Applied Magnetic Resonance最新文献

Relaxation times of manganese(IV) complexes of mandelate, metformin, and sorbitol were measured at X-band from 4.2 to 70, 25, or 20 K, respectively. The Mn(IV) oxidation state was confirmed by chemical titrations. The X-band continuous wave and field-swept echo-detected spectra were simulated with |D| = 0.077 ± 0.004 cm⁻¹, E = 0.0 for Mn(IV) mandelate, |D| = 0.30 ± 0.03 cm⁻¹, E = 0.054 ± 0.007 cm⁻¹ for Mn(IV)metformin, and |D| = 0.37 ± 0.007 cm⁻¹, E = 0.070 ± 0.001 cm⁻¹ for Mn(IV)sorbitol. The relaxation rates (1/T_m and 1/T₁) increase with increasing zero-field splitting. Empirical modeling of the temperature dependence of T₁ at temperatures above about 10 K is consistent with a Raman process.

Water cut is a critical parameter in reservoir evaluation because it strongly influences residual oil estimates. Conventional water cut calculation methods often lack effectiveness in complex reservoirs, leading to low prediction accuracy. This study addresses the Triassic Chang 8 Formation in the Hongde region by proposing an empirical water cut prediction method that uses nuclear magnetic resonance (NMR) logging to improve precision. The methodology comprises several steps: first, combining NMR measurements and relative permeability experiments on 20 core samples clarified the impact of pore structure on relative permeability, and an NMR T₂-derived parameter was defined to quantify pore structure. Subsequently, the target formation was classified into three formation types, and a relative permeability prediction model was developed for each type using NMR logging. Following this, models were established to estimate water saturation, irreducible water saturation, and irreducible oil saturation so these inputs could be derived from conventional well logging data. Finally, a formula for calculating reservoir water cut based on Darcy’s law was derived and applied to field data in the target reservoirs to predict water cut continuously. Comparison of predicted water cut values with drill stem test data demonstrated the efficacy of the proposed model, achieving an accuracy of 83.3%. This methodology holds promise for optimizing oilfield production development with reliable outcomes.

Nuclear magnetic resonance (NMR) spectroscopy is an indispensable tool for analysing molecular structures and dynamics. Its applicability for reaction monitoring, especially of heterogeneously catalysed hydrogenation reactions, is limited by its low sensitivity and high cost associated with high-field NMR technology. This study describes approaches to overcome these challenges by employing a cost-effective benchtop NMR spectrometer combined with parahydrogen induced polarization (PHIP) to enhance sensitivity. The research focuses on the real-time monitoring of catalytic hydrogenations, fundamental reactions in synthetic chemistry and industrial processes. As a versatile model reaction, the hydrogenation of propene employing different catalysts is studied. The experimental setup includes a parahydrogen generator, a controllable gas flow system, and a low-field benchtop NMR spectrometer enabling in-situ and ex-situ hydrogenation experiments. Both in-situ and ex-situ experiments can be performed for monitoring gas-phase hydrogenation reactions. The setup's adaptability to different catalysts and reaction conditions, coupled with its cost efficiency, will make it accessible to a larger number of laboratories in the future.

Continuous-wave optically detected magnetic resonance (CW-ODMR) measurements with nitrogen-vacancy (NV) spins in diamond are used for sensing DC magnetic fields from nearby magnetic targets. However, this technique suffers from ambiguities in the extraction of the magnetic field components when resonances due to different NV orientation classes overlap with each other. Here, we perform detailed experimental and theoretical studies of such effects on NV ensembles experiencing low to moderate bias magnetic fields. In particular, through symmetry considerations, we systematically examine the ODMR response of different NV orientation classes as a function of the orientation of the magnetic field vector. Our studies are of importance for performing a careful and detailed analysis of the ODMR spectra in order to infer the vector magnetic field information. Our results find application in the studies of magnetic samples that require a low applied bias field and can also be potentially adapted to defect spins in other solid-state systems.

Electron Spin Resonance (ESR) spectroscopy provides a powerful tool for investigating paramagnetic species generated during thermal treatment of organic matter. In this study, ESR was employed to examine heat-induced free radicals on the surface of baked rice pudding, a heterogeneous organic system containing carbohydrates that undergo thermally driven chemical transformations. Systematic measurements were performed to analyze the evolution of ESR signal intensity, peak-to-peak line width, and g-value as functions of heating temperature and duration. The results demonstrate that radical formation becomes significant above 200 °C, reaches a maximum at 350 °C, and decreases at higher temperatures. The g-values shift toward the free-electron value (g = 2.0023) with increasing temperature, reflecting changes in the electronic environment of the radicals. Kinetic analysis of time-dependent spectra yielded an activation energy of 12.8 kJ/mol for radical formation, consistent with values reported in other foods. Moreover, the radicals exhibited remarkable stability under ambient conditions, indicating persistent paramagnetic centers in the burnt surface layer. These findings highlight the applicability of ESR spectroscopy for characterizing thermally generated free radicals in heterogeneous organic systems. The study not only provides quantitative insight into the radical formation mechanisms but also demonstrates the use of a widely available food material as a model system for exploring spin dynamics under thermal treatment.

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.