Magnetic Resonance in Chemistry最新文献

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.

Hydrogels can be combined with molecular carriers to achieve controlled delivery of hydrophobic drugs. The purpose of this study was to use an experimental protocol consisting of spatially localized magnetic resonance (MR) techniques to investigate the changes in a poly(N-isopropylacrylamide) P(NIPAM) hydrogel incorporating $�\beta$-cyclodextrins ($�\beta$CD) undergoing a volume phase transition (VPT). The MR protocol presented in this study allows to follow the shrinking of the hydrogel and the release of $�\beta$CD, with subsequent determination of the self-diffusion coefficients of both water and $�\beta$CD in the hydrogel. The obtained data enable a detailed correlation of the change in hydrogel structure and spatial variation in gel volume and the corresponding time-dependent spatial variation in the concentration of $�\beta$CD.

Curcuminoids, including curcumin, demethoxycurcumin, and bisdemethoxycurcumin, are vital for quality control in food, nutraceuticals, and pharmaceuticals. Conventional 1D ¹H NMR can face challenges in spectral interpretation when dealing with overlapping signals and complex coupling patterns, especially in structurally similar compounds like curcuminoids. This study explores the use of selective homodecoupled 1D ¹H NMR spectroscopy as a complementary technique to enhance spectral resolution and facilitate peak assignment in curcuminoid analysis. By collapsing multiplet structures such as doublets observed in the 6.6- to 6.8-ppm region for vinylic protons into singlets, this method offers improved spectral clarity. Although absolute quantification still requires deconvolution, the approach aids in more straightforward relative integration and identification of components within curcuminoid mixtures from turmeric samples. The results demonstrate improved interpretability compared with conventional ¹H NMR under similar conditions. Comparative analysis with HPLC showed excellent agreement, with standard deviations under 2% for most samples. The selective homodecoupled 1D ¹H NMR method proved robust and reliable, offering an effective tool for profiling curcuminoids and potential application to other natural product mixtures.

Carbones bear the same resonance contributor X⁺–C²⁻–Y⁺ (X⁺, Y⁺ = PR₃⁺, CR₂⁺, SR₂⁺, SeR₂⁺, S⁺R₂ = NR) and exhibit unique bonding and donating properties at the central carbon atom. Both the analogues of carbones C⁺–Z²⁻–C⁺ (Z = Si, Ge, Sn, Pb) and the large number of charged main group homologues C=Z=C (Z = B⁻, Al⁻, Ga⁻, N⁺, P⁺, As⁺, Sb⁺, Bi⁺, O²⁺, S²⁺, Se²⁺ and Te²⁺) are known for comparable bonding and donating properties. The electronic structure of the carbone homologues and analogues has been studied on basis of both their geometry and their spatial magnetic properties (through-space-NMR-shieldings [TSNMRSs]) with regard to the present dominating electronic structure (beside carbone-like [⁺C–Z²⁻–C⁺] also allene-like [C=Z=C] or carbene-like [⁺C–Z⁻=C]). TSNMRS values have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and the results visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The synergy of geometry (bond lengths, bond angles of linear, bent, orthogonal or twisted structures) and the spatial magnetic properties (anisotropy effect of C=C in allene-like or partial C=C double bonds in carbene-like structures, and the ball-like anisotropy effect of central hetero atom Z of carbone-like structures) provide a comprehensive picture of the respective structure and the dominating resonance contributor.

Verbascoside and isoverbascoside are phenylethanoid glycosides with reported biological activities such as neuroprotection, hepatoprotection, anti-inflammatory, antimicrobial, anticancer, and antioxidant properties. These compounds are constitutively present in roots, stems, leaves, and flowers of various plant species, including Tecoma stans. In Mexico, this plant is traditionally used as a safe and effective herbal treatment for chronic diseases and its complications including diabetes and renal and hepatic disorders. The potential pharmacological applications of verbascoside and isoverbascoside have conducted efforts to produce these compounds in cell and plant tissue cultures. In this study, T. stans root and plantlet in vitro cultures were established as potential sources of verbascoside and isoverbascoside, and NMR was used as primary analytical tool. As a first step, proton and bidimensional NMR analysis confirmed the presence of verbascoside and isoverbascoside in T. stans in vitro culture extracts. Subsequently, their contents were quantified by means of quantitative NMR (qNMR) based on the external standard PULCON method. Furthermore, ¹H-NMR spectral data were used to develop a descriptive PLS-DA model, which confirms the qNMR results. This model indicated that differences in the amounts and proportions of verbascoside and isoverbascoside produced by roots and plantlets are the primary factors in distinguishing these samples. These results demonstrate the capability of T. stans in vitro systems as biotechnological tools for obtaining phenylethanoids with high pharmacological potential and confirm the broad applicability of NMR as an analytical platform. However, additional experiments are necessary to improve the phenylethanoids glucoside yields and support the validation of the qNMR method.