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Journal of Magnetic Resonance

D Levi Craft, Reilly E Sonstrom, Virginia G Rovnyak, David Rovnyak
A flexible strategy for choosing samples nonuniformly from a Nyquist grid using the concept of statistical quantiles is presented for broad classes of NMR experimentation. Quantile-directed scheduling is intuitive and flexible for any weighting function, promotes reproducibility and seed independence, and is generalizable to multiple dimensions. In brief, weighting functions are divided into regions of equal probability, which define the samples to be acquired. Quantile scheduling therefore achieves close adherence to a probability distribution function, thereby minimizing gaps for any given degree of subsampling of the Nyquist grid...
February 13, 2018: Journal of Magnetic Resonance
Mark S Conradi, Stephen A Altobelli, Nicholas J Sowko, Susan H Conradi, Eiichi Fukushima
Earth's field NMR has been developed to detect oil trapped under or in Arctic sea-ice. A large challenge, addressed here, is the suppression of the water signal that dominates the oil signal. Selective suppression of water is based on relaxation time T 1 because of the negligible chemical shifts in the weak earth's magnetic field, making all proton signals overlap spectroscopically. The first approach is inversion-null recovery, modified for use with pre-polarization. The requirements for efficient inversion over a wide range of B 1 and subsequent adiabatic reorientation of the magnetization to align with the static field are stressed...
February 7, 2018: Journal of Magnetic Resonance
Nino Wili, Gunnar Jeschke
A new ultra-wide band (UWB) pulse EPR method is introduced for observing all nuclear frequencies of a paramagnetic center in a single shot. It is based on burning spectral holes with a high turning angle (HTA) pulse that excites forbidden transitions and subsequent detection of the hole pattern by a chirp echo. We term this method Chirp Echo Epr SpectroscopY (CHEESY)-detected NMR. The approach is a revival of FT EPR-detected NMR. It yields similar spectra and the same type of information as electron-electron double resonance (ELDOR)-detected NMR, but with a multiplex advantage...
February 6, 2018: Journal of Magnetic Resonance
Tangi Jézéquel, Virginie Silvestre, Katy Dinis, Patrick Giraudeau, Serge Akoka
Isotope ratio monitoring by 13 C NMR spectrometry (irm- 13 C NMR) provides the complete 13 C intramolecular position-specific composition at natural abundance. It represents a powerful tool to track the (bio)chemical pathway which has led to the synthesis of targeted molecules, since it allows Position-specific Isotope Analysis (PSIA). Due to the very small composition range (which represents the range of variation of the isotopic composition of a given nuclei) of 13 C natural abundance values (50‰), irm- 13 C NMR requires a 1‰ accuracy and thus highly quantitative analysis by 13 C NMR...
February 6, 2018: Journal of Magnetic Resonance
A Lauerer, R Kurzhals, H Toufar, D Freude, J Kärger
The two-region model for analyzing signal attenuation in pulsed field gradient (PFG) NMR diffusion studies with molecules in compartmented media implies that, on their trajectory, molecules get from one region (one type of compartment) into the other one with a constant (i.e. a time-invariant) probability. This pattern has proved to serve as a good approach for considering guest diffusion in beds of nanoporous host materials, with the two regions ("compartments") identified as the intra- and intercrystalline pore spaces...
February 2, 2018: Journal of Magnetic Resonance
Kurt Majewski
Exact solutions of the Bloch equations with T1- and T2-relaxation terms for piecewise constant magnetic fields are numerically challenging. We therefore investigate an approximation for the achieved magnetization in which rotations and relaxations are split into separate operations. We develop an estimate for its accuracy and explicit first and second order derivatives with respect to the complex excitation radio frequency voltages. In practice, the deviation between an exact solution of the Bloch equations and this rotation relaxation splitting approximation seems negligible...
February 2, 2018: Journal of Magnetic Resonance
Thomas H Edwards, Stefan Stoll
Tikhonov regularization is the most commonly used method for extracting distance distributions from experimental double electron-electron resonance (DEER) spectroscopy data. This method requires the selection of a regularization parameter, α, and a regularization operator, L. We analyze the performance of a large set of α selection methods and several regularization operators, using a test set of over half a million synthetic noisy DEER traces. These are generated from distance distributions obtained from in silico double labeling of a protein crystal structure of T4 lysozyme with the spin label MTSSL...
February 1, 2018: Journal of Magnetic Resonance
Alan Band, Matthew P Donohue, Boris Epel, Shraeya Madhu, Veronika A Szalai
We present a 34 GHz continuous wave (CW)/pulsed electron paramagnetic resonance (EPR) spectrometer capable of pulse-shaping that is based on a versatile microwave bridge design. The bridge radio frequency (RF)-in/RF-out design (500 MHz to 1 GHz input/output passband, 500 MHz instantaneous input/output bandwidth) creates a flexible platform with which to compare a variety of excitation and detection methods utilizing commercially available equipment external to the bridge. We use three sources of RF input to implement typical functions associated with CW and pulse EPR spectroscopic measurements...
February 1, 2018: Journal of Magnetic Resonance
Mark S Conradi, Stephen A Altobelli, Nicholas J Sowko, Susan H Conradi, Eiichi Fukushima
Adiabatic NMR sweep pulses are described for inversion and excitation in very low magnetic fields B0 and with broad distribution of excitation field amplitude B1. Two aspects distinguish the low field case: (1) when B1 is comparable to or greater than B0, the rotating field approximation fails and (2) inversion sweeps cannot extend to values well below the Larmor frequency because they would approach or pass through zero frequency. Three approaches to inversion are described. The first is a conventional tangent frequency sweep down to the Larmor frequency, a 180° phase shift, and a sweep back up to the starting frequency...
February 1, 2018: Journal of Magnetic Resonance
Thierry Dubroca, Adam N Smith, Kevin J Pike, Stuart Froud, Richard Wylde, Bianca Trociewitz, Johannes McKay, Frederic Mentink-Vigier, Johan van Tol, Sungsool Wi, William Brey, Joanna R Long, Lucio Frydman, Stephen Hill
Nuclear magnetic resonance (NMR) is an intrinsically insensitive technique, with Boltzmann distributions of nuclear spin states on the order of parts per million in conventional magnetic fields. To overcome this limitation, dynamic nuclear polarization (DNP) can be used to gain up to three orders of magnitude in signal enhancement, which can decrease experimental time by up to six orders of magnitude. In DNP experiments, nuclear spin polarization is enhanced by transferring the relatively larger electron polarization to NMR active nuclei via microwave irradiation...
January 31, 2018: Journal of Magnetic Resonance
Tom Brenner, Johnny Chen, Tim Stait-Gardner, Gang Zheng, Shingo Matsukawa, William S Price
A new family of binomial-like inversion sequences, named jump-and-return sandwiches (JRS), has been developed by inserting a binomial-like sequence into a standard jump-and-return sequence, discovered through use of a stochastic Genetic Algorithm optimisation. Compared to currently used binomial-like inversion sequences (e.g., 3-9-19 and W5), the new sequences afford wider inversion bands and narrower non-inversion bands with an equal number of pulses. As an example, two jump-and-return sandwich 10-pulse sequences achieved 95% inversion at offsets corresponding to 9...
January 31, 2018: Journal of Magnetic Resonance
Eleonora Cavallari, Carla Carrera, Silvio Aime, Francesca Reineri
The use of [1- 13 C]pyruvate, hyperpolarized by dissolution-Dynamic Nuclear Polarization (d-DNP), in in vivo metabolic studies has developed quickly, thanks to the imaging probe's diagnostic relevance. Nevertheless, the cost of a d-DNP polarizer is quite high and the speed of hyperpolarization process is relatively slow, meaning that its use is limited to few research laboratories. ParaHydrogen Induced Polarization Side Arm Hydrogenation (PHIP-SAH) (Reineri et al., 2015) is a cost effective and easy-to-handle method that produces 13 C-MR hyperpolarization in [1- 13 C]pyruvate and other metabolites...
January 31, 2018: Journal of Magnetic Resonance
J Beerwerth, M Storek, D Greim, J Lueg, R Siegel, B Cetinkaya, W Hiller, H Zimmermann, J Senker, R Böhmer
Polycrystalline dimethyl sulfone is studied using central-transition oxygen-17 exchange NMR. The quadrupolar and chemical shift tensors are determined by combining quantum chemical calculations with line shape analyses of rigid-lattice spectra measured for stationary and rotating samples at several external magnetic fields. Quantum chemical computations predict that the largest principal axes of the chemical shift anisotropy and electrical field gradient tensors enclose an angle of about 73°. This prediction is successfully tested by comparison with absorption spectra recorded at three different external magnetic fields...
January 31, 2018: Journal of Magnetic Resonance
Ēriks Kupče, Julien Trébosc, Barbara Perrone, Olivier Lafon, Jean-Paul Amoureux
We propose a dipolar HMQC Hadamard-encoded (D-HMQC-Hn) experiment for fast 2D correlations of abundant nuclei in solids. The main limitation of the Hadamard methods resides in the length of the encoding pulses, which results from a compromise between the selectivity and the sensitivity due to losses. For this reason, these methods should mainly be used with sparse spectra, and they profit from the increased separation of the resonances at high magnetic fields. In the case of the D-HMQC-Hnexperiments, we give a simple rule that allows directly setting the optimum length of the selective pulses, versus the minimum separation of the resonances in the indirect dimension...
January 31, 2018: Journal of Magnetic Resonance
Snædís Björgvinsdóttir, Brennan J Walder, Arthur C Pinon, Jayasubba Reddy Yarava, Lyndon Emsley
DNP methods can provide significant sensitivity enhancements in magic angle spinning solid-state NMR, but in systems with long polarization build up times long recycling periods are required to optimize sensitivity. We show how the sensitivity of such experiments can be improved by the classic flip-back method to recover bulk proton magnetization following continuous wave proton heteronuclear decoupling. Experiments were performed on formulations with characteristic build-up times spanning two orders of magnitude: a bulk BDPA radical doped o-terphenyl glass and microcrystalline samples of theophylline, l-histidine monohydrochloride monohydrate, and salicylic acid impregnated by incipient wetness...
January 31, 2018: Journal of Magnetic Resonance
D Koh, J Felder, N J Shah
MRI volume coils can be represented by equivalent lumped element circuits and for a variety of these circuit configurations analytical design equations have been presented. The unification of several volume coil topologies results in a two-dimensional gridded equivalent lumped element circuit which compromises the birdcage resonator, its multiple endring derivative but also novel structures like the capacitive coupled ring resonator. The theory section analyzes a general two-dimensional circuit by noting that its current distribution can be decomposed into a longitudinal and an azimuthal dependency...
January 25, 2018: Journal of Magnetic Resonance
Sergey L Veber, Sergey V Tumanov, Elena Yu Fursova, Oleg A Shevchenko, Yaroslav V Getmanov, Mikhail A Scheglov, Vitaly V Kubarev, Daria A Shevchenko, Iaroslav I Gorbachev, Tatiana V Salikova, Gennady N Kulipanov, Victor I Ovcharenko, Matvey V Fedin
Electron Paramagnetic Resonance (EPR) station at the Novosibirsk Free Electron Laser (NovoFEL) user facility is described. It is based on X-band (∼9 GHz) EPR spectrometer and operates in both Continuous Wave (CW) and Time-Resolved (TR) modes, each allowing detection of either direct or indirect influence of high-power NovoFEL light (THz and mid-IR) on the spin system under study. The optics components including two parabolic mirrors, shutters, optical chopper and multimodal waveguide allow the light of NovoFEL to be directly fed into the EPR resonator...
January 12, 2018: Journal of Magnetic Resonance
Melissa Van Landeghem, Wouter Maes, Etienne Goovaerts, Sabine Van Doorslaer
We present a combined high-field EPR and DFT study of light-induced radicals in the bulk heterojunction blend of PBDB-T:ITIC, currently one of the highest efficiency non-fullerene donor:acceptor combinations in organic photovoltaics. We demonstrate two different approaches for disentangling the strongly overlapping high-field EPR spectra of the positive and negative polarons after charge separation: (1) relaxation-filtered field-swept EPR based on the difference in T1 spin-relaxation times and (2) field-swept EDNMR-induced EPR by exploiting the presence of 14N hyperfine couplings in only one of the radical species, the small molecule acceptor radical...
January 11, 2018: Journal of Magnetic Resonance
M Ibrahim, C I Pardi, T W C Brown, P J McDonald
Improvement in the signal-to-noise ratio of Nuclear Magnetic Resonance (NMR) systems may be achieved either by increasing the signal amplitude or by decreasing the noise. The noise has multiple origins - not all of which are strictly "noise": incoherent thermal noise originating in the probe and pre-amplifiers, probe ring down or acoustic noise and coherent externally broadcast radio frequency transmissions. The last cannot always be shielded in open access experiments. In this paper, we show that pulsed, low radio-frequency data communications are a significant source of broadcast interference...
January 7, 2018: Journal of Magnetic Resonance
S Vashaee, M Li, B Newling, B MacMillan, F Marica, H T Kwak, J Gao, A M Al-Harbi, B J Balcom
A novel slice-selective T1-T2 measurement is proposed to measure spatially resolved T1-T2 distributions. An adiabatic inversion pulse is employed for slice-selection. The slice-selective pulse is able to select a quasi-rectangular slice, on the order of 1 mm, at an arbitrary position within the sample.The method does not employ conventional selective excitation in which selective excitation is often accomplished by rotation of the longitudinal magnetization in the slice of interest into the transverse plane, but rather a subtraction based on CPMG data acquired with and without adiabatic inversion slice selection...
January 4, 2018: Journal of Magnetic Resonance
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