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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
Deisy Dos Santos Freitas, Wilian da Silva Nunes, Rafael do Prado Apparecido, Thiago Inácio Barros Lopes, Glaucia Braz Alcantara
Ilex paraguariensis (mate) is a species native to South America and is widely consumed in countries such Argentina, Uruguay, Paraguay and Brazil. Mate consumption is associated with several phytotherapeutic functions, in addition to its cultural and regional importance. However, the harvest period can affect the properties of the mate, due to variations in the constituent proportions, as a consequence of seasonal changes. In this work, we employed NMR and chemometrics to evaluate the chemical variations in leaf extracts of Ilex paraguariensis over the four seasons of the year...
January 6, 2018: Magnetic Resonance in Chemistry: MRC
Nan Ding, Li Han, Yi Jiang, Guiding Li, Jiang Liu, Yu Mu, Xueshi Huang
No abstract text is available yet for this article.
January 5, 2018: Magnetic Resonance in Chemistry: MRC
H M Zhang, W B Xiao, Xiong Wan
Based on the studies of the EPR parameters for two types of the Cu2+ centers in Cd(HCOO)2 ·2H2 O by using the high-order perturbation formulas for a 3d9 ion in a rhombically elongated octahedron, local structure of the doped copper ion is determined. Research suggests that the impurity Cu2+ replaces the host Cd2+ and undergoes the local rhombic elongation distortion, characterized by the axial elongation ratios of 4.1%, and 3.8% along the z-axis and the planar bond length variation ratios of 3.8%, and 3.1% along the x-axis and y-axis, for Cu2+ centers, I and II, respectively...
January 4, 2018: Magnetic Resonance in Chemistry: MRC
Teodor Parella
Two-dimensional J-resolved (Jres) NMR experiments offer a simple, user-friendly spectral representation where the information of coupling constants and chemical shifts are separated into two orthogonal frequency axis. Since its initial proposal forty years ago, Jres has been the focus of considerable interest both in improving the basic pulse sequence and in its successful application to a wide range of studies. Here, the latest developments in the design of novel Jres pulse schemes are reviewed, mainly focusing on obtaining pure absorption lineshapes, minimizing strong coupling artifacts, and also optimizing sensitivity and experimental measurements...
January 3, 2018: Magnetic Resonance in Chemistry: MRC
M R Hossain, D Wray, A Paul, P C Griffiths
Measurement of the spin-spin NMR relaxation time (or its inverse, the rate) of water molecules in aqueous nanoparticle dispersions has become a popular approach to probe of the nature and structure of the particle surface and any adsorbed species. Here, we report on the characterisation of aqueous dispersions of hollow amorphous nanoparticles, that have two liquid accessible surfaces (inner cavity surface and outer shell surface), plus the solid (silica) and core-shell (titania-silica) nanoparticle precursors from which the hollow particles have been prepared...
December 26, 2017: Magnetic Resonance in Chemistry: MRC
Juan A Aguilar, Alan M Kenwright
Historically, the resolution of multidimensional NMR has been orders of magnitude lower than the intrinsic resolution that NMR spectrometers are capable of producing. The slowness of Nyquist sampling, as well as the existence of signals as multiplets instead of singlets have been two of the main reasons for this underperformance. Fortunately, two compressive techniques have appeared that can overcome these limitations. Compressive sensing, also known as compressed sampling, (CS), avoids the first limitation exploiting the compressibility of typical NMR spectra, thus allowing sampling at sub-Nyquist rates, while pure shift techniques eliminate the second issue "compressing" multiplets into singlets...
December 26, 2017: Magnetic Resonance in Chemistry: MRC
Jörg Döpfert, Matthias Schnurr, Martin Kunth, Honor May Rose, Andreas Hennig, Leif Schröder
We propose a method to dynamically monitor the progress of an enzymatic reaction using NMR of hyperpolarized 129 Xe in a host-guest system. It is based on a displacement assay originally designed for fluorescence experiments that exploits the competitive binding of the enzymatic product on the one hand and a reporter dye on the other hand to a supramolecular host. Recently, this assay has been successfully transferred to NMR, using xenon as a reporter, cucurbit[6]uril as supramolecular host, and Hyper-CEST as detection technique...
December 23, 2017: Magnetic Resonance in Chemistry: MRC
Philip Norcott, Michael J Burns, Peter J Rayner, Ryan E Mewis, Simon B Duckett
By introducing a range of 2 H labels into pyridine and the para-substituted agents methyl isonicotinate and isonicotinamide we significantly improve their NMR detectability in conjunction with the Signal Amplification by Reversible Exchange (SABRE) process. We describe how the rates of T1 relaxation for the remaining 1 H nuclei are increased and show how this leads to a concomitant increase in the level of 1 H and 13 C hyperpolarization that can ultimately be detected.
December 23, 2017: Magnetic Resonance in Chemistry: MRC
Peter Kiraly, Mathias Nilsson, Gareth A Morris
Pure shift NMR spectroscopy has become an efficient tool for improving resolution in proton NMR spectra by removing the effect of homonuclear couplings. The introduction of real-time acquisition methods has allowed the main drawback of pure shift NMR, the long experiment times needed, to be circumvented. Real-time methods use periodic application of J-refocusing pulse sequence elements, acquiring a single free induction decay, in contrast to previous methods that construct a pure shift interferogram by concatenating excerpts from multiple free induction decays...
December 23, 2017: Magnetic Resonance in Chemistry: MRC
Javeed Ahmad Sheikh, Vladimir I Bakhmutov, Abraham Clearfield
Multinuclear solid-state NMR and PXRD data collected for phosphonate materials Zr(O3 PC6 H4 PO3 )·3.6H2 O and Sn(O3 PC6 H4 PO3 )0.85 (O3 POH)0.30 ·3.09H2 O have resulted in the layered structure, where the phosphonic acids cross link the layers. The main structural motif (the 111 connectivity in the PO3 group) has been established by determination of CSA parameters for phosphorus nuclei in the phosphonate groups. An analysis of the variable-temperature 31 P T1 measurements and the shapes of the phosphorus resonances in the 31 P static NMR spectra have resulted in the dipolar mechanism of the phosphorus spin-lattice relaxation, where the rotating phenylene rings reorient dipolar vectors P···H as a driving force of the relaxation process...
December 18, 2017: Magnetic Resonance in Chemistry: MRC
Nancy Jaiswal, Nisha Raikwal, Himanshu Pandey, Nipanshu Agarwal, Ashish Arora, Krishna Mohan Poluri, Dinesh Kumar
Helicobacter pylori (H. pylori) colonizes under harsh acidic/oxidative stress conditions of human gastrointestinal tract and can survive there for infinitely longer durations of host life. The bacterium expresses several harbinger proteins to facilitate its persistent colonization under such conditions. One such protein in H. pylori is Histone like DNA binding protein (Hup) which in its homo-dimeric form binds to DNA to perform various DNA dependent cellular activities. Further, it also plays an important role in protecting the genomic DNA from oxidative stress and acidic denaturation...
December 14, 2017: Magnetic Resonance in Chemistry: MRC
István Timári, Katalin E Kövér
Long-range heteronuclear coupling constants convey invaluable information for stereochemical and conformational analysis of molecules from synthetic and natural origin. Here we report a real-time Zangger-Sterk CPMG-HSQMBC method for the precise and direct measurement of multiple-bond heteronuclear couplings. It is demonstrated that the real-time acquisition strategy combined with multiple slice selective excitation can provide substantial improvement in sensitivity (or reduction of experimental time) as compared to other variants of broadband homonuclear decoupled HSQMBC methods published previously...
December 14, 2017: Magnetic Resonance in Chemistry: MRC
Kathrin Buchberger, Martin Walenta, Klaus Zangger
The measurement of small homonuclear coupling constants is often prevented by either their small size and/or overlap with other signal splittings. Here we present a real-time method to extract such couplings without interference from other splittings, with a resolution that is beyond conventional NMR spectra. In this real-time J-upscaled SERF experiment, homonuclear coupling is removed by slice-selective pure shift NMR, while scalar coupling to only one selected signal is reintroduced by selective refocusing (SERF)...
December 14, 2017: Magnetic Resonance in Chemistry: MRC
Marta Brucka, Kirill Sheberstov, Damien Jeannerat
The two most compelling methods for broadband homonuclear decoupling currently available, Zangger-Sterk (ZS) and PSYCHE, were successfully adapted and tested on the 13 C isotope. When applied during the indirect carbon dimension of the HSQC experiment, they both entirely eliminated the extended carbon-carbon multiplet structures observed in this dimension of a non-decoupled HSQC spectrum of 13 C-enriched cholesterol. The optimized selective pulse modulated using novel non-equidistant scheme for multi-site refocusing (ZS) and the small flip angle saltire chirps (PSYCHE) both proved to be robust and efficient in providing decoupled spectra with a sensitivity of about 25% that of the non-decoupled HSQC spectra with improved quality compared to earlier results...
December 13, 2017: Magnetic Resonance in Chemistry: MRC
Veera Mohana Rao Kakita, Jagadeesh Bharatam
The present manuscript reports development and applications of real-time homonuclear broadband decoupled pure shift version of in-phase zero-quantum filtered COSY (PS-IPZF-COSY) and clean in-phase COSY (PS-CLIP-COSY) pulse schemes. In contrast to the conventional COSY schemes, these PS-versions provide enhanced spectral resolution and simplify the chemical shift correlation analysis of scalar coupled spins in complex organic molecules, which are exemplified for erythromycin A, estradiol and a mixture of estradiol and testosterone...
December 12, 2017: Magnetic Resonance in Chemistry: MRC
Sandeep Kumar Mishra, N Suryaprakash
The limited chemical shift range of protons and pairwise interaction among all the abundant nuclear spins of a molecule make 1 H spectrum too complicated. As a consequence the straightforward analysis and the accurate extraction of their interaction strengths from the 1 H spectrum of a complex spin system is formidably difficult or often impossible. This problem persists in the determination of scalar couplings be it between two abundant homonuclear spins or between 1 H and an abundant heteronuclear spin (viz...
December 12, 2017: Magnetic Resonance in Chemistry: MRC
Alexey S Kiryutin, Alexandra V Yurkovskaya, Herbert Zimmermann, Hans-Martin Vieth, Konstantin L Ivanov
SABRE (Signal Amplification By Reversible Exchange) is a promising hyperpolarization technique, which makes use of spin order transfer from parahydrogen (the H2 molecule in its singlet spin state) to a to-be-polarized substrate in a transient organometallic complex, termed the SABRE complex. In this work we present an experimental method for measuring the magnetic field dependence of the SABRE effect over an ultra-wide field range, namely, from 10 nT to 10 T. This approach gives a way to determine the complete magnetic field dependence of SABRE-derived polarization...
December 12, 2017: Magnetic Resonance in Chemistry: MRC
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