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Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for identifying the various allomorphs of cellulose, for example quantifying the proportions of cellulose Iα and Iβ allomorphs in the crystalline domains of various native celluloses. While marine invertebrate animals known as tunicates produce nearly pure cellulose Iβ, solid-state NMR reveals that bacterial cellulose is dominated by the Iα allomorph, but also has additional signals arising from a secondary crystalline form that are normally attributed to cellulose Iβ. However, in this paper we show that the 13C chemical shifts and correlation patterns in 2D NMR spectra for this secondary crystalline form in bacterial cellulose are not the same as those found in cellulose Iβ spectra reported for tunicate cellulose. In order to reach this conclusion, it was necessary to ensure all spectra were correctly set to the same chemical shift scale. In doing so, it became apparent there were spectral features for bacterial cellulose that were entirely consistent with previously reported spectra of bacterial cellulose but did not match those of the Iβ allomorph found in tunicate cellulose. Through a careful and detailed analysis of the 1D and 2D NMR spectra of three 13C-enriched bacterial cellulose samples, two sets of correlated 13C chemical shifts for this secondary crystalline form were identified. The fact that these chemical shifts and correlation patterns are different than those of tunicate cellulose suggests that there exists some sort of structural variation from the Iβ allomorph in bacterial cellulose since the 13C NMR spectrum closely resembles, but is not identical to, the 13C spectrum of the Iβ allomorph found in tunicate cellulose. [ABSTRACT FROM AUTHOR]

In this study, we subjected 5,5-diethoxy-4-oxopent-2-enal (DOPE), a model amino acids cross-linking reagent, to reactions with N-acetylcysteine (Ac-Cys) and Nα-acetyllysine (Ac-Lys), and identified three pyrrole cross-links. The compounds were isolated and their structures were rigorously determined by spectrometric and spectroscopic methods, including 2D NMR experiments. The use of 2D NMR spectroscopy was crucial to determine the position of the substituents in the pyrrole rings. The products were identified as 2,4-, 2,3-, and 2,5-substituted pyrroles. The data obtained from their structural characterisation can help similar studies on amino acids modifications induced by analogous bifunctional carbonyl compounds. Our results show that the study of pathways in which model electrophiles modify amino acids may be helpful for similar studies dealing with identification of structural changes in cysteine- and lysine-containing proteins associated with oxidative stress. [ABSTRACT FROM AUTHOR]

Lignin is considered a promising renewable source of valuable chemical compounds and a feedstock for the production of various materials. Its suitability for certain directions of processing is determined by the chemical structure of its macromolecules. Its formation depends on botanical origin, isolation procedure and other factors. Due to the complexity of the chemical composition, revealing the structural differences between lignins of various origins is a challenging task and requires the use of the most informative methods for obtaining and processing data. In the present study, a combination of two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy and multivariate analysis of heteronuclear single quantum coherence (HSQC) spectra is proposed. Principal component analysis and hierarchical cluster analysis techniques demonstrated the possibility to effectively classify lignins at the level of belonging to classes and families of plants, and in some cases individual species, with an error rate for data classification of 2.3%. The reverse transformation of loading plots into the corresponding HSQC loading spectra allowed for structural information to be obtained about the latent components of lignins and their structural fragments (biomarkers) responsible for certain differences. As a result of the analysis of 34 coniferous, deciduous, and herbaceous lignins, 10 groups of key substructures were established. In addition to syringyl, guaiacyl, and p-hydroxyphenyl monomeric units, they include various terminal substructures: dihydroconiferyl alcohol, balanopholin, cinnamic acids, and tricin. It was shown that, in some cases, the substructures formed during the partial destruction of biopolymer macromolecules also have a significant effect on the classification of lignins of various origins. [ABSTRACT FROM AUTHOR]

Two forms were found in the NMR spectra of N6-substituted 2-chloroadenosines. The proportion of the mini-form was 11–32% of the main form. It was characterized by a separate set of signals in COSY, 15N-HMBC and other NMR spectra. We assumed that the mini-form arises due to the formation of an intramolecular hydrogen bond between the N7 atom of purine and the N6–CH proton of the substituent. The 1H,15N-HMBC spectrum confirmed the presence of a hydrogen bond in the mini-form of the nucleoside and its absence in the main form. Compounds incapable of forming such a hydrogen bond were synthesized. In these compounds, either the N7 atom of the purine or the N6–CH proton of the substituent was absent. The mini-form was not found in the NMR spectra of these nucleosides, confirming the importance of the intramolecular hydrogen bond in its formation. [ABSTRACT FROM AUTHOR]

Life found various ways to thrive in hostile desert environments. Common adaptation mechanisms are protection against desiccation and UV radiation in biofilms and biocrusts as well as the hypolithic and endolithic colonization of rocks. One of those hostile regions is the Atacama Desert in Northern Chile with its hyperarid core, counted among the most arid places on Earth. Besides the aridity, life faces severe restrictions in these surroundings, e.g. extremely high UV radiation, scarce nutrient supply, and immense salt concentrations. Still, microbial communities and soil organic matter are crucial for the stability of soils and surface sediments in arid ecosystems. Combining molecular mass spectrometry for lipid biomarkers, scanning electron microscopy, and nuclear magnetic resonance spectroscopy, we individually investigated two factors that are of particular importance for the stability of dryland landscapes now and in the future: 1) We studied biogeochemical traces (organic remnants) in surface sediments along an aridity gradient with regard to possible decomposition and/or sequestration of organic compounds. 2) We investigated the interaction of lithobiontic and endolithic microbial communities with the mineral surface with special regard to the stability of soil and surface sediment structures in different areas of the Atacama Desert: in the region of the Salar Grande, Pisagua, and the Quebrada da Aroma. We analyzed halite- and calcium sulfate-dominated evaporitic crusts with and without visible microbial colonization. Organic traces were present in all investigated samples. Following an aridity gradient along the Quebrada de Aroma from an annual precipitation of about 20 mm to the hyperarid core with approx. 2 mm, we found a decrease in functionalized molecular compounds and plant-derived biomarkers (long-chain fatty acids, sterols) as well as an increase in aromatic hydrocarbons, indicating strongly decomposed remnants of plants and microorganisms. The investigation of halite- and calcium sulfate-dominated evaporitic crusts from the Salar Grande, Pisagua, and Aroma region revealed tight interactions of microorganisms with the mineral substrate. Indications of recent bacterial activity were ubiquitous (e.g. short-chain membrane fatty acids, carbohydrates of extracellular polymeric substances (EPS)). Scanning electron microscopy revealed that especially the microbial EPS within evaporites seems to biochemically stabilize mineral aggregates by agglutination. Moreover, fungal biomarkers showed that fungi and fungal parts of lichen were not only present at the surface of physical soil crusts but form widespread networks in the crusts and thereby contribute significantly to the physical stabilization of soils and surface sediments and erosion protection. • Traces of endolithic and hypolithic life are widespread in the hyperarid core of the Atacama Desert • Increasing aridity is reflected in a decreasing presence of organic matter and a relative increase in aromatic compounds • Microbial stabilization mechanisms (fungal hyphae networks, EPS) are also active under hyperarid conditions [ABSTRACT FROM AUTHOR]

An isocyanate-terminated hyperbranched polymer (HBI) was successfully synthesized by reacting hyperbranched polyester (BoltornTM HB-20) with isophorone diisocyanate (IPDI). Gel permeation chromatography (GPC) was used to monitor the molecular weight and its distribution changes during the synthesis. The structure and composition of IPDI were characterized by 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. The structure of HBI was confirmed by one-dimensional 1H, 13C NMR, and distortionless enhancement by polarization transfer (DEPT) NMR spectroscopy as well as two-dimensional heteronuclear multiple bond coherence (2D-HMBC) and heteronuclear single quantum coherence (HSQC) NMR spectroscopy. Furthermore, HBI was reacted with methoxypolyethylene glycols (MPEG) to obtain a water-dispersible polyisocyanate with hyperbranched structure. [ABSTRACT FROM AUTHOR]

Calibration transfer is commonly used for spectra obtained on different spectrometers or other conditions. This paper reports a multivariate transfer approach for 2D diffusion‐ordered spectroscopy (DOSY) measurements among high‐resolution nuclear magnetic resonance (NMR) spectrometers on the basis of partial least squares (PLS) regression. As the test system previously published quantitative model to predict molecular weight of heparin, low molecular weight heparin (LMWH) was used. For multivariate modeling, piecewise direct standardization (PDS) and direct standardization (DS) were employed. PDS showed the best performance for estimating heparin molecular weight resulting in a significant decrease in root mean square error of prediction (RMSEP) from 647 and 393 Da without standardization to 513 and 135 Da when PDS was applied for heparin and LMWH, respectively. DS is not recommended for high‐resolution NMR data. The study showed the success of standardization procedure in cases when multivariate models have to be applied to the 2D NMR spectra recorded on different NMR spectrometers. The proposed approach appears to be a valuable achievement towards application of transfer models also to 2D NMR data. A problem of data standardization exist, when multivariate model has to be applied to the 2D spectra recorded on a secondary NMR spectrometer. Piecewise direct standardization (PDS) successfully performed PLS calibration transfer between NMR devices with different configuration regarding quantitative assessment of heparin molecular weight. [ABSTRACT FROM AUTHOR]

Innovative processes for converting carbohydrates to materials and fuels form the basis for profitable bio-based economies of the future. For such innovation, approaches that provide detailed structural information would be desirable to detect uncharted chemistries of carbohydrate conversion. Among the most important value-added products accessible though conversion of biomass is 5-hydroxymethylfurfural (HMF), whose market values strongly depends on the quality of the product. Here, we use high-field in situ NMR spectroscopy to shed light on obscure competing reactions of CrCl3-catalyzed carbohydrate conversion to HMF in water. High-field NMR spectroscopy has enormous prowess in distinguishing isomeric and dehydrated products formed from glucose. Previously unidentified compounds were identified with this approach and include anhydrosugars and a variety of branched and linear mono- and disaccharides. Other identified compounds leverage the understanding of the active catalyst species. In addition to providing mechanistic insight, the approaches and findings described herein help to measure and manage carbon balances and product quality in HMF production. [ABSTRACT FROM AUTHOR]

The leaf essential oil of Laggera pterodonta (DC.) Sch. Bip. ex Oliv. (Asteraceae) collected in the Eastern Côte d'Ivoire was investigated using a combination of chromatographic (GC-RI, CC, pc-GC) and spectroscopic (GC-MS, 13C NMR) techniques. Eighty-three components accounting for 98.0% of the whole composition were identified with 2,5-dimethoxy-p-cymene (43.3%), sabinene (14.1%), α-humulene (9.8%), (E)-β-caryophyllene (7.2%) and germacrene D (5.2%) as major compounds. This study led to the structural elucidation of a new natural compound, (3αH,4βH,6αH,1αMe)-1,6-epoxy-3-hydroxycarvotanacetone, angelic acid ester from the leaf oil by 1D and 2D NMR spectroscopy. [ABSTRACT FROM AUTHOR]

Two unexpected and unusual vindoline trimers, a ketone and a methyl ether cation, were isolated from a reaction aimed at producing new, synthetically modified vinca alkaloids. The presence of several very similar molecular subunits in these products resulted in highly congested 1H and 13C NMR spectra, whereby their structure elucidation and proper spectroscopic characterization turned out to be a rather challenging task. To overcome this problem, non-uniform sampling was applied as a resolution enhancement tool on an 800 MHz NMR spectrometer. Our present description of how we accomplished both the structure determination and full NMR assignment of these molecules via the use of state-of-the-art NMR and MS techniques is not only paramount in proving their structure, but also exemplifies how—contrary to a common notion—difficult it can be to solve the structure of small molecules even with the aid of the latest NMR and MS methods. [ABSTRACT FROM AUTHOR]

An unexpected generation of a 5,7-bicyclic framework from 5-aminopyrazoles and 2,5-dimethoxytetrahydrofuran was detected in the synthesis of originally desired 5-pyrrol-1-ylpyrazoles. To gain insight about the structure and behavior of the novel studied compounds, heteronuclear 2D NMR (including 1 H 15 N, 19 F 13 C and 19 F 15 N correlations), single-crystal X-Ray diffraction structural analysis and HR-MS were exploited. Four other syntheses were designed to obtain the pyrazoloazepines by independent reaction pathways which never yielded the desired bicyclic products obtained before. The reaction conditions of the original Clauson-Kaas synthesis were optimized to yield the pyrazoloazepines in reasonable yields. [ABSTRACT FROM AUTHOR]

Organic soils in boreal ecosystems and peatlands represent a huge global carbon pool and their composition strongly affects soil properties. Nevertheless, the characterization of soil organic matter (SOM) molecular composition, which is essential for elucidating soil carbon processes and turnover, is not easily achieved, and further advances in the area are greatly needed. Two dimensional (2D) liquid state 1 H– 13 C nuclear magnetic resonance (NMR) spectroscopy has been used on dimethyl sulfoxide (DMSO) extracts of SOM to achieve molecular level characterization, with signals from many identifiable molecular groups observable. Here we show that a simple and fast sample preparation allows acquisition of 2D 1 H– 13 C NMR spectra from extracts of plant litter and organic layers in boreal ecosystems, with fast data acquisition. Our 2D NMR spectra revealed several differences in the DMSO extracts of different tree litter samples, O-horizons of forest soil, peat-forming moss ( Sphagnum ) and peat. The results mirror established differences between OM in soils and litter of different forest ecosystems (e.g. between deciduous and coniferous litter) but also provide indications for research to untangle previously conflicting results (e.g. cutin degradation in soil or carbohydrate degradation in peat). Thus, combination of 2D NMR methods can greatly improve analysis of litter composition and SOM composition, thereby facilitating the elucidation of their roles in biogeochemical and ecological processes that are critical for foreseeing feedback mechanisms for SOM turnover as a result of global environmental change. [ABSTRACT FROM AUTHOR]

A complementary application of three analytical techniques, viz. multidimensional nuclear magnetic resonance spectroscopy (NMR), mass spectrometry (MS), and single-crystal X-ray diffractometry was required to identify and refine two natural products isolated from Millettia versicolor and solvent of crystallization. The two compounds, namely 3-(2 H-1,3-benzodioxol-5-yl)-6-methoxy-8,8-dimethyl-4 H,8 H-pyrano[2,3- h]chromen-4-one, or durmillone, (I), and (2 E)-1-(4-{[(2 E)-3,7-dimethylocta-2,6-dien-1-yl]oxy}-2-hydroxyphenyl)-3-(4-hydroxyphenyl)prop-2-en-1-one, (II), could not be separated by routine column chromatography and cocrystallized in a 2:1 ratio with 0.13 molecules of ethanol solvent. Compound (II) and ethanol could not be initially identified by single-crystal X-ray analysis due to complex disorder in the aliphatic chain region of (II). Mass spectrometry ensured that (II) represented only one species disordered over several positions in the solid state, rather than several species cohabitating on the same crystallographic site. The atomic identification and connectivity in (II) were established by several 2D (two-dimensional) NMR techniques, which in turn relied on a knowledge of its exact mass. The derived connectivity was then used in the single-crystal analysis to model the disorder of the aliphatic chain in (II) over three positions and allowed identification of a partially occupied ethanol solvent molecule that was disordered over an inversion center. The disordered moieties were refined with restraints and constraints. [ABSTRACT FROM AUTHOR]

The synthesis of 2,3,4,5,10,11-hexahydro-1H-diben- zo[b,e][1,4]diazepin-1-ones was revisited and a catalyst-free method was established, by exploring the reactivity of 3-[(2-aminoaryl)amino]dimedones towards carbonylated electrophiles. 2D NMR and single-crystal X-ray diffraction studies were used to characterize the structures unequivocally and to review the mechanism leading to the formation of supposed positional isomers. The action of 3-[(2-aminoaryl)amino]di- medones on chromene-3-carboxylic acid, fumaryl, and oxalyl chloride has led to dibenzo[b,e][1,4]diazepin-1-one ring opening to produce novel Z-configured enaminone and linear diamides. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) is one of the most widely used analytical techniques in numerous domains where molecules are objects of investigation. However, major limitations of multidimensional NMR experiments come from their low sensitivity and from the long times needed for their acquisition. In order to overcome such limitations, fast repetition NMR techniques allowed for the reduction of 2D experimental time and for the conversion of the gained time into a higher number of scans leading to a better sensitivity. Thus, fast repetition 2D heteronuclear NMR techniques have allowed new advances in NMR, especially to access infomation on low abundant nuclei, to enhance the detection of low concentrated compounds and to probe weak interactions like hydrogen bonds at natural abundance. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A primary goal of metabolomics is the characterization of a potentially very large number of metabolites that are part of complex mixtures. Application to biofluids and tissue samples offers insights into biochemical metabolic pathways and their role in health and disease. 1D 1H and 2D 13C-1H HSQC NMR spectra are most commonly used for this purpose. They yield quantitative information about each proton of the mixture, but do not tell which protons belong to the same molecule. Interpretation requires the use of NMR spectral databases, which naturally limits these investigations to known metabolites. Here, a new method is presented that uses complementary ion exchange resin beads to differentially attenuate 2D NMR cross-peaks that belong to different metabolites. Based on their characteristic attenuation patterns, cross-peaks could be clustered and assigned to individual molecules, including unknown metabolites with multiple spin systems, as demonstrated for a metabolite model mixture and E. coli cell lysate. [ABSTRACT FROM AUTHOR]

• Accurate characterization of pore structure of different coal ranks using 2D NMR. • Characterize the pore throat characteristics of different coal ranks. • Analyze T 1 -T 2 spectra and 3D peak map to obtain the development of coal pores. In order to accurately characterize the porosity and pore throat structure of different coal grades under liquid nitrogen fracturing cycles, this paper tests the T 2 and T 1 -T 2 sequences of different grades of coal samples (lignite, bituminous coal and anthracite) before and after the fracturing cycles. The results show that the total pore space of A, L and B is arranged in descending order according to the initial state. The internal porous throat distribution of lignite and anthracite coal samples is wider. With the increase of the number of fracturing cycles, the internal pore space of the three coal grade coal samples has been improved, of which lignite has the largest lifting rate; The internal porous throat distribution of L coal samples was reduced by 0.97%. The internal pore space of B and A coal samples increased by 34.62% and 6.33%, respectively, the pore-throat distribution increased by 28.96% and 16.98%, respectively. [ABSTRACT FROM AUTHOR]

• Steroidal-chromium carbonyl complexes have been shown to keep a significant affinity for the estradiol receptor. • Use of techniques newly available in the early 1980s, such as 2D NMR and Fourier transform IR, to characterize bioorganometallic molecules and to use them as non-radioactive tracers for detection of estradiol receptors in breast cancer cells. • Carbonyl Metallo-Immuno Assay (CMIA) is a non-isotopic immunoassay that allows the simultaneous multi-assay of three antiepileptic drugs (carbamazepin, phenobarbital and diphenylhydantoin). Bioorganometallic chemistry is now a maturing field attracting researchers around the world, and also across the Periodic Table. It has found applications in a broad range of areas such as drug discovery, biocatalysis and imaging. We review here the first experiments carried out in the early 1980′s at the Ecole Nationale Supérieure de Chimie de Paris under the leadership of Gérard Jaouen, a key figure and visionary in the development of this theme. However, they also required important contributions from Canadian collaborators with expertise in NMR and IR spectroscopy, together with the availability of more powerful and versatile instrumentation. This collaboration found its fulfillment in the demonstration of the use of metal carbonyl complexes (exemplified by an estradiol derivative labeled by a Cr(CO) 3 unit) as non-isotopic tracers allowing the detection of estradiol receptors, an essential marker for setting up a targeted therapy for breast cancer. This approach was based on the premise that the intense metal carbonyl stretching vibrations are found in a window (2100–1850 cm−1) where the protein itself does not absorb. The field was extended to the arena of non-isotopic immunoassays, including the simultaneous detection of multiple antiepileptic drugs bearing metal carbonyl labels. More recently, taking advantage of the new technique of atomic force microscopy-infrared spectroscopy (AFM-IR) it has been possible to accomplish direct tracing of these complexes in cells. The contributions of the original group of workers in the field are highlighted, and placed in the perspective of today's subsequent emphasis on the management of previously untreatable cancers. [Display omitted] [ABSTRACT FROM AUTHOR]

• A new joint experiment is designed for petrophysical evaluation in shale. • Dissolved methanol can be used to identify hydrogen components in shale. • 1D/2D translational diffusion model is introduced for theoretical analysis of shale NMR mechanism. • A comprehensive interpretation scheme of shale is established based on T 1 / T 2 - T 2 map. • Wettability and mobility characteristics of shale are provided through interpretation scheme. Shale oil is one of the important unconventional fossil fuels resources. Understanding the petrophysical properties of shale contributes to the exploration and clean production of shale oil resources. 1H nuclear magnetic resonance (NMR) is a potential technique that can provide for shale petrophysical properties. However, current NMR-based technique for shale petrophysical characterization, due to the complexity of shale, usually requires some auxiliary geochemical experiments. Since a multi-step solvent extraction (MSSE) experiment has a merit in separating hydrocarbons and water in shale, in this work, two-dimensional (2D) NMR measurements combined with MSSE experiments were proposed for the first time to study the petrophysical properties of shale. A mixture of dichloromethane and methanol in a ration of 9:1 was prepared as a solvent for the extraction. Sufficient natural air-drying time allows for the removal of dichloromethane while retaining methanol. The comprehensive experiments show that the signal change induced by residual methanol from T 1 / T 2 - T 2 map, before and after extraction and natural air-drying, can be used to identify pore-fluid and evaluate the mobility of hydrocarbon. For insight into the essence of experimental phenomena, quasi-1D/2D translational diffusion model were employed to analyze the T 1 / T 2 and T 2 responses of pore fluids. Wettability characteristics and detailed hydrocarbon mobility of shale were obtained from the theoretical analyses based on the translational diffusion models and T 1 / T 2 - T 2 map. Combined the experimental results with the theoretical analysis, a comprehensive interpretation scheme was established for shale based on the T 1 / T 2 - T 2 map, including fluid identification, wettability evaluation, and hydrocarbon mobility characterization. [ABSTRACT FROM AUTHOR]

NMR spectroscopy with compact instruments opens new perspectives for the use of NMR. While the field strength of compact instruments is low, they potentially match today's high-field instruments in methodical diversity, although by default they are operated in non-expert mode with a mouse click. Because size and price are low, they open new opportunities for the use of NMR spectroscopy. One is product and quality control and another is real-time reaction monitoring in the academic and industrial research laboratory on the workbench by observing nuclei such as 1 H, 13 C, 31 P, 19 F, 7 Li and 11 B. With compact NMR spectrometers, not only standard one-dimensional experiments can be executed to retrieve chemical information but also the two-dimensional experiments such as HSQC, HMBC, HETCOR and COSY. The state of the art and progress in compact NMR spectroscopy is reviewed concerning 1D and 2D spectroscopy along with their use in product control and reaction monitoring. [ABSTRACT FROM AUTHOR]

Conformational analysis of eight-membered P,N-heterocycles (PR') in the solution has been performed by means of NMR spectroscopy and quantum chemical calculations. The equilibrium of the С-symmetrical (crown, major) and С-symmetrical ( chair-boat, minor) forms of the compounds has been revealed, the transition barriers being of about 12 kcal/mol. The presence of an aromatic substituent at the nitrogen atom significantly shifts the equilibrium towards the dominating form. [ABSTRACT FROM AUTHOR]

4- N , N -dimethylamino-4′- N ′-methyl-stilbazolium tosylate (DAST) crystal has excellent properties of nonlinear optics and electro-optical effect, and it can be used in the fields of radiation and detection through wave bands from infrared to terahertz. Besides, DAST thin films have exhibited their excellent properties and have expanded application fields of DAST material. CD 3 OD was chosen as the solvent to conduct 1 H NMR, 13 C NMR, 1 H– 1 H COSY, 1 H– 13 C HSQC and 1 H– 13 C HMBC characterization of DAST respectively. All peaks in 1 H and 13 C NMR spectra of DAST were assigned with assistance of 2D NMR correlation peaks. [ABSTRACT FROM AUTHOR]

NMR is a powerful tool for the analysis of complex mixtures and the identification of individual components. Two-dimensional (2D) NMR potentially offers a wealth of information, but resolution is often sacrificed in order to contain experimental times. We explore the use of non-uniform sampling (NUS) to increase substantially the resolution of 2D NMR spectra of complex mixtures of small molecules, with no increase in experimental time. Two common pulse sequences for metabolomics applications are analysed, HSQC and TOCSY. Specific attention is paid to sensitivity in resolution-enhanced NUS spectra, using the signal-to-maximum-noise ratio as a metric. With a careful choice of sampling schedule and reconstruction algorithm, resolution in the 13C dimension for HSQC is increased by a factor of at least 32, with no loss in sensitivity and no spurious peaks. For TOCSY, multiplets can be resolved in the indirect dimension in a reasonable experimental time. These properties should increase the usefulness of 2D NMR for metabolomics applications by, for example, increasing the chances of metabolite identification. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Zamioculcas zamiifolia , an unusually drought resistant medicinal plant native to tropical east Africa and subtropical southeast Africa, including the countries Kenya, Malawi, Mozambique, South-Africa, Tanzania and Zimbabwe, is described as a living fossil which may have evolved as early as 42 million years ago. It belongs to the notoriously toxic family Araceae giving it, through association, a reputation for being toxic; despite little or no systematic evidence exists to support this claim. As an ancient plant it has sustained substantial climate changes and attacks from millions of generations of pathogenic microorganisms, which encouraged search for novel natural products from this source. Seven natural products have been characterized from leaves and petioles of Z. zamiifolia , including the novel main compound of the leaves, apigenin 6- C -(6″-(3-hydroxy-3-methyl-glutaroyl)-ß-glucopyranoside). The structure determinations were based on extensive use of 2D NMR spectroscopic techniques and high-resolution mass spectrometry. Initial toxicological experiment on extracts from Z. zamiifolia using brine shrimp lethality assay did not indicate lethality to the shrimps providing disproving evidence for the assumption of Z. zamiifolia's toxic character. [ABSTRACT FROM AUTHOR]

Phytochemical study on rhizomes of Beesia calthifolia resulted in the isolation of five new ( 1 – 5 ) and three known ( 6 – 8 ) cycloartane triterpenoids possessing a hemiketal or ketal group at C-24 from the EtOAc fraction of 95% ethanol extract. Their structures were determined by spectroscopic and chemical methods, especially HRMS and 2D NMR techniques. Compounds 3 and 4 showed potential hepatoprotective activities against d -galactosamine induced human hepatic L02 cell damage. [ABSTRACT FROM AUTHOR]

In this study, we have synthesized and elucidated the structure of the H1 histamine antagonist, 2-(1-methylpiperidin-4-ylidene)-4,7-diazatricyclo[8.4.0.0 (3,7) ]tetradeca-1(14),3,5,10,12-pentaene-6-carbaldehyde in the solution and solid-state. We have also studied the thermal dilapidation of the compound. Solution structure analysis was achieved by employing NMR spectroscopy including 2D experiments NOESY, HSQC and HMBC, while solid state investigations were undertaken using SXRD, PXRD, TGA, DSC, and IR spectroscopy. For the first time the single crystal structure of alcaftadine has now been solved. Crystallographic data are as follows: monoclinic, Cc, a = 11.5694(6) Å, b = 14.5864(6) Å, c = 10.2688(4) Å, α = 90°, β = 111.793(3)°, γ = 90°, V = 1609.07(13) Å 3 , Z = 4. The Hirshfeld surface analyses also have been performed using the crystal structure. [ABSTRACT FROM AUTHOR]

Quantitative 2D NMR is a powerful analytical tool which is widely used to determine the concentration of small molecules in complex samples. Due to the site-specific response of the 2D NMR signal, the determination of absolute concentrations requires the use of a calibration or standard addition approach, where the analyte acts as its own reference. Standard addition methods, where the targeted sample is gradually spiked with known amounts of the targeted analyte, are particularly well-suited for quantitative 2D NMR of small molecules. This paper explores the potential of such quantitative 2D NMR approaches for the quantitative analysis of a high molecular weight polysaccharide. The results highlight that the standard addition method leads to a strong under-estimation of the target concentration, whatever the 2D NMR pulse sequence. Diffusion measurements show that a change in the macromolecular organization of the studied polysaccharide is the most probable hypothesis to explain the non-linear evolution of the 2D NMR signal with concentration. In spite of this non-linearity – the detailed explanation of which is out of the scope of this paper – we demonstrate that accurate quantitative results can still be obtained provided that an external calibration is performed with a wide range of concentrations surrounding the target value. This study opens the way to a number of studies where 2D NMR is needed for the quantitative analysis of macromolecules. [ABSTRACT FROM AUTHOR]

Four new oleanane-type saponins 3- O -α- l -rhamnopyranosyl-(1 → 4)-β- d -glucuronopyranosyl-22- O -β,β-dimethylacryloylA1-barrigenol ( 1 ), 3- O -α- l -rhamnopyranosyl-(1 → 4)-β- d -glucuronopyranosyl-22- O -angeloylA1-barrigenol ( 2 ), 3- O -β- d -glucopyranosyl-(1 → 2)-[β- d -glucopyranosyl-(1 → 6)]-β- d -glucopyranosyl-21,22,28- O -triacetyl-(3β,21β,22α)-olean-12-en-16-one ( 3 ), and 3- O -β- d -glucopyranosyl-(1 → 2)-glucopyranosyl-22- O -β- d -glucopyranosylsteganogenin ( 4 ), along with the known 3- O -β- d -galactopyranosyl-(1 → 2)-[α- l -arabinopyranosyl-(1 → 3)]-β- d -glucuronopyranosyl-22- O -angeloylA1-barrigenol and 3- O -α- l -rhamnopyranosyl-(1 → 4)-β- d -glucuronopyranosyloleanolic acid, were isolated from a methanol extract of the roots of Eryngium kotschyi by multiple chromatographic steps. Saponins 3 and 4 are unusual by the original structure of their aglycon. Compound 3 possessed an oleanane-type skeleton with a 21,22,28-triacetylation and a ketone function at the C-16 position. For compound 4 , the 17,22-seco-oleanolic acid skeleton is rarely found in natural saponins. [ABSTRACT FROM AUTHOR]

• New Pyranonicotinonitrile/Chromene-3-carbonitrile are synthesized from DHA by MCR. • All compounds are fully characterized by 2D NMR and mass spectroscopy. • Antioxidant and antimicrobial activities are evaluated in-vitro. • Molecular docking of PBPs, TMK and z protein are studied on active compounds. [Display omitted] Dehydroacetic acid (DHA) and derivatives are widely used in the synthesis of pharmacologically active heterocyclic compounds. In this study, two new series of pyranonicotinonitriles and chromene-3-carbonitriles have been synthesized under microwave irradiation using DHA synthons, as starting materials, through multicomponent reaction (MCR), involving domino Knoevenagel-Michael addition or one pot intramolecular cyclization. All the resulting heterocyclic compounds have been characterized by 1H NMR and 13C NMR, 2D NMR (HSQC, HMBC) and mass spectroscopy. Mass peaks of the synthetized compounds correspond perfectly to molecular ions [ M + H ] or [ M +Na]. Notably, 1H NMR spectra of all the compounds display a characteristic doublet at δ H 6.07 ppm, which is assigned to the pyran-2-one heterocycle. Biological activities, such as the antioxidant DPPH radical scavenging and antibacterial/antifungal assays against ATCC strains have been evaluated in -vitro. Results showed that all compounds are capable to reduce DPPH with different IC 50 values. The germs sensitivity towards the synthesized compounds is variable with Staphylococcus aureus being the most sensitive bacteria. Further docking simulations have been carried out targeting S. aureus penicillin binding proteins group (PBP2, PBP3 and PBP4) and thymidylate kinase (TMK) and the cell division Z ring protein (FtsZ) using AutoDock Vina software. The validity of docking results have been confirmed based on the best affinity scores and types of interactions. The molecular mechanisms of the synthesized heterocycles towards target proteins involved in S. aureus growth have been predicted through molecular docking studies. [ABSTRACT FROM AUTHOR]

A simple experiment for E limination of A rtifacts in NMR S pectroscop Y (EASY) was introduced in Part I, and it was shown that NMR probe background signals, spectral distortions due to deadtime effects, and acoustic ringing can be eliminated simultaneously from solid-state NMR spectra. In this Part II, it is shown that acoustic ringing suppression can be improved up to one order of magnitude compared to the original EASY pulse sequence by inserting a delay τ between the two data acquisition scans of the EASY pulse sequence. The achievable ringing suppression depends on the length of this delay and is limited by the spin-lattice relaxation time T 1 . Furthermore, EASY is considered in conjunction with NMR of quadrupolar nuclei. For strong second-order broadening, EASY can be used to acquire either pure central transition MAS patterns or pure satellite transition NMR spectra. Two further modifications to EASY are introduced. One concerns improved ringing artifact suppression in experiments in which the central transition NMR signal is amplified by Rotor Assisted Population Transfer (RAPT). The second EASY modification enables the acquisition of quantitative NMR spectra if signals with different quadrupole coupling constants are present. In addition, acoustic ringing and 11 B stator signals are removed. Finally, it is demonstrated that the basic idea of EASY for removing ringing artifacts can be realized for heteronuclear one-dimensional and hetero- and homo-nuclear multi-dimensional NMR experiments using extended phase cycling. 15 N{ 1 H} CPMAS and 15 N 2D Exchange NMR spectroscopy are considered as examples. [ABSTRACT FROM AUTHOR]

We have revisited the synthesis of a series of ICT fluorophores, which were reported to have a core structure of 8-oxo-8H-acenaphtho[1,2-b]pyrrol-9-carbonitrile. However, based on the 2D NMR and X-ray diffraction analysis, their core structure was corrected as 1-oxo-1H-phenalene-2,3-dicarbonitrile (1). Compound 1 shows a highly electron-deficient nature and can easily undergo oxidative SNArH reaction on the naphthyl ring to produce a series of novel ICT fluorophores. The regioselectivity of this substitution reaction was studied by introduction of representative nucleophiles. Moreover, due to the strong rigidity and efficient ICT nature, the obtained fluorescent dyes display very good spectroscopic properties even in an aqueous environment. [ABSTRACT FROM AUTHOR]

Abstract: Metasequoia glyptostroboides, a tree native to China, is described as a living fossil and has existed for millions of years. The oldest fossils recorded have been dated to the late Cretaceous era. During the time of its existence, the molecular defence system of the tree has apparently resisted millions of generations of pathogens, which encouraged search for novel natural product from this source. Eight compounds have been characterised from needles of M. glyptostroboides, including the novel natural product 6-carboxydihydroresveratrol 3-O-β-glucopyranoside. The structure determinations were based on extensive use of 2D NMR spectroscopic techniques and high-resolution mass spectrometry. [Copyright &y& Elsevier]

Urea-formaldehyde resins are bulk products of the chemical industry. Their synthesis involves a complex reaction network. The present work contributes to its elucidation by presenting results from detailed NMR spectroscopic studies with different methods. Besides1H NMR and13C NMR,15N NMR spectroscopy is also applied.15N-enriched urea was used for the investigations. A detailed NMR signal assignment and a model of the reaction network of the hydroxymethylation step of the synthesis are presented. Because of its higher spectral dispersion and the fact that all key reactions directly involve the nitrogen centers,15N NMR provides a much larger amount of detail than do1H and13C NMR spectroscopy. Symmetric and asymmetric dimethylol urea can be clearly distinguished and separated from monomethylol urea, trimethylol urea, and methylene-bridged urea. The existence of hemiformals of methylol urea is confirmed. 1,3,5-Oxadiazinan-4-on (uron) and its derivatives were not found in the reaction mixtures investigated here but were prepared via alternative routes. The molar ratios of formaldehyde to urea were 1, 2, and 4, the pH values 7.5 and 8.5, and the reaction temperature 60 °C. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Highlights: [•] Rhenium(V)porphyrins were synthesized. [•] UV–Visible, IR, 1Н, 2D NMR spectra for title compounds were studied. [•] The compounds do not undergo M N bonds dissociation in strong acids. [•] The compounds form the stable π-cation radicals . [ABSTRACT FROM AUTHOR]

Abstract: Three new spirostane-type glycosides (1–3) were isolated from the whole plant of Allium flavum. Their structures were elucidated mainly by 2D NMR spectroscopic analysis and mass spectrometry as (20S,25R)-2α-hydroxyspirost-5-en-3β-yl O-β-d-xylopyranosyl-(1→3)-[β-d-galactopyranosyl-(1→2)]-β-d-galactopyranosyl-(1→4)-β-d-galactopyranoside (1), (20S,25R)-2α-hydroxyspirost-5-en-3β-yl O-β-d-xylopyranosyl-(1→3)-[β-d-glucopyranosyl-(1→2)]-β-d-galactopyranosyl-(1→4)-β-d-galactopyranoside (2), and (20S,25R)-spirost-5-en-3β-yl O-α-l-rhamnopyranosyl-(1→4)-[β-d-glucopyranosyl-(1→2)]-β-d-glucopyranoside (3). The three saponins were evaluated for cytotoxicity against a human cancer cell line (colorectal SW480). [Copyright &y& Elsevier]

Highlights: [•] Site selectivity and regioselectivity of the [2+3] cycloaddition reaction was established by 2D NMR spectroscopy. [•] Outstanding effect of carbohydrate-ytterbium triflate catalysts on selectivity of the reaction was demonstrated. [•] Influence of alkene electron densities on cycloaddition to cyclohexene derivatives was found. [•] Complete 1H and 13C NMR characterization of 3a,4,5,6,7,7a-hexahydro-1,2-benzoxazoles was achieved. [Copyright &y& Elsevier]

Smith et al. recently reported dye analysis of a carpet fragment thought by some to be from a 15th century silk-knotted Persian carpet [Smith et al., Forensic Science International: Synergy 2021; 3:100130]. Sample threads were found to contain several synthetic dyes from the late 19th century, including Congo red, which was first synthesized in 1883, indicating that the carpet is a modern object. Two mysterious compounds designated as A and B of unknown identity were also detected with Congo red in similar amounts on the object. This paper reports the structural elucidation of A and B using high resolution mass spectrometry and multidimensional NMR spectroscopy. To our knowledge, these compounds have never been reported before. Additionally, experiments are described demonstrating that A and B were products from the reaction of Congo red with formaldehyde. Previously unknown homologs of A and B were also formed when Congo red was reacted with acetaldehyde, pentanal, and hexanal, indicating a common reaction mechanism. Uv–Vis spectra of the homologs suggest that aldehyde exposure can cause an overall color change in objects dyed with Congo red. A historic dye swatch book containing cotton skeins dyed with the colorants benzopurpurine 4B and deltapurpurine 5B, which are of the same chemical class as Congo red, and exhibiting a faded appearance, were found to contain dye derivatives analogous to A and B. Chemical mechanisms proposed for the formation of compounds A and B are discussed, along with the possible origins of the formaldehyde exposure. The concept of 'chemical fading,' is adduced to heighten the awareness of the exposure of historic dyed textiles to the harmful effects of formaldehyde, a common museum and household pollutant. [Display omitted] • Congo red reacts with the pollutant formaldehyde to form compounds A and B. • Structures of A and B established by HR-MS and multidimensional NMR data. • Uv–Vis spectra indicate compound A to still be red, but B is colorless. • Formaldehyde can cause chemical fading of Congo red dyed objects. • Simple alkanals react with Congo red to form derivatives analogous to A and B. [ABSTRACT FROM AUTHOR]

[Display omitted] • CoSeM, a reference-less method for reducing k/t 1 -noise by ca. 3-fold, is introduced. • The approach operates on the basis of combined masking/compressed sensing fully sampled 2D sets. • The method is general, does not require a reference, improves SNR in 2D spectra/images, retains quantitativeness, and does not affect spectral/spatial resolution. Both in spectroscopy and imaging, t 1 -noise arising from instabilities such as temperature alterations, field-related frequency drifts, electronic and sample-spinning instabilities, or motions in in vivo experiments, affects many 2D Magnetic Resonance experiments. This work introduces a post-processing method that aims to attenuate t 1 - noise, by suitably averaging multiple signals/representations that have been reconstructed from the sampled data. The ensuing Compressed Sensing Multiplicative (CoSeM) denoising starts from a fully sampled 2D MR data set, discards random indirect-domain points, and makes up for these missing, masked data, by a compressed sensing reconstruction of the now incompletely sampled 2D data set. This procedure is repeated for multiple renditions of the masked data –some of which will have been more strongly affected by t 1 -noise than others. This leads to a large set of 2D NMR spectra/images compatible with the collected data; CoSeM chooses out of these those renditions that reduce the noise according to a suitable criterion, and then sums up their spectra/images leading to a reduction in t 1 -noise. The performance of the method was assessed in synthetic data, as well as in numerous different experiments: 2D solid and solution state NMR, 2D localized MRS of live brains, and 2D abdominal MRI. Throughout all these data, CoSeM processing evidenced 2–3 fold increases in SNR, without introducing biases, false peaks, or spectral/image blurring. CoSeM also retains a quantitative linearity in the information –allowing, for instance, reliable T 1 inversion-recovery MRI mapping experiments. [ABSTRACT FROM AUTHOR]

1H and 13С NMR spectral assignments have been provided for low-molecular reference monomers, poly(diphenyleneoxidephthalide) and periodic copoly(arylenephthalide) derivatives such as AB, ABB, and ABBB (where A = terphenylenephthalide and B = diphenyleneoxidephthalide) using 1H-1H COSY, 1H-13C HSQC and HMBC NMR techniques. Distinctive 13C NMR chemical shifts of a main chain have been observed containing fragments of similar structures and lateral phthalate groups being part of various diads. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The synthesis and NMR elucidation of eight novel peptides incorporating the pentacycloundecane (PCU)-derived hydroxy acid are reported. The PCU cage amino acids were synthesized as racemates and the incorporation of the PCU-derived hydroxy acid with natural ( S)-amino acids produced inseparable diastereomeric peptides. A series of overlapping signals from the cage and that of the peptide side chain was observed in the H- and C-NMR spectra, complicating the elucidation thereof. Two-dimensional NMR techniques proved to be a very useful tool in overcoming these difficulties. These compounds are potential HIV protease inhibitors. [ABSTRACT FROM AUTHOR]

Abstract: A new sulfated acetamido-heteropolysaccharide, HPS4-2A, was obtained by aqueous extraction followed by precipitation with ethanol and fractionation with DEAE column chromatography from Radix Hedysari. It was composed of rhamnose, arabinose, glucose, galactose and 2-acetamido-2-deoxy-d-galactose in the molar ratio of 10.09%:25.90%:25.90%:25.0%:12.30%. Elemental analysis indicated that HPS4-2A was a sulfated polysaccharide containing small amount of sulfate groups (1.87%). Partial acid hydrolysis, GC, GC–MS, 1D and 2D NMR spectroscopy analysis of the HPS4-2A revealed a predominance of glucose, galactose and 2-acetamido-2-deoxy-d-galactose linked in a highly-branched structure. The molecular weight of HPS4-2A was determined by HPSEC and HPSEC-MALLS. AFM study indicated that HPS4-2A took a highly branched conformation, which in consistent with the result studied by SEC-MALLS. Structural features of HPS4-2A were also investigated by SEM and TEM. Antioxidant assays demonstrated that HPS4-2A possessed of strong DPPH and hydroxyl radicals scavenging activities, suggesting that HPS4-2A could potentially be used as natural antioxidant. [Copyright &y& Elsevier]

Abstract: The structure of gum arabic (Acacia seyal) has been studied using methylation analysis and 2D (COSY, TOCSY, HMQC and HMBC) NMR spectroscopy. Galacturonic acid (13.66%) is a major component not previously identified. The backbone is made up of 1,3-linked galactopyranosyl (Galp) residues substituted at O-2, O-6 or O-4 positions, which are terminated with mainly arabinofuranosyl (Araf), galacturonopyranosyl (GalpA), rhamnopyranosyl (Rhap), but occasionally with arabinopyranosyl (Arap), and glucuronopyranosyl (GlcpA) residues. There are long side chains of →3)-α-l-Araf-(1→ and →2)-α-l-Araf-(1→ linked to the backbone. [Copyright &y& Elsevier]

Abstract: Nuclear magnetic resonance (NMR) offers great potential for quantitative analysis of metabolic samples, but accurate and precise quantitative analysis is often made difficult by a high degree of spectral overlap. Multi-dimensional NMR offers an interesting alternative, as it provides a much better discrimination of resonances. However, its use for quantitative analysis is limited by its long acquisition duration and its multi-impulsional character. Nevertheless, numerous improvements in the quantitative performance of 2D NMR have been made during the past decade, facilitating a wide range of applications. This review assesses the recent contributions brought to the field of quantitative 2D NMR, and provides a survey of recent studies of metabolic samples using this methodology. The ongoing need for developing and optimizing powerful tools is first examined. It highlights the necessity of reducing the experimental duration, resulting in a fast 2D NMR approach. This methodology is then described, relying on recent applications to metabolic samples. The last section of the chapter describes a more recent approach, ultrafast 2D NMR, which makes it possible to record multi-dimensional spectra in a single scan. The principles and the analytical performances of this novel methodology are described, as well as its perspectives in terms of quantitative analysis. [Copyright &y& Elsevier]

A new flavanol, named songarin A (1), was isolated from Cynomorium songaricum Rupr. The structure was established on the basis of spectroscopic methods including 2D NMR techniques. Compound 1 displayed the protective effect against d-galactosamine-induced HepG2 damage and reduced the damage from 58.64% to 22.26%. [ABSTRACT FROM AUTHOR]