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doi: 10.1002/mrc.5394pmid: 37724053
A new quantitative nuclear magnetic resonance (qNMR) method, called qNMRw, using water as the internal calibrant has been developed. Its principles, procedures, calculations, and test results are presented here. It is shown to avoid the difficulties created by moisture present in other reference materials. High precision and accuracy can be achieved with qNMRw. The method can be used for analyzing technical materials, herbicide formulation products, and other types of chemical samples. It can also be used to measure the purity and concentration of materials to be used as quantitation calibrants.
Kandarakova, Irina; Yakushkin, Stanislav; Nesterov, Nikolay; Philippov, Alexey; Martyanov, Oleg
doi: 10.1002/mrc.5385pmid: 37681399
Highly dispersed Ni‐TiO2 catalyst has been studied in the process of preparation and under catalytic transfer hydrogenation reaction conditions in supercritical 2‐propanol (250°C, 70 bar) using electron spin resonance in situ. Electron spin resonance in situ has been used to study the process of the catalyst passivation and subsequent reduction of the oxide layer in the gas flow. Reduction of the NiO layer on the surface of passivated Ni nanoparticles has been detected in supercritical 2‐propanol, which is in agreement with kinetic modeling data. It has been found that the reduction of the nickel oxide layer in supercritical 2‐propanol occurs at a lower temperature compared with the reduction in hydrogen flow, according to in situ electron spin resonance study.
doi: 10.1002/mrc.5386pmid: 37583258
The quick identification of known organic low molecular weight compounds, also known as structural dereplication, is a highly important task in the chemical profiling of natural resource extracts. To that end, a method that relies on carbon‐13 nuclear magnetic resonance (NMR) spectroscopy, elaborated in earlier works of the author's research group, requires the availability of a dedicated database that establishes relationships between chemical structures, biological and chemical taxonomy, and spectroscopy. The construction of such a database, called acd_lotus, was reported earlier, and its usefulness was illustrated by only three examples. This article presents the results of structure searches carried out starting from 58 carbon‐13 NMR data sets recorded on compounds selected in the metabolomics section of the biological magnetic resonance bank (BMRB). Two compound retrieval methods were employed. The first one involves searching in the acd_lotus database using commercial software. The second one operates through the freely accessible web interface of the nmrshiftdb2 database, which includes the compounds present in acd_lotus and many others. The two structural dereplication methods have proved to be efficient and can be used together in a complementary way.
Masuda, Yuichi; Ohki, Shinobu; Mogami, Yuuki; Deguchi, Kenzo; Hashi, Kenjiro; Goto, Atsushi; Shimizu, Tadashi; Yamada, Kazuhiko
doi: 10.1002/mrc.5387pmid: 37612854
Sulfur‐33(33S) stable‐isotope labeled taurine, 2‐aminoethanesulfonic acid, has been synthesized, and a series of solution and solid‐state 33S nuclear magnetic resonance (NMR) experiments at 14.1 and 18.8 T, respectively, have been carried out at room temperature. The single peak of a solution 33S NMR spectrum in 0.1‐mM [33S]‐taurine in D2O can be observed with the signal‐to‐noise (S/N) ratio of 9 in 40,000 scans, which paves the way toward in vivo analysis of pharmacokinetics and metabolism of 33S‐labeled taurine. Undistorted magic‐angle‐spinning (MAS) and static 33S NMR spectra of polycrystalline [33S]‐taurine are observed with sufficient S/N ratios for analysis, and the magnitudes of 33S EFG and CS tensors can be obtained.
Zheng, Zhaoxi; Su, Yongchao; Schmidt‐Rohr, Klaus
doi: 10.1002/mrc.5390pmid: 37649159
Hydroxypropyl methylcellulose acetyl succinate (HPMCAS) is widely used as a pharmaceutical excipient, making a detailed understanding of its tunable structure important for formulation design. Several recently reported peak assignments in the solid‐state 13C NMR spectrum of HPMCAS have been corrected here using peak integrals in quantitative spectra, spectral editing, empirical chemical‐shift predictions based on solution NMR, and full spectrum simulation analogous to deconvolution. Unlike in cellulose, the strong peak at 84 ppm must be assigned to C2 and C3 methyl ethers, instead of regular C4 of cellulose. The proposed assignment of signals at <65 ppm to OCH sites, including C5 of cellulose, could not be confirmed. CH2 spectral editing showed two resolved OCH2 bands, a more intense one from O‐CH2 ethers of C6 at >69 ppm and a smaller one from its esters and possibly residual CH2‐OH groups, near 63 ppm. The strong intensities of resolved signals of acetyl, succinoyl, and oxypropyl substituents indicated the substitution of >85% of the OH groups in HPMCAS. The side‐group concentrations in three different grades of HPMCAS were quantified.
Mycroft, Coral; Smith, Marshall J.; Nilsson, Mathias; Morris, Gareth A.; Castañar, Laura
doi: 10.1002/mrc.5393pmid: 37688573
NMR measurements of molecules containing sparse fluorine atoms are becoming increasingly common due to their prevalence in medicinal chemistry. However, the presence of both homonuclear and heteronuclear scalar couplings severely complicates their analysis by NMR. In complex systems, FESTA, a heteronuclear spectral editing method, allows simplified 1H NMR spectra to be obtained containing only 1H signals from the same spin system as a chosen 19F. Despite spectral simplification, signal overlap due to the presence of scalar couplings is often a problem in FESTA spectra. Here, we report a new experiment that combines FESTA and pure shift methods to provide fully decoupled ultra‐high resolution FESTA spectra showing a single signal for each 1H chemical environment. The utility of the method is demonstrated for the analysis of two complex fluorine‐containing mixtures of pharmaceutical and biochemical interest.
Góñez, Karen V.; García, Juan Suárez; Sardina, F. Javier; Pazos, Yolanda; Saá, Ángela; Martín−Pastor, Manuel
doi: 10.1002/mrc.5396pmid: 37727038
One‐dimensional selective NMR experiments relying on a J‐filter element are proposed to isolate specific signals in crowded 1H spectral regions. The J‐filter allows the edition or filtering of signals in a region of interest of the spectrum by exploiting the specific values of their 1H‐1H coupling constants and certain parameters of protons coupled to them that appear in less congested parts of the spectrum (chemical shifts and coupling constants). The new experiments permitted the isolation of specific peaks of phytosterol components in a sample obtained from a liquid nutraceutical recommended for lowering blood cholesterol levels in regions with complete overlap in the 1H spectrum.
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