Applied Magnetic Resonance最新文献

In this paper, we demonstrate the possibility of simultaneously detecting six nuclei with different gyromagnetic ratios, whose Larmor frequencies lie in the range of 5.2–21.1 MHz. The application of the undersampling method allowed the subspectra of both low-frequency nuclei (¹³C, ²³Na, ²⁷Al, ⁵⁵Mn) and high-frequency nuclei (protons ¹H and fluorine ¹⁹F) to be represented within a narrow spectral window of < 0.13 MHz. Two favorable factors were exploited: the close proximity of the Larmor frequencies for different magnetic isotopes at a low field (0.5 T), and the specific design of our circuitry—particularly the proximity of the intermediate frequency of the heterodyne receiver (22 MHz) to the Larmor frequencies of protons and fluorine (21.1 MHz and 19.8 MHz, respectively). Signals were detected from four samples placed inside a 6-turn loop coil. The spins were excited by a single composite pulse consisting of six successive rectangular pulses with carrier frequencies equal to the Larmor frequencies of the detected nuclei. This article presents data on the dependence of the signal-to-noise ratio (SNR) on the spectral window width, discusses the influence of electromagnetic interference, and notes the need to account for receiver-specific characteristics in double resonance NMR experiments. Methods have been proposed to enhance the efficiency of the technique and increase its sensitivity, enabling its use for tasks typically addressed with dual-receiver systems.

Over the past several decades, water–fuel emulsions have been actively investigated because their use can significantly improve the performance and environmental characteristics of diesel engines. However, the stability of such emulsions, governed by phase separation of fuel and water, remains a pressing issue. Determining the water content in emulsified diesel fuel provides insight into emulsion stability. In this work, we describe a new method for determining the proton surface relaxivity at the water–fuel interface based on the kinetics of water‑drop sedimentation in the gravitational field and the transverse NMR relaxation time of ¹H nuclei in the water droplets. Unlike traditional sedimentation analysis by continuous weighing of the sediment, the proposed approach uses continuous monitoring of the NMR relaxation time T₂. It is assumed that the spin–spin relaxation time is proportional to the sediment mass. The kinetics of T₂‑time changes during sedimentation of emulsion water droplets was studied. To obtain the water‑drop size distribution, the T₂(t) data array was processed numerically. The applicability of the proposed method to highly dispersed water–fuel emulsions is limited by the very slow settling of small droplets in the gravitational field. The results obtained here can be useful for dispersion analysis of any organic emulsion containing micrometer‑sized droplets of an immiscible liquid.

Curtisia dentata is traditionally used across southern Africa to treat gastrointestinal issues, sexually transmitted infections, malaria, tuberculosis, as an emetic, purgative, blood purifier, and aphrodisiac. Betulinic acid, a key triterpenoid isolated from the stem-bark of C. dentata, is linked to several of these traditional therapeutic applications and demonstrates broad pharmacological activity. However, natural variation and its impact on the doses delivered in C. dentata traditional preparations remain poorly characterized, constraining our ability to assess their therapeutic consistency. This study quantified inter-individual and seasonal variation in betulinic acid in stem-bark collected from ten C. dentata trees in Nkandla Forest Reserve, KwaZulu-Natal, South Africa, between January and September 2019, and evaluated the implications for the consistency and biological activity of ethnomedicinal doses. Quantitative proton nuclear magnetic resonance spectroscopy (¹H qNMR) targeting the isopropenyl proton signals at H_δ 4.61 and 4.74 ppm revealed concentrations ranging from 0.046 to 0.291 mg/g of dry stem-bark. Significant variability occurred among individual trees and across seasons, with the highest levels in mid-summer and early autumn and the lowest in mid-winter. These fluctuations indicate that traditional decoctions where small quantities of stem-bark are boiled in large water volumes may yield markedly different betulinic acid concentrations, in some cases below thresholds required for pharmacological activity. The results highlight the need for improved standardization and dosage guidance to enhance the therapeutic reliability of C. dentata-based traditional medicines.

Hitoshi Ohta gives a selection of his biographical experiences which have shaped his academic and personal life.

We have developed a magnetic resonance equipment for low temperature and high magnetic fields, aiming at Dynamic Nuclear Polarization-Nuclear Magnetic Resonance (DNP-NMR) and Electron-Nuclear DOuble Resonance (ENDOR) of diluted spin system using with electron spin resonance (ESR). In this study, we developed a cylindrical resonator with a submicron-thick gold film for millimeter-wave band ESR/NMR double magnetic resonance by exploiting the frequency dependence of the skin depth. ESR measurements were performed using the fabricated resonator at approximately 130 GHz and in the temperature range of 3–70 K of BDPA diluted to 100 mM in polystyrene. ESR sensitivity was obtained from the measurements. The ¹⁹F-NMR signal from the sample holder was also successfully observed.

Terahertz electron spin resonance (THz ESR) measurements of the S = 1/2 frustrated J₁–J₂ chain material NaCuMoO₄(OH) were conducted on a quasi-single-crystal (QSC) sample in a pulsed high magnetic field. The QSC sample was fabricated by modulating the rotation of powder sample in a static magnetic field, resulting in three-dimensional alignment. This paper presents the fabrication method for the QSC sample which was confirmed by the Laue pattern obtained by X-ray diffraction, and the degree of orientation indicated by the anisotropic spectrum of ESR. The THz ESR measurements on the QSC sample of NaCuMoO₄(OH) were performed from 0.06 to 1.56 THz, and we observed ESR spectra for the single axis (b-axis) above the saturation field. We demonstrate that the fabrication of magnetically aligned samples allows the observation of sharp single-axis absorption, even in the THz ESR range, which is challenging for a powder samples with a broad linewidth. Furthermore, we establish that this method is an effective approach for investigating magnetic anisotropy, even in antiferromagnetic powder samples.

We report electron spin resonance studies of double perovskite Ba(_2)CoWO(_6) single crystals. Above (T_textrm{N} = 14) K, we observe a paramagnetic resonance with (g_textrm{eff}simeq 3.66). Upon cooling, this mode transforms into a broad antiferromagnetic resonance (AFMR) with a zero-field energy gap of about 200 GHz. The AFMR becomes barely detectable at low magnetic fields, indicating unusually strong decay processes. We argue that symmetry-allowed anisotropic spin–spin interactions are a possible reason for the pronounced spin-wave damping. Linear spin-wave theory calculations support this scenario.

Following our recent study, the current work performed to explore and elucidate the impacts of the length/angle of hydrogen bonds (H-bonds) of N–H···O/C–H···O type and the percentage s-character of the σ*_N–H/σ*_C–H antibonds partner in the charge transfer (CT) interactions on the nuclear shielding, anisotropy, quadrupole coupling constant, and asymmetry parameters of the imide, amide, carboxamide, and annular nitrogens/methine, methylene, and methyl carbons in the interacting inhibitor–residue pairs in capuramycin, carbacaprazamycin, 3ʹ-hydroxymureidomycin A, and muraymycin D2 binding pockets of MraY_AA–inhibitor complexes (labeled as the QM models I–IV). The cited parameters were calculated at the M06-2X/6-31G** level by including the solvent effects using the polarizable continuum model. In the cases of the imide, amide, carboxamide, and annular nitrogens, the results outlined that a reduction in the H-bond length and an increase in s-character of the N hybrid in the σ*_N–H antibond are associated with a decrease in the ¹⁵N nuclear shielding as well as in the ¹⁴N quadrupole coupling constant but with an enhancement in the ¹⁵N anisotropy and also in the ¹⁴N asymmetry parameter. The similar trends were observed for the nuclear shielding–length, nuclear shielding–s-character, anisotropy–length, anisotropy–s-character correlations of the methine, methylene, and methyl carbons. In addition, when the angles of C–H···O H-bonds are close to 180°, the ¹³C anisotropies increase, while the ¹³C nuclear shieldings decrease. The information obtained here has an immense impact on predicting the behavior of the ¹⁵N/¹³C chemical shifts with the H-bonding characteristics in the protein–ligand complexes.