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Journal of Magnetic Resonance

Alessandro V Matheoud, Nergiz Sahin, Giovanni Boero
Single-chip microwave oscillators are promising devices for inductive electron spin resonance spectroscopy (ESR) experiments on nanoliter and subnanoliter samples. Two major problems of the previously reported designs were the large minimum microwave magnetic field (0.1-0.7 mT) and large power consumption (0.5-200 mW), severely limiting their use for the investigation of samples having long relaxation times and for operation at low temperatures. Here we report on the design and characterization of a single-chip ESR detector operating with a microwave magnetic field and a power consumption orders of magnitude lower compared with previous designs...
July 5, 2018: Journal of Magnetic Resonance
Norbert W Lutz, Monique Bernard
Magnesium(II) is the second most abundant intracellular cation in mammals. Non-invasive 31 P MRS is currently used to measure intracellular free Mg2+ levels in studies of magnesium deficiency disorders. However, this technique only provides one [Mg2+ ] value for a given tissue volume (or voxel), based on the chemical shift of the ATP-β (or NTP-β) resonance. We present here an approach for quantifying tissue heterogeneity in regard to [Mg2+ ], by way of multiple 31 P MRS-derived descriptors characterizing the statistical intra-volume distribution of free [Mg2+ ] values...
June 30, 2018: Journal of Magnetic Resonance
Mason Greer, Cheng Chen, Soumyajit Mandal
In this work, low-field proton (1 H) and sodium (23 Na) relaxation and diffusion measurements are used to detect and classify different types of food products. A compact and low-cost system based on a small 0.5 T permanent magnet has been developed to autonomously authenticate such products. The system uses a simple but efficient double-tuned matching network suitable for 1 H/23 Na NMR. Various machine learning algorithms are used to classify food samples based on T1 -T2 and D-T2 data generated by the system, and the accuracy and prediction speed of these algorithms are studied in detail...
June 30, 2018: Journal of Magnetic Resonance
Zhiwei Qiao, Zheng Zhang, Xiaochuan Pan, Boris Epel, Gage Redler, Dan Xia, Howard Halpern
Electron paramagnetic resonance imaging (EPRI) can yield information about the 3-dimensional (3D) spatial distribution of the unpaired-electron-spin density from which the spatial distribution of oxygen concentration within tumor tissue, referred to as the oxygen image or electron paramagnetic resonance (EPR) image in this work, can be derived. Existing algorithms for reconstruction of EPR images often require data collected at a large number of densely sampled projection views, resulting in a prolonged data-acquisition time and consequently numerous practical challenges especially to in vivo animal EPRI...
June 26, 2018: Journal of Magnetic Resonance
Behzad Mohebbi, Amir Hossein Tavangarrad, Jan Claussen, Bernhard Blümich, S Majid Hassanizadeh, Rodrigo Rosati
Offering multifaceted applications, thin fibrous porous materials are mostly used in stacks of layers, each layer having a defined functionality. Since only a few pores exist across a layer a couple of hundred microns thick, the interface between layers may significantly affect liquid ingress. Thus, the main objective of the study is to substantiate that an interface layer is present during liquid infiltration between stacked thin fibrous layers and that it affects the fluid transport properties. A compact single-sided NMR device with a low static gradient of about 2 T/m perpendicular to the sensor surface and a uniform magnetic field in lateral directions was used to profile a 2-mm thick slice in one shot...
June 25, 2018: Journal of Magnetic Resonance
Jiangyu Cui, Jun Li, Xiaomei Liu, Xinhua Peng, Riqiang Fu
Multiple pulse sequences are often used to manipulate spin Hamiltonians in solid-state nuclear magnetic resonance spectroscopy. In this paper, we analyze multiple pulse sequences using the well-known average Hamiltonian theory. We first expand the resulting average Hamiltonian into a reachable set of sub-Hamiltonians and then develop a general procedure using both flip-angle and phase of the applied pulses as control variables to select any of those sub-Hamiltonians. We use this method to analyze solid-echo based sequences and to design new proton-proton homonuclear decoupling sequences in static solids...
June 23, 2018: Journal of Magnetic Resonance
Igor Serša, Urša Mikac
Number of NMR/MRI studies on batteries is rapidly increasing in the past decade. As the test batteries designed for the studies contain metal parts such as electrodes and lead wires as well as other conductive parts (electrolyte), which all present obstacles for good MR signal reception, understanding of the role of battery design and of battery interactions with magnetic field is of a key importance for a successful performance of the experiments. For the study, five different samples mimicking a real battery cell were made...
June 23, 2018: Journal of Magnetic Resonance
Jeffrey W Simkins, Philip S Stewart, Joseph D Seymour
19 F magnetic resonance has been used in the medical field for quantifying oxygenation in blood, tissues, and tumors. The 19 F NMR oximetry technique exploits the affinity of molecular oxygen for liquid fluorocarbon phases, and the resulting linear dependence of 19 F spin-lattice relaxation rate R1 on local oxygen concentration. Bacterial biofilms, aggregates of bacteria encased in a self-secreted matrix of extracellular polymers, are important in environmental, industrial, and clinical settings and oxygen gradients represent a critical determinant of biofilm function...
June 22, 2018: Journal of Magnetic Resonance
A Reci, A J Sederman, L F Gladden
Sampling strategies are often central to experimental design. Choosing efficiently which data to acquire can improve the estimation of parameters and reduce the acquisition time. This work is focused on designing optimal sampling patterns for Nuclear Magnetic Resonance (NMR) applications, illustrated with respect to the best estimate of the parameters characterising a lognormal distribution. Lognormal distributions are commonly used as fitting models for distributions of spin-lattice relaxation time constants, spin-spin relaxation time constants and diffusion coefficients...
June 19, 2018: Journal of Magnetic Resonance
Dariusz Gołowicz, Mateusz Urbańczyk, Alexandra Shchukina, Krzysztof Kazimierczuk
Nuclear magnetic resonance (NMR) spectroscopy is frequently applied in quantitative chemical analysis (qNMR). It is easy to measure one-dimensional (1D) NMR spectra in a quantitative regime (with appropriately long relaxation delays and acquisition times); however, their applicability is limited in the case of complex samples with severe peak overlap. Two-dimensional (2D) NMR solves the overlap problem, but at the cost of biasing peak intensities and hence quantitativeness. This is partly due to the uneven coherence transfer between excited/detected 1 H nuclei and the heteronuclei coupled to them (typically 13 C)...
June 19, 2018: Journal of Magnetic Resonance
Joel Lapin, Alexander A Nevzorov
An automated technique for the sequential assignment of NMR backbone resonances of oriented protein samples has been developed and tested based on 15 N-15 N homonuclear exchange and spin-exchanged separated local-field spectra. By treating the experimental spectral intensity as a pseudopotential, the Monte-Carlo Simulated Annealing algorithm has been employed to seek lowest-energy assignment solutions over a large sampling space where direct enumeration would be unfeasible. The determined sequential assignments have been scored based on the positions of the crosspeaks resulting from the possible orders for the main peaks...
June 16, 2018: Journal of Magnetic Resonance
Susanne Penzel, Albert A Smith, Matthias Ernst, Beat H Meier
Fast magic-angle spinning, coupled with 1 H detection is a powerful method to improve spectral resolution and signal to noise in solid-state NMR spectra. Commercial probes now provide spinning frequencies in excess of 100 kHz. Then, one has sufficient resolution in the 1 H dimension to directly detect protons, which have a gyromagnetic ratio approximately four times larger than 13 C spins. However, the gains in sensitivity can quickly be lost if the rotation angle is not set precisely. The most common method of magic-angle calibration is to optimize the number of rotary echoes, or sideband intensity, observed on a sample of KBr...
June 15, 2018: Journal of Magnetic Resonance
Qiang Wang, Julien Trébosc, Yixuan Li, Oliver Lafon, Shaohui Xin, Jun Xu, Bingwen Hu, Ningdong Feng, Jean-Paul Amoureux, Feng Deng
We introduce two MAS schemes that allow manipulating the satellite-transition (ST) populations of half-integer quadrupolar nuclei, and which both exhibit improved robustness to the quadrupolar coupling constant (CQ ). These schemes, called quadruple frequency sweep (QFS) or quadruple WURST (QWURST) are the sums of two DFS or four WURST to efficiently invert the ST populations of nuclei subject to large or small quadrupole interactions, simultaneously. These quadruple sweeps methods only require 6% more rf-power than the double sweeps ones...
June 14, 2018: Journal of Magnetic Resonance
Veera Mohana Rao Kakita, Ēriks Kupče, Jagadeesh Bharatam, Ramakrishna V Hosur
Novel two dimensional Hadamard encoding/decoding based pure shift NMR acquisition techniques (TOCSY and HSQC) have been developed, which provide chemical shift information at ultra high resolution in very short spectrometer times. The efficacy of these methods for rapid assignment of chemical shifts in complex NMR spectra of organic molecules/natural products has been demonstrated. This would be of great help for rapid analysis of samples during separation of complex mixtures.
June 13, 2018: Journal of Magnetic Resonance
Pavlo Bielytskyi, Daniel Gräsing, Kaustubh R Mote, Karthick Babu Sai Sankar Gupta, Shimon Vega, P K Madhu, A Alia, Jörg Matysik
In the present study, we exploit the light-induced hyperpolarization occurring on 13 C nuclei due to the solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) effect to boost the NMR signal intensity of selected protons via inverse cross-polarization. Such hyperpolarization transfer is implemented into 1 H-detected two-dimensional 13 C-1 H correlation magic-angle-spinning (MAS) NMR experiment to study protons in frozen photosynthetic reaction centers (RCs). As a first trial, the performance of such an experiment is tested on selectively 13 C labeled RCs from the purple bacteria of Rhodobacter sphaeroides...
June 8, 2018: Journal of Magnetic Resonance
Peyman Sakhaii, Bojan Bohorc, Wolfgang Bermel
A new experiment for recording double quantum spectra is introduced. The 2D DQ NMR experiment yields phase sensitive spectra with double quantum frequencies in F1 . The appearance of remote peaks is vastly suppressed by using a small flip angle double quantum excitation and reconversion. Pulse sequences and phase sensitive processing are discussed. The complexity of the SQ antiphase magnetization given in larger proton spin networks could be reduced by using the option of band selective decoupling during the preparation period...
May 24, 2018: Journal of Magnetic Resonance
Dennis J Sorce, Shalom Michaeli
In the present study we derive expressions for relaxation rate functions due to dipolar interactions between identical spins in the rotating frames of rank greater than or equal to 3. The rotating frames are produced due to fictitious magnetic field as generated by amplitude and frequency modulated radiofrequency (RF) pulses operating in non-adiabatic regime. This solution provides a means for description of the relaxations during method entitled Relaxation Along a Fictitious Field (RAFF) in the rotating frame of rank n (RAFFn), in which a fictitious field is created in a coordinate frame undergoing multi-fold rotation about n axes (i...
May 24, 2018: Journal of Magnetic Resonance
Peter Kiraly, Mathias Nilsson, Gareth A Morris
Homonuclear decoupling can give impressive improvements in spectral resolution when overlapping multiplet structures limit the interpretability of NMR spectra. General homodecoupling methods ("pure shift NMR") typically use either interferogram-style acquisition, which is slow but gives optimum resolution, or real-time acquisition, which is fast but gives broader lines. Here we describe an alternative data acquisition strategy that allows rapid acquisition without resolution loss, illustrating the method with band-selective homodecoupling experiments and demonstrating its advantages over competing methods...
May 19, 2018: Journal of Magnetic Resonance
Sergey Milikisiyants, Maxim A Voinov, Alex I Smirnov
EPR pulsed dipolar spectroscopy (PDS) is indispensable for measurements of nm-scale distances between electronic spins in biological and other systems. While several useful modifications and pulse sequences for PDS have been developed in recent years, DEER experiments utilizing pump and observer pulses at two different frequencies remain the most popular for practical applications. One of the major drawbacks of all the available DEER approaches is the presence of a significant unmodulated fraction in the detected signal that arises from an incomplete inversion of the coupled spins by the pump pulse...
May 17, 2018: Journal of Magnetic Resonance
Laura A Buchanan, Lukas B Woodcock, Richard W Quine, George A Rinard, Sandra S Eaton, Gareth R Eaton
In rapid scan EPR the rapidly-changing magnetic field induces a background signal that may be larger than the EPR signal. A method has been developed to correct for that background signal by acquiring two sets of data, denoted as scan 1 and scan 2. In scan 2 the external field B0 is reversed and the data acquisition trigger is offset by one half cycle of the scan field relative to the settings used in scan 1. For data acquired with a cross-loop resonator subtraction of scan 2 from scan 1 cancels the background and enhances the EPR signal...
May 17, 2018: Journal of Magnetic Resonance
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