Authors:Kathryn E. Washburn; Evan R. McCarney Pages: 429 - 464 Abstract: Nuclear magnetic resonance relaxometry measurements are frequently used to quantify sample constituents. The standard approach for quantification involves converting the time-domain data to a distribution of characteristic times, either by fitting a fixed number of exponentials or performing an inverse Laplace transform, and then integrating the area under the peaks. We evaluated an alternative method to quantify relaxometry data. Partial least squares (PLS) analysis was applied directly to a variety of simulated time-domain relaxation data under diverse conditions to predict constituent content and results were compared to the standard analysis methods. For many situations, PLS analysis displayed superior performance for quantification than the standard analyses. The technique consistently produced better predictions at lower signal to noise. This robustness to noise makes it an appealing alternative for analysing data from applications that typically have low SNR, such as one-sided sensors, surface measurements, or well-logging. The method also enabled quantification of relaxation rates too close to be separated by an inverse Laplace transform. This capability may allow quantification to be performed using only one-dimensional relaxation data where multi-dimensional measurements were previously necessary to provide constituent separation. The method also enabled quantification of relaxometry data without the need for human interpretation or prior knowledge of what relaxation time is associated with a given constituent. These advantages make PLS analysis an appealing alternative for quantification of relaxometry data in many situations. PubDate: 2018-05-01 DOI: 10.1007/s00723-018-0991-4 Issue No:Vol. 49, No. 5 (2018)
Authors:Xiaoyu Fan; Qiusheng Lian; Baoshun Shi Pages: 465 - 477 Abstract: Compressed-sensing magnetic resonance imaging (CSMRI) aims to reconstruct the magnetic resonance (MR) image from highly undersampled K-space data. In order to improve the reconstruction quality of the MR image, this paper proposes a new gradient-based tight frame (TFG) learning algorithm (TFG-MRI) for CSMRI. TFG-MRI effectively integrates the tight frame learning technique and total variation into the same framework. In TFG-MRI, the inherent gradient sparsity of the MR image in gradient domain is utilized to represent the sparse prior knowledge, and the sparse priors in the horizontal and vertical gradient directions are exploited to learn adaptive tight frames for reconstructing the desired images. Particularly, we employ the l0-norm to promote the sparsity of the gradient image. The sparse representations of TFG are adapted for the horizontal and vertical gradient information of MR images. TFG-MRI can effectively help to capture edge contour structures in the gradient images, and to preserve more detail information of MR images. The experimental results demonstrate that the proposed TFG-MRI can reconstruct MR images more clearly in various sampling schemes. Compared with the existing MR image reconstruction algorithms, TFG-MRI can achieve higher accurate image reconstruction quality and better robustness to noises. PubDate: 2018-05-01 DOI: 10.1007/s00723-018-0988-z Issue No:Vol. 49, No. 5 (2018)
Authors:N. A. Chumakova; T. A. Ivanova; E. N. Golubeva; A. I. Kokorin Pages: 511 - 522 Abstract: The precision of measuring concentrations of nirtoxide radicals in polymeric matrixes using modern electron paramagnetic resonance spectrometer is analyzed. The contributions of the radical nature and concentration, signal-to-noise ratio, and the integration procedure are tested as factors influencing on the precision of the measurement. It has shown that recording spectra with modern EPR spectrometer with possibility of computer analysis of spectra, the contribution of the integration error to the total error strongly depends on the signal-to-noise ratio. If the ratio is < 20, its contribution increases fast with the decrease of this parameter. If this ratio is ≥ 20, the input of the integration error becomes negligible, and the main contribution to the total error of concentration measurements comes from errors of the Q-factor determination, which are usually close to 8–10%. PubDate: 2018-05-01 DOI: 10.1007/s00723-018-0992-3 Issue No:Vol. 49, No. 5 (2018)
Authors:Nikolay V. Anisimov; Olga S. Pavlova Pages: 523 - 532 Abstract: The article describes experiments on the simultaneous recording nuclear magnetic resonance signals from two nuclei with different gyromagnetic ratios—1H and 19F, 13C and 23Na. It is shown that large frequency detunings or/and low sampling rates are not an obstacle to their realization even in a relatively weak (0.5 T) field. We use undersampling technique when registering the response of the spin system. In this case, the sampling frequency is much less than the distance between the Larmor frequencies for the indicated nuclear pairs. It gives the effect of multiple aliasing. Fourier processing of the response produces a spectrum consisting of two subspectra, each of which corresponds to specific nucleus of the investigated pair. The subordination of the spectral peaks in each subspectrum is the same as the spectrum obtained by the usual way. Two variants of the radio-frequency excitation of the spin system (single and double pulse) are considered. A formula for calculating the excitation frequency and sampling rate, which ensures a rational distribution of the lines in the hybrid spectrum, is proposed. PubDate: 2018-05-01 DOI: 10.1007/s00723-018-0998-x Issue No:Vol. 49, No. 5 (2018)
Authors:J. L. Yoder; P. E. Magnelind; M. A. Espy; M. T. Janicke Abstract: Nuclear magnetic resonance (NMR) spectroscopy in portable, permanent magnet-based spectrometers is primarily limited to nuclei with higher gyromagnetic ratio, γ, such as 1H, 19F, and 31P due to the limited field strength achievable in these systems. Overhauser effect dynamic nuclear polarization (O-DNP), which transfers polarization from an unpaired electron to a nucleus by saturating an electron paramagnetic resonance transition with an oscillating radio frequency magnetic field, B1e, can increase the polarization of low γ nuclei by hundreds or even thousands, enabling detection in a portable system. We have investigated the potential for O-DNP to enhance signals using (4-amino-2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO hereafter) as a source of unpaired electrons in a homebuilt ultra-low field (ULF) O-DNP-NMR spectrometer. We have found, in general, that larger concentrations of TEMPO are required for effective O-DNP with low γ nuclei, which has a number of important effects. Spin exchange effects cause the EPR lines to overlap and ultimately merge at high concentrations of TEMPO, fundamentally increasing the maximum possible enhancement, while the electron–electron dipolar interaction reduces both longitudinal and transverse relaxation times for the electrons, dramatically increasing the required B1e strength. The relationship between TEMPO concentration, B1e magnitude and O-DNP enhancement is quantified, and strategies for achieving these fields are discussed. PubDate: 2018-05-28 DOI: 10.1007/s00723-018-1014-1
Authors:Mi Liu; Ranhong Xie; Hongjun Xu; Songtao Wu; Rukai Zhu; Zhiguo Mao Abstract: The accurate prediction of capillary pressure curves is of great significance for the evaluation of pore structure in tight sandstone reservoirs. In this paper, a hybrid model is proposed to predict the mercury injection capillary pressure (MICP) curve using multiple characteristic parameters of the nuclear magnetic resonance (NMR) transverse relaxation (T2) distribution; models based on the capillary pressure point and on the non-wetting phase saturation point are combined. Because of the high level of multicollinearity among the characteristic parameters of the NMR T2 distribution, the partial least squares method is used to solve the model coefficients. The leave-one-out cross-validation (LOOCV) method is used to determine the optimal combination of parameters of the hybrid model, i.e., the number of latent variables of the model based on the capillary pressure point, the number of latent variables of the model based on the non-wetting phase saturation point, and the location of the splicing point. The result of model self-testing, the result of the LOOCV, and the analysis of the generalization ability all indicate that the hybrid model has high accuracy and strong stability for MICP curves prediction. The prediction results in tight sandstone reservoirs further verify the effectiveness of this method. PubDate: 2018-05-24 DOI: 10.1007/s00723-018-1024-z
Authors:N. A. Sergeev; A. M. Panich; S. D. Goren Abstract: We applied 13C and 205Tl NMR for studying alignment of particles of graphene and high temperature superconductor (Tl0.5Pb0.5)(Ba0.2Sr0.8)2Ca2Cu3O y caused by magnetic field. These compounds have layered structure and reveal anisotropic magnetic susceptibility. We found that the field of 8 T causes minor alignment of powder graphene and somewhat better alignment of fluffy graphene particles. Herewith the effect of alignment is well pronounced in 205Tl spectra of the superconducting particles fixed in epoxy in the field of 8 T. This effect is reflected in the 205Tl line shape measured in a magnetic field of 1.17 T and becomes much more pronounced in measurements made in high magnetic field of 8 T. Spectra simulations allow determining the degree of the particles’ alignment. PubDate: 2018-05-23 DOI: 10.1007/s00723-018-1013-2
Authors:A. J. Barakat; L. Pel; O. C. G. Adan Abstract: In this study a specialized high-temperature nuclear magnetic resonance (NMR) setup is presented for measuring free moisture in monolithic refractory castables during one-sided heating (100–300 °C). This setup makes use of a high thermal-stability Birdcage-coil for measuring the quantitative moisture content at high-temperatures, while also utilizing a mini-coil for calibrating transverse relaxation changes, as a function of temperature and hydration state, taking place in the sample throughout a drying experiment. We employ a high-temperature correction scheme that calibrates the effects of rising temperatures on the NMR signal. With this configuration, we can non-destructively measure moisture and temperature profiles continuously and achieve a spatial resolution of 2–3 mm for samples as long as 74 mm. After applying the NMR correction, we can extract information about the physical and chemical components of water as they are released from the porous matrix during first heat up. As a model material, we demonstrate the capability of our setup with a conventional castable after it has been cast and cured for 48 h. PubDate: 2018-05-18 DOI: 10.1007/s00723-018-1018-x
Authors:Michael Kespe; Eva Förster; Hermann Nirschl; Gisela Guthausen Abstract: Process and reaction monitoring by nuclear magnetic resonance (NMR) spectroscopy has attracted considerable attention in the last years not only because of the new generation of low-field NMR spectrometers, but also because of an industrial need of more effectivity and process optimization via real-time monitoring of process and reaction details by diverse analytical tools. Most often, bypass solutions are realized in liquid state monitoring, which leads to questions of residence time distribution, mixing phenomena and accuracy of concentration determination. Exploring chemical engineering knowledge of fluid dynamics and combining it with NMR knowledge of magnetization buildup allow the calculation of magnetization in NMR measurements on flowing substances. This approach reveals the essential parameters to be considered when constructing flow cells and when processing data in NMR process monitoring. 3D computational fluid dynamics combined with Bloch equations allows detailed time and spatially resolved insights into the significant mechanisms of magnetization distribution and opens up new possibilities for experiment design in flow NMR. An experimental confirmation was provided by MRI experiments. PubDate: 2018-05-18 DOI: 10.1007/s00723-018-1016-z
Authors:A. V. Manzhurtsev; O. R. Vasiukova; V. V. Sergeeva; N. L. Zaitseva; P. E. Menshchikov; I. A. Melnikov; T. A. Akhadov; N. A. Semenova Abstract: For the first time, the effects of one hyperbaric oxygenation (HBO) session on cellular phosphate metabolite levels and pH were investigated in vivo. 31P magnetic resonance spectroscopy was used in this study. The optimized protocol of Image-Selected Invivo Spectroscopy pulse sequence for 31P MRS was applied to increase SNR of ATP resonances. An activation of energy metabolism that manifested in the decrease of creatine phosphate and pHint after an HBO session is revealed. The growth of the α-ATP signal is elucidated as well, while other ATP resonances remain unchanged. This might reflect the increase in nicotinamide adenine dinucleotide (NAD) concentration. The rise of its level as well as the detected creatine phosphate expenses immediately after HBO may denote the activation of fast NAD synthesis pathways. PubDate: 2018-05-17 DOI: 10.1007/s00723-018-1019-9
Authors:Muhammad Bilal; Jawad Ali Shah; I. M. Qureshi; Abdul Haseeb Ahmed Abstract: Iterative shrinkage algorithms like parallel coordinate descent and separable surrogate functional use wavelet thresholding with uniform and empirically selected threshold values to recover the under-sampled magnetic resonance (MR) images. In this paper, an adaptive thresholding parameter, for the recovery of static and dynamic MR images, is derived and used in wavelet domain shrinkage. A modified iterative shrinkage thresholding algorithm based on the derived parameter is also proposed. Simulation results show that adaptive wavelet thresholding yields significantly higher signal-to-noise ratio and correlation than the fixed thresholding value. The algorithm based on the adaptive threshold is experimentally tested for static and dynamic MR images with varying acceleration rates, and it has been shown that it outperforms the fixed thresholding value algorithm. PubDate: 2018-05-17 DOI: 10.1007/s00723-018-1022-1
Authors:A. A. Sukhanov; M. D. Mamedov; K. Möbius; A. Yu. Semenov; K. M. Salikhov Abstract: The main observation in this work is a decrease in the modulation frequency of the primary electron spin-echo decay (ESEEM) of the \({\text{P}}_{ 7 0 0}^{ + }\) cofactor in the reaction center of Photosystem I (PS I) from cyanobacteria Synechocystis sp. PCC 6803 embedded in dry trehalose matrix as the temperature rises from 150 K to room temperature. From the previous studies of the EPR spectrum shape of this system, it is known that, in dry trehalose matrix at room temperature, the distance between \({\text{P}}_{ 7 0 0}^{ + }\) and \({\text{A}}_{ 1}^{ - }\) spins does not increase compared to the distance measured in glycerol–water solution at cryogenic temperature. From the present ESEEM study, we conclude that the decrease of modulation frequency with rising temperature in trehalose matrix can be fully attributed to the influence of accelerated spin–lattice relaxation of \({\text{A}}_{ 1}^{ - }\) . Our calculations show that this requires a decrease in the spin–lattice relaxation time from 3 to 1 μs. To the best of our knowledge, this is the first time that a shift in the ESEEM frequency due to the dipole–dipole interaction between the spins is observed that is caused by spin–lattice relaxation. Based on the above-mentioned results, we formulate a model of the protective effect of trehalose matrix on the electron transfer in the reaction center of PS I that is based on different hydrogen-bond networks between trehalose, local water, and protein. PubDate: 2018-05-17 DOI: 10.1007/s00723-018-1017-y
Authors:Hirona Takahashi; Kenta Hagiwara; Akio Kawai Abstract: Addition reaction of photo-generated organic radicals to maleic anhydride (MA), that is a common monomer in polymerization, was studied by time-resolved (TR)- and pulsed electron paramagnetic resonance (EPR) spectroscopic methods. The radicals examined are 2-hydroxypropyl (2Hy-Pr), diphenylphosphine oxide (DPPO) and hydroxycyclohexyl (Hy-CyH). Analysis of TR-EPR spectra gave the structures of adduct radicals. The addition rate constants of the radicals generated by the photolysis of initiators were measured by electron spin echo detection method. It was found that the addition reaction rate constants of 2Hy-Pr, DPPO and Hy-CyH radicals to MA show exceptionally smaller values than those estimated by the theoretical reaction model based on enthalpy and polar effects. PubDate: 2018-05-05 DOI: 10.1007/s00723-018-1015-0
Authors:Hiroki Nagashima; Hiroyuki Mino Abstract: Angular dependence of the proton matrix electron nuclear double resonance (ENDOR) spectra was investigated in the oriented Ca2+-depleted Photosystem II (PS II). Six pairs of the proton signals have been previously detected in the untreated PS II and one of the six pairs has been disappeared in the Ca2+-depleted PS II (Nagashima and Mino, J Biol Chem 290:28166–28174, 2015), where the proton signals with 4 MHz separation were lost and assigned to the proton closest to the terminal Mn, labeled as Mn4 in the Mn cluster. In the oriented Ca2+-depleted PS II, the proton signal with 4 MHz separation was disappeared when the external magnetic field is parallel to the membrane normal n (θ = 0°). A pair of broad ENDOR signals with 1.4–2.0 MHz hyperfine coupling was detected in the oriented Ca2+-depleted PS II at θ = 90°. These results indicate the Ca2+-depletion derives the rearrangement of the hydrogen bonding of the water molecule surrounded Mn cluster. PubDate: 2018-04-27 DOI: 10.1007/s00723-018-1006-1
Authors:Yu. S. Chernyshev; A. S. Koneva; E. A. Safonova Abstract: In comparison with the conventional ionic liquids, water-miscible amino acid ionic liquids (AAILs) are considered as more biodegradable and biocompatible, less toxic, and as able to enhance the biomaterials stability. An application of some long-chain ionic liquids in catalysis, extraction, etc. requests the detailed analysis of ionic and water transport properties of their diluted aqueous solutions close to the area of its critical micelle concentration (cmc). In this work, the molecular transport properties of two 1-methyl-3-octylimidazolium-based AAILs, [C8mim][Val], and [C8mim][Leu] (with anions of l-Leucine or l-Valine), in the aqueous solutions were studied by measuring the self-diffusion coefficients and the solution’ viscosities in the temperature ranges 273–343 K at the AAIL’s concentrations below and above its cmc. The data on self-diffusion coefficients of water molecules and cations/anions of AAILs are discussed in terms of activation energies and of hydration effects. Above the cmc, the [C8mim][Val] molecules demonstrate the strengthening effect on the solvent structure, while the molecules of [C8mim][Leu] have structure-destructive effect. The results obtained for the relative dynamic viscosities show a decrease of micellar size with increasing temperature. In addition, it was found that the degrees of counterion binding for both AAILs are higher than for 1-methyl-3-octylimidazolium halides. PubDate: 2018-04-27 DOI: 10.1007/s00723-018-1008-z
Authors:Keiko Kuwabara; Yasuhiro Sakurai; Hodaka Sanuki; Chie Morimoto; Yong Li; Yusuke Miyake; Kenji Kanaori; Kunihiko Tajima Abstract: A stopped-flow-electron paramagnetic resonance (EPR) method was applied for the detection of short-lived radicals of flavonoids bearing a catechol moiety as the B-ring, such as flavonols (quercetin, fisetin, and rutin), flavanones (eriodictyol and taxifolin), flavanols (catechin and epicatechin), and flavone (luteolin). 15N-labeled sodium salt of nitrosodisulfonate (15NDS) was employed to obtain the highly resolved EPR hyperfine structure (hfs) of flavonoid-derived semiquinone radicals under stoichiometrically regulated reaction conditions in aqueous media (pH 10). The EPR hfs of these flavonoids radicals, except catechin and epicatechin, were recorded. Based on the g value and the proton hyperfine coupling constants (hfcc), these flavonoid-derived radicals were assigned to be semiquinone radicals of the catechol moiety (B-ring). For example, the observed EPR hyperfine structure (hfs) of the luteolin radical (Lut−·) was composed of four sets of doublet splitting, which could be ascribed to the three protons of the B-ring (a2′ = 0.136, a5′ = 0.102, and a6′ = 0.272 mT) and a vinyl proton of the C-ring (a3 = 0.099 mT). In addition, the characteristically small doublet splitting resolved for the fisetin anion radical (Fis−·, 0.028 mT) was assigned to the aromatic proton at the C5 carbon of the A-ring, indicating that the unpaired electron of the radials was partially delocalized onto the A-ring through the π bonds involved in the vinyl-carbonyl moiety of the C-ring. The hfcc of the methine protons at the C2 carbon of taxifolin and eriodictyol-derived radicals (Tax−· and Eri−·) was, respectively, evaluated to be 0.102 and 0.230 mT. The assignment of the proton hfcc of flavonoid-derived semiquinone radicals will be discussed in relation with the molecular structure of the C-ring. PubDate: 2018-04-26 DOI: 10.1007/s00723-018-1012-3
Authors:Annalise R. Pfaff; Klaus Woelk Abstract: Frequency-selective inversion of magnetization is often achieved by long, low-power adiabatic RF pulses. Because these pulses can last hundreds of milliseconds, substantial relaxation of magnetization can occur during their application. Recently, a numerical model was introduced that allows an approximation of relaxation during frequency-selective adiabatic pulses for fast-tumbling small molecules in non-viscous solutions using only standard T1 and T2 relaxation times. This model is now extended to conditions in which net magnetization is not at its thermodynamic equilibrium prior to the adiabatic inversion. Simulated and experimental data reveal that the amplitude of net magnetization after an adiabatic inversion with the HS1 hyperbolic secant pulse can be approximated by a linear function of the magnetization before the pulse, depending only on T1 and T2 relaxation. The model presented here is particularly applicable to solvent-suppression sequences that utilize multiple adiabatic inversions, such as the multiple inversion-recovery nulling sequence EXCEPT. Tabulated slope and intercept values for the linear relationship are provided to facilitate a convenient optimization of pulse sequences that utilize HS1 frequency-selective adiabatic inversions. PubDate: 2018-02-26 DOI: 10.1007/s00723-018-0989-y
Authors:A. M. Kusova; A. E. Sitnitsky; Yu. F. Zuev Abstract: The concentration dependences of self-diffusion coefficient for intrinsically disordered milk protein αS-casein were studied by pulsed field gradient nuclear magnetic resonance. The experimental data were analyzed in a view of phenomenological approach based on the frictional formalism of non-equilibrium thermodynamics by Vink. The results of αS-CN hydrodynamic study showed that at low- and high-protein concentrations, αS-CN exists in the different structural forms. At low concentrations in the rather broad concentration range, protein remains monomeric but with greater hydrodynamic size than have rigid globular proteins of the equal mass. At high concentrations beyond the definite protein content, αS-CN tends to form associates. The application of the Vink’s approach to αS-CN testifies that the role of flexible domains in the process of self-diffusion is mainly in increasing the friction of between αS-CN molecules due to their inter-entanglement. The latter physically means that when αS-CN molecules cling each other by their flexible domains, this phenomenon provides much more efficient friction than their interaction with solvent molecules. PubDate: 2018-02-19 DOI: 10.1007/s00723-018-0990-5
Authors:Archie Cable; Eteri Svanidze; Jessica Santiago; Emilia Morosan; Jörg Sichelschmidt Abstract: The electron spin resonance (ESR) of conduction electrons is reported for the weak itinerant ferromagnet Sc \(_{3.1}\) In which, upon chemical substitution with Lu, shows a suppression of ferromagnetic correlations. A well-defined ESR lineshape of Dysonian type characterizes the spectra. The ESR linewidth, determined by the spin dynamics, displays a broad minimum only for the Sc \(_{3.1}\) In compound. We discuss the results using the mechanism of exchange enhancement of spin-lifetimes. PubDate: 2018-02-13 DOI: 10.1007/s00723-018-0987-0
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