Applied Magnetic Resonance最新文献

Studies were carried out on the effect of additional continuous magnetic saturation of the NMR line on nuclear spin relaxation in a NaF single crystal before and after γ-irradiation. The times of magnetization recovery after inversion were measured at room temperature using a Bruker Avance 400 pulse spectrometer. The magnetic saturation was obtained by exciting a long additional resonance pulse. Two main contributions to relaxation for quadrupole ²³Na nuclei, due to spin-phonon coupling in a regular crystalline lattice and due to magnetic centers, were separated by suppressing the latter contribution. γ-irradiation was shown to enhance spin relaxation, however, the magnetic saturation does not suppress the contribution of color centers. The times corresponding to ²³Na relaxation due to spin-phonon coupling in a regular lattice, due to magnetic centers and color centers were evaluated. It was shown that the rate of spin–lattice relaxation for dipole ¹⁹F nuclei was not affected by magnetic saturation.

Diclofenac is a non-steroidal anti-inflammatory drug (NSAID). Here, we use double electron–electron resonance (DEER, also known as PELDOR) to study the interaction of spin-labeled diclofenac (diclofenac-SL) with three types of model membranes consisting of palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), an equimolar mixture of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), and this mixture with the addition of 20 mol% cholesterol. The results suggest that lipid-mediated lateral clustering of diclofenac-SL molecules occurs in all cases. For the POPC bilayer, alternative clustering takes place in two opposite leaflets, with random distribution of the molecules within the clusters. For DOPC/DPPC and DOPC/DPPC/cholesterol bilayers, diclofenac-SL molecules are separated by a distance of at least 1.4 nm. DOPC/DPPC/cholesterol bilayers are known to form nanoscale liquid disordered and liquid ordered lateral structures, the latter called lipid rafts. For this case, diclofenac-SL molecules were found to be captured by lipid rafts, forming a quasi-regular two-dimensional substructure in them with a “superlattice” parameter of ~ 3.0 nm.

The field of research on magnetic van der Waals compounds—a special subclass of quasi-two-dimensional materials—is currently rapidly expanding due to the relevance of these compounds to fundamental research where they serve as a playground for the investigation of different models of quantum magnetism and also in view of their unique magneto-electronic and magneto-optical properties pertinent to novel technological applications. The electron spin resonance (ESR) spectroscopy plays an important role in the exploration of the rich magnetic behavior of van der Waals compounds due to its high sensitivity to magnetic anisotropies and unprecedentedly high energy resolution that altogether enable one to obtain thorough insights into the details of the spin structure in the magnetically ordered state and the low-energy spin dynamics in the ordered and paramagnetic phases. This article provides an overview of the recent achievements in this field made by the ESR spectroscopic techniques encompassing representatives of antiferro- and ferromagnetic van der Waals compounds of different crystal structures and chemical composition as well as of a special category of these materials termed magnetic topological insulators.

Microporous aluminophosphates (AlPOs) are prospective materials that can be used as molecular sieves and adsorbents in their pure form or catalysts and catalyst supports when some of the sites are substituted with heteroatoms. One of the approaches to create and finely tune Brønsted acid sites in AlPO is simultaneous introduction of Si and B into the framework. However, boron substitution of AlPOs is briefly studied and proceeds with difficulties. Here, we apply multinuclear solid-state nuclear magnetic resonance together with DFT calculations to investigate the behavior of aluminophosphate AlPO-5 and its boron-substituted analogue BAPO-5 upon interaction with water. We demonstrate that the structure of AlPO-5 facilitates a homogeneous distribution of water molecules and makes BAPO-5 less susceptible to hydrolysis compared to microporous AlPO-11 and BAPO-11.

We study 25–120 GHz electron spin resonance in a quasi-two-dimensional (S=) 3/2 antiferromagnet on an isosceles triangular lattice Cs(_2)CoCl(_4). Due to the frustration of the exchange interaction along the lateral sides of the triangles, the exchange network may be viewed as a quasi-one-dimensional system of weakly interacting chains. The strong single-ion anisotropy of Co(^{2+}) allows a pseudospin (s=) 1/2 formulation of the problem. We observe in experiments a well-pronounced temperature crossover from the ESR of individual pseudospins with a g-factor of 3.3 (corresponding well to individual pseudospins s=1/2) to ESR spectrum shifted strongly down in frequency at the temperature range below 1 K. This shifted ESR spectrum corresponds well to the singularity at the lower boundary of the quasi-spinon continuum of an XXZ spin chain in a transverse field, calculated in theory by Bruognolo et al., in Phys Rev B 94:085136, 2016 and by Laurell et al., in Phys Rev Lett 127:037201, 2021.

Gallium alloys are widespread materials in microelectronics and are promising as components of nanocomposites for using in soft robotics, wearable electronics, and sensors. Here, we present NMR studies of the impact of a particular nanoconfinement on the phase diagram for the GaInSn eutectic alloy in a porous Al₂O₃ ceramic template with the middle pore size 11 nm. Measurements of the NMR spectra and Knight shifts were carried out for ⁷¹Ga, ⁶⁹Ga, and ¹¹⁵In isotopes from 180 to 310 K. The precipitation of gallium-rich segregates with crystalline structures of α- and β-Ga was found at cooling. The evolution of the NMR lines during cooling and warming evidenced the occurrence of the liquid–liquid-phase transition in the melt fraction with pronounced amount of indium. The results obtained for the GaInSn alloy embedded into the porous aluminum oxide ceramic were found to differ remarkably from the phase diagrams of the alloy confined within silica opal and glass porous matrices.

The purpose of this study was to evaluate the importance of automated lateral and medial temporal volume measurement technique for the early diagnosis of Alzheimer's disease (AD). A cross-sectional T1-weighted magnetic resonance image was obtained from 39 healthy adults and 39 patients with mild AD. The study demonstrates significant volume loss in the lateral temporal lobe (LTL) and medial temporal lobe (MTL) regions of the brain in early cases of AD, suggesting that volume loss could be used as a viable biomarker for mild AD diagnosis. Using a deep learning-based auto-segmentation network (CINet), the study accurately estimates the volumes of various LTL and MTL brain regions. Notably, higher volume loss is observed in the left MTL and LTL regions compared to the right, indicating an asymmetric impact in mild AD. The study underscores the significance of automated technique for AD diagnosis and monitoring disease progression, contributing valuable insights for potential early interventions.

The Lindblad equation for dissipative open systems is applied for an investigation of relaxation of multiple-quantum (MQ) NMR coherences in two-spin systems. We choose two examples of two-spin systems. One of them is the zigzag proton chain in a single crystal of hambergite in such an orientation that one of the two intra-chain dipolar coupling constants becomes zero. Then, the chain consists of well-isolated pairs of spins, with the spins of each pair coupled by the dipole–dipole interaction. The second example of a two-spin system is a single crystal of gypsum in which protons belong to water molecules. The MQ NMR dynamics with relaxation was investigated for different preparation times of the MQ NMR experiment.

The development of ecofriendly electrolytes for lithium-ion batteries is one of the actual tasks of modern electrochemistry. In particular, to this purpose, the highly concentrated ternary aqueous systems based on lithium acetate (LiOAc) have been actively investigated. Here, the diffusion coefficients of ⁷Li⁺ and ¹³³Cs⁺ cations, OAc^– anion, as well as water (¹H), in ternary aqueous solutions of cesium and lithium acetates in a range of temperature (– 15 ÷ 35 °C) have been measured using the PFG NMR method. A direct attempt to interpret the obtained dependences within the framework of the Stokes–Einstein model led to the fact that the calculated hydrodynamic radius of the Cs⁺ cation turned out to be noticeably smaller than its crystallographic one. An approach to describing the high rate of diffusion of cesium cations is proposed, based on taking into account the local viscosity near cations of both types. The use of the approach allowed us to calculate more correctly the hydrodynamic radii of cations, while remaining within the framework of the Stokes–Einstein model. As a result, it has been possible to describe the features of translational motion of components in a complex system that is interesting for electrochemical applications.

The gradient coils represent an indispensable constituent within magnetic resonance imaging systems. Their performance significantly impacts the quality of images, particularly the nonlinearity of the gradient magnetic field. Due to the presence of ferromagnetic materials surrounding the gradient coil in the permanent magnet system, the magnetic field of the gradient coil experiences influence. Consideration must be given to ferromagnetic materials during the design phase. The objective of this study is to design gradient coils that mitigates the impact of ferromagnetic materials on gradient field linearity. In this paper, the original coil structure is formulated utilizing the discrete trajectory method, while introducing mirrored current to elucidate the effects of ferromagnetic material. Through the integration of these two methods, gradient coil structures with excellent linearity are achieved. Ultimately, the optimal gradient coils are fabricated, and computational as well as experimental findings demonstrate concordance between measured nonlinear degree and efficiency of the gradient coils with theoretical calculations in the presence of ferromagnetic materials.