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Journal of Magnetic Resonance

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https://www.readbyqxmd.com/read/28318908/selected-topics-in-solution-phase-biomolecular-nmr-spectroscopy
#1
EDITORIAL
Lewis E Kay, Lucio Frydman
No abstract text is available yet for this article.
March 16, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28301804/reconstructing-diffusion-ordered-nmr-spectroscopy-by-simultaneous-inversion-of-laplace-transform
#2
Bin Yuan, Yiming Ding, Ghulam M Kamal, Limin Shao, Zhiming Zhou, Bin Jiang, Peng Sun, Xu Zhang, Maili Liu
2D diffusion-ordered NMR spectroscopy (DOSY) has been widely recognized as a powerful tool for analyzing mixtures and probing inter-molecular interactions in situ. But it is difficult to differentiate molecules with similar diffusion coefficients in presence of overlapped spectra. Its performance is susceptible to the number of chemical components, and usually gets worse when the number of components increases. Here, to alleviate the problem, numerical simultaneous inversion of Laplace transform (SILT) of many related variables is proposed for reconstructing DOSY spectrum (SILT-DOSY)...
March 7, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28314207/a-pulse-sequence-for-singlet-to-heteronuclear-magnetization-transfer-s2hm
#3
Gabriele Stevanato, James Eills, Christian Bengs, Giuseppe Pileio
We have recently demonstrated, in the context of para-hydrogen induced polarization (PHIP), the conversion of hyperpolarized proton singlet order into heteronuclear magnetisation can be efficiently achieved via a new sequence named S2hM (Singlet to heteronuclear Magnetisation). In this paper we give a detailed theoretical description, supported by an experimental illustration, of S2hM. Theory and experiments on thermally polarized samples demonstrate the proposed method is robust to frequency offset mismatches and radiofrequency field inhomogeneities...
March 6, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28314206/comparison-of-potassium-and-sodium-binding-in-vivo-and-in-agarose-samples-using-tqtppi-pulse-sequence
#4
Victor D Schepkin, Andreas Neubauer, Armin M Nagel, Thomas F Budinger
Potassium and sodium specific binding in vivo were explored at 21.1T by triple quantum (TQ) magnetic resonance (MR) signals without filtration to achieve high sensitivities and precise quantifications. The pulse sequence used time proportional phase increments (TPPI). During simultaneous phase-time increments, it provided total single quantum (SQ) and TQ MR signals in the second dimension at single and triple quantum frequencies, respectively. The detection of both TQ and SQ signals was performed at identical experimental conditions and the resulting TQ signal equals 60±3% of the SQ signal when all ions experience sufficient time for binding...
March 6, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28285144/low-cost-pseudo-halbach-dipole-magnets-for-nmr
#5
Michael C D Tayler, Dimitrios Sakellariou
We present designs for compact, inexpensive and strong dipole permanent magnets aimed primarily at magnetic resonance applications where prepolarization and detection occur at different locations. Low-homogeneity magnets with a 7.5mm bore size and field up to nearly 2T are constructed using low-cost starting materials, standard workshop tools and only few hours of labor - an achievable project for a student or postdoc with spare time. As an application example we show how our magnet was used to polarize the nuclear spins in approximately 1mL of pure [(13)C]-methanol prior to detection of its high-resolution NMR spectrum at zero field (measurement field below 10(-10)T), where signals appear at multiples of the carbon-hydrogen spin-spin coupling frequency (1)JCH=140...
March 6, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28285143/adiabatic-sweep-cross-polarization-magic-angle-spinning-nmr-of-half-integer-quadrupolar-spins
#6
Sungsool Wi, Chul Kim, Robert Schurko, Lucio Frydman
The use of frequency-swept radiofrequency (rf) pulses for enhancing signals in the magic-angle spinning (MAS) spectra of half-integer quadrupolar nuclides was explored. The broadband adiabatic inversion cross-polarization magic-angle spinning (BRAIN-CPMAS) method, involving an adiabatic inversion pulse on the S-channel and a simultaneous rectangular spin-lock pulse on the I-channel ((1)H), was applied to I(1/2)→S(3/2) systems. Optimal BRAIN-CPMAS matching conditions were found to involve low rf pulse strengths for both the I- and S-spin channels...
March 2, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28288418/-click-analytics-for-click-chemistry-a-simple-method-for-calibration-free-evaluation-of-online-nmr-spectra
#7
Aleksandra Michalik-Onichimowska, Simon Kern, Jens Riedel, Ulrich Panne, Rudibert King, Michael Maiwald
Driven mostly by the search for chemical syntheses under biocompatible conditions, so called "click" chemistry rapidly became a growing field of research. The resulting simple one-pot reactions are so far only scarcely accompanied by an adequate optimization via comparably straightforward and robust analysis techniques possessing short set-up times. Here, we report on a fast and reliable calibration-free online NMR monitoring approach for technical mixtures. It combines a versatile fluidic system, continuous-flow measurement of (1)H spectra with a time interval of 20s per spectrum, and a robust, fully automated algorithm to interpret the obtained data...
March 1, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28288417/solvent-suppression-in-dnp-enhanced-solid-state-nmr
#8
Jayasubba Reddy Yarava, Sachin Rama Chaudhari, Aaron J Rossini, Anne Lesage, Lyndon Emsley
We show how DNP enhanced solid-state NMR spectra can be dramatically simplified by suppression of solvent signals. This is achieved by (i) exploiting the paramagnetic relaxation enhancement of solvent signals relative to materials substrates, or (ii) by using short cross-polarization contact times to transfer hyperpolarization to only directly bonded carbon-13 nuclei in frozen solutions. The methods are evaluated for organic microcrystals, surfaces and frozen solutions. We show how this allows for the acquisition of high-resolution DNP enhanced proton-proton correlation experiments to measure inter-nuclear proximities in an organic solid...
March 1, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28319851/-31-p-dephased-13-c-detected-redor-for-nmr-crystallography-at-natural-isotopic-abundance
#9
Alexander I Greenwood, Mary C Clay, Chad M Rienstra
Typically, the process of NMR-based structure determination relies on accurately measuring a large number of internuclear distances to serve as restraints for simulated annealing calculations. In solids, the rotational-echo double-resonance (REDOR) experiment is a widely used approach to determine heteronuclear dipolar couplings corresponding to distances usually in the range of 1.5-8Å. A challenge in the interpretation of REDOR data is the degeneracy of symmetric subunits in an oligomer or equivalent molecules in a crystal lattice, which produce REDOR trajectories that depend explicitly on two or more distances instead of one...
February 28, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28282586/mapping-axonal-density-and-average-diameter-using-non-monotonic-time-dependent-gradient-echo-mri
#10
Daniel Nunes, Tomás L Cruz, Sune N Jespersen, Noam Shemesh
White Matter (WM) microstructures, such as axonal density and average diameter, are crucial to the normal function of the Central Nervous System (CNS) as they are closely related with axonal conduction velocities. Conversely, disruptions of these microstructural features may result in severe neurological deficits, suggesting that their noninvasive mapping could be an important step towards diagnosing and following pathophysiology. Whereas diffusion based MRI methods have been proposed to map these features, they typically entail the application of powerful gradients, which are rarely available in the clinic, or extremely long acquisition schemes to extract information from parameter-intensive models...
February 28, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28262561/non-uniformly-weighted-sampling-for-faster-localized-two-dimensional-correlated-spectroscopy-of-the-brain-in-vivo
#11
Gaurav Verma, Sanjeev Chawla, Rajakumar Nagarajan, Zohaib Iqbal, M Albert Thomas, Harish Poptani
Two-dimensional localized correlated spectroscopy (2D L-COSY) offers greater spectral dispersion than conventional one-dimensional (1D) MRS techniques, yet long acquisition times and limited post-processing support have slowed its clinical adoption. Improving acquisition efficiency and developing versatile post-processing techniques can bolster the clinical viability of 2D MRS. The purpose of this study was to implement a non-uniformly weighted sampling (NUWS) scheme for faster acquisition of 2D-MRS. A NUWS 2D L-COSY sequence was developed for 7T whole-body MRI...
February 22, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28237893/dynamic-nuclear-polarization-via-thermal-mixing-beyond-the-high-temperature-approximation
#12
W Th Wenckebach
Dynamic Nuclear Polarization (DNP) via the mechanism of thermal mixing has proven itself most powerful for the orientation of nuclear spins in polarized targets and hyperpolarization for magnetic resonance imaging (MRI). Unfortunately, theoretical descriptions of this mechanism have been limited to using-at least partially-the high temperature approximation, in which Boltzmann factors are expanded linearly. However, the high nuclear spin polarization required and obtained for these applications does not justify such approximations...
February 20, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28236786/new-resonator-geometries-for-ice-decoupling-of-loop-arrays
#13
Xinqiang Yan, John C Gore, William A Grissom
RF arrays with a large number of independent coil elements are advantageous for parallel transmission (pTx) and reception at high fields. One of the main challenges in designing RF arrays is to minimize the electromagnetic (EM) coupling between the coil elements. The induced current elimination (ICE) method, which uses additional resonator elements to cancel coils' mutual EM coupling, has proven to be a simple and efficient solution for decoupling microstrip, L/C loop, monopole and dipole arrays. However, in previous embodiments of conventional ICE decoupling, the decoupling elements acted as "magnetic-walls" with low transmit fields and consequently low MR signal near them...
February 16, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28267666/rf-inhomogeneity-compensation-using-method-of-fourier-synthesis
#14
Navin Khaneja
In this paper, we propose a new method for design of composite pulses that are robust to rf-amplitude (rf-inhomogeneity). We call this, the method of Fourier synthesis. The method is general enough to design excitation, inversion, refocusing or arbitary flip angle pulses that are robust to rf-amplitude. The method can be tailored to have amplitude selective excitation. We experimentally show rf-compensation over a order of magnitude (20db) variation in rf-amplitude. The method is expected to find use in invivo NMR studies using surface coils, where there is large dispersion in rf-amplitude over the sample...
February 15, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28258025/coherence-transfer-and-electron-t1-t2-relaxation-in-nitroxide-spin-labels
#15
Derek Marsh
Abragam's double-commutator spin operator method is used to analyse: 1) electron coherence transfer by intermolecular dipolar interaction between spin-label radicals, and 2) longitudinal and transverse electron spin relaxation by rotational modulation of the Zeeman and nitrogen-hyperfine anisotropies of isolated nitroxide spin labels. Results compatible with earlier treatments by Redfield theory are obtained without specifically evaluating matrix elements. Extension to single-transition operators for isolated nitroxides predicts electron coherence transfer by pseudosecular electron-nuclear dipolar interaction, in the absence of intermolecular dipolar coupling...
February 15, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28226294/extruded-dielectric-sample-tubes-of-complex-cross-section-for-epr-signal-enhancement-of-aqueous-samples
#16
Jason W Sidabras, Richard R Mett, James S Hyde
This paper builds on the work of Mett and Hyde (2003) and Sidabras et al. (2005) where multiple flat aqueous sample cells placed perpendicular to electric fields in microwave cavities were used to reduce the RF losses and increase the EPR signal. In this work, we present three novel sample holders for loop-gap resonators (LGRs) and cylindrical cavity geometries. Two sample holders have been commissioned and built by polytetrafluoroethylene (PTFE) extrusion techniques: a 1mm O.D. capillary with a septum down the middle, named DoubleDee, and a 3...
February 14, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28222392/endor-with-band-selective-shaped-inversion-pulses
#17
Claudia E Tait, Stefan Stoll
Electron Nuclear DOuble Resonance (ENDOR) is based on the measurement of nuclear transition frequencies through detection of changes in the polarization of electron transitions. In Davies ENDOR, the initial polarization is generated by a selective microwave inversion pulse. The rectangular inversion pulses typically used are characterized by a relatively low selectivity, with full inversion achieved only for a limited number of spin packets with small resonance offsets. With the introduction of pulse shaping to EPR, the rectangular inversion pulses can be replaced with shaped pulses with increased selectivity...
February 12, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28219822/ultrafast-acquisition-of-1-h-1-h-dipolar-correlation-experiments-in-spinning-elastomers
#18
Laetitia Rouger, Maxime Yon, Vincent Sarou-Kanian, Franck Fayon, Jean-Nicolas Dumez, Patrick Giraudeau
We show that two widely used 2D solid-state NMR (ssNMR) pulse sequences can be implemented in an ultrafast (UF) manner, and yield 2D spectra of elastomers in a single scan, under magic-angle spinning. UF 2D ssNMR provides an acceleration of one to several orders of magnitude for classic experiments.
February 9, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28232286/t2-selective-%C3%AF-echo-planar-imaging-for-porous-media-mri
#19
Dan Xiao, Bruce J Balcom
The π Echo Planar Imaging (PEPI) method has recently been modified to permit proton density imaging of fluids in porous media with moderate T2 and short T2(∗) signal components. In many applications, it is desirable to discriminate multiple T2 components within each image voxel. T2 selective imaging is explored in this paper through adiabatic inversion as a magnetization preparation with PEPI readout. When prior information of the sample relaxation times is known, responses of different species to broadband adiabatic inversion pulses can be predicted by Bloch equation simulation...
February 8, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28213048/low-field-single-sided-nmr-for-one-shot-1d-mapping-application-to-membranes
#20
Patrick Judeinstein, Filippo Ferdeghini, Rodrigo Oliveira-Silva, Jean-Marc Zanotti, Dimitrios Sakellariou
Many single-sided permanent magnet NMR systems have been proposed over the years allowing for 1D proton-density profiling, diffusion measurements and relaxometry. In this manuscript we make use of a recently published unilateral magnet for low-field NMR exhibiting an extremely uniform magnetic field gradient with moderate strength and cylindrical symmetry, allowing for a well-defined sweet spot. Combined with a goniometer, our system is used to characterize precisely the uniformity of its gradient and to achieve micrometric precision 1D profiling, as well as spatially localized relaxometry and diffusometry on thick (∼150μm) membrane samples...
February 8, 2017: Journal of Magnetic Resonance
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