation of small and medium molecules, which, however are hampered in the presence of large J-coupling network. Further, enhanced spectral resolution is often essential for precise determination of a specific set of1 H-1 H J-couplings amongst the complex J-multiplets. In the light of the recent advancements in homodecoupling pure shift strategies, here we report absorption mode, band-selective refocused pure shift spin-echo (BSR-PSSE) method, which helps in determining1 H-1 H J-couplings from crowded spectral regions...
February 27, 2018: Magnetic Resonance in Chemistry: MRC
M A R Anjum, Pawel A Dmochowski, Paul D Teal
Fast, accurate and automatic extraction of parameters of nuclear magnetic resonance Free Induction Decay (FID) signal for chemical spectroscopy is a challenging problem. Recently, the Steiglitz-McBride Algorithm (SMA) has been shown to exhibit superior performance in terms of speed, accuracy and automation when applied to the extraction of T2 relaxation parameters for myelin water imaging of brain. Applying it to FID data reveals that it falls short of the second objective, the accuracy. Especially, it struggles with the issue of missed spectral peaks when applied to chemical samples with relatively dense frequency spectra...
February 23, 2018: Magnetic Resonance in Chemistry: MRC
Benno Meier
Quantum-rotor-induced polarization is closely related to para-hydrogen-induced polarization. In both cases the hyperpolarized spin order derives from rotational interaction, and the Pauli principle by which the symmetry of the rotational ground state dictates the symmetry of the associated nuclear spin state. In quantum-rotor-induced polarization there may be several spin states associated with the rotational ground state, and the hyperpolarization is typically generated by hetero-nuclear cross-relaxation. This review discusses preconditions for quantum-rotor-induced polarization for both the 1-dimensional methyl rotor and the asymmetric rotor H 217O@C60 , i...
February 20, 2018: Magnetic Resonance in Chemistry: MRC
Inés Rodríguez-Arias, Alberto Rosso, Andrea De Luca
The solid effect is one of the simplest and most effective mechanisms for Dynamic Nuclear Polarization. It involves the exchange of polarization between one electron and one nuclear spin coupled via the hyperfine interaction. Even for such a small spin system, the theoretical understanding is complicated by the contact with the lattice and the microwave irradiation. Both being weak, they can be treated within perturbation theory. In this work, we analyze the two most popular perturbation schemes: the Zeeman and the eigenstate-based approaches which differ in the way the hyperfine interaction is treated...
February 20, 2018: Magnetic Resonance in Chemistry: MRC
Ville-Veikko Telkki
Laplace NMR, dealing with NMR relaxation and diffusion experiments, reveals details of molecular motion and provides chemical resolution complementary to NMR spectra. Laplace NMR has witnessed a great progress in past decades due to the development of methodology and signal processing, and it has lots of extremely interesting applications in various fields, including chemistry, biochemistry, geology, archaeology and medicine. The aim of this minireview is to give a pedagogically oriented overview of Laplace NMR...
February 13, 2018: Magnetic Resonance in Chemistry: MRC
Valentin A Semenov, Dmitry O Samultsev, Leonid B Krivdin
15 N NMR chemical shifts in the representative series of Schiff bases together with their protonated forms have been calculated at the DFT level in comparison with available experiment. A number of functionals and basis sets have been tested in terms of a better agreement with experiment. Complimentary to gas phase results, two solvation models, namely a classical Tomasi's PCM and that in combination with an explicit inclusion of one molecule of solvent into calculation space to form supermolecule 1:1 (SM+PCM) were examined...
February 9, 2018: Magnetic Resonance in Chemistry: MRC
Yu Yu Rusakov, I L Rusaskova
In this paper we have investigated the cumulative peculiarity of the "heavy atom on light atom" effect on the 13 C NMR chemical shifts, initiated by the adjacent chalcogens. For this purpose, the most accurate hybrid computational scheme for the calculation of chemical shifts of carbon nuclei, directly bonded with several heavy chalcogens, is introduced and attested on the representative series of molecules. The best hybrid scheme combines the nonrelativistic coupled cluster-based approach with the different types of corrections, including vibrational, solvent and relativistic...
February 7, 2018: Magnetic Resonance in Chemistry: MRC
Nilamoni Nath, Priyakshi Bordoloi, Bhaskar Barman, Bikash Baishya, Sachin R Chaudhari
Enantiodiscrimination and their quantification using Nuclear Magnetic Resonance (NMR) spectroscopy has always been a subject of great interest. Proton is the nucleus of choice for enantiodiscrimination due to its high sensitivity and ubiquitous presence in nature. Despite its advantages, enantiodiscrimination suffers from extensive signal splitting by the proton-proton scalar couplings, which give complex multiplets that spread over a frequency range of some tens of hertz. These multiplets often overlap, further complicating interpretation of the spectra and quantifications...
February 7, 2018: Magnetic Resonance in Chemistry: MRC
Beom Soo Kim, Seunghyun Ahn, Dongsoo Koh, Somi Kim Cho, Yeon Woo Song, Jiha Sung, Yoongho Lim
No abstract text is available yet for this article.
February 7, 2018: Magnetic Resonance in Chemistry: MRC
D Pitoux, Z Hu, B Plainchont, D Merlet, J Farjon, D Bonnaffé, N Giraud
We report the application of pure shift and J-edited NMR spectroscopies to the structural analysis of a protected maltotrioside synthetic intermediate whose crowded 1 H spectrum displays highly crowded regions. The analytical strategy is based on the implementation of J-edited and TOCSY experiments whose resolution is optimized by the use of broadband homonuclear decoupling and selective refocusing techniques, to assign and measure chemical shifts and homonuclear scalar couplings with high accuracy. The resulting data show a high level of complementarity, providing a detailed insight into each sub-unit of this oligomeric saccharide, even for proton sites whose NMR signals strongly overlap...
February 3, 2018: Magnetic Resonance in Chemistry: MRC
Laura Castañar, Guilherme Dal Poggetto, Adam Colbourne, Gareth A Morris, Mathias Nilsson
The GNAT (General NMR Analysis Toolbox) is a free and open-source software package for processing, visualizing and analysing NMR data. It supersedes the popular DOSY Toolbox, which has a narrower focus on diffusion NMR. Data import of most common formats from the major NMR platforms is supported, as well as a GNAT generic format. Key basic processing of NMR data (e.g. Fourier transformation, baseline correction, phasing) is catered for within the programme, as well as more advanced techniques (e.g. reference deconvolution, pure shift FID reconstruction)...
February 2, 2018: Magnetic Resonance in Chemistry: MRC
Rafael C G Pereira, Daniel C F Soares, Diogo C P Oliveira, Grasiely F de Sousa, Sidney A Vieira-Filho, Maria O Mercadante-Simões, Ivana Lula, Armando Silva-Cunha, Lucienir P Duarte
No abstract text is available yet for this article.
January 31, 2018: Magnetic Resonance in Chemistry: MRC
Teobald Kupka, Aneta Buczek, Małgorzata Broda, Łukasz Gajda, Monika Ignasiak
Self consistent field Hartree-Fock (SCF-HF), density functional theory (DFT: B3LYP, KT1, KT2 and KT3) and coupled-cluster (CC) calculations of the nuclear magnetic shielding constants of BH and BH3 molecules have been conducted to characterize the convergence of individual results obtained with correlation- and polarization-consistent basis sets. The individual 11 B and 1 H NMR parameters were estimated in the complete basis set limit (CBS) and compared with benchmark literature results. The SCF-HF and DFT-B3LYP predicted boron shieldings and shielding anisotropies of BH significantly differed from the results obtained by coupled-cluster with single, double and perturbative treatment of triple excitations, CCSD(T) approach...
January 23, 2018: Magnetic Resonance in Chemistry: MRC
Peter Bigler, Julien Furrer
In this contribution, we show that the magnitude of heteronuclear long-range coupling constants can be directly extracted from the classical 1D HMBC spectra, as all multiplet lines of a cross peak always and exclusively vanish for the condition Δ = k/n JCH . To the best of our knowledge this feature of the classical HMBC has not yet been noticed and exploited. This condition holds true, irrespective of the magnitude and numbers of additional active and passive homonuclear n JHH' couplings. Alternatively the n JCH value may also be evaluated by fitting the peak's intensity in the individual spectra to its simple sin(πn JCH Δ)exp(-Δ/T2eff ) dependence...
January 15, 2018: Magnetic Resonance in Chemistry: MRC
Pavel Kessler, Markus Godejohann
This paper introduces CMC-se - a program for computer assisted structure elucidation. In the experimental part, the combination of modern analytical methods (LC-SPE-NMR/MS) and structure elucidation software is used for the identification of tentative markers in red wines.
January 13, 2018: Magnetic Resonance in Chemistry: MRC
Fernando Hallwass, Rubens R Teles, Erich Hellemann, Christian Griesinger, Roberto R Gil, Armando Navarro-Vázquez
Mechanical compression of polymer gels provides a simple way for the measurement of Residual Chemical Shift Anisotropies (RCSAs), which then can be employed, on its own, or in combination with Residual Dipolar Couplings (RDCs), for structural elucidation purposes. RCSAs measured using compression devices needed a posteriori correction to account for the increase of the polymer to solvent ratio inside the swollen gel. This correction has been cast before in terms of a single free parameter which, as shown here, can be simultaneously optimized along with the components of the alignment tensor while still retaining discriminating power of the different relative configurations as illustrated in the stereochemical analysis of α-santonin and 10-epi-8-deoxycumambrin B...
January 11, 2018: Magnetic Resonance in Chemistry: MRC
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