Authors:A. A. Sukhanov; Yu. E. Kandrashkin; V. K. Voronkova; V. S. Tyurin Pages: 239 - 253 Abstract: The results of the electron paramagnetic resonance (EPR) and transient EPR (TREPR) of copper complexes of coproporphyrin I in different solvents before and after the laser pulse photo-excitation have been presented. Continuous-wave EPR spectra of the CuCPP-1 complex in o-terphenyl indicate the presence of only monomer fragments, while in the solution of the chloroform and isopropanol mixture, the complexes dimerize and the amount of dimers is five times larger than that of monomer complexes. Parameters describing EPR spectra of monomer and dimer CuCPP-1 complexes have been determined. It was established that the fine structure tensor of the dimer complex is rotated with respect to the g-tensor, which coincides with the tensor of monomer complexes. TREPR spectra of CuCPP-1 complexes in o-terphenyl and in the chloroform and isopropanol mixture after the laser photo-excitation are mainly due to spin-polarized ground states of monomer and dimer complexes, respectively. The TREPR spectra of the monomer CuCPP-1 show the emissive spin-polarized signal of the ground state. For dimer fragments, the net polarization is observed in the form of absorption and there is a small contribution from the multiplet polarization, which decays fast in time. The time dependence of TREPR of CuCPP-1 complexes in the chloroform and isopropanol mixture is described with allowance for these contributions from the ground state of the dimer and the contribution from the ground state of the monomer, which is manifested at larger times. Differences in the spin polarization of ground states and their possible origin are discussed. PubDate: 2018-03-01 DOI: 10.1007/s00723-017-0961-2 Issue No:Vol. 49, No. 3 (2018)
Authors:A. S. Poryvaev; A. M. Sheveleva; P. A. Demakov; S. S. Arzumanov; A. G. Stepanov; D. N. Dybtsev; M. V. Fedin Pages: 255 - 264 Abstract: Gas separation and storage are the hot topics for addressing current challenges in energy and environmental science, including the air pollution problems and alternative fuels, and metal–organic frameworks (MOFs) have a great potential in these fields. Herewith, we present the electron paramagnetic resonance (EPR) study of the adsorption of several gases (hydrogen D2, methane 13CH4 and CD4, and carbon dioxide 13CO2) in Cu2+-doped MOF [Zn2(1,4-bdc)2(dabco)]. The obtained compound of composition [Zn1.993Cu0.007(1,4-bdc)2(dabco)] is suitable for studying adsorption geometries at Cu2+ ions and in their closest environments using pulse EPR. In attempt to characterize D2, 13CH4, CD4, and 13CO2 adsorption sites, we applied echo-detected EPR along with hyperfine sublevel correlation spectroscopy and pulse electron-nuclear double resonance spectroscopy. Altogether, these methods demonstrated the preferred location of gas molecules in the framework being at least 6 Å away from the copper ions. In addition, EPR spectroscopy allowed determination of the proton environment of copper and confirmed its incorporation into the MOF lattice, which is hard to establish using other techniques. PubDate: 2018-03-01 DOI: 10.1007/s00723-017-0962-1 Issue No:Vol. 49, No. 3 (2018)
Authors:Ivan O. Timofeev; Olesya A. Krumkacheva; Matvey V. Fedin; Galina G. Karpova; Elena G. Bagryanskaya Pages: 265 - 276 Abstract: Pulse dipolar electron paramagnetic resonance spectroscopy provides means of distance measurements in the range of ~ 1.5–10 nm between two spin labels tethered to a biological system. However, the extraction of distance distribution between spin labels is an ill-posed mathematical problem. The most common approach for obtaining distance distribution employs Tikhonov regularization method, where a regularization parameter characterizing the smoothness of distribution is introduced. However, in case of multi-modal distance distributions with peaks of different widths, the use of a single regularization parameter might lead to certain distortions of actual distribution shapes. Recently, a multi-Gaussian Monte Carlo approach was proposed for eliminating this drawback and verified for model biradicals [1]. In the present work, we for the first time test this approach on complicated biological systems exhibiting multi-modal distance distributions. We apply multi-Gaussian analysis to pulsed electron–electron double resonance data of supramolecular ribosomal complexes, where the 11-mer oligoribonucleotide (MR) bearing two nitroxide labels at its termini is used as a reporter. Calculated distance distributions reveal the same conformations of MR as those obtained by Tikhonov regularization, but feature the peaks having different widths, which leads to a better resolution in several cases. The advantages, complications, and further perspectives of application of Monte-Carlo-based multi-Gaussian approach to real biological systems are discussed. PubDate: 2018-03-01 DOI: 10.1007/s00723-017-0965-y Issue No:Vol. 49, No. 3 (2018)
Authors:M. Cheng; X. X. Wu; W. C. Zheng Pages: 277 - 283 Abstract: The high-order perturbation formulas founded on the two-mechanism model are applied in this paper to compute the spin-Hamiltonian parameters (g factors g //, g ⊥ and zero-field splitting D) of the trigonal Mn4+ centers in Y2Ti2O7:Mn4+ crystal. In this model, besides the contributions from the traditional crystal-field (CF) mechanism (in the CF theory) related to CF excited states, those from the charge-transfer (CT) mechanism connected with CT excited states are contained. The calculated results are reasonably coincident with the observed values. The calculations show that the contributions of CT mechanism to spin-Hamiltonian parameters (in particular, the g factors) for (MnO6)8− clusters are large and cannot be neglected. The defect structure of trigonal (MnO6)8− clusters in Y2Ti2O7:Mn4+ crystals is also evaluated. The results are discussed. PubDate: 2018-03-01 DOI: 10.1007/s00723-017-0972-z Issue No:Vol. 49, No. 3 (2018)
Authors:Kirill F. Sheberstov; Hans-Martin Vieth; Herbert Zimmermann; Konstantin L. Ivanov; Alexey S. Kiryutin; Alexandra V. Yurkovskaya Pages: 293 - 307 Abstract: We provide a detailed evaluation of nuclear magnetic resonance (NMR) parameters of the cis- and trans-isomers of azobenzene (AB). For determining the NMR parameters, such as proton–proton and proton–nitrogen J-couplings and chemical shifts, we compared NMR spectra of three different isotopomers of AB: the doubly 15N labeled azobenzene, 15N,15N′-AB, and two partially deuterated AB isotopomers with a single 15N atom. For the total lineshape analysis of NMR spectra, we used the recently developed ANATOLIA software package. The determined NMR parameters allowed us to optimize experiments for investigating singlet long-lived spin states (LLSs) of 15N spin pairs and to measure LLS lifetimes in cis-AB and trans-AB. Magnetization-to-singlet-to-magnetization conversion has been performed using the SLIC and APSOC techniques, providing a degree of conversion up to 17 and 24% of the initial magnetization, respectively. Our approach is useful for optimizing the performance of experiments with singlet LLSs; such LLSs can be exploited for preserving spin hyperpolarization, for probing slow molecular dynamics, slow chemical processes and also slow transport processes. PubDate: 2018-03-01 DOI: 10.1007/s00723-017-0968-8 Issue No:Vol. 49, No. 3 (2018)
Authors:Nikolay V. Anisimov; Olga S. Pavlova Pages: 165 - 174 Abstract: The data of magnetic resonance imaging (MRI) studies include not only grayscale images, but also textual information associated with them —personal data about the patient, parameters of scanning and data processing, etc. This information is stored separately from graphic images. Therefore, the possibility for its correction and loss cannot be excluded. In this paper, the method of generation of marker information on diagnostic images is described. The marker information, as a textual analogue, is entered on the image during an MRI scan and becomes an integral part of the diagnostic material along with the images of anatomical structures. The method is realized by using the selective radiofrequency presaturation of non-scanable slices oriented perpendicularly to the scanned slices. It leads to the formation of bands of reduced signal in the areas of intersections of these slices on images. In this case, the band thicknesses are equal to the thicknesses of non-scanable slices. Different combinations of these bands (marker lines) are formed directly on images and can contain information about MRI studies. This information is determined not only by positions and angle orientations of bands, but also by their thickness, total brightness and brightness distribution in the transverse direction of these bands. The examples of introducing and positioning the marker information in conventional MRI studies are presented. PubDate: 2018-02-01 DOI: 10.1007/s00723-017-0944-3 Issue No:Vol. 49, No. 2 (2018)
Authors:Irina G. Agafonova; Vladimir N. Kotelnikov; Boris I. Geltser; Natalya G. Kolosova; Valentin A. Stonik Pages: 217 - 225 Abstract: The renovascular model of arterial hypertension (AH) was induced in Wistar and OXYS strains. The model of AH was verified by magnetic resonance angiography. It was shown that histochrome enhances the vasodilatory effect of selective beta1 blocker, nebivalol, against cerebral and renal arteries using a combined therapy in this model. Monotherapy with histochrome had no significant effect on blood pressure. The angioprotective effect of histochrome in the combined therapy was significantly more expressed in hypertensive OXYS rats compared to hypertensive Wistar rats as shown by magnetic resonance imaging (MRI) morphometry. These differences were more observable in the intrarenal part of renal arteries. The degree of regional discirculation of arteries was calculated by the Cerebro-Renal Vascular Index, which confirms the therapeutic advantage of combined therapy with histochrome and nebivalol in the background of AH. Thus, comparative MRI angiography and MRI morphometry of the cerebral and renal arteries in hypertensive Wistar and OXYS strain rats showed that histochrome expands the therapeutic potential of nebivalol due to angioprotective effects in the vascular region of the target organs. PubDate: 2018-02-01 DOI: 10.1007/s00723-017-0960-3 Issue No:Vol. 49, No. 2 (2018)
Authors:Josilei da Silva Ferreira; Tiago Bueno Moraes; Luiz Alberto Colnago; Fabíola Manhas Verbi Pereira Abstract: Time-domain nuclear magnetic resonance (NMR) has been widely used in food science. In this work, we demonstrate that the NMR decay obtained with the Carr–Purcell–Meiboom–Gill (CPMG) sequence can be used to estimate the peroxidase activity (PA) in cassava roots. This enzyme has been involved in post-harvest physiological deterioration (PPD), which limits the storage of fresh cassava to a few days. Cassava is a staple food for almost one billion people in tropical areas in Americas, Africa and Asia. A multivariate method using CPMG data and reference values of PA from a standard biochemical assay was built with 216 measurements for non-refrigerated and refrigerated samples of cassava roots. The figures of merit of the global partial least squares model using both types of roots showed a 0.06 μmol min−1 limit of detection (LOD) and a 0.2 μmol min−1 limit of quantification (LOQ) for PA, with 0.4 [intensity (a.u.)/(μmol min−1)] sensitivity and a standard error of cross-validation (SECV) of 0.7 μmol min−1. All of the results demonstrated that TD-NMR has the potential to predict PA in cassava roots that is indicative of the PPD problem. PubDate: 2018-02-26 DOI: 10.1007/s00723-018-0995-0
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:Ruoheng Sun; Peter Jakes; Svitlana Eurich; Désirée van Holt; Shuo Yang; Melanie Homberger; Ulrich Simon; Hans Kungl; Rüdiger-A. Eichel Abstract: Spinel-type lithium manganese oxides are considered as promising cathode materials for lithium-ion batteries. Trace amounts of Li2MnO3 usually occur as a secondary phase in lithium-manganese spinels in the common high-temperature, solid-state synthesis, affecting the overall Li–Mn stoichiometry in the spinel phase and thereby the electrochemical performance. However, the formation of Li2MnO3 lower than 1 wt.% can hardly be quantified by the conventional analytical techniques. In this work, we synthesized lithium-manganese spinels with different Li/Mn molar ratios and demonstrate that electron paramagnetic resonance (EPR) enables quantifying trace amounts of Li2MnO3 below 10−2 wt.% in the synthesized products. The results reveal that the formation of Li2MnO3 secondary phase is favored by lithium excess in the synthesis. Based on the quantitative evaluation of the EPR data, precise determining Li–Mn stoichiometry in the spinel phase in Li1+xMn2−xO4 materials can be assessed. Accordingly, it is possible to estimate the amount of lithium on 16d-sites in the Li-rich manganese spinels. PubDate: 2018-02-13 DOI: 10.1007/s00723-018-0983-4
Authors:A. O. Antonenko; D. Yu. Nefedov; E. V. Charnaya; S. V. Naumov; V. V. Marchenkov Abstract: 77Se nuclear magnetic resonance (NMR) measurements in the Bi2Se3 topological insulator single crystal were carried out at temperatures 15.8, 88, and 293 K. Bismuth selenide single crystalline plate was studied in the orientation when the crystallographic c-axis was parallel to the external magnetic field B0. We observed two component NMR spectra at the three temperatures. It was shown that the NMR spectrum almost did not move with decreasing temperature and the density of charge carriers did not follow the thermal activation law. PubDate: 2018-02-13 DOI: 10.1007/s00723-018-0986-1
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
Authors:V. N. Verkhovlyuk; V. I. Borovkov; V. A. Bagryansky; S. B. Zikirin; A. I. Taratayko; O. A. Anisimov; Yu. N. Molin Abstract: The hyperfine structure has been resolved in the optically detected electron spin resonance (OD ESR) spectra of radical ion pairs generated by ionizing radiation at a low dopant concentration in a solid polyethylene matrix at room temperature. The different organic molecules that can capture electrons and holes were used as the dopants. The spin-lattice relaxation times T1 for radical ions of dopants were estimated to be tens of microseconds. The temperature dependence of OD ESR signal intensity indicates the diffusion-assisted mechanism of recombination of radical ion pairs in polyethylene. PubDate: 2018-02-09 DOI: 10.1007/s00723-018-0978-1
Authors:A. A. Akovantseva; V. N. Bagratashvili; N. A. Chumakova; E. N. Golubeva; O. I. Gromov; S. V. Kuzin; M. Ya. Melnikov; P. S. Timashev Abstract: The aim of the research was to test the advantages of spin probe electron paramagnetic resonance approach in studying polymers impregnation with organic molecules in supercritical CO2 (scCO2) The impregnation of bisphenol A polycarbonate with the spin probe TEMPOL was carried out at 307–343 K and 11.6–35 MPa. The mean and local concentrations of the spin probe in the polymer were evaluated. An increase in temperature and pressure resulted in a more even distribution of the dopant in the polymer matrix. It was observed that, at 307 K and 19.6 MPa, the spin probe was located only near the surface of the sample. Local mobility of the spin probe molecules was found to be similar in polycarbonate films impregnated in scCO2 and cast from dichloroethane solution. It was shown that changes in the structure of the surface and bulk of the polymer detected by the atomic force and optical polarization microscopy are not directly related with the distribution of the dopant molecules and their average content in the polymer. PubDate: 2018-02-08 DOI: 10.1007/s00723-018-0984-3
Authors:S. V. Yurtaeva; M. Yu. Volkov; G. G. Yafarova; D. I. Silantyeva; E. I. Yamalitdinova Abstract: The 31P nuclear magnetic resonance spectroscopy technique was applied to study the blood of rats with a 3-day spinal cord injury and control rats. Phosphorus-containing blood metabolites: 2,3-diphosphoglycerates, inorganic phosphates, phospholipids, ATP and adenosine monophosphates were detected and quantitatively evaluated. It was found that the amount of 2,3-diphosphoglycerates, inorganic phosphates, phospholipids and adenosine monophosphates increase, and pH of the blood decreases after spinal cord injury. The results demonstrate increased hypoxia in injured rats. PubDate: 2018-02-06 DOI: 10.1007/s00723-018-0982-5
Authors:Dong-hui Xing; Yi-ren Fan; Shao-gui Deng; Xin-min Ge; Jian-yu Liu; Fei Wu Abstract: Nuclear magnetic resonance (NMR) plays a significant role in porous media analysis and petroleum exploration, but its response is significantly influenced by the internal magnetic field gradient in fluid saturated porous medium, which obviously limits the accuracy of rock core analysis and logging interpretation. The influential factors of the internal magnetic field gradient in formation and its influences on NMR response are studied in this paper, based on NMR mechanism through one- and two-dimensional core NMR experiments. The results indicate that the internal magnetic field gradient is positively correlated with the static magnetic field strength and the magnetic susceptibility difference between pore fluid and solid grains, while it presents negative correlation with pore radius. The internal magnetic field gradient produces an additional diffusion relaxation in hydrogen relaxation system and accelerates the attenuation of magnetization vector. As a result, T2 spectrum shifts to the left and NMR porosity and diffusion coefficient of the fluid could be inaccurate. This research sets a foundation for the NMR porosity correction and fluid distribution on T2-G maps based on the internal magnetic field gradient correction. PubDate: 2018-01-15 DOI: 10.1007/s00723-018-0979-0
Authors:R. S. Kashaev Abstract: Using nuclear (proton) magnetic resonance relaxometry (NMRR) was studied oil disperse systems. Dependences of NMR–relaxation parameters—spin–lattice T1i, spin–spin T2i relaxation times, proton populations P1i and P2i, and petrophysical correlations were received for light and heavy oils. Experimental results are interpreted on the base of structure-dynamical ordering of oil molecules with structure unit formation. PubDate: 2018-01-15 DOI: 10.1007/s00723-018-0977-2
Authors:R. M. Peng; Y. Mei; H. G. Liu; W. C. Zheng Abstract: The spin-Hamiltonian parameters (g factors g//, g⊥ and zero-field splitting D) of the trigonal Cr3+ centers in Cr3+-doped ABO3 (A = Sc, In, Lu) borate crystals are computed from both the complete diagonalization (of energy matrix) method and also the perturbation method based on the two-spin–orbit-parameter model, where the contributions to spin-Hamiltonian parameters due to both the spin–orbit parameter of central d n ion and that of ligands via covalence effect are considered. The calculated results are compatible with those available in experiments. The defect structures of the trigonal (CrO6)9− octahedral centers are also evaluated from the calculations. It is found that the trigonal (MO6)9− octahedra change from the elongation in the host crystals to the compression in the impurity centers because of the large size and nature mismatch substitution in these Cr3+-doped ABO3 crystals. The results are discussed. PubDate: 2018-01-13 DOI: 10.1007/s00723-017-0976-8
Authors:Yongfeng Xu; Qingqing Wen; Hongyi Yang; Kai Zhong Abstract: Copper foil has been widely employed in conventional radio frequency (RF) birdcage coils for magnetic resonance imaging (MRI). However, for ultrahigh-field (UHF) MRI, current density distribution on the copper foil is concentrated on the surface and the edge due to proximity effect. This increases the effective resistance and distorts the circumferential sinusoidal current distribution on the birdcage coils, resulting in low signal-to-noise ratio (SNR) and inhomogeneous distribution of RF magnetic (B1) field. In this context, multiple parallel round wires were proposed as legs of a birdcage coil to optimize current density distribution and to improve the SNR and the B1 field homogeneity. The design was compared with three conventional birdcage coils with different width flat strip surface legs for a 9.4 T (T) MRI system, e.g., narrow-leg birdcage coil (NL), medium-leg birdcage coil (ML), broad-leg birdcage coil (BL) and the multiple parallel round wire-leg birdcage coil (WL). Studies were carried out in in vitro saline phantom as well as in vivo mouse brain. WL showed higher coil quality factor Q and more homogeneous B1 field distribution compared to the other three conventional birdcage coils. Furthermore, WL showed 12, 10 and 13% SNR increase, respectively, compared to NL, ML and BL. It was proposed that conductor’s shape optimization could be an effective approach to improve RF coil performance for UHF MRI. PubDate: 2017-12-11 DOI: 10.1007/s00723-017-0963-0
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