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Journal of Magnetic Resonance

Linn W Thrane, Joseph D Seymour, Sarah L Codd
High-field nuclear magnetic resonance (NMR) relaxometry and diffusometry along with magnetic resonance imaging were used to monitor phase transition molecular dynamics during hydrate formation occurring in water droplets dispersed in liquid cyclopentane. 1D T2 relaxation measurements indicate the extent of hydrate formation as well as a reduction in water droplet size with progression of hydrate growth. MRI intensity maps and T2 relaxation maps indicate spatially dependent hydrate formation rates due to the heterogeneity of the system...
April 4, 2019: Journal of Magnetic Resonance
Igor Tkach, Isabel Bejenke, Fabian Hecker, Annemarie Kehl, Müge Kasanmascheff, Igor Gromov, Ion Prisecaru, Peter Höfer, Markus Hiller, Marina Bennati
We present and discuss the performance of 1 H electron-nuclear double resonance (ENDOR) at 263 GHz/9.4 T by employing a prototype, commercial quasi optical spectrometer. Basic instrumental features of the setup are described alongside a comprehensive characterization of the new ENDOR probe head design. The performance of three different ENDOR pulse sequences (Davies, Mims and CP-ENDOR) is evaluated using the 1 H BDPA radical. A key feature of 263 GHz spectroscopy - the increase in orientation selectivity in comparison with 94 GHz experiments - is discussed in detail...
April 3, 2019: Journal of Magnetic Resonance
Evgeny Nimerovsky
1 H NMR relaxometry of saturated rock samples has become a useful tool for the characterization of porosity and transport phenomena of enclosed fluids. The pore size can be measured using the difference between inverse relaxation values of protons absorbed by the saturated rock and that present in the bulk fluids. These experiments are usually performed at low magnetic fields to reduce the influence of the diffusion on the relaxation values in the presence of Internal Gradient Fields. Recently, sodium ions have become objects of investigation...
April 3, 2019: Journal of Magnetic Resonance
Chukun Gao, Patrick T Judge, Erika L Sesti, Lauren E Price, Nicholas Alaniva, Edward P Saliba, Brice J Albert, Nathan J Soper, Pin-Hui Chen, Alexander B Barnes
Spherical rotors in magic angle spinning (MAS) experiments have significant advantages over traditional cylindrical rotors including simplified spinning implementation, easy sample exchange, more efficient microwave coupling for dynamic nuclear polarization (DNP), and feasibility of downscaling to access higher spinning frequencies. Here, we implement spherical rotors with 4 mm outside diameter (o.d.) and demonstrate spinning >28 kHz using a single aperture for spinning gas. We show a modified stator geometry to improve fiber optic detection, increase NMR filling factor, and improve alignment for sample exchange and microwave irradiation...
April 1, 2019: Journal of Magnetic Resonance
Jens D Haller, Andrea Bodor, Burkhard Luy
We introduce a novel selective inversion element for chunked homonuclear decoupling that combines isotope selection via BIRD-filtering with band-selective inversion on the X-heteronucleus and allows efficient real-time decoupling of homonuclear and heteronuclear couplings. It is especially suitable for uniformly isotope-labeled compounds. We discuss in detail the inversion element based on band-selective refocusing on the X-nuclei (BASEREX), highlighting in particular the role of appropriate band-selective shaped refocusing pulses and the application of broadband X-pulses for an effective BIRDd element during homodecoupling...
March 30, 2019: Journal of Magnetic Resonance
Frank Löhr, Jakob Gebel, Erik Henrich, Christopher Hein, Volker Dötsch
Combinatorial selective isotope labeling is a valuable tool to facilitate polypeptide backbone resonance assignment in cases of low sensitivity or extensive chemical shift degeneracy. It involves recording of 15 N-HSQC and 2D HN-projections of triple-resonance spectra on a limited set of samples containing different combinations of labeled and unlabeled amino acid types. Using labeling schemes in which the three backbone heteronuclei (amide nitrogen, α-carbon and carbonyl carbon) are enriched in 15 N or 13 C isotopes - individually as well as simultaneously - usually yields abundant amino-acid type information of consecutive residues i and i - 1...
March 29, 2019: Journal of Magnetic Resonance
Robin Guehne, Vojtěch Chlan, Grant V M Williams, Shen V Chong, Kazuo Kadowaki, Andreas Pöppl, Jürgen Haase
Three-dimensional topological insulators are an important class of modern materials, and a strong spin-orbit coupling is involved in making the bulk electronic states very different from those near the surface. Bi2 Se3 is a model compound, and 209 Bi NMR is employed here to investigate the bulk properties of the material with focus on the quadrupole splitting. It will be shown that this splitting measures the energy band inversion induced by spin-orbit coupling in quantitative agreement with first-principle calculations...
March 29, 2019: Journal of Magnetic Resonance
Armin Purea, Christian Reiter, Alexandros I Dimitriadis, Emile de Rijk, Fabien Aussenac, Ivan Sergeyev, Melanie Rosay, Frank Engelke
We consider the geometry of a radially irradiated microwave beam in MAS DNP NMR probes and its impact on DNP enhancement. Two related characteristic features are found to be relevant: (i) the focus of the microwave beam on the DNP MAS sample and (ii) the microwave magnetic field magnitude in the sample. We present a waveguide coupler setup that enables us to significantly improve beam focus and field magnitude in 1.3 mm MAS DNP probes at a microwave frequency of 263 GHz, which results in an increase of the DNP enhancement by a factor of 2 compared to previous standard hardware setups...
March 28, 2019: Journal of Magnetic Resonance
Mohammadali Foroozandeh, Mathias Nilsson, Gareth A Morris
The design and application of ultra-broadband excitation pulses have been among the most interesting and timely areas in NMR and EPR methodology in recent years, due especially to advances in hardware design in EPR, the advent and popularity of high- and ultrahigh-field NMR, and the application of numerical methods like optimal control theory to the design and optimization of radiofrequency pulses and pulse sequences. In this communication, we present a short, robust, and flexible version of the CHORUS family of constant-phase, very broadband excitation sequences...
March 26, 2019: Journal of Magnetic Resonance
Daiane S Carvalho, Danilo G B da Silva, Fernando Hallwass, Armando Navarro-Vázquez
Chemically cross-linked polyacrylontrile polymer gels, have been prepared as an alignment medium compatible with DMSO-d6 . These gels allow measurement of residual dipolar couplings (RDCs) and residual chemical shift anisotropies (RCSAs) with good accuracy as tested with brucine and α-santonin natural compounds. The gels can be reversibly compressed allowing easy measurement of RCSAs. They also present good physical homogeneity, clean HSQC spectra with little background 1 H signals, and allow unambiguous referencing of 13 C spectra for RCSA extraction...
March 15, 2019: Journal of Magnetic Resonance
Zhiguo Wang, Xiang Peng, Rui Zhang, Hui Luo, Hong Guo
We report a new kind of interaction between overlapping Rb-Xe spin ensembles polarized by spin-exchange optical pumping. The Rb acts as both a medium to optically polarize the Xe spins and as a magnetometer to probe the precession of Xe spins. When Xe spins precess, they result in the precession of Rb spins. Like the radiation damping effect caused by the coil in conventional NMR systems, the precessing Rb spins lead to damping and a frequency-shift for the precessing Xe spins. When Xe spins are operated in a free-induction decay mode, the transverse relaxation time and oscillating frequency of Xe spins change due to the "radiation damping" effect of Rb spins...
March 15, 2019: Journal of Magnetic Resonance
Ilya M Litvak, Adrian Griffin, Joana Paulino, Wenping Mao, Peter Gor'kov, Kiran K Shetty, William W Brey
Powered resistive and resistive-superconductive hybrid magnets can reach fields higher than superconducting NMR magnets but lack the field homogeneity and temporal stability needed for high resolution NMR. Due to field fluctuations in powered magnets, commercially available mapping systems fail to produce maps of these magnets with sufficient reproducibility, thus hampering attempts to improve homogeneity of the field they generate. Starting with a commercial mapper, we built a mapping system which uses a two-channel (measurement + reference) mapper probe...
March 5, 2019: Journal of Magnetic Resonance
Alexander M Funk, Xiaodong Wen, Thomas Hever, Nesmine R Maptue, Chalermchai Khemtong, A D Sherry, Craig R Malloy
This study was designed to determine the effects of deuteration in pyruvate on exchange reactions in alanine aminotransferase (ALT), lactate dehydrogenase (LDH) and flux through pyruvate dehydrogenase (PDH). Although deuteration of a 13 C enriched substrate is commonly used to increase the lifetime of a probe for hyperpolarization experiments, the potential impact of kinetic isotope effects on such substitutions has not been studied in detail. Metabolism of deuterated pyruvate was investigated in isolated rat hearts...
March 4, 2019: Journal of Magnetic Resonance
Stuart J Elliott, Gabriele Stevanato
We introduce a simple strategy to access and readout nuclear singlet order based on the alternate repetition of hard pulses and delays. We demonstrate the general applicability of the method by accessing nuclear singlet order in spin systems characterized by diverse coupling regimes. We show that the method is highly efficient in the strong-coupling and chemical equivalence regimes, and can overcome some limitations of other well-established and more elaborated pulse sequences. A simulation package is provided which allows the determination of pulse sequence parameters...
March 4, 2019: Journal of Magnetic Resonance
Maria Grazia Concilio, Peter Kiraly, Gareth A Morris
Diffusion-ordered spectroscopy experiments in which existing delays in a parent pulse sequence are used for diffusion encoding - iDOSY experiments - are potentially attractive because of their simplicity and sensitivity. However the calculation of diffusional attenuation in Zangger-Sterk pure shift iDOSY experiments is a very difficult problem to attack analytically, and is more easily approached numerically. Numerical simulations show that for typical experimental conditions, the dependence of diffusional attenuation on diffusion-encoding gradient amplitude is well represented by a shifted Gaussian function...
March 2, 2019: Journal of Magnetic Resonance
E T Montrazi, T J Bonagamba
The Inversion-Recovery (IR) technique has already been proposed to be used as a T1 -filter for T2 -T2 Exchange experiments. However, when the Exchange experiments are employed for studying samples that show T1 distributions, where the pools are defined by broad relaxation time distributions, e.g. porous media, IR might be difficult to be used as a filter. This paper presents the difficulties found when using IR and proposes the use of Saturation-Recovery (SR) technique as an alternative to T1 -filter.
March 2, 2019: Journal of Magnetic Resonance
Can Evren Yarman, Jonathan Mitchell
We present a nonlinear inversion method for generating sparse solutions to the Fredholm Integral equation describing two-dimensional distributions of nuclear magnetic resonance (NMR) relaxation times or diffusion coefficients. Our greedy variational method approximates the distribution of exponential rate constants using a sum of Dirac delta functions, which constitute our dictionary elements. The greedy nature of the method promotes sparsity in the representation by iteratively increasing the number of terms...
March 1, 2019: Journal of Magnetic Resonance
S G J van Meerten, W M J Franssen, A P M Kentgens
For solid-state NMR or for unconventional experiments only a very limited number of modern processing and simulation software packages are available. For this reason, we have developed ssNake, an NMR processing program which provides both interactive and script-based processing tools. ssNake is aimed at solid-state NMR experiments, but can also be used for liquid-state experiments. It can read various data formats, including those from all major spectrometer vendors. It has extensive fitting capabilities, which can be used for spectrum deconvolution...
March 1, 2019: Journal of Magnetic Resonance
Henrik Nicolay Sørgård, John Georg Seland
This study presents a two-dimensional NMR pulse sequence for obtaining spatially resolved correlations between magnetic susceptibility induced internal gradients (G0 ), and both the apparent difference in magnetic susceptibility (Δχapp ) and spectral frequency (Δν). G0 -Δχapp correlations were utilized to generate spatially resolved pore size distributions, while the G0 -Δν correlations were used to additionally evaluate sample heterogeneity. The spatially resolved measurements were performed on a water saturated heterogeneous porous sample which contains one layer of 5-50 μm glass spheres (top layer) and one layer of 140-165 μm glass spheres (bottom layer)...
March 1, 2019: Journal of Magnetic Resonance
Pu Duan, Klaus Schmidt-Rohr
A convenient one-dimensional magic-angle spinning NMR method is presented that provides selective NMR spectra of COH moieties in uniformly 13 C-enriched organic materials. This method, termed hydroxyl-proton selection (HOPS), eliminates the magnetization of protons directly bonded to carbons by recoupling the 1 H-13 C dipolar interaction for a short time (∼70 μs), which also serves as a chemical-shift filter to suppress 1 H magnetization of CH3 groups. After cross polarization to 13 C, the signals of COH and COOH carbons are observed selectively...
February 27, 2019: Journal of Magnetic Resonance
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