Magnetic Resonance in Chemistry最新文献

Diffusion tensor imaging (DTI) is an established magnetic resonance imaging (MRI) technique for characterizing tissue structure in medical science. However, the method has seen virtually no application outside of that field. One of the biggest obstructions to broader use of the technique is that it requires expensive high-field MRI equipment, limiting its application to large research institutions and hospitals. Recently, benchtop MRI systems capable of performing DTI experiments have come onto the market. In this article, we present the first evaluation of benchtop DTI technology, focusing on the applications in food science. Three basic measurements are performed to assess the capabilities of the system. Advantages and disadvantages of the benchtop measurements compared to traditional high-field equipment are discussed. Although the benchtop systems have limitations, the low cost and ease of use open an important new avenue for sample characterization in food science.

Multinuclear (¹H, ³¹P, and ¹⁹F) DOSY technique has been used under variable temperature conditions, in order to establish the optimal conditions for obtaining reliable data at variable temperatures, while keeping experimental settings as simple as possible (e.g., using standard NMR tubes). For this goal, we have used the methodology developed in 2003 by Martínez-Viviente and Pregosin, but using more modern pulse sequences specially designed to avoid the effects of convection upon DOSY experiments. We have written new pulse sequences (modifying existing standard ones) in order to use proton/heteronuclear decoupling (in this last case, with the possibility also of adiabatic decoupling). We have performed extensive measurements, covering all possible variables: type of instrument/probe, solvent volatility, calibration of the instrument gradients, spinning/non-spinning of the sample, proton decoupling, heteronuclear decoupling (standard or adiabatic), and so on. The ensemble of all these measurements has allowed us to design a protocol for simple measurement of DOSY at variable temperature in a standard NMR lab, without any need of special instruments/probes or glassware.

In this study, the ferromagneticresonance (FMR) technique was used to investigate the magnetic structure of nickel-containing xAl₂O₃-[88% ZrO₂–12% CeO₂] catalysts (where x = 5, 20, 50, and 75 mol.%) for ethanol dry reforming (EDR). We have shown that it is possible to determine the deactivation effect of the EDR reaction on the catalysts using FMR spectroscopy. The deactivation of nickel nanoparticles on the catalyst's surface can proceed via two potential pathways: carbonization and sintering. Active carbonization of the nickel-containing catalyst can be detected by a decrease in the FMR signal linewidth, while sintering can be identified from FMR linewidth increase. While, the relative shape of the nickel nanoparticles can be found from the asymmetry parameter of the FMR spectrum.

The proper quantitative NMR (qNMR) setup requires efficient relaxation of all active nuclei between scans. To achieve this, the spectroscopist has to know the longitudinal relaxation constant ($�{�T�}_{�1�}$) for each nucleus involved in the experiment and set the interscan delay to at least five times the longest $�{�T�}_{�1�}$. The $�{�T�}_{�1�}$ is most commonly measured using the inversion–recovery method, which is essentially the acquisition of a series of spectra with increasing delay between 180° and 90° pulses. Unfortunately, the inversion–recovery experiment can last hours if a long $�{�T�}_{�1�}$ is expected. In this paper, we show how to perform it faster by employing sweeping apparatus for polarisation enhancement (SWAPE)—an apparatus that can shift the sample vertically synchronously to the pulse sequence. In brief, the inversion recovery occurs in the sample parts that are shifted away from the RF coil, while other spins in an active volume are excited and measured. This way, the long, passive delays are avoided, and the experiment is shortened several times. We demonstrate its potential on the formic acid sample, a commonly used qNMR reference standard. The resulting $�{�T�}_{�1�}�=�12.99�\pm �0.73$ s is in good agreement with the one measured using the conventional approach, $�{�T�}_{�1�}�=�14.48�\pm �0.82$ s, requiring approximately 5.8 times less acquisition time.

Documentation of the historical developments plays a vital role in recognising the pioneering contributions by the scientists of the previous generations. As we progress, there is a high chance of missing out on those contributions. In this special issue which is devoted to recounting the contributions of Indian scientists in the area of magnetic resonance, the present article is an effort to put on record the invaluable contributions by the previous generations which have indeed been quite substantial. It is an effort which is certainly not exhaustive, but a sincere effort has been made to be as inclusive as possible. The article focuses mostly on Nuclear Magnetic Resonance (NMR). It is also not a document to highlight the contributions of the present generations, since the individual scientists of the present era will be writing separate articles focusing on their own achievements, in this special issue. Moreover, I may not be doing justice to their contents, on one hand, and may run the risk of bias of inclusion on the other.