利用^(1)H NMR测定姜中姜辣素与姜黄素

该研究采用核磁共振氢谱(proton nuclear magnetic resonance,^(1)H NMR)技术对冻干生姜与烘干生姜中的姜辣素和姜黄素类化合物的变化进行定性定量分析,发现姜中姜辣素提取物主要包括6-姜酚、8-姜酚、10-姜酚等姜酚类物质以及少量姜烯酚。经过烘干处理后,总姜酚的含量由(1.5±0.3)mg/g降低至(0.89±0.06)mg/g(鲜重),总姜辣素的含量由(2.3±0.4)mg/g降低至(1.4±0.1)mg/g,6-姜烯酚的含量由(4.8×10^(-3)±2.7×10^(-3))mg/g升高至(0.0209±0.0004)mg/g。烘干后姜黄素类化合物的含量由(4.4±0.2)mg/100 g降低至(1.5±0.6)mg/100 g,香草醛的含量由(1.20±0.07)mg/100 g升高至(1.87±0.01)mg/100 g,说明热处理会导致生姜中的姜辣素与姜黄素类化合物降解,姜酚类物质向姜烯酚转化。该试验结果为研究姜中姜辣素与姜黄素类化合物的变化机理以及姜制品的生产与工艺优化提供了参考。

All-atom Molecular Dynamic Simulations and NMR Spectra Study on Intermolecular Interactions of N,N-dimethylacetamide-Water System

N,N-dimethylacetamide （DMA） has been investigated extensively in studying models of peptide bonds. An all-atom MD simulation and the NMR spectra were performed to investigate the interactions in the DMA- water system. The radial distribution functions （RDFs） and the hydrogen-bonding network were used in MD simulations. There are strong hydrogen bonds and weak C-H…O contacts in the mixtures, as shown by the analysis of the RDFs. The insight structures in the DMA-water mixtures can be classified into different regions by the analysis of the hydrogen-bonding network. Chemical shifts of the hydrogen atom of water molecule with concentration and temperatures are adopted to study the interactions in the mixtures. The results of NMR spectra show good agreement with the statistical results of hydrogen bonds in MD simulations.

烟草果胶和纤维素含量^(13)C MultiCP/MAS NMR同时测量

果胶和纤维素是烟草细胞壁的重要组成成分,其含量对烟草品质与安全性产生重要影响。传统分析方法难以实现果胶和纤维素的同时定量。本文在优化核磁共振波谱序列条件的基础上,采用固体^(13)C多重交叉极化/魔角旋转核磁共振波谱分析技术(^(13)C MultiCP/MAS NMR)建立了烟草果胶和纤维素含量的同时测量新方法。方法以聚半乳糖醛酸和微晶纤维素为标准物质,以3-(三甲基甲硅烷基)丙酸-d4钠盐(TMSP)做为内标物质,分别建立内标法标准曲线,相关系数R2为0.999 0和0.998 2。果胶测量的检出限和定量限分别为0.38和1.28 mg·g^(–1),精密度(RSD,n=5)小于3.05%。纤维素测量的检出限和定量限为1.01和3.32 mg·g^(–1),精密度(RSD,n=5)小于2.74%。应用本方法测量烟梗、烟草薄片和烟叶等不同类型样品中的果胶和纤维素含量,并对比烟草行业标准方法的测量结果,果胶含量的相对误差在-0.95%至4.51%之间,纤维素含量的相对误差在0.77%至2.46%之间。表明^(13)C MultiCP/MAS NMR方法快速,准确,适合批量样品的分析测量,为果胶和纤维素等细胞壁类大分子的同时定量分析提供重要技术支持。

Postmortem ^(7)Li NMR analysis for assessing the reversibility of lithium metal electrodes in lithium metal batteries

Despite the proficiency of lithium(Li)-7 NMR spectroscopy in delineating the physical and chemical states of Li metal electrodes,challenges in specimen preparation and interpretation impede its progress.In this study,we conducted a comprehensive postmortem analysis utilizing ^(7)Li NMR,employing a stan-dard magic angle spinning probe to examine protective-layer coated Li metal electrodes and LiAg alloy electrodes against bare Li metal electrodes within Li metal batteries(LMBs).Our investigation explores the effects of sample burrs,alignment with the magnetic field,the existence of liquid electrolytes,and precycling on the ^(7)Li NMR signals.Through contrasting NMR spectra before and after cycling,we identi-fied alterations in Li^(0) and Li^(+) signals attributable to the degradation of the Li metal electrode.Our NMR analyses decisively demonstrate the efficacy of the protective layer in mitigating dendrite and solid elec-trolyte interphase formation.Moreover,we noted that Li*ions near the Li metal surface exhibit magnetic susceptibility anisotropy,revealing a novel approach to studying diamagnetic species on Li metal elec-trodes in LMBs.This study provides valuable insights and practical guidelines for characterizing distinct lithium states within LMBs.

Unveiling structural and dynamical features of chromatin using NMR spectroscopy This article is part of the virtual special issue“Solid-state NMR studies on polymers and biological solids”

Eukaryotic deoxyribonucleic acid(DNA)is wrapped around histone octamers(HOs)to form nucleosome core particles(NCPs),which in turn interact with linker DNA and linker histones to assemble chromatin fibers with more complex,high-order structures.The molecular properties of chromatin are dynamically regulated by several factors,such as post-translational modifications and effector proteins,to maintain genome stability.In the past two decades,high-resolution techniques have led to many breakthroughs in understanding the molecular mechanisms that govern chromatin regulation.Nuclear magnetic resonance(NMR)has emerged as one of the major techniques in this field,providing new insights into the nucleosomes and nucleosome-protein complexes in different states ranging from soluble form to condensed states.Solution-state NMR has proven valuable in elucidating the conformational dynamics and molecular interactions for histone N-terminal tails,histone core regions and DNA with the combination of specific isotopic labeling.Solid-state NMR,which is not constrained by the high molecular weights of complexes like nucleosomes,has been applied to capture the structural and dynamical characteristics of both flexible tails and rigid histone core regions in nucleosomes and their complexes with effector proteins.Furthermore,the combination of the two techniques allows tracking molecular properties of nucleosomes during phase separation processes,which potentially play essential roles in chromatin regulation.This review summarizes recent advances in NMR studies of chromatin structure and dynamics.It highlighted that NMR revealed unique molecular characteristics for nucleosomes that are often invisible experimentally by other techniques like cryogenic electron microscopy(cryo-EM)and X-ray diffraction(XRD).I envision that,with future ef-forts such as the development of NMR methods and optimization of sample production protocols,solution-state NMR and solid-state NMR will provide invaluable information to expand our understanding of chromatin activity and its regulatory processes.

Solid-state NMR of vulcanized natural rubber/butadiene rubber blends:Local organization and cross-linking heterogeneities This article is part of the virtual special issue“Solid-state NMR studies on polymers and biological solids”

Elastomer blends,among which natural rubber(NR)and butadiene rubber(BR),are involved in many components of the automotive/tire industry.A comprehensive understanding of their mechanical behavior requires,among other features,a detailed description of the crosslink density in these mixtures.In the case of vulcanized immiscible blends,the distribution of the cross-link density within each of the NR-and BR-rich domains is key information,but difficult to determine using the conventional approaches used for one-component crosslinked elastomers.In this study,the vulcanization within NR/BR blends is investigated using a robust^(1)H double-quantum(DQ)MAS recoupling experiment,BaBa-xy16.Two kinds of cross-linked NR/BR blends were considered with two different microstructures for the BR component.The bulk organization of the resulting blends was first probed by analyzing the^(1)H spin-lattice relaxation behavior.In a second step,BaBa-xy16 was used to investigate,in a selective way,the cross-link heterogeneities within NR/BR blends.In particular,for immiscible NR/BR mixtures,the distribution of the cross-link density between both phases was compared and the observed differences were discussed.

Unexpected temperature dependence of^(1)H paramagnetic shift in MAS NMR of nickelocene

This work revisits the temperature dependence of^(1)H paramagnetic shift in nickelocene as a potential nuclear magnetic resonance(NMR)thermometer under fast magic angle spinning(MAS)rate.Surprisingly,an abnormal temperature dependence of^(1)H paramagnetic shift has been observed.In addition to a 1/T dependence term,a 1/T^(2)dependence term must be included to correctly describe the curvature behavior of the δ^(1)H-T correlation under fast MAS rate.

Application of NMR Relaxometry to Study Nanostructured Poly(vinyl alcohol)/MMT/Cephalexin Materials for Use in Drug Delivery Systems

Polymers containing nanoparticles dispersed and distributed in the matrix can be used for control of drug release. In this work, hydrophilic matrix systems were prepared using poly(vinyl alcohol) and unmodified clay containing the same amount of cephalexin. The materials were obtained through in situ polymerization and were characterized by the conventional technique of FTIR and NMR relaxometry, through determination of proton spin-lattice relaxation time, in order to understand the molecular behavior of the new materials. The NMR relaxometry data showed that the new materials containing low quantities of clay (0.25% and 0.75%) and the same amount of cephalexin (0.5 g) had very good dispersion and distribution of the clay and drug in the polymer matrix. The combination of clay and cephalexin formed a more homogenous material with a narrow domain curve and low relaxation values. The material containing 0.25% clay presented a mixed morphology, with part exfoliated and part intercalated, as could be seen from the relaxation domain distribution, which was larger than that for material with 0.75% clay.

Operando NMR methods for studying electrocatalysis

The combination of electrochemical measurements with spectroscopic characterizations provides valuable insights into reaction mechanisms.Nuclear magnetic resonance(NMR)spectroscopy,as a powerful technique due to its atomic specificity and versatility in studying gas,liquid,and solid,allows the study of electrolyte solution,catalyst and catalyst-adsorbate interfaces.When applied in operando,NMR can offer molecular-level insights into various electrochemical processes.Operando NMR has been applied extensively in battery research,but relatively underexplored for electrocatalysis in the past two decades.In this mini review,we first introduce the operando electrochemical NMR setups,categorized by different probe designs.Then we review the applications of operando NMR for monitoring the electrolyte solution and the catalyst-adsorbate interface.Considering the high environmental impact of electrochemical conversion of CO_(2)into value-added products,we zoom in to the use of operando NMR in studying electrochemical CO_(2)reduction.Finally,we provide our perspective on further developing and applying operando NMR methods for understanding the complex reaction network of Cu-catalyzed electrochemical CO_(2)reduction.

Structural analysis of silk using solid-state NMR

Silkworms and spiders are capable of generating fibers that are both highly durable and elastic in a short span of time,using a silk solution stored within their bodies at room temperature and normal atmospheric pressure.The dragline silk fiber,which is essentially a spider's lifeline,surpasses the strength of a steel wire of equivalent thickness.Regrettably,humans have yet to replicate this process to produce fibers with similar high strength and elasticity in an eco-friendly manner.Therefore,it is of utmost importance to thoroughly comprehend the extraordinary structure and fibrillation mechanism of silk,and leverage this understanding in the manufacturing of high-strength,high-elasticity fibers.This review will delve into the recent progress in comprehending the structure of silks derived from silkworms and spiders,emphasizing the distinctive attributes of solidstate NMR.

Structure and ion transport properties of organic ionic compounds revealed by NMR

Organic ionic plastic crystals(OIPCs)are emerging as an important material family for solid-state electrolytes and many other applications.They have significant advantages over conventional electrolyte materials,such as high ionic conductivity,non-flammability,and plasticity.Various nuclear magnetic resonance(NMR)spectroscopy techniques including solid-state NMR,pulsed-field gradient(PFG)NMR,and magnetic resonance imaging(MRI)etc.,provide us a versatile toolkit to understand the fundamental level structures,molecular dynamics,and ionic interactions in these materials.This article reviews the commonly used NMR methods including solid-and solution-state NMR,PFG-NMR,dynamic nuclear polarization(DNP)and the application of these methods in revealing the microscopic level structures and ion-transport mechanisms in OIPC materials.

Solid-state NMR of the retinal protonated Schiff base in microbial rhodopsins

Rhodopsin is a seven-helical transmembrane protein with a retinal chromophore covalently bound to a conserved lysine in helix G via a retinal protonated Schiff base(RPSB).Microbial rhodopsins absorb light through chromophore and play a fundamental role in optogenetics.Numerous microbial rhodopsins have been discovered,contributing to diverse functions and colors.Solid-state NMR spectroscopy has been instrumental in elucidating the conformation of chromophores and the three-dimensional structure of microbial rhodopsins.This review focuses on the 15N chemical shift values of RPSB and summarizes recent progress in the field.We displayed the correlation between the 15N isotropic chemical shift values of RPSB and the maximum absorption wavelength of rhodopsin using solid-state NMR spectroscopy.

A study on the temperature sensitivity of NMR porosity in porous media based on the intensity of magnetization Dedicated to the special issue “Magnetic Resonance in Porous Media”

The measurement of nuclear magnetic resonance(NMR)porosity is affected by temperature.Without considering the impact of NMR logging tools,this phenomenon is mainly caused by variations in magnetization intensity of the measured system due to temperature fluctuations and difference between the temperature of the porous medium and calibration sample.In this study,the effect of temperature was explained based on the thermodynamic theory,and the rules of NMR porosity responses to temperature changes were identified through core physics experiments.In addition,a method for correcting the influence of temperature on NMR porosity measurement was proposed,and the possible factors that may affect its application were also discussed.

Structural Elucidation of the Polymeric Condensed Tannins of Acacia nilotica Subspecies by ^(13)C NMR, MALDI-TOF and TMA as Sources of Bioadhesives

Tannin was extracted from different subspecies of Acacia nilotica,Acacia nilotica nilotica(Ann),Acacia nilotica tomentosa(Ant)and Acacia nilotica adansonii(Ana).The aim was to elucidate their structure and evaluate their reactivity as bioadhesives in the wood industry.The extracts were prepared by hot water extraction(90°C tem-perature).Their gel time with paraformaldehyde was used atfirst to compare their reactivity.The tannin contents and the percentage of total polyphenolic materials in different solutions of the extracts spray dried powder were determined by the hide powder method.Concentrated solutions(47%)were tested by both MALDI ToF,13CNMR.The thermomechanical analysis(TMA)was performed to evaluate their modulus of elasticity(MOE)at different pHs.The gel times of all the three tannin extracts showed that their reactivity and it was com-parable to other known procyanidin/prodelphinidin tannin extract types.Ana,Ann and Ant showed highest per-cent of total polyphenolic materials at 70%,64%,and 57%,respectively.The 13CNMR spectra showed that the three subspecies of condensed tannins were mainly constituted of procyanidins(PC)and prodelphinidins(PD)in slightly different ratios.Ann(56.5%PC and 43.4%PD),Ant(57%PC and 43%PD)and Ana(58%PC and 42%PD).MALDI–TOF spectra showed the presence offlavonoid monomers,and oligomers some of which linked to short carbohydrates monomers or dimers.TMA revealed that the three types of tannins had high MOE at their initial pH(5).

Facile identification of fluorosurfactant category in aqueous film-forming foam concentrates via optimized^(19)F NMR

Aqueous film-forming foams(AFFFs)are the primary source of toxic perfluoroalkyl and polyfluoroalkyl substances(PFAS)in wastewater.Thus,it is urgent to develop a facile and fast method for identifying fluorosurfactants in commercially available AFFFs.In this work,fluorine nuclear magnetic resonance(^(19)F NMR)spectroscopy was optimized to measure AFFFs directly with the extra addition of 5%D_(2)O as the locking reagent,and high-quality spectra could be acquired within 4 min(0.1%fluorosurfactant content).Recovery experiments demonstrated that the use of different AFFFs had no marked influence on the quantitative analysis of fluorosurfactants.Such method works with low-field NMR spectroscopy(1.4 T)as well.Two-dimensional(2D)^(19)F COSY NMR was used to make signal assignments for different fluorosurfactant derivatives.The optimized ^(19)F NMR could quantify the commercially available fluorosurfactants in different AFFFs,identify them being in either the perfluorooctane sulfonate(PFOS)or fluorotelomer sulfonic acid(FTS)categories,and distinguish the head-group of PFOS and FTS derivatives,which exhibits great potentials in the developments of relevant commercial detections.

^(13)C NMR、FT-IR、Raman和建模技术对烟煤和无烟煤分子结构的应用研究

【目的】探究高精度煤的结构演化及其机理的定量表征。【方法】通过显微组分鉴定、镜质体反射率、工业品质、元素分析和光谱分析,确定了烟煤(FS1)和无烟煤(ZY1)碳骨架结构、官能团的赋存状态等信息,并通过计算机辅助分子设计建立2个分子结构模型。【结果】结果表明,随着煤化作用的进行,烟煤到无烟煤过程中,亚甲基的损失速率比甲基的损失速率快,芳香性增强,芳香环的脂肪族链变短且支化度较高,含氧官能团逐渐减少,煤结晶程度增强,煤的化学结构趋于成熟稳定,且煤中的脂肪碳减少,芳香碳增加,甲基碳和亚甲基碳含量减少。经过多次尝试确定了芳香炭、脂肪族侧链和氧官能团之间的键合模式,获得最终的分子结构模型:C_(175)H_(162)O_(13)N_(2)(FS1)、C_(190)H_(159)O_(5)N_(3)(ZY1).该模型较好地反映煤的真实结构,模拟的^(13)C NMR光谱与实验光谱具有良好的一致性。上述研究为不同变质程度煤的分子结构演化提供了理论参考,为建立高可信度的分子结构表征提供了方法。

Matrix Assisted Laser Desorption Ionization Time of Flight(MALDI-TOF)-Mass Spectrometry and^(13)C-NMR-Identified New Compounds in Paraberlinia bifoliolata(Ekop-Beli)Bark Tannins

Extracts of plant origin,particularly tannins,are attracting growing interest for the sustainable development of materials in the industrial sector.The discovery of new tannins is therefore necessary.The aim of this work was to contribute to the understanding of the properties of Paraberlinia bifoliolata tannin by Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectroscopy MALDI-TOF/MS and Carbon 13 Nuclear Magnetic Resonance(13C NMR).The chemical composition of tannin extracted from Paraberlinia bifoliolata bark was determined,as was the mechanical strength of the resin hardened with Acacia nilotica extracts.Yield by successive water extraction was 35%.MALDI-TOF/MS analysis revealed the presence of three new compounds in this tannin,previously unknown in this family of extracts.These are 3-hydroxyproline acid,N-methyl-4-hydroxypipecolic acid and N-methyl-5-dihydroxypipecolic acid.The identification of the above molecules means that this tannin can be used for industrial applications,as a resin in the manufacture of particleboard and in the formulation of green corrosion inhibitors.This information is reinforced by 13C NMR spectrometry,which indicates the presence of several polyflavonoid units,confirming the condensed nature of the tannin.Thermomechanical analysis of the resin formed by the purified tannin of Paraberlinia bifoliolata to which a vegetal biohardener has been added provided a Modulus of Elasticity(MOE)value of 4840 MPa at 150℃,confirming its possible use as a binder resin in the manufacture of wood panels as well as for the formulation of a corrosion inhibitor.

Enantiodifferentiation of chiral diols and diphenols via recognition-enabled chromatographic^(19)F NMR

A novel and efficient method for distinguishing between chiral diols and diphenols has been established through the use of^(19)F NMR spectroscopy.Central to this system's efficacy is a chiral amine,strategically modified with a CF_(3)group.This amine reacts in-situ with 2-formylphenylboronic acid to create a chiral^(19)F-labeled probe.This probe demonstrates discriminatory capabilities by interacting with hydroxy-containing analytes to form boronic esters.These esters produce distinct^(19)F NMR signals that vary according to their stereoconfiguration,facilitating accurate chiral differentiation.The method's resolution capacity was demonstrated by successfully identifying 12 distinct chiral analytes(six pairs of enantiomers)in complex mixtures,highlighting its extensive potential in diverse chiral analysis applications.

Molecular structure characterization of middle-high rank coal via^(13)C NMR,XPS,and FTIR spectroscopy

Elemental analysis,nuclear magnetic resonance carbon spectroscopy(^(13)C-NMR),X-ray photoelectron spectroscopy(XPS)and Fourier transform infrared spectroscopy(FTIR)experiments were carried out to determine the existence of aromatic structure,heteroatom structure and fat structure in coal.MS(materials studio)software was used to optimize and construct a 3D molecular structure model of coal.A method for establishing a coal molecular structure model was formed,which was“determination of key structures in coal,construction of planar molecular structure model,and optimization of three-dimensional molecular structure model”.The structural differences were compared and analyzed.The results show that with the increase of coal rank,the dehydrogenation of cycloalkanes in coal is continuously enhanced,and the content of heteroatoms in the aromatic ring decreases.The heteroatoms and branch chains in the coal are reduced,and the structure is more orderly and tight.The stability of the structure is determined by theπ-πinteraction between the aromatic rings in the nonbonding energy EN.Key Stretching Energy The size of EB determines how tight the structure is.The research results provide a method and reference for the study of the molecular structure of medium and high coal ranks.

Fluid identification and tight oil layer classification for the southwestern Mahu Sag,Junggar Basin using NMR logging-based spectrum decomposition

The intricate distribution of oil and water in tight rocks makes pinpointing oil layers challenging.While conventional identification methods offer potential solutions,their limited accuracy precludes them from being effective in their applications to unconventional reservoirs.This study employed nuclear magnetic resonance(NMR)spectrum decomposition to dissect the NMR T_(2)spectrum into multiple subspectra.Furthermore,it employed laboratory NMR experiments to ascertain the fluid properties of these sub-spectra,aiming to enhance identification accuracy.The findings indicate that fluids of distinct properties overlap in the T_(2)spectra,with bound water,movable water,bound oil,and movable oil appearing sequentially from the low-value zone to the high-value zone.Consequently,an oil layer classification scheme was proposed,which considers the physical properties of reservoirs,oil-bearing capacity,and the characteristics of both mobility and the oil-water two-phase flow.When applied to tight oil layer identification,the scheme's outcomes align closely with actual test results.A horizontal well,deployed based on these findings,has produced high-yield industrial oil flow,underscoring the precision and dependability of this new approach.