Magnetic Resonance in Chemistry最新文献

HRMAS (high-resolution magic angle spinning) nuclear magnetic resonance (NMR) spectroscopy of low-density polyethylene (LDPE) affords ¹H and ¹³C NMR spectra with superior resolution. For acquiring HRMAS NMR spectra, the polymer is first swollen with representative organic solvents. Then, the samples are measured with a conventional solid-state NMR spectrometer in the wideline mode or at the low spinning speed of 2 kHz. Anisotropic interactions like CSA (chemical shift anisotropy) and dipolar interactions are reduced due to the additional mobility of the polymer chains in the presence of the solvent within the polymer network. The combined effect of this mobility and MAS leads to signals with substantially reduced halfwidths as compared to classic MAS of the dry polymer. With HRMAS, all signals of the polymer become visible, and the spectra can be used for a quick and easy assessment of the polymer swelling behavior in diverse solvents. Being able to characterize polymers on the molecular level, and identifying the solvents that penetrate the polymer network best, enables the study of post-synthesis modifications of the polymers. It is demonstrated by paramagnetic HRMAS that the metallocene nickelocene (Cp₂Ni) penetrates the LDPE network along with the solvent and is homogeneously dispersed in the polymer. SEM images prove that the structure of the polymer is not altered by the presence of a solvent and Cp₂Ni. The impact of the paramagnetic Cp₂Ni on the ¹H signal halfwidth and T₁ time of LDPE is studied. HRMAS allows a quick assessment of metal complexes regarding their ability to penetrate the LDPE network and therefore supports future studies of catalytic polymer degradation.

A chemically cross-linked version of polystyrene is presented here that allows the preparation of reversibly mechanically compressible gels as NMR weakly aligning media. The gels can be successfully swollen in aromatic solvents such as toluene-d₈ and pyridine-d₅, as well as in CDCl₃, and provided accurate measurements of ¹D_CH RDCs and ¹³C-RCSAs.

In this work, we introduce a novel NMR apodization function designed to enhance spectral resolution while maintaining compatibility with qNMR standards. This function is based on a modified Savitzky-Golay filter, adapted for time-domain application. It effectively suppresses the negative components typically associated with derivative spectra, while also ensuring the preservation of quantitative integrity in NMR analyses.

Forensic laboratories play a pivotal role in identifying and quantifying drugs in police seizures, often using spectroscopic techniques in combination with chromatographic methods that rely on chemical reference substances (CRS). The demand for a wide variety of CRS is critical, not only for common drugs like cocaine but also for the rapidly increasing number of new psychoactive substances (NPS), which emerge weekly. However, acquiring CRS is costly and bureaucratic because of the restricted circulation of these substances. Nuclear magnetic resonance (NMR) offers a viable alternative to identifying and quantifying substances without the need for specific CRS for each analyte. Although NMR equipment is commonly available at universities, it is typically absent from police laboratories because of its high initial cost. This work highlights a successful partnership between a forensic laboratory and university-based NMR facilities as a cost-effective strategy for obtaining CRS. A case study involving four substances-cocaine, two recently scheduled NPS, metonitazene and dipentylone, and ADB-5'Br-BUTINACA-demonstrates the effectiveness of this collaboration. This partnership allowed the generation of conclusive reports for seized substances, providing early warnings about NPS and helping to prevent potential outbreaks and public health crises. Additionally, the strategy facilitated the acquisition of expensive CRS from samples that would otherwise be destroyed, at a reduced cost and within a shorter timeframe. Furthermore, this partnership enhances student training in advanced instrumental analysis and research, showcasing the benefits of collaboration between forensic and academic institutions.

Two new alkaloids, named migenomycin I (1) and II (2), along with nine known compounds (3-11), were isolated from the fungus Rhizopus oryzae from Atractylodes macrocephala Koidz. The structures of compounds 1 and 2 were determined by spectroscopic methods (MS, NMR, and CD). All compounds were isolated from Rhizopus oryzae for the first time. In addition, the antitumor activities of compounds 1 and 2 and the hypoglycemic activities of most compounds were evaluated.

Present review focuses on the most recent advances in the NMR of the coal-derived humic and fulvic acids, covering exclusively the results of the liquid-phase NMR and leaving apart an overwhelming amount of publications dealing with the solid-state NMR investigations in this field (the latter are comprehensively reviewed elsewhere). Owing to the complexity of humic and fulvic acids together with other coal-derived products, their ¹H and ¹³C NMR spectra consist of a number of overlapping signals belonging to different hydrocarbon types. Comprehensive studies of humic and fulvic acids by means of NMR revealed characteristic functional groups of their composition together with spectral regions in which they resonate. Quantitative ¹H and ¹³C NMR spectra characterize aromatic and saturated carbons spread over many structural moieties, which provides a solid guideline into molecular structure of humic and fulvic acids together with parent coal-derived products. Nowadays, quantitative ¹³C NMR measurements yield information about a variety of structural parameters such as functional group distribution, aromaticity, degree of condensation of aromatic rings, and medium chain lengths together with many other more specific parameters. The structural NMR studies of the coal-derived products are developing on a background of a marked progress in experimental and computational NMR. Discussed in the present review are the most recent advances in the liquid-state NMR studies of the coal-derived humic and fulvic acids together with their processing products.

One new monacolin analog, monacolin V (1), together with two new monacolin-like natural products, 6-hydroxyl monacolin P (2) and 3-keto monacolin S (3), were isolated from the ethyl acetate portion of red yeast rice ethanol extract. Their structures were identified by HRESIMS and NMR experiments, and the complete assignments of ¹H and ¹³C NMR data for three compounds were obtained by the aid of HSQC, HMBC, ¹H-¹H COSY, and NOESY data. This is the first time that the NMR data of compounds 2 and 3 have been fully assigned.

Chemical investigation of the Liuweizhiji Gegen-Sangshen oral liquid afforded one new diphenyl ether derivative (1), together with one known compound (2). Their structures were established by 1D and 2D NMR, and HR-ESI-MS spectroscopic analysis and the absolute configuration of 1 was confirmed by ECD calculation. Compounds 1 and 2 were evaluated for the cytotoxic activities, and compounds 1 and 2 showed weak cytotoxic activities towards HepG2 human liver cancer cells, with IC₅₀ values of 97.3 and 79.6 μM, respectively.

In solid-state nuclear magnetic resonance (ssNMR) spectroscopy, fast magic angle spinning (MAS) is a potent technique that efficiently reduces line broadening and makes it possible to probe structural details of biological systems in high resolution. However, its utilization in studying complex heterogeneous biomaterials such as bone in their native state has been limited. The present study has demonstrated the feasibility of acquiring two-dimensional (2D) ¹H-¹H correlation spectra for native bone using multiple-quantum/single-quantum correlation experiments (MQ/SQ) at fast MAS (70 kHz). This method uncovered distinct ¹H-¹H dipolar coupling networks involving long-chain charged residues of collagen protein, highlighting their role in maintaining the stability of the collagen triple helix. Our study opens up new avenues for ¹H-detected multi-quantum-based experiments at fast MAS on native collagen-containing biological systems to explore their complex heterogeneous structural details more efficiently.

The complete ¹H and ¹³C NMR assignments of a trimeric vindoline together with its individual components, dimeric vindolicine and monomeric vindoline, are performed based on a thorough analysis of the ROESY, COSY, HSQC, and HMBC spectra in combination with the state-of-the-art quantum-chemical calculations. A spatial structure of vindoline trimer is determined by means of computational conformational analysis in combination with the probability distribution map of its basic conformers. On the example of monoterpene indole alkaloid, the trimer vindoline, the present study reveals the power of modern computational NMR to perform identification and stereochemical studies of large natural compounds with some limitations, which may arise in the quantum chemical computing workflow.