Complete Nuclear Magnetic Resonance Research Articles

Complete 1H and 13C NMR assignment of cellulose oligomer in LiCl/DMSO

High-resolution solution-state 1H, 13C, and various 2D nuclear magnetic resonance (NMR) spectra of cellulose were obtained using cellulose oligomer dissolved in LiCl/dimethyl sulfoxide, which enabled the assignment of all 1H and 13C resonances. The observed resonances were classified into four groups of glucose rings, corresponding to internal residue, non-reducing end, and reducing ends with α- and β-anomeric configurations. This assignment included the OH protons, which are difficult to assign in cellulose using other solvent systems. NMR measurements and assignments were performed using different LiCl concentrations because information on the hydroxy protons is important for understanding the interaction between cellulose and the solvent. The resonances from the OH protons shifted downfield with increasing LiCl concentration, suggesting that LiCl was attracted to the hydroxy groups of cellulose in solution. Moreover, the magnitude of the shifts varied depending on the positions of the hydroxy groups, which indicated the regioselectivity of the interaction between LiCl and the cellulose hydroxy groups.Graphical abstract

NMR Immunosensor Based on a Targeted Gadolinium Nanoprobe for Detecting Salmonella in Milk.

Detecting harmful pathogens in food is not only a crucial aspect of food quality management but also an effective way to ensure public health. In this paper, a complete nuclear magnetic resonance biosensor based on a novel gadolinium (Gd)-targeting molecular probe was developed for the detection of Salmonella in milk. First, streptavidin was conjugated to the activated macromolecular polyaspartic acid (PASP) via an amide reaction to generate SA-PASP. Subsequently, the strong chelating and adsorption properties of PASP toward the lanthanide metal gadolinium ions were exploited to generate the magnetic complex (SA-PASP-Gd). Finally, the magnetic complex was linked to biotinylated antibodies to obtain the bioprobe and achieve the capture of Salmonella. Under optimal experimental conditions, the sensor we have constructed can achieve a rapid detection of Salmonella within 1.5 h, with a detection limit of 7.1 × 103 cfu mL-1.

Radical scavenging dihydroxycinnamic natural compounds from Trianthema pentandra

BackgroundTrianthema pentandra is a promising plant with numerous medical applications. Previous studies have confirmed that the plant is strongly cytotoxic in brine shrimp lethality tests and has antibacterial effects. However, the compounds responsible for these biological activities have not been identified. This study aimed to screen plants in an antiradical assay using 1,1-diphenyl-2-picrylhydrazyl (DPPH). This assay was used to guide the isolation of active compounds, which were identified at the molecular structural level by spectroscopic methods. MethodsThe plant was extracted using ethanol, labelled F1 and fractionated by solvents of different polarities (F2 chloroform, F4 ethyl acetate, F5 aqueous methanol, and F6 n-hexane). The ethyl acetate and aqueous methanol (F4 and F5) fractions were selected for further purification based on their yields and activities. They were run on chloroform-methanol and n-hexane-ethyl acetate gradients, respectively. Fractions resulting from column chromatography were further screened for DPPH antioxidant activity, upon which fraction F5–1–077 had unusually high activity (IC50 = 3.57 µg/ml). Further purification of these fractions through recrystallization and high-performance liquid chromatography (HPLC) led to the isolation of three compounds. Results: Among these compounds, two were identified and characterized using FT-IR, LC-MS, and complete nuclear magnetic resonance (NMR) data, and 2,3-dihydroxycinnamic acid ethyl ester and its analog acid were isolated from the ethyl acetate fraction (F4). The former compound has been proven to have good activity in comparison with standards, ascorbic acid, and butylated hydroxytoluene (BHT), even at a low concentration of 5 µg/ml with an IC50 value of 0.13 µg/ml in the DPPH assay. The molecular docking data supported the potent activity of the compound with binding affinity, ∆G = -6.4 kcal/mol compared to the ascorbic acid (∆G = -5.0 kcal/mol) used as standard. ConclusionThis study serves as a groundbreaking foundation for the investigation of the natural dihydroxycinnamic compounds present in this plant.

1H and 13C chemical shift-structure effects in anhydrous β-caffeine and four caffeine-diacid cocrystals probed by solid-state NMR experiments and DFT calculations.

By using density functional theory (DFT) calculations, we refined the H atom positions in the structures of β-caffeine (C), α-oxalic acid (OA; (COOH)2), α-(COOH)2·2H2O, β-malonic acid (MA), β-glutaric acid (GA), and I-maleic acid (ME), along with their corresponding cocrystals of 2 : 1 (2C-OA, 2C-MA) or 1 : 1 (C-GA, C-ME) stoichiometry. The corresponding 13C/1H chemical shifts obtained by gauge including projector augmented wave (GIPAW) calculations agreed overall very well with results from magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy experiments. Chemical-shift/structure trends of the precursors and cocrystals were examined, where good linear correlations resulted for all COO1H sites against the H⋯O and/or H⋯N H-bond distance, whereas a general correlation was neither found for the aliphatic/caffeine-stemming 1H sites nor any 13C chemical shift against either the intermolecular hydrogen- or tetrel-bond distance, except for the 13COOH sites of the 2C-OA, 2C-MA, and C-GA cocrystals, which are involved in a strong COOH⋯N bond with caffeine that is responsible for the main supramolecular stabilization of the cocrystal. We provide the first complete 13C NMR spectral assignment of the structurally disordered anhydrous β-caffeine polymorph. The results are discussed in relation to previous literature on the disordered α-caffeine polymorph and the ordered hydrated counterpart, along with recommendations for NMR experimentation that will secure sufficient 13C signal-resolution for reliable resonance/site assignments.

Metabolic Signature of Healthy Lifestyle and Risk of Rheumatoid Arthritis: Observational and Mendelian Randomization Study

BackgroundAlthough substantial evidence reveals that healthy lifestyle behaviors are associated with a lower risk of rheumatoid arthritis (RA), the underlying metabolic mechanisms remain unclear. ObjectivesThis study aimed to identify the metabolic signature reflecting a healthy lifestyle and investigate its observational and genetic linkage with RA risk. MethodsThis study included 87,258 UK Biobank participants (557 cases with incident RA) aged 37–73 y with complete lifestyle, genotyping, and nuclear magnetic resonance (NMR) metabolomics data. A healthy lifestyle was assessed based on 5 factors: healthy diet, regular exercise, not smoking, moderate alcohol consumption, and normal body mass index. The metabolic signature was developed by summing the selected metabolites’ concentrations weighted by the coefficients using elastic net regression. We used the multivariate Cox model to assess the associations between metabolic signatures and RA risk, and examined the mediating role of the metabolic signature in the impact of a healthy lifestyle on RA. We performed genome-wide association analysis (GWAS) to obtain genetic variants associated with the metabolic signature and then conducted Mendelian randomization (MR) analyses to detect causality. ResultsThe metabolic signature comprised 81 metabolites, robustly correlated with a healthy lifestyle (r = 0.45, P = 4.2 × 10−15). The metabolic signature was inversely associated with RA risk (HR per standard deviation (SD) increment: 0.76; 95% CI: 0.70–0.83), and largely explained the protective effects of healthy lifestyle on RA with 64% (95% CI: 50.4–83.3) mediation proportion. 1- and 2-sample MR analyses also consistently showed the associations of genetically inferred per SD increment in metabolic signature with a reduction in RA risk (HR: 0.84; 95% CI: 0.75–0.94; and P = 0.002 and OR: 0.84; 95% CI: 0.73–0.97; and P = 0.02, respectively). ConclusionsOur findings implicate that the metabolic signature reflecting healthy lifestyle is a potential causal mediator in the development of RA, highlighting the importance of early lifestyle intervention and metabolic status tracking for precise prevention of RA.

Equilibrating magnetic dispersion and magnet homogeneity for the high-resolution proton nuclear magnetic resonance of monosubstituted naphthalenes

Accurate chemical shift and coupling constant for 1- and 2-naphthyl derivatives were decipher by iterative full spin analysis. Each of the seven magnetically nonequivalent H2–H8 atoms in 1-naphthyl derivatives, or of the H1, H3–H8 atoms in 2-naphthyl derivatives were unambiguously identified by analyzing their intra- and inter-ring coupling constants at 300 MHz and by two-dimensional homo- and heteronuclear experiments at 750 MHz. 13C chemical shifts were also determined during this study, from where some literature ambiguities were resolved using long-range C–H correlations at 750 MHz. The complete proton nuclear magnetic resonance parameters are herein ascribed for the first time.

A fast low rank Vandermonde factorization reconstruction method for non-uniformly sampled 2D NMR spectroscopy

As an indispensable analytical method in the fields of chemistry and medicine, nuclear magnetic resonance (NMR) spectroscopy is widely adopted for analyzing the composition and structure of substances. However, the data acquisition period for high-resolution NMR spectra is extremely long. Therefore, non-uniform sampling is commonly adopted to reduce the measurement time and the complete NMR signal can be obtained by appropriate reconstruction algorithms. Recently, it was found that NMR signal can be reconstructed well by low-rank Hankel matrix completion. However, the computational time required for this method to reconstruct two-dimensional (2D) and higher dimensional signals is relatively long because it increases rapidly as spectral resolution improves. In this paper, we propose a novel low rank minimization method to alleviate this problem by utilizing the unexploited property that a 2D NMR signal can be decomposed into two Vandermonde matrices. However, minimizing the rank necessitates the time-consuming singular value decomposition (SVD). Thus we introduce a matrix bi-factorization idea into the method to reduce the time complexity and greatly mitigate the time required by the SVD. Experiments on synthetic data and realistic NMR spectroscopy data demonstrate that compared with the state-of-the-art nuclear norm based minimization and fast iterative hard thresholding algorithms, the computational time of the proposed algorithm is significantly reduced, and high reconstruction accuracy can be ensured at the same time.

Efficient purification of the diarylheptanoid oregonin from red alder (Alnus rubra) leaves and bark combining aqueous extraction, spray drying and flash-chromatography.

The diarylheptanoid xyloside oregonin ((5S)-1,7-bis(3,4-dihydroxyphenyl)-5-(β-d-xylopyranosyloxy)-heptan-3-one) has significant medicinal potential and is found at high concentration in leaves and bark of red alder (Alnus rubra). To establish inexpensive and easily scaled methods for the extraction and purification of oregonin from timber by-products. We developed a method combining aqueous extraction with spray drying of red alder extract into a powder, thus reducing the need for organic solvents used in traditional Soxhlet extraction or in solvent partitioning. Flash chromatography was utilised to purify oregonin from crude spray-dried alder extract. Crude spray-dried alder extract was comprised of an average of 9% of the diarylheptanoid compound oregonin. Less than 10% thermal degradation of oregonin was observed using extraction temperatures between 25°C and 50°C, followed by spray drying. The structure of purified oregonin was validated using high-performance liquid chromatography (HPLC), mass spectrometry (MS), ultraviolet spectroscopy (UV), and nuclear magnetic resonance (NMR). The developed method was robust, repeatable, and yielded purified oregonin of greater than > 95% purity (average of 95.8%). Our analysis represents the most complete NMR characterisation of oregonin reported to date.

Non-polar secondary metabolites and essential oil of ex situ propagated and cultivated Sideritis syriaca L. subsp. syriaca (Lamiaceae) with consolidated identity (DNA Barcoding): towards a potential new industrial crop

Over the past decade, perennial plants of the genus Sideritis L. have attracted great scientific interest and they have become the subject of several studies, including the European Union’s herbal monograph. The present study aimed to explore the identity of a biotype of S. syriaca subsp. syriaca documented with DNA barcoding, investigated its macro- and micro- propagation and to study the chemical profile of the dichloromethane extract, as well as of the Essential Oil (EO) of the ex situ propagated and cultivated plant material. An improved in vitro propagation protocol, as well as pioneer effective propagation with cuttings (both at commercially acceptable rates) are provided for a DNA-barcoded biotype of Sideritis syriaca L. subsp. syriaca (malotira, Cretan mountain tea) which is a single-island endemic plant of Crete (Greece), with declining wild populations due to over collection. From the aerial parts of ex situ propagated and cultivated material (harvested in July) two phytosterols (β-sitosterol and stigmasterol), two ent-kaurene diterpenes; siderol and eubotriol, as well as one methylated flavone (xanthomicrol) have been isolated. This is the first time that eubotriol has been isolated from this taxon. The structures of the isolated compounds have been established by spectroscopic means and the complete Nuclear Magnetic Resonance (NMR) assignments for eubotriol are presented. Moreover, the essential oil was obtained by hydrodistillation of the plant material during the flowering stage and was analyzed by Gas Chromatography-Mass Spectrometry (GC–MS). Forty-four compounds were identified. The monoterpene hydrocarbons constituted the major fraction of the essential oil (34.2%), while β-phellandrene (18.5%) and kaur-15-ene (or ent-kaur-15-ene; 17.3%) were the main compounds. In conclusion, the above results document the first necessary steps taken for the ex situ conservation and sustainable exploitation of a new industrial crop with promising potential.

Structural and Bioactivity Characterization of Filipin Derivatives from Engineered Streptomyces filipinensis Strains Reveals Clues for Reduced Haemolytic Action.

The rise in the number of immunocompromised patients has led to an increased incidence of fungal infections, with high rates of morbidity and mortality. Furthermore, misuse of antifungals has boosted the number of resistant strains to these agents; thus, there is urgent need for new drugs against these infections. Here, the in vitro antifungal activity of filipin III metabolic intermediates has been characterized against a battery of opportunistic pathogenic fungi—Candida albicans, Candida glabrata, Candida krusei, Cryptococcus neoformans, Trichosporon cutaneum, Trichosporon asahii, Aspergillus nidulans, Aspergillus niger, and Aspergillus fumigatus—using the Clinical and Laboratory Standards Institute broth microdilution method. Structural characterization of these compounds was undertaken by mass spectrometry (MS) and nuclear magnetic resonance (NMR) following HPLC purification. Complete NMR assignments were obtained for the first time for filipins I and II. In vitro haemolytic assays revealed that the haemolytic action of these compounds relies largely on the presence of a hydroxyl function at C26, since derivatives lacking such moiety show remarkably reduced activity. Two of these derivatives, 1′-hydroxyfilipin I and filipin I, show decreased toxicity towards cholesterol-containing membranes while retaining potent antifungal activity, and could constitute excellent leads for the development of efficient pharmaceuticals, particularly against Cryptococcosis.

A combined NMR, MD and DFT conformational analysis of 9-O-acetyl sialic acid-containing GM3 ganglioside glycan and its 9-N-acetyl mimic.

O-Acetylation of carbohydrates such as sialic acids is common in nature, but its role is not clearly understood due to the lability of O-acetyl groups. We demonstrated previously that 9-acetamido-9-deoxy-N-acetylneuraminic acid (Neu5Ac9NAc) is a chemically and biologically stable mimic of the 9-O-acetyl-N-acetylneuraminic acid (Neu5,9Ac2) of the corresponding sialoglycans. Here, a systematic nuclear magnetic resonance (NMR) spectroscopic and molecular dynamics (MD) simulation study was undertaken for Neu5,9Ac2-containing GM3 ganglioside glycan (GM3-glycan) and its Neu5Ac9NAc analog. GM3-glycan with Neu5Ac as the non-O-acetyl form of Neu5,9Ac2 was used as a control. Complete 1H and 13C NMR chemical shift assignments, three-bond 1H-13C trans-glycosidic coupling constants (3JCH), accurate 1H-1H coupling constants (3JHH), nuclear Overhauser effects and hydrogen bonding detection were carried out. Results show that structural modification (O- or N-acetylation) on the C-9 of Neu5Ac in GM3 glycan does not cause significant conformational changes on either its glycosidic dihedral angles or its secondary structure. All structural differences are confined to the Neu5Ac glycerol chain, and minor temperature-dependent changes are seen in the aglycone portion. We also used Density Functional Theory (DFT) quantum mechanical calculations to improve currently used 3JHH Karplus relations. Furthermore, OH chemical shifts were assigned at -10°C and no evidence of an intramolecular hydrogen bond was observed. The results provide additional evidence regarding structural similarities between sialosides containing 9-N-acetylated and 9-O-acetylated Neu5Ac and support the opportunity of using 9-N-acetylated Neu5Ac as a stable mimic to study the biochemical role of 9-O-acetylated Neu5Ac.

Configurational Study of Diastereoisomeric Royleanone Diterpenoids From Salvia concolor

The known diterpenoids horminone (1) and taxoquinone (2) as a mixture, and pure 6,7-dehydroroyleanone (7) were isolated from the aerial parts of not yet studied Salvia concolor Lamb. Although 1 and 2 are known, the 1H Nuclear Magnetic Resonance (NMR) data of their acetyl derivatives 4 to 6 are only partially described. Moreover, the 13C NMR data assignments for 4 and 6 show some inconsistencies and reveal better agreement with those we obtained for diastereoisomeric 3 and 5. Since stereochemical aspects were in doubt, it was considered as mandatory to unambiguously determine the absolute configuration of 3 to 6 using vibrational circular dichroism spectroscopy, which then allowed the complete 1H and 13C NMR chemical shift assignments of 4 to 6.

Function and solution structure of the Arabidopsis thaliana RALF8 peptide.

We report the recombinant preparation from Escherichia coli cells of samples of two closely related, small, secreted cysteine‐rich plant peptides: rapid alkalinization factor 1 (RALF1) and rapid alkalinization factor 8 (RALF8). Purified samples of the native sequence of RALF8 exhibited well‐resolved nuclear magnetic resonance (NMR) spectra and also biological activity through interaction with a plant receptor kinase, cytoplasmic calcium mobilization, and in vivo root growth suppression. By contrast, RALF1 could only be isolated from inclusion bodies as a construct containing an N‐terminal His‐tag; its poorly resolved NMR spectrum was indicative of aggregation. We prepared samples of the RALF8 peptide labeled with 15N and 13C for NMR analysis and obtained near complete 1H, 13C, and 15N NMR assignments; determined the disulfide pairing of its four cysteine residues; and examined its solution structure. RALF8 is mostly disordered except for the two loops spanned by each of its two disulfide bridges.

A Complete and Unambiguous 1H and 13C NMR Signals Assignment of para- Naphthoquinones, ortho- and para-Furanonaphthoquinones

A complete and unambiguous assignment of 1H and 13C nuclear magnetic resonance (NMR) signals of 29 naphthoquinones is reported on the basis of one- and two-dimensional NMR techniques (1H, 13C, 1H-1H correlated spectroscopy (COSY) and 1H-13C heteronuclear multiple-bond correlation (HMBC)). This is the first report distinguishing data between para-naphthoquinones, ortho- and para-furanonaphthoquinones isomers.

Unexpected dimerization of a tripeptide comprising a β,γ-diamino acid.

We have previously reported the synthesis of enantiopure β,γ-diamino acids and relevant short α/γ-peptide containing such building blocks. Complete nuclear magnetic resonance (NMR) studies, together with molecular modeling, highlighted the ability of a β,γ-diamino acid to induce various intramolecular turns. In this paper, we describe for the first time the formation of a dimeric structure constituted by α/γ/α-tripeptide and stabilized by intermolecular interactions. A structural model is proposed based on extensive NMR measurements.

A multidimensional 1H NMR lipidomics workflow to address chemical food safety issues.

Although it is still at a very early stage compared to its mass spectrometry (MS) counterpart, proton nuclear magnetic resonance (NMR) lipidomics is worth being investigated as an original and complementary solution for lipidomics. Dedicated sample preparation protocols and adapted data acquisition methods have to be developed to set up an NMR lipidomics workflow; in particular, the considerable overlap observed for lipid signals on 1D spectra may hamper its applicability. The study describes the development of a complete proton NMR lipidomics workflow for application to serum fingerprinting. It includes the assessment of fast 2D NMR strategies, which, besides reducing signal overlap by spreading the signals along a second dimension, offer compatibility with the high-throughput requirements of food quality characterization. The robustness of the developed sample preparation protocol is assessed in terms of repeatability and ability to provide informative fingerprints; further, different NMR acquisition schemes-including classical 1D, fast 2D based on non-uniform sampling or ultrafast schemes-are evaluated and compared. Finally, as a proof of concept, the developed workflow is applied to characterize lipid profiles disruption in serum from β-agonists diet fed pigs. Our results show the ability of the workflow to discriminate efficiently sample groups based on their lipidic profile, while using fast 2D NMR methods in an automated acquisition framework. This work demonstrates the potential of fast multidimensional 1H NMR-suited with an appropriate sample preparation-for lipidomics fingerprinting as well as its applicability to address chemical food safety issues.

Complete NMR assignment of a bisecting hybrid-type oligosaccharide transferred by Mucor hiemalis endo-β-N-acetylglucosaminidase

This study describes the complete nuclear magnetic resonance (NMR) spectral assignment of a bisecting hybrid-type oligosaccharide 1, transferred by Mucor hiemalis endo-β-N-acetylglucosaminidase (Endo-M). Through 1H- and 13C-NMR, DQF-COSY, HSQC, HMBC, TOCSY, and NOESY experiments, we determine the structure of the glycoside linkage formed by the Endo-M transglycosylation, i.e., the connection between GlcNAc and GlcNAc in oligosaccharide 1.

Cytotoxic Properties and Complete Nuclear Magnetic Resonance Assignment of Isolated Xanthones from the Root of Garcinia cowa Roxb.

Objective:To isolate compounds from the roots of Garcinia cowa and to evaluated their cytotoxic activity against breast (MCF-7), prostate (DU-145), and lung (H-460) cell lines.Materials and Methods:The ground air-dried root was sequentially macerated with hexane, dichloromethane (DCM), ethyl acetate (EtOAc), and methanol. The DCM soluble extract was fractionated by vacuum liquid chromatography, column chromatography, and radial chromatography over silica gel with hexane, EtOAc and methanol as eluent in progressively increasing polarity manner; to yield three compounds. Their structures were elucidated based on their spectroscopic data and their comparison with those of the literature. The cytotoxicity of isolated compounds was carried out against human cell lines by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric assay. The extract was added at various concentrations (0.1, 1, 10 and 100 mg/ml). The level of cytotoxicity was determined by calculating the level of IC50 that was based on the percentage of the cell death following the 24 h incubation with the extract.Results:Phytochemical study on the roots of G. cowa yielded rubraxanthone (3), cowanine (4) and 1,5-dihydroxyxanthone (5). Compound 4 with an IC50 value of 4.1 ± 1.0 μM, 5.4 ± 2.3 μM and 11.3 ± 10.0 μM against MCF-7, H-460, and DU-145, respectively while compound 3 was found to be in active.Conclusion:The results indicate that G. cowa roots could be important sources of natural cytotoxic compounds.SUMMARY Isolation of cytotoxic compounds from Garcinia cowaCowanine is the active constituent from the roots of Garcinia cowaComplete nuclear magnetic resonance assignment of isolated compoundsMS fragmentation of rubraxanthone.

ChemInform Abstract: Broadband Solid‐State MAS NMR of Paramagnetic Systems

AbstractReview: 103 refs.

A parametric finite element solution of the generalised Bloch–Torrey equation for arbitrary domains

Nuclear magnetic resonance (NMR) has proven of enormous value in the investigation of porous media. Its use allows to study pore size distributions, tortuosity, and permeability as a function of the relaxation time, diffusivity, and flow. This information plays an important role in plenty of applications, ranging from oil industry to medical diagnosis. A complete NMR analysis involves the solution of the Bloch–Torrey (BT) equation. However, solving this equation analytically becomes intractable for all but the simplest geometries.We present an efficient numerical framework for solving the complete BT equation in arbitrarily complex domains. In addition to the standard BT equation, the generalised BT formulation takes into account the flow and relaxation terms, allowing a better representation of the phenomena under scope. The presented framework is flexible enough to deal parametrically with any order of convergence in the spatial domain. The major advantage of such approach is to allow both faster computations and sensitivity analyses over realistic geometries. Moreover, we developed a second-order implicit scheme for the temporal discretisation with similar computational demands as the existing explicit methods. This represents a huge step forward for obtaining reliable results with few iterations. Comparisons with analytical solutions and real data show the flexibility and accuracy of the proposed methodology.