Conventional 1H NMR Research Articles

Improved Quantification by Nuclear Magnetic Resonance Spectroscopy of the Fatty Acid Ester Composition of Extra Virgin Olive Oils.

Analysis of foods, which are typically highly complex mixtures, by 1H NMR can be difficult because the prevalence of signal overlap complicates characterization and quantification. The various components of a food sample may have a wide range of concentrations, leading to a high dynamic range NMR spectrum and complicating the analysis of less concentrated species. One source of this complication is the presence of 13C satellites, peaks that appear either side of a parent peak with ∼0.56% of its intensity. Satellites of concentrated species can easily be comparable in intensity to the signals of minor components, and can partly or wholly obscure them. This is commonly seen in olive oil samples, leading to inaccurate calculation of the fatty acid ester composition of the oil, used for determining the quality of edible oils and for detecting adulteration. Here, we show that the recently introduced Destruction of Interfering Satellites by Perfect Echo Low-pass filtration (DISPEL) experiment is able to suppress 13C satellites and can substantially improve the accuracy of integration of minor signals. The DISPEL experiment does not require any complicated optimization, working “out of the box” with standard parameters, and incurs no significant loss of sensitivity. It has the potential to become the default experiment, replacing conventional 1D 1H NMR, for quantitative analysis of olive oil.

Detection of glucose-derived d- and l-lactate in cancer cells by the use of a chiral NMR shift reagent

BackgroundExcessive lactate production, a hallmark of cancer, is largely formed by the reduction of pyruvate via lactate dehydrogenase (LDH) to l-lactate. Although d-lactate can also be produced from glucose via the methylglyoxal pathway in small amounts, less is known about the amount of d-lactate produced in cancer cells. Since the stereoisomers of lactate cannot be distinguished by conventional 1H NMR spectroscopy, a chiral NMR shift reagent was used to fully resolve the 1H NMR resonances of d- and l-lactate.MethodsThe production of l-lactate from glucose and d-lactate from methylglyoxal was first demonstrated in freshly isolated red blood cells using the chiral NMR shift reagent, YbDO3A-trisamide. Then, two different cell lines with high GLO1 expression (H1648 and H 1395) were selected from a panel of over 80 well-characterized human NSCLC cell lines, grown to confluence in standard tissue culture media, washed with phosphate-buffered saline, and exposed to glucose in a buffer for 4 h. After 4 h, a small volume of extracellular fluid was collected and mixed with YbDO3A-trisamide for analysis by 1H NMR spectroscopy.ResultsA suspension of freshly isolated red blood cells exposed to 5mM glucose produced l-lactate as expected but very little d-lactate. To evaluate the utility of the chiral NMR shift reagent, methylglyoxal was then added to red cells along with glucose to stimulate the production of d-lactate via the glyoxalate pathway. In this case, both d-lactate and l-lactate were produced and their NMR chemical shifts assigned. NSCLC cell lines with different expression levels of GLO1 produced both l- and d-lactate after incubation with glucose and glutamine alone. A GLO1-deleted parental cell line (3553T3) showed no production of d-lactate from glucose while re-expression of GLO1 resulted in higher production of d-lactate.ConclusionsThe shift-reagent-aided NMR technique demonstrates that d-lactate is produced from glucose in NSCLC cells via the methylglyoxal pathway. The biological role of d-lactate is uncertain but a convenient method for monitoring d-lactate production could provide new insights into the biological roles of d- versus l-lactate in cancer metabolism.

Synthesis of Boroxine and Dioxaborole Covalent Organic Frameworks via Transesterification and Metathesis of Pinacol Boronates.

Boroxine and dioxaborole are the first and some of the most studied synthons of covalent organic frameworks (COFs). Despite their wide application in the design of functional COFs over the last 15 years, their synthesis still relies on the original Yaghi's condensation of boronic acids (with itself or with polyfunctional catechols), some of which are difficult to prepare, poorly soluble, or unstable in the presence of water. Here, we propose a new synthetic approach to boroxine COFs (on the basis of the transesterification of pinacol aryl boronates (aryl-Bpins) with methyl boronic acid (MBA) and dioxaborole COFs (through the metathesis of pinacol boronates with MBA-protected catechols). The aryl-Bpin and MBA-protected catechols are easy to purify, highly soluble, and bench-stable. Furthermore, the kinetic analysis of the two model reactions reveals high reversibility (Keq ∼ 1) and facile control over the equilibrium. Unlike the conventional condensation, which forms water as a byproduct, the byproduct of the metathesis (MBA pinacolate) allows for easy kinetic measurements of the COF formation by conventional 1H NMR. We show the generality of this approach by the synthesis of seven known boroxine/dioxaborole COFs whose crystallinity is better or equal to those reported by conventional condensation. We also apply metathesis polymerization to obtain two new COFs, Py4THB and B2HHTP, whose synthesis was previously precluded by the insolubility and hydrolytic instability, respectively, of the boronic acid precursors.

PSYCHE-A Valuable Experiment in Plant NMR-Metabolomics.

1H-NMR is a very reproducible spectroscopic method and, therefore, a powerful tool for the metabolomic analysis of biological samples. However, due to the high complexity of natural samples, such as plant extracts, the evaluation of spectra is difficult because of signal overlap. The new NMR “Pure Shift” methods improve spectral resolution by suppressing homonuclear coupling and turning multiplets into singlets. The PSYCHE (Pure Shift yielded by Chirp excitation) and the Zangger–Sterk pulse sequence were tested. The parameters of the more suitable PSYCHE experiment were optimized, and the extracts of 21 Hypericum species were measured. Different evaluation criteria were used to compare the suitability of the PSYCHE experiment with conventional 1H-NMR. The relationship between the integral of a signal and the related bin value established by linear regression demonstrates an equal representation of the integrals in binned PSYCHE spectra compared to conventional 1H-NMR. Using multivariate data analysis based on both techniques reveals comparable results. The obtained data demonstrate that Pure Shift spectra can support the evaluation of conventional 1H-NMR experiments.

Large-Scale Evaluation of Major Soluble Macromolecular Components of Fish Muscle from a Conventional 1H-NMR Spectral Database.

Conventional proton nuclear magnetic resonance (1H-NMR) has been widely used for identification and quantification of small molecular components in food. However, identification of major soluble macromolecular components from conventional 1H-NMR spectra is difficult. This is because the baseline appearance is masked by the dense and high-intensity signals from small molecular components present in the sample mixtures. In this study, we introduced an integrated analytical strategy based on the combination of additional measurement using a diffusion filter, covariation peak separation, and matrix decomposition in a small-scale training dataset. This strategy is aimed to extract signal profiles of soluble macromolecular components from conventional 1H-NMR spectral data in a large-scale dataset without the requirement of re-measurement. We applied this method to the conventional 1H-NMR spectra of water-soluble fish muscle extracts and investigated the distribution characteristics of fish diversity and muscle soluble macromolecular components, such as lipids and collagens. We identified a cluster of fish species with low content of lipids and high content of collagens in muscle, which showed great potential for the development of functional foods. Because this mechanical data processing method requires additional measurement of only a small-scale training dataset without special sample pretreatment, it should be immediately applicable to extract macromolecular signals from accumulated conventional 1H-NMR databases of other complex gelatinous mixtures in foods.

Thiol-ene coupling reaction achievement and monitoring by "in situ" UV irradiation NMR spectroscopy.

In this study, the possibilities of a new “in situ” LED UV illumination NMR spectroscopic technique for performing an initiator-free thiol–ene “click” coupling reaction of an allyl-functionalized poly(allyl glycidyl ether) (PAGE) prepolymer with a number of mono- and di-oligo polyethylene glycol (PEG) thiols is demonstrated. The state-of-the-art setup constructed with LEDs as UV light sources that illuminate through optical fibers directly into an NMR testing tube at a fixed wavelength of 365 nm is appropriate for various polymeric materials and biologically active substances. The selected experimental protocol uses a series of periods of irradiation and dark periods, thus providing opportunities to conduct an effective thiol–ene “click” reaction and simultaneously study the kinetics of the photochemical reaction with the exposure time, as well as macromolecular association directly in a solution applying the whole types of NMR methods: from conventional 1H or 13C NMR to diffusion NMR spectroscopy (DOSY). In addition, the molecular mass characteristics of the prepared copolymers were studied by gel-permeation chromatography (GPC). The observed differences in the reaction rates as well as in the size of species formed (the corresponding hydrodynamic radiuses Rh of aggregates) as a result of the coupling process of parent PAGE prepolymers and model PEG thiols were thoroughly discussed and the reaction pathway proposed.

Quantitative NMR-Based Metabolomics on Tissue Biomarkers and Its Translation into In Vivo Magnetic Resonance Spectroscopy.

Nuclear magnetic resonance (NMR) spectroscopy is an established analytical platform for analyzing metabolic profiles of cells, tissues, and body fluids. There are several advantages in introducing an NMR-based study design into metabolomics studies, including a fast and comprehensive detection, characterization, and quantification of dozens of endogenous metabolites in a single NMR spectrum. Quantitative proton 1H-NMR is the most useful NMR-based platform for metabolomics. The frozen tissues can be analyzed noninvasively using a high-resolution magic angle spinning (HR-MAS) 1H-NMR spectroscopy; or several extraction techniques can be applied to detect additional metabolites using a conventional liquid-based NMR technique. In this chapter, we report on tissue collection, handling, extraction methods, and 1H-NMR acquisition protocols developed in the past decades for a precise and quantitative NMR-metabolomics approach. The NMR acquisition protocols (both HR-MAS and conventional 1H-NMR spectroscopy) and spectral analysis steps are also presented. Since NMR can be applied "in vivo" using horizontal bore MRI scanners, several in vivo sequences for localized 1H-MRS (magnetic resonance spectroscopy) are presented which can be directly applied for noninvasive detection of brain metabolites.

New dansyl labeled polysilane: Synthesis, characterization and sensor application

This work describes a polysilane-dansyl graft copolymer obtained by addition of N-methacryloyloxyethylcarbamoyl-5-(dimethylaminonaphthalene-1-sulfonohydrazine) to SiH reactive groups of poly[methyl(H)-co-diphenyl]silane. The synthesis approach is thermally initiated by 1,1′-azobis (cyclohexanecarbonitrile) as a radical hydrosilylation process promotor. The resulted material is a complex fluorescent nanocomposite which combines the optical properties of several chromophores like the methylhydrosilyls and diphenylsilyls segments, dansyl moieties and silicon quantum dots. Attachment of the dansyl moieties directly to the sigma conjugated chain of polysilane results in a strong emission signal in the visible region. Conventional FTIR, 1H NMR, GPC, TGA and UV–Vis analysis were used to evidence the chemical structure in relation with the optical properties. Since the signal corresponding to the silicon quantum dots is also present the nanocomposite could be used in a multichannel detection system in biological environments. The sensing capacity toward some particular cations has been successfully tested.

Correlation Method for Conversion Determination of Biodiesel Obtained from Different Alcohols by 1H NMR Spectroscopy

This work presents a correlation method that uses 1H NMR spectra for determining the conversion during transesterification of vegetable oil with 10 alcohols: methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, 1-pentanol, isopentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-decanol, 1-dodecanol, and benzyl alcohol. Conversions ranging from 70 to 99%, depending on primary alcohol used, are obtained using organic catalyst N,N′,N″-tris(3-(dimethylamino)propyl)guanidine. Catalysts, alcohols, and intermediate products can cause signal overlapping, debilitating the use of the conventional 1H NMR method. Thus, our method uses the correlation between the triplet signal of α-carbonylmethylene and two signals of unsaturated parts of the fatty acid chain, where signal overlapping does not occur, hence, adding robustness and flexibility to the method. The method is applicable for unsaturated oils and is not affected by the amounts of residual alcohol, catalyst, or intermediate products, making it...

Integrated Analytical and Statistical Two-Dimensional Spectroscopy Strategy for Metabolite Identification: Application to Dietary Biomarkers.

A major purpose of exploratory metabolic profiling is for the identification of molecular species that are statistically associated with specific biological or medical outcomes; unfortunately, the structure elucidation process of unknowns is often a major bottleneck in this process. We present here new holistic strategies that combine different statistical spectroscopic and analytical techniques to improve and simplify the process of metabolite identification. We exemplify these strategies using study data collected as part of a dietary intervention to improve health and which elicits a relatively subtle suite of changes from complex molecular profiles. We identify three new dietary biomarkers related to the consumption of peas (N-methyl nicotinic acid), apples (rhamnitol), and onions (N-acetyl-S-(1Z)-propenyl-cysteine-sulfoxide) that can be used to enhance dietary assessment and assess adherence to diet. As part of the strategy, we introduce a new probabilistic statistical spectroscopy tool, RED-STORM (Resolution EnhanceD SubseT Optimization by Reference Matching), that uses 2D J-resolved 1H NMR spectra for enhanced information recovery using the Bayesian paradigm to extract a subset of spectra with similar spectral signatures to a reference. RED-STORM provided new information for subsequent experiments (e.g., 2D-NMR spectroscopy, solid-phase extraction, liquid chromatography prefaced mass spectrometry) used to ultimately identify an unknown compound. In summary, we illustrate the benefit of acquiring J-resolved experiments alongside conventional 1D 1H NMR as part of routine metabolic profiling in large data sets and show that application of complementary statistical and analytical techniques for the identification of unknown metabolites can be used to save valuable time and resources.

QM-HiFSA-Aided Structure Determination of Succinilenes A-D, New Triene Polyols from a Marine-Derived Streptomyces sp.

Based on profiles of secondary metabolites produced by marine bacteria obtained using LC/MS, succinilenes A–D (1–4), new triene polyols, were discovered from a culture of a Streptomyces strain SAK1, which was collected in the southern area of Jeju Island, Republic of Korea. The gross structures of 1–4 were primarily determined through analysis of NMR spectra. The double bond geometries of the succinilenes, which could not be established from conventional 1H NMR spectra because of the highly overlapped olefinic signals, were successfully deciphered using the recently developed quantum-mechanics-driven 1H iterative full spin analysis (QM-HiFSA). Succinilenes A–C (1–3) displayed inhibitory effects against lipopolysaccharide (LPS)-induced nitric oxide (NO) production, indicating their anti-inflammatory significance. These three compounds (1–3) commonly bear a succinic acid moiety, although succinilene D (4), which did not inhibit NO production, does not have this moiety in its structure. The absolute configurations of succinilenes A–D (1–4) were established through J-based configuration analysis, the modified Mosher’s method following methanolysis, and CD spectral analysis.

An approach to the simultaneous quantitative analysis of metabolites in table wines by 1H NMR self-constructed three-dimensional spectra

Wine consists of several hundred components with different concentrations, including water, ethanol, glycerol, organic acids and sugars. Accurate quantification of target compounds in such complex samples is a difficult task based on conventional 1H NMR spectra due to some challenges. In this paper, the three-dimensional spectrum was constructed firstly by simply repeating 1H NMR spectrum itself so as to extract the features of target compounds by Tchebichef moment method. A proof-of-concept model system, the determination of five metabolites in wines was utilized to evaluate the performance of the proposed strategy. The results indicate that the proposed approach can provide accurate and reliable concentration predictions, probably the best results ever achieved using PLS and interval-PLS methods. Our novel strategy has not only good performance but also does not require laborious multi-step and subjective pretreatments. Therefore, it is expected that the proposed method could extend the application of conventional 1H NMR.

Tetrahedral rigid core antenna chromophores bearing bay-substituted perylenediimides

Two new representative methane- and adamantane-centered ‘antenna’ tetramers bearing bay-substituted π-conjugated phenylethynyl-perylenediimides (PDICCPh) as chromophoric subunits, tetrakis-[1-(4-ethynylphenyl)-N,N′-bis(1-hexylheptyl)-perylene-3,4:9,10-tetracarboxylic diimide]-methane (1) and tetrakis-1,3,5,7-[1-(4-ethynylphenyl)-N,N′-bis(1-hexylheptyl)-perylene-3,4:9,10-tetracarboxylic diimide]-adamantane (2), have been synthesized and their structural aspects have been thoroughly investigated by NMR spectroscopy. These PDI tetramers (1 and 2) represent the first successful example of incorporating the bay-substituted phenylethynyl-perylenediimides into the large rigid core tetrahedral frameworks. In these PDI tetramers, dynamic NMR experiments revealed the existence of perylene-centered conformational dynamic equilibrium (ΔG≠=15−17 kcal/mol), the primary cause of the observed spectral broadening in conventional 1H NMR spectra (295 K). In addition, PDI tetramers 1 and 2 were found to possess exceptional (photo)chemical stability, and their corresponding photophysical properties (ɛmax∼180,000; τFL=6.9 ns; ΦFL∼60%) make them viable candidates for various photonic applications and are in good agreement with other related multichromophoric PDI-based systems.

Quick measurement of 1H–19F scalar couplings from the complex NMR spectra by real-time spin edition

Most often the measurement of nJHF from the conventional 1D 1H NMR spectrum is severely hindered consequent to similar magnitudes of JHF and JHH couplings and the spectral multiplicity pattern. The present study reports a new 1D NMR technique based on real time spin edition, which removes all JHF and JHH while retaining only nJHF of a chosen fluorine. The obtained spectrum is significantly simplified and permits straightforward determination of all possible nJHF values of a chosen fluorine. Due to one dimensional nature, the method is much faster compared to 2D GET-SERF by 1–2 orders of magnitude.

NMR and EPR Characterization of Functionalized Nanodiamonds

We investigated the potential of solid-state NMR using magic angle spinning (MAS) with and without dynamic nuclear polarization (DNP) and electron paramagnetic resonance (EPR) for the characterization of functionalized nanodiamonds (NDs). We showed that conventional 1H, 31P, and 13C solid-state NMR spectra allow differentiating in a straightforward way NDs from commercial sources and custom-made NDs bearing aromatic or aliphatic phosphonate moieties at their surface. Besides, the short nuclear relaxation times prove the close proximity between the endogenous paramagnetic centers of NDs and the grafted organic moieties. EPR spectra confirmed the presence of these paramagnetic centers in functionalized NDs, which are centered on dangling bonds as well as a few N0 defects, corresponding to the substitution of carbon atoms by nitrogen ones. Hyperfine sublevel correlation spectroscopy indicates that the N0 paramagnetic centers are mostly located in the disordered shell of NDs. Preliminary DNP-enhanced NMR expe...

Thermodynamic properties and spectral investigation of dilute sulfur dioxide in binary system N,N-dimethylformamide + diethylene glycol

In this work, isothermal gas–liquid equilibrium (GLE) data were measured for dilute SO2 in the binary system N,N-dimethylformamide (DMF) (1)+diethylene glycol (DEG) (2) at T=(298.15, 303.15, 313.15, and 318.15) K and p=122.66kPa. Based on the GLE data, Henry’s law constants were obtained by fitting the linear slope of GLE data, and the thermodynamic parameters were calculated. The thermodynamic results showed that the dissolving processes of dilute SO2 in the binary system are spontaneous, enthalpy driving, and reversible behavior. When conventional UV, FT-IR, and 1H NMR spectroscopic techniques were used for inspection of spectral changes of dilute SO2 in the binary system DMF (1)+DEG (2), the spectral results suggest that hydrogen bonding and interaction of carbonyl oxygen atoms in DMF with hydroxyl hydrogen atoms in DEG were formed as HCO⋯HOCH2CH2OCH2CH2OH⋯, and the strong absorption capability of SO2 in the binary system can be due to the intermolecular S⋯O interaction as the formation HCO⋯(O)SO.

Palladium catalyzed Mizoroki–Heck and Suzuki–Miyaura reactions using naphthalenomethyl-substituted imidazolidin-2-ylidene ligands in aqueous media

Naphthalenomethyl-substituted imidazolidinium salts (1a-g) were prepared and characterized by conventional spectroscopic methods, 1H NMR, 13C NMR, FTIR, and elemental analysis techniques. The in situ prepared three component systems naphthalenomethyl-substituted imidazolidinium salts, Pd(OAc)2, and K2CO3 catalyzed quantitatively the Mizoroki–Heck and Suzuki–Miyaura coupling of aryl halides under mild conditions in aqueous media.

In situ analysis of [8-13C-7-15N]-double-labelled theophylline by a triple resonance NMR technique

[8-13C-7-15N]-labelled theophylline was synthesized and applied for in situ analysis using a 1H–{13C–15N} triple resonance NMR technique. The triple resonance analysis enabled selective detection of labelled theophylline in a mixture containing excess amino acids or crude mouse liver extract, where conventional 1H NMR analysis suffers from difficulty because of background signals.

Universal Polymer Analysis by 1H NMR Using Complementary Trimethylsilyl End Groups

New degenerative chain transfer agents, namely 4-(trimethylsilyl)benzyl 4'-(trimethylsilyl)butane-dithioate, 4-(trimethylsilyl)benzyl 3'-(trimethylsilyl)propyl trithiocarbonate and their 3-(trimethylsilyl)benzyl isomers, that are two-fold labeled with complementary trimethylsilyl (TMS) markers, were designed and shown to be powerful tools for universal polymer analysis by conventional (1)H NMR spectroscopy. Their use in controlled free radical polymerization, here the reversible addition-fragmentation chain transfer (RAFT) method, resulted in polymers with low polydispersities up to high molar masses, as well as with defined complementary TMS end groups. Thus, routine (1)H NMR spectra allowed facile determination of the molar masses of polymers of various chemical structures up to at least 10(5) g/mol, and simultaneously provided crucial information about the content of end groups that is typically >95% when polymerizations are correctly performed. Polymerizations were carried out in various solvents for two standard monomers, namely n-butyl acrylate and styrene, as well as for two specialty monomers, so-called inimers, namely 2-(2-chloropropionyloxy)ethyl acrylate and 2-(2-chloropropionyloxy)ethyl acrylamide. The complementary end group markers revealed marked differences in the suitability of commonly used solvents for RAFT polymerization. The results demonstrate-beyond good polymerization control-that the new RAFT agents are universal, powerful tools for facile polymer analysis by routine (1)H NMR spectroscopy, of their absolute molar masses as well as of the content of end groups. This is crucial information, e.g., for the synthesis of high-quality telechelics and, in particular, of block copolymers, which is difficult to obtain by other methods. Preliminary screening experiments indicate that similar uses can be envisaged for analogous ATRP systems.

General Strategy for High-Density Covalent Functionalization of Diamond Nanoparticles Using Fenton Chemistry

Diamond nanoparticles (npD) from detonation do not undergo covalent functionalization to a large extent, as assessed by conventional IR and NMR spectroscopy. This low level of surface modification is due to the low density of surface hydroxyl groups and the presence of soot matter covering npD. We have found that the Fenton reaction of npD remarkably increases the density of surface OH groups, decreases the undesirable amorphous soot matter, and makes possible the subsequent high-density covalent functionalization of these nanoparticles. In this way, the polarity and solubility of npD can be controlled and, besides by IR spectroscopy, we have shown that it is even possible to characterize the resulting diamond nanoparticles by conventional solution 1H NMR spectroscopy in which the signals corresponding to the proton ligands can be monitored.