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Journal of Magnetic Resonance

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https://www.readbyqxmd.com/read/29040869/accessing-the-long-time-limit-in-diffusion-nmr-the-case-of-singlet-assisted-diffusive-diffraction-q-space
#1
Giuseppe Pileio, Sylwia Ostrowska
The latest developments in the field of long-lived spin states are merged with pulsed-field gradient techniques to extend the diffusion time beyond what is currently achievable in standard q-space diffusive-diffraction studies. The method uses nearly-equivalent spin-1/2 pairs that let diffusion times of the order of many minutes to be measured allowing access to the long-time limit in cavities of macroscopic size (millimeters). A pulse sequence suitable to exploit this regime has been developed and validated with the use of numerical simulations and experiments...
October 9, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/29028542/spectral-diffusion-and-dynamic-nuclear-polarization-beyond-the-high-temperature-approximation
#2
W Th Wenckebach
Dynamic Nuclear Polarization (DNP) has proven itself most powerful for the orientation of nuclear spins in polarized targets and for hyperpolarization in magnetic resonance imaging (MRI). Unfortunately, the theoretical description of some of the processes involved in DNP invokes the high temperature approximation, in which Boltzmann factors are expanded up to first order, while the high electron and nuclear spin polarization required for many applications do not justify such an approximation. A previous article extended the description of one of the mechanisms of DNP-thermal mixing-beyond the high temperature approximation (Wenckebach, 2017)...
October 4, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/29028544/predicting-the-effect-of-relaxation-during-frequency-selective-adiabatic-pulses
#3
Annalise R Pfaff, Cailyn E McKee, Klaus Woelk
Adiabatic half and full passages are invaluable for achieving uniform, B1-insensitive excitation or inversion of macroscopic magnetization across a well-defined range of NMR frequencies. To accomplish narrow frequency ranges with adiabatic pulses (<100Hz), long pulse durations at low RF power levels are necessary, and relaxation during these pulses may no longer be negligible. A numerical, discrete recursive combination of the Bloch equations for longitudinal and transverse relaxation with the optimized equation for adiabatic angular motion of magnetization is used to calculate the trajectory of magnetization including its relaxation during adiabatic hyperbolic secant pulses...
October 3, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/29024876/design-of-a-dielectric-resonator-receive-array-at-7-tesla-using-detunable-ceramic-resonators
#4
Thomas Ruytenberg, Andrew G Webb
Ceramic-based dielectric resonators can be used for high frequency magnetic resonance imaging and microscopy. When used as elements in a transmit array, the intrinsically low inter-element coupling allows flexibility in designing different geometric arrangements for different regions-of-interest. However, without being able to detune such resonators, they cannot be used as elements in a receive-only array. Here, we propose and implement a method, based on mode-disruption, for detuning ceramic-based dielectric resonators to enable them to be used as receive-only elements...
October 3, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/29028543/a-pulse-programmable-parahydrogen-polarizer-using-a-tunable-electromagnet-and-dual-channel-nmr-spectrometer
#5
Aaron M Coffey, Roman V Shchepin, Bibo Feng, Raul D Colon, Ken Wilkens, Kevin W Waddell, Eduard Y Chekmenev
Applications of parahydrogen induced polarization (PHIP) often warrant conversion of the chemically-synthesized singlet-state spin order into net heteronuclear magnetization. In order to obtain optimal yields from the overall hyperpolarization process, catalytic hydrogenation must be tightly synchronized to subsequent radiofrequency (RF) transformations of spin order. Commercial NMR consoles are designed to synchronize applied waves on multiple channels and consequently are well-suited as controllers for these types of hyperpolarization experiments that require tight coordination of RF and non-RF events...
September 30, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28963919/parallel-acquisition-of-slice-selective-1-h-1-h-soft-cosy-spectra
#6
Upendra Singh, Ajay Verma, Bikash Baishya
A method is demonstrated for parallel acquisition of several slice selective soft COSY proton spectra. Application of a slice selective mixing pulse in a selective correlation experiment allows slice selective coherence transfer between different coupled spin pairs. During such slice selective coherence transfer, the spin states of the passive spins are undisturbed. In other words, slice selective coherence transfer executes spin-state selective coherence transfer between a given spin and all its coupled neighbours...
September 20, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28961477/design-and-testing-of-a-750mhz-cw-epr-digital-console-for-small-animal-imaging
#7
Hideo Sato-Akaba, Miho C Emoto, Hiroshi Hirata, Hirotada G Fujii
This paper describes the development of a digital console for three-dimensional (3D) continuous wave electron paramagnetic resonance (CW-EPR) imaging of a small animal to improve the signal-to-noise ratio and lower the cost of the EPR imaging system. A RF generation board, an RF acquisition board and a digital signal processing (DSP) & control board were built for the digital EPR detection. Direct sampling of the reflected RF signal from a resonator (approximately 750MHz), which contains the EPR signal, was carried out using a band-pass subsampling method...
September 20, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28961480/transient-noe-enhancement-in-solid-state-mas-nmr-of-mobile-systems
#8
Jiangyu Cui, Jun Li, Xinhua Peng, Riqiang Fu
It has been known that the heteronuclear cross-relaxation affects the dilute S spin magnetization along the longitudinal direction, causing an overshoot phenomenon for those mobile systems in spin-lattice relaxation rate measurements. Here, we analyze the Solomon equations for an I-S system and derive the transient cross relaxation effect as to when an overshoot phenomenon would take place and what the maximum enhancement could be at the time of the overshoot. In order to utilize such a transient nuclear Overhauser effect (NOE), we first time apply it to dynamic solid samples by inverting the (1)H magnetization prior to the excitation of the S spin...
September 19, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28961478/refocusing-pulses-a-strategy-to-improve-efficiency-of-phase-modulated-heteronuclear-decoupling-schemes-in-mas-solid-state-nmr
#9
Mukul G Jain, K N Sreedevi, Asif Equbal, P K Madhu, Vipin Agarwal
The strategy of using π pulses in conjunction with continuous-wave radio-frequency fields to refocus spin interactions has lead to robust and efficient family of heteronuclear decoupling schemes in magic-angle spinning solid-state NMR, denoted as, rCW schemes. Here, we investigate the generality of the application of such refocussing pulses in other phase-modulated decoupling schemes, notably the super-cycled XiX decoupling. XiX is a commonly used heteronuclear decoupling scheme under conditions of fast MAS and low-amplitude radio-frequency irradiation...
September 19, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28957683/measurement-of-amide-proton-chemical-shift-anisotropy-in-perdeuterated-proteins-using-csa-amplification
#10
Yuwei Ge, Ivan Hung, Xiaoli Liu, Maili Liu, Zhehong Gan, Conggang Li
Measuring (1)H chemical shift anisotropy (CSA) is useful for probing proton environments and dynamics but remains a challenge due to strong homonuclear interaction and relatively small shift anisotropy, especially in proteins with multiple proton sites. Here the extended chemical shift anisotropy amplification (xCSA) method is applied for amide proton CSA measurement in uniformly (2)H enriched proteins under fast magic angle spinning. The xCSA method is capable of distinguishing the sign of the CSA asymmetry parameter, complimenting other multiple-pulse recoupling methods...
September 19, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28972888/the-rate-of-lactate-production-from-glucose-in-hearts-is-not-altered-by-per-deuteration-of-glucose
#11
Alexander M Funk, Brian L Anderson, Xiaodong Wen, Thomas Hever, Chalermchai Khemtong, Zoltan Kovacs, A Dean Sherry, Craig R Malloy
This study was designed to determine whether perdeuterated glucose experiences a kinetic isotope effect (KIE) as glucose passes through glycolysis and is further oxidized in the tricarboxylic acid (TCA) cycle. Metabolism of deuterated glucose was investigated in two groups of perfused rat hearts. The control group was supplied with a 1:1 mixture of [U-(13)C6]glucose and [1,6-(13)C2]glucose, while the experimental group received [U-(13)C6,U-(2)H7]glucose and [1,6-(13)C2]glucose. Tissue extracts were analyzed by (1)H, (2)H and proton-decoupled (13)C NMR spectroscopy...
September 18, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28938135/bang-bang-optimal-control-of-large-spin-systems-enhancement-of-13-c-13-c-singlet-order-at-natural-abundance
#12
Deepak Khurana, T S Mahesh
Using a bang-bang optimal control technique, we transfer polarization from a set of abundant high-γ nuclei directly to singlet order of a low-γ spin-pair. This approach is analogous to algorithmic cooling (AC) procedure used in quantum state purification. Specifically, we apply this method for enhancing the singlet order in a natural abundant (13)C- (13)C spin pair by exploiting nine equivalent protons of an 11-spin system. Compared to the standard method not involving polarization transfer, we find an enhancement of singlet order by about 3...
September 14, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28926738/effect-of-convection-and-b1-inhomogeneity-on-singlet-relaxation-experiments
#13
B Kharkov, X Duan, J W Canary, A Jerschow
Nuclear spin singlet lifetimes can often exceed the T1 length scales by a large factor. This property makes them suitable for polarization storage. The measurement of such long lifetimes itself can become challenging due to the influence of even very weak relaxation mechanisms. Here we show that a judicious choice of the singlet-to-triplet conversion method is highly important in order to achieve reliable singlet relaxation measurements. In particular, we identify thermal convection, in connection with B1 field gradients, asa significant apparent decay mechanism, which limits the ability to measure the true singlet state lifetimes...
September 12, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28946058/radiofrequency-fields-in-mas-solid-state-nmr-probes
#14
Zdeněk Tošner, Armin Purea, Jochem O Struppe, Sebastian Wegner, Frank Engelke, Steffen J Glaser, Bernd Reif
We present a detailed analysis of the radiofrequency (RF) field over full volume of a rotor that is generated in a solenoid coil. On top of the usually considered static distribution of amplitudes along the coil axis we describe dynamic radial RF inhomogeneities induced by sample rotation. During magic angle spinning (MAS), the mechanical rotation of the sample about the magic angle, a spin packet travels through areas of different RF fields and experiences periodical modulations of both the RF amplitude and the phase...
September 6, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28938134/long-lived-states-detect-interactions-between-small-molecules-and-diamagnetic-metal-ions
#15
Cristina Stavarache, Anamaria Hanganu, Anca Paun, Codruta Paraschivescu, Mihaela Matache, Paul R Vasos
Long-lived states of nuclear spin order were used for the first time to probe interactions between molecules and diamagnetic metal ions. Proton spin states with lifetimes twice as long as the spin-lattice relaxation time constants of the same nuclei were promoted on the methoxyphenyl and tolyl substituents of a 1,3,4-oxadiazole derivative. The transient interaction of this oxadiazole derivative with silver(I) ions significantly speeds up the relaxation rate constants of proton long-lived states. The interactions between silver and organic compounds lead to the formation of coordination polymers that can be used for the preparation of bio-compatible materials...
September 6, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28961479/a-method-for-measurement-of-spin-spin-couplings-with-sub-mhz-precision-using-zero-to-ultralow-field-nuclear-magnetic-resonance
#16
A Wilzewski, S Afach, J W Blanchard, D Budker
We present a method which allows for the extraction of physical quantities directly from zero- to ultralow-field nuclear magnetic resonance (ZULF NMR) data. A numerical density matrix evolution is used to simulate ZULF NMR spectra of several molecules in order to fit experimental data. The method is utilized to determine the indirect spin-spin couplings (J-couplings) in these systems, which is achieved with precision of 10(-2)-10(-4)Hz. The simulated and measured spectra are compared to earlier research. Agreement and improved precision are achieved for most of the J-coupling estimates...
September 1, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28957684/retaining-both-discrete-and-smooth-features-in-1d-and-2d-nmr-relaxation-and-diffusion-experiments
#17
A Reci, A J Sederman, L F Gladden
A new method of regularization of 1D and 2D NMR relaxation and diffusion experiments is proposed and a robust algorithm for its implementation is introduced. The new form of regularization, termed the Modified Total Generalized Variation (MTGV) regularization, offers a compromise between distinguishing discrete and smooth features in the reconstructed distributions. The method is compared to the conventional method of Tikhonov regularization and the recently proposed method of L1 regularization, when applied to simulated data of 1D spin-lattice relaxation, T1, 1D spin-spin relaxation, T2, and 2D T1-T2 NMR experiments...
September 1, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28890288/nmr-spectroscopy-up-to-35-2t-using-a-series-connected-hybrid-magnet
#18
Zhehong Gan, Ivan Hung, Xiaoling Wang, Joana Paulino, Gang Wu, Ilya M Litvak, Peter L Gor'kov, William W Brey, Pietro Lendi, Jeffrey L Schiano, Mark D Bird, Iain R Dixon, Jack Toth, Gregory S Boebinger, Timothy A Cross
The National High Magnetic Field Laboratory has brought to field a Series-Connected Hybrid magnet for NMR spectroscopy. As a DC powered magnet it can be operated at fields up to 36.1T. The series connection between a superconducting outsert and a resistive insert dramatically minimizes the high frequency fluctuations of the magnetic field typically observed in purely resistive magnets. Current-density-grading among various resistive coils was used for improved field homogeneity. The 48mm magnet bore and 42mm outer diameter of the probes leaves limited space for conventional shims and consequently a combination of resistive and ferromagnetic shims are used...
August 24, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28822304/a-flow-through-elevated-temperature-and-pressure-nmr-apparatus-for-in-situ-co2-sequestration-studies
#19
Erika L Sesti, Jinlei Cui, Sophia E Hayes, Mark S Conradi
We report an apparatus for in-situ nuclear magnetic resonance (NMR) studies of chemical reactions of dissolved (13)CO2 with minerals (rock or powder) under continuous flow. The operating range of the apparatus is 18-150°C and 1-140bar. A flow pump is used to circulate a CO2-water solution, with a heated mixing vessel where CO2 gas equilibrates with a water solution. The NMR probe is built around a strong zirconia ceramic vessel, with o-ring sealed connections; the mineral is contained inside. The horizontal orientation of the zirconia vessels allows use of a radio frequency (rf) solenoid for improved spin sensitivity...
August 12, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28803092/uniform-field-loop-gap-resonator-and-rectangular-teu02-for-aqueous-sample-epr-at-94ghz
#20
Jason W Sidabras, Tadeusz Sarna, Richard R Mett, James S Hyde
In this work we present the design and implementation of two uniform-field resonators: a seven-loop-six-gap loop-gap resonator (LGR) and a rectangular TEU02 cavity resonator. Each resonator has uniform-field-producing end-sections. These resonators have been designed for electron paramagnetic resonance (EPR) of aqueous samples at 94GHz. The LGR geometry employs low-loss Rexolite end-sections to improve the field homogeneity over a 3mm sample region-of-interest from near-cosine distribution to 90% uniform. The LGR was designed to accommodate large degassable Polytetrafluorethylen (PTFE) tubes (0...
August 5, 2017: Journal of Magnetic Resonance
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