高效液相色谱－核磁共振联用技术及其应用

高效液相色谱－核磁共振（ＨＰＬＣ－ＮＭＲ）在线联用技术是同时进行未知混合物的分离和结构鉴定的最好手段之一。详细介绍了在ＨＰＬＣ－ＮＭＲ联用技术中１Ｈ谱的分辨率、检测限和多重溶剂峰抑制的最新进展，并简要评述了其它分离方法与ＮＭＲ联用情况     

高效液相色谱－核磁共振联用技术及其应用

高效液相色谱－核共共振在线联用技术是同时进行未知混合物的分离和结构鉴定的量好手段之一。详细介绍了在ＨＰＬＣ－ＮＭＲ联用技术中Ｈ谱的分辨率，检测限手多重溶剂峰抑制的最新进展，并简要评述了其它分离方法与ＮＭＲ联用情况。     

Separation and characterization of alkyl phenol formaldehyde resins demulsifier by adsorption chromatography, gel permeation chromatography, infrared spectrometry and nuclear magnetic resonance spectroscopy

This paper deals with the separation and characterization of alkyl phenol formaldehyde resins demulsifier by infrared spectrometry and nuclear magnetic resonance spectroscopy after separation of the different surfactants and low molecular additives by adsorption chromatography. Firstly, the types of surfactants are identified by methylene blue chloride-chloroform test method and the elemental analysis such as Ca, K, Mg, Na, P, S and N. Then, the different surfactants and low molecular components are separated by adsorption chromatography after parts of low molecular components are dried in an oven, and the molecular weight distribution is measured by gel permeation chromatography also. Finally, the separated surfactants are determined by Fourier transform infrared (FTIR) spectrometry and nuclear magnetic resonance (NMR) spectroscopy. The distortionless enhancement by polarization transfer (DEPT), H, C correlated spectroscopy (H, C-COSY), H, H correlated spectroscopy (H, H-COSY) and heteronuclear multiple-bond correlation (HMBC) spectroscopy are applied to determine the molecular structures.     

Biosurfactants—An Overview

The large structural and functional variety of bio-surfactants (BS), which are produced by microorganisms, leads to the use of several methods to study these amphiphilic molecules. This review seeks to consolidate information on various surface-active product extraction techniques, microbiological screening methodologies, and analytical terminologies utilized in this sector. The potential benefits and drawbacks of various approaches for studying cell biomass or microbial culture broth for the generation of surface-reactive chemicals are also discussed. Additionally, the most popular techniques for detection, structural characterization, and purification of a variety of BS are introduced. A number of straightforward techniques are described in detail, including dialysis, ion exchange, solvent extraction, ultrafiltration, lyophilization, and thin layer chromatography (TLC). In addition to more sophisticated techniques like nuclear magnetic resonance (NMR), fast atom bombardment mass spectroscopy (FAB-MS), gas chromatography-mass spectroscopy (GC-MS), high-pressure liquid chromatography (HPLC), and infrared (IR), proteolysis and sequencing of amino acid are also explained. In this field of study, it is quite necessary to combine several analytical techniques, and it often takes multiple iterations to purify, isolate, and characterize different surface-active substances. The numerous approaches that are essential for researching bio-surfactants are covered in this review.     

The potentiality of NMR-based metabolomics in food science and food authentication assessment

In the last years, there was an increasing interest on nuclear magnetic resonance (NMR) spectroscopy, whose applications experienced an exponential growth in several research fields, particularly in food science. NMR was initially developed as the elective technique for structure elucidation of single molecules and nowadays is playing a dominant role in complex mixtures investigations. In the era of the “omics” techniques, NMR was rapidly enrolled as one of the most powerful methods to approach metabolomics studies. Its use in analytical routines, characterized by rapid and reproducible measurements, would provide the identification of a wide range of chemical compounds simultaneously, disclosing sophisticated frauds or addressing the geographical origin, as well as revealing potential markers for other authentication purposes. The great economic value of high-quality or guaranteed foods demands highly detailed characterization to protect both consumers and producers from frauds. The present scenario suggests metabolomics as the privileged approach of modern analytical studies for the next decades. The large potentiality of high-resolution NMR techniques is here presented through specific applications and using different approaches focused on the authentication process of some foods, like tomato paste, saffron, honey, roasted coffee, and balsamic and traditional balsamic vinegar of Modena, with a particular focus on geographical origin characterization, ageing determination, and fraud detection.     

Microstructural Characterization of Diblock Copolymers Formed by Styrene and Different Methacrylic Units

FT-IR, DSC, and NMR techniques allowed the structural characterization of four copolymers formed by styrene and methacrylic units (methacrylic acid (MAA), dimethylamine ethyl methacrylate (DMAEMA), sodium methacrylate (MANa), and 1-hydroxyethyl methacrylate (HEMA). The copolymer composition was studied by Fourier transform-infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. The thermal behavior of the block copolymers was analyzed by differential scanning calorimetry (DSC). Three of the four copolymers showed two transitions caused by changes in the polymer heat capacity (ΔCp) of each block. Diffusion-ordered spectroscopy (DOSY) experiments were used to distinguish copolymer from homopolymer mixtures. Finally, the triad-level stereosequences of styrene-methacrylic copolymers were obtained using ¹³C NMR. The results indicate that by increasing the alkyl-substituent length in the methacrylic block, the probability of syndiotactic polymerization increases.     

Deep Learning-Based Method for Compound Identification in NMR Spectra of Mixtures

Nuclear magnetic resonance (NMR) spectroscopy is highly unbiased and reproducible, which provides us a powerful tool to analyze mixtures consisting of small molecules. However, the compound identification in NMR spectra of mixtures is highly challenging because of chemical shift variations of the same compound in different mixtures and peak overlapping among molecules. Here, we present a pseudo-Siamese convolutional neural network method (pSCNN) to identify compounds in mixtures for NMR spectroscopy. A data augmentation method was implemented for the superposition of several NMR spectra sampled from a spectral database with random noises. The augmented dataset was split and used to train, validate and test the pSCNN model. Two experimental NMR datasets (flavor mixtures and additional flavor mixture) were acquired to benchmark its performance in real applications. The results show that the proposed method can achieve good performances in the augmented test set (ACC = 99.80%, TPR = 99.70% and FPR = 0.10%), the flavor mixtures dataset (ACC = 97.62%, TPR = 96.44% and FPR = 2.29%) and the additional flavor mixture dataset (ACC = 91.67%, TPR = 100.00% and FPR = 10.53%). We have demonstrated that the translational invariance of convolutional neural networks can solve the chemical shift variation problem in NMR spectra. In summary, pSCNN is an off-the-shelf method to identify compounds in mixtures for NMR spectroscopy because of its accuracy in compound identification and robustness to chemical shift variation.     

Identification and Quantification of Hydrocarbon Functional Groups in Gasoline Using 1H-NMR Spectroscopy for Property Prediction

Gasoline is one of the most important distillate fuels obtained from crude refining; it is mainly used as an automotive fuel to propel spark-ignited (SI) engines. It is a complex hydrocarbon fuel that is known to possess several hundred individual molecules of varying sizes and chemical classes. These large numbers of individual molecules can be assembled into a finite set of molecular moieties or functional groups that can independently represent the chemical composition. Identification and quantification of groups enables the prediction of many fuel properties that otherwise may be difficult and expensive to measure experimentally. In the present work, high resolution ¹H nuclear magnetic resonance (NMR) spectroscopy, an advanced structure elucidation technique, was employed for the molecular characterization of a gasoline sample in order to analyze the functional groups. The chemical composition of the gasoline sample was then expressed using six hydrocarbon functional groups, as follows: paraffinic groups (CH, CH₂ and CH₃), naphthenic CH-CH₂ groups and aromatic C-CH groups. The obtained functional groups were then used to predict a number of fuel properties, including research octane number (RON), motor octane number (MON), derived cetane number (DCN), threshold sooting index (TSI) and yield sooting index (YSI).     

13C nuclear magnetic resonance spectroscopy for determining the different components of epicuticular waxes of olive fruit (Olea europaea) Dritta cultivar

¹³C nuclear magnetic resonance spectroscopy (NMR) was applied to determine the different components of apolar and polar fractions which were isolated by column chromatography from the crude chloroform-soluble waxes of olive fruits (Olea europaea) Dritta cultivar.¹³C NMR enabled the determination in the wax apolar fraction, of aliphatic aldehydes, and of benzyl, alkyl and glyceryl esters. In particular, the fatty acid composition of alkyl esters, comprising saturated and unsaturated oleic and linoleic acids, was determined. Acyl chain composition and the chain composition of 1,3- and 2-glycerol positions were also determined for triacylglycerols of olive fruit waxes.Oleanolic and maslinic acids were confirmed to be the major components of wax polar fraction. Complete assignments of ¹³C NMR chemical shifts of oleanolic and maslinic acids as a mixture were achieved by using homonuclear correlation spectroscopy with gradient (g-COSY), attached proton test (APT), inverse-detected heteronuclear single-quantum coherence with gradient (g-HSQC), high-resolution heteronuclear correlation spectroscopy (HETCOR) for C-H directly attached pairs and C-H long-range-coupled experiments.     

Antineoplastic and Antitrypanosomal Properties of Propolis from Tetragonula biroi Friese

Propolis, popularly known as bee glue, is a resinous, sticky substance produced by different bee species across the globe. Studies on the biological properties of propolis from the Philippines are rare. Hence, the current study aims at the chemical characterization of propolis produced by the stingless bees Tetragonula biroi Friese from the Philippines and to investigate its antitrypanosomal and anticancer properties. The determination of the chemical composition and characterization of propolis samples was achieved using liquid chromatography–mass spectrometry (LC-MS), -high-performance liquid chromatography–evaporative light scattering detector (HPLC-ELSD), and nuclear magnetic resonance (NMR) spectroscopy. Three major triterpenes were isolated and identified using HRESI-MS and ¹H/¹³C NMR techniques. The spectral studies confirmed the presence of compounds such as isomangiferolic acid, 27-hydoxymangiferonic acid, and 27-hydroxyisomangiferolic acid. All crude propolis samples, isolated fractions, and pure compounds demonstrated moderate antitrypanosomal and anticancer properties compared to control drugs. Amongst the tested compounds, 27-hydoxymangiferonic acid exhibited the highest antitrypanosomal activity at a concentration of 11.6 µg/mL. The highest anticancer effect was demonstrated by the Ph-2 fraction, followed by 27-hydroxyisomangiferolic acid, with IC50 values of 129.6 and 153.3 µg/mL. Thus, it can be concluded that the observed biological activity of Philippine propolis is due to the combinatorial effect or synergistic action of the active compounds 27-hydoxymangiferonic acid and 27-hydroxyisomangiferolic acid.     

High Temperature Interaction Chromatography of Olefin Copolymers

Summary: The synthesis and characterization of polyolefins continues to be one of the most important areas for academic and industrial polymer research. One consequence of the development of new “tailor-made” polyolefins is the need for new and improved analytical techniques for the analysis of polyolefins with respect to molar mass and chemical composition distribution. The present article briefly reviews different new and relevant chromatographic techniques for polyolefin analysis. For the fast analysis of the chemical composition distribution of polyolefins a new high-temperature gradient high-performance liquid chromatography (HPLC) system has been introduced. The efficiency of this system for the separation of various olefin copolymers is demonstrated. The correlation between elution volume and chemical composition can be accessed by on-line coupling of high temperature HPLC with FTIR spectroscopy. For the elucidation of the chemical composition as a function of molar mass high-temperature size exclusion chromatography and ¹H-NMR spectroscopy can be coupled. It is shown that the on-line NMR analysis of chromatographic fractions yields information on microstructure and chemical composition in addition to molar mass distribution.     

Thermal stability of P3HT and P3HT:PCBM blends in the molten state

The thermal stability of poly(3-hexylthiophene) (P3HT) in its molten state was investigated in air and nitrogen atmospheres under no illumination conditions, with the aim of testing the feasibility of processing it using polymer melt techniques. A large set of different experimental characterization techniques was used including thermogravimetric analysis (TGA), rotational rheometry, infrared spectroscopy (FTIR-ATR), proton nuclear magnetic resonance spectroscopy (¹H-NMR), gel permeation chromatography (GPC), UV-Vis and fluorescence spectroscopy. The results obtained strongly suggest that the processing of P3HT in its molten state is possible, without noticeable degradation, if carried out under nitrogen atmosphere and if the processing (residence) times are relatively short. Conversely, as expected, in a normal air atmosphere P3HT degrades rapidly at temperatures above its melting point. The effect of PCBM on the thermal stability of P3HT:PCBM blends in the molten state was also studied using TGA, and in air atmosphere PCBM is shown to delay oxidation.     

活泼氢的核磁共振氢谱

核磁共振氢谱是有机化合物结构表征中最常使用的波谱方法之一,提供了有机化合物质子的化学位移、积分面积和耦合裂分等信息。常见的活泼氢是与氧、氮和硫共价相连的氢原子,存在着快速交换机制,与碳上的氢有显著的差异。在不同条件下活泼氢化学位移不固定、峰形多变并且耦合裂分情况复杂。本文探讨了如何通过核磁共振氢谱解析活泼氢,培养学生对谱图进行观察、分析以及结构推导的能力。     

Using one-dimensional (1D) and two-dimensional (2D) quantitative proton (1H) nuclear magnetic resonance spectroscopy (q NMR) for the identification and quantification of taste compounds in raw onion (Allium cepa L.) bulbs and in aqueous solutions where onion tissues are soaked

Solutions obtained by soaking onion (Allium cepa L.) bulbs samples in water are frequently consumed, either directly or as part of dishes, both at home or in the food industry. However, little information is available regarding the extracted metabolites and the extraction mechanisms. In this article, the composition of raw onion extracts and of aqueous solutions where raw onion tissues were soaked was investigated directly by quantitative proton nuclear magnetic resonance spectroscopy (q (1)H NMR). The assignment of NMR signals was performed, with less than 3% (in area) of unidentified peaks. Analyses of one-dimensional (1)H NMR spectra with additional two-dimensional NMR studies showed 20 regions of interest where 3 saccharides, 17 amino acids, and 5 organic acids were detected and quantified. Resonance assignment with chemical shift was done for each saccharide, as well as for each amino acid and organic acid, with additional work on spin-spin coupling pattern and on observed and not observed correlations from correlation spectroscopy studies. Quantification of saccharides was performed and qualified by works on peak decomposition algorithms. Complementary studies by high-performance liquid chromatography, mass spectroscopy and tandem mass spectroscopy, and thin layer chromatography and preparative layer chromatography were carried out in order to validate the NMR results on identification.     

Superlattice of octanethiol-protected copper nanoparticles

The synthesis and spectroscopic characterizations of size-controlled Cu nanoparticles forming self-assembled 2D superlattices with hexagonal packing are described. The scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), thermal gravimetric analysis (TGA), and electron spectroscopy for chemical analysis (ESCA) techniques were used to characterize the octanethiol-protected copper nanoparticles.     

Enzyme-catalyzed reaction of OPD-H_2O_2-HRP voltammetric enzyme-linked immunoassay system

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Characterizing plant cell wall derived oligosaccharides using hydrophilic interaction chromatography with mass spectrometry detection

Analysis of complex mixtures of plant cell wall derived oligosaccharides is still challenging and multiple analytical techniques are often required for separation and characterization of these mixtures. In this work it is demonstrated that hydrophilic interaction chromatography coupled with evaporative light scattering and mass spectrometry detection (HILIC-ELSD-MS(n)) is a valuable tool for identification of a wide range of neutral and acidic cell wall derived oligosaccharides. The separation potential for acidic oligosaccharides observed with HILIC is much better compared to other existing techniques, like capillary electrophoresis, reversed phase and porous-graphitized carbon chromatography. Important structural information, such as presence of methyl esters and acetyl groups, is retained during analysis. Separation of acidic oligosaccharides with equal charge yet with different degrees of polymerization can be obtained. The efficient coupling of HILIC with ELSD and MS(n)-detection enables characterization and quantification of many different oligosaccharide structures present in complex mixtures. This makes HILIC-ELSD-MS(n) a versatile and powerful additional technique in plant cell wall analysis.     

Critical comments on accuracy of quantitative determination of natural humic matter by solid state (13)C NMR spectroscopy

Structural information of natural organic matter (NOM) at the molecular level is very essential in understanding their nature and reactivity. Nuclear magnetic resonance (NMR) is an excellent tool for estimating the gross chemical composition of the very complex humic matter (HM). A well-known fact is that the solid state ¹³C NMR spectral analysis is very parameter-sensitive especially in the study of the heterogenous HM (e.g. baseline corrections, different pulse techniques and spinning rates of the rotor vs. different disruptive sidebands in the spectra). This being the case, it has been emphasized the importance of qualitative and quantitative analyses for generating as real spectra as possible by means of different pulse and polarization techniques, sampling spinning rates as well as certain correction factors. In the present study a practical accuracy for quantitative determination of NOM type material by solid state ¹³C NMR spectroscopy was assessed using a known HM sample. Different magnetic-field strengths, sampling spinning rates, single and ramped amplitude cross polarization techniques and TOSS pulse sequence were applied for obtaining a more reliable insight into the disruptive effect of the chemical shift anisotropy (CSA), especially the most disturbing first order spinning side bands (SSB). The results demonstrated that the SSB problem is not so significant as sometimes stated, at least in the context of HM samples and in the light of the overall reproducibility and uncertainty connected with the sample itself.     

Solid-state NMR spectroscopy of the quadrupolar halogens: chlorine-35/37, bromine-79/81, and iodine-127

A thorough review of 35/37Cl, 79/81Br, and 127I solid-state nuclear magnetic resonance (SSNMR) data is presented. Isotropic chemical shifts (CS), quadrupolar coupling constants, and other available information on the magnitude and orientation of the CS and electric field gradient (EFG) tensors for chlorine, bromine, and iodine in diverse chemical compounds is tabulated on the basis of over 200 references. Our coverage is through July 2005. Special emphasis is placed on the information available from the study of powdered diamagnetic solids in high magnetic fields. Our survey indicates a recent notable increase in the number of applications of solid-state quadrupolar halogen NMR, particularly 35Cl NMR, as high magnetic fields have become more widely available to solid-state NMR spectroscopists. We conclude with an assessment of possible future directions for research involving 35/37Cl, 79/81Br, and 127I solid-state NMR spectroscopy.     

双碳醇水溶液的1H NMR实验与理论分析

In this study, ¹H nuclear magnetic resonance (NMR) measurements and quantum chemistry (QC) studies of ethanol (ET)-water mixtures and ethylene glycol (EG)-water mixtures are carried out at different temperatures to discuss the interactions between water and the alcohols present in the mixtures. From ¹H NMR spectra, it is observed that the chemical shift of the water proton shows two different trends in the ET-water mixtures and the EG-water mixtures. With increasing water concentration, the water proton chemical shift decreases dramatically for ET-water mixtures, while the chemical shift increases slowly for EG-water mixtures. The alcohol hydroxyl proton resonance peaks of both ET and EG shift to lower field with decreasing water concentration. It is found that the resonance peaks of all alkyl protons shift monotonically to low field with increasing alcohol concentration at different temperatures. The geometry optimization results indicate the formation of H-bonds between the water molecules and the hydroxyl groups of the alcohols alongside the weakening of O-H bonds in the alcohols, which results in an O-H bond length decrease. It is interesting to note that the bond length values computed for C-C, C-H and O-H bond in both ET and EG are larger when calculated at the density functional theory (DFT) (B3LYP) level than when calculated using Hartree-Fock (HF) level of theory with the same polarization function and diffusion function. However, the O-H…O H-bond computed at HF level of theory is stronger than that calculated at DFT level of theory. The theoretical results are in good agreement with the experimental ones. In the calculation of NMR chemical shift, DFT(B3LYP) is better than HF, which implies that for the same method, the larger the basis sets are, the more accurate are the calculated values.