Background: As one of the most important economic crops, tobacco products have a long history and dominate the development of the world economy. Pectin, as a complex colloidal substance widely present in plant cell walls, its content is an important factor affecting the safety of tobacco smoking. Objective: This study aimed to analyze the content and structure of pectin in tobacco samples. Methods: In this study, tobacco pectin was extracted by ultrasonic-assisted ionic liquid extraction, and the 13C MultiCP/MAS NMR spectral analysis of pectin was conducted. Results: The type of extractant, duration of ultrasonication, extraction temperature, and solid-liquid ratio were optimized. Under the conditions of using 1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) as the extractant, the solid-liquid ratio of 1:20 g/mL, and the ultrasonic power of 600 w for 30 min at 30°C, the yield of 23.7% of tobacco stem pectin and the purity of 54.2% could be obtained. The optimized MultiCP sequence parameters, with 10 CP cycles of 1.0 ms and the repolarization time of 50 ms could obtain high-resolution spectra within a time of 1.0 h. The C-6 peaks of the pectin in spectra were fitted using the spectral deconvolution technique and calculated the methylesterification (DM) of the tobacco pectin, which was generally less than 50% and belonged to the low methyl esterification pectin. The pectin content of the tobacco sample was calculated using the standard curve method with the addition of dimethyl sulfone (DMS) as an internal reference. The results of this method were consistent with the colorimetric method. Conclusion: The 13C MultiCP/MAS NMR method has the advantages of being green, fast, and accurate and provides a new technical tool for quantitative and qualitative studies of cell wall substances in tobacco samples.
Layered metal hydroxides can be exfoliated into functional nanosheets via solvent intercalation, yet probing the atomic-level solvation processes remains challenging. Herein, we employ 79/81 Br solid-state nuclear magnetic resonance (SSNMR) spectroscopy to directly probe the local environments of interlayer anions in bromide-intercalated layered yttrium hydroxide (LYH-Br). Upon treatment with a series of solvents of varying polarity, the overall spectral lineshapes remain largely unchanged in weakly interacting systems (toluene (PhMe), acetone (ACE), isopropanol (IPA)), indicating preservation of the local structural framework. Increasing solvent polarity leads to a reduction in 79 Br NMR signal intensity, particularly in the case of formamide (FM). By combining complementary characterization techniques and transverse relaxation analysis, we show that this signal attenuation originates from shortened T 2 relaxation times rather than structural degradation. These results reveal that polar solvent intercalation perturbs the local dynamics and solvation environment of interlayer Br − anions. Furthermore, solvent-induced effects are largely reversible for PhMe, ACE, IPA and N, N-dimethylformamide (DMF) upon vacuum drying, whereas FM remains trapped within the interlayer spaces, illustrating stronger host-guest interactions and altered local dynamics. This work demonstrates solid-state 79/81 Br NMR as a powerful tool for directly distinguishing solvation-driven intercalation mechanisms in layered materials.
A machine learning methodology using deep neural network (DNN) for interpreting multidimensional solid-state nuclear magnetic resonance (SSNMR) of various synthetic and natural polymers is presented. The separated local field (SLF) SSNMR which correlates local well-defined heteronuclear dipolar with the tensor orientation of the chemical shift anisotropy (CSA) of spin in the solid state can provide valuable structure and molecular dynamics information of synthetic and biopolymers. Compared with the traditional linear least-square fitting, the proposed DNN-based methodology can efficiently and accurately determine the tensor orientation of CSA of both 13 C and 15 N in all four samples. The method achieves prediction precisions of the Euler angles with < ±5° and is characterized by low training costs and high efficiency (<1 s). The feasibility and robustness of the DNN-based analysis methodology are confirmed by comparison to reported-literature values. This strategy is expected to aid in the interpretation of complex multidimensional NMR spectra of complicated polymer system.
危险品化学品经营许可证（带存储）