Automatic NMR-based protocol for assessment of honey authenticity.

H NMR analysis of organic extracts of honey is a powerful technique to confirm its botanical origin, thanks to the presence of signals that are specific to each floral typology. Similarly, signals from bee metabolites provide an important tool to verify honey entomological origin. Here, we present a method for honey screening that does not require any detailed analysis of the NMR spectrum for the detection and quantification of such markers.

NMR Discrimination of d- and l-α-Amino Acids at Submicromolar Concentration via Parahydrogen-Induced Hyperpolarization.

Differentiation of enantiomers represents an important research area for pharmaceutical, chemical, and food industries. However, enantiomer separation is a laborious task that demands complex analytical techniques, specialized equipment, and expert personnel. In this respect, discrimination and quantification of d- and l-α-amino acids is no exception, generally requiring extensive sample manipulation, including isolation, functionalization, and chiral separation.

Analysis of Complex Mixtures by Chemosensing NMR Using -Hydrogen-Induced Hyperpolarization.

Nuclear magnetic resonance (NMR) is a powerful technique for chemical analysis. The use of NMR to investigate dilute analytes in complex systems is, however, hampered by its relatively low sensitivity. An additional obstacle is represented by the NMR signal overlap.

Parahydrogen Hyperpolarization Allows Direct NMR Detection of α-Amino Acids in Complex (Bio)mixtures.

The scope of non-hydrogenative parahydrogen hyperpolarization (nhPHIP) techniques has been expanding over the last years, with the continuous addition of important classes of substrates. For example, pyruvate can now be hyperpolarized using the Signal Amplification By Reversible Exchange (SABRE) technique, offering a fast, efficient and low-cost PHIP alternative to Dynamic Nuclear Polarization for metabolic imaging studies. Still, important biomolecules such as amino acids have so far resisted PHIP, unless properly functionalized.

An approach to fast 2D nuclear magnetic resonance at low concentration based on p-H -induced polarization and nonuniform sampling.

Recent developments in para-hydrogen-induced polarization (PHIP) methods allow the nuclear magnetic resonance (NMR) detection of specific classes of compounds, down to sub-micromolar concentration in solution. However, when dealing with complex mixtures, signal resolution requires the acquisition of 2D PHIP-NMR spectra, which often results in long experimental times. This strongly limits the applicability of these 2D PHIP-NMR techniques in areas in which high-throughput analysis is required.

Floral origin modulates the content of a lipid marker in Apis mellifera honey.

The compound DAGE (DiAcyl Glyceryl Ether, 1-stearyl-2,3-dioleoyl glycerol), present in Apis mellifera honey, is a lipidic entomological marker secreted by the salivary glands of worker bees. Its content was determined by NMR, analyzing the organic extracts of a number of Italian honeys of different floral typology. We have found that the DAGE content is related to the botanical origin of honey.

Determination of hydrogen exchange and relaxation parameters in PHIP complexes at micromolar concentrations.

Non-hydrogenative para-hydrogen-induced polarization (PHIP) is a fast, efficient and relatively inexpensive approach to enhance nuclear magnetic resonance (NMR) signals of small molecules in solution. The efficiency of this technique depends on the interplay of NMR relaxation and kinetic processes, which, at high concentrations, can be characterized by selective inversion experiments. However, in the case of dilute solutions this approach is clearly not viable.

NMR carbohydrate profile in tracing acacia honey authenticity.

The sugar profile in honey can be used as a fingerprint to confirm the authenticity or reveal the adulteration of the product by sweetener addition. In this work, we have accurately determined the profile of 20 minor saccharides in a set of 46 European acacia honeys using a recently proposed NMR approach based on the CSSF-TOCSY experiment. Comparison of this reference profile with the sugar composition of several Chinese honey samples of the same declared botanical origin has revealed important differences.

Parahydrogen induced hyperpolarization provides a tool for NMR metabolomics at nanomolar concentrations.

An NMR approach based on parahydrogen hyperpolarization is presented to detect and resolve specific classes of metabolites in complex biomixtures at down to nanomolar concentrations. We demonstrate our method on solid phase extracts of urine, by simultaneously observing hundreds of metabolites well below the limits of detection of thermal NMR.

Trace analysis in water-alcohol mixtures by continuous p-H hyperpolarization at high magnetic field.

Nuclear magnetic resonance (NMR) studies of complex mixtures are often limited by the low sensitivity of the technique and by spectral overlap. We have recently reported on an NMR chemosensor on the basis of para-Hydrogen Induced Polarization that potentially addresses both these issues, albeit for specific classes of compounds. This approach makes use of Signal Amplification By Reversible Exchange (SABRE) catalysts in methanol and allows selective detection and quantification of dilute analytes in complex mixtures.

DOSY Analysis of Micromolar Analytes: Resolving Dilute Mixtures by SABRE Hyperpolarization.

DOSY is an NMR spectroscopy technique that resolves resonances according to the analytes' diffusion coefficients. It has found use in correlating NMR signals and estimating the number of components in mixtures. Applications of DOSY in dilute mixtures are, however, held back by excessively long measurement times.

High field hyperpolarization-EXSY experiment for fast determination of dissociation rates in SABRE complexes.

SABRE (Signal Amplification By Reversible Exchange) is a nuclear spin hyperpolarization technique based on the reversible concurrent binding of small molecules and para-hydrogen (p-H) to an iridium metal complex in solution. At low magnetic field, spontaneous conversion of p-H spin order to enhanced longitudinal magnetization of the nuclear spins of the other ligands occurs. Subsequent complex dissociation results in hyperpolarized substrate molecules in solution.

Stable isotope labeling methods for DNA.

NMR is a powerful method for studying proteins and nucleic acids in solution. The study of nucleic acids by NMR is far more challenging than for proteins, which is mainly due to the limited number of building blocks and unfavorable spectral properties. For NMR studies of DNA molecules, (site specific) isotope enrichment is required to facilitate specific NMR experiments and applications.

A New Ir-NHC Catalyst for Signal Amplification by Reversible Exchange in D2 O.

NMR signal amplification by reversible exchange (SABRE) has been observed for pyridine, methyl nicotinate, N-methylnicotinamide, and nicotinamide in D2 O with the new catalyst [Ir(Cl)(IDEG)(COD)] (IDEG=1,3-bis(3,4,5-tris(diethyleneglycol)benzyl)imidazole-2-ylidene). During the activation and hyperpolarization steps, exclusively D2 O was used, resulting in the first fully biocompatible SABRE system. Hyperpolarized (1) H substrate signals were observed at 42.

Efficient and Selective Chemical Labeling of Electrochemically Generated Peptides Based on Spirolactone Chemistry.

Specific digestion of proteins is an essential step for mass spectrometry-based proteomics, and the chemical labeling of the resulting peptides is often used for peptide enrichment or the introduction of desirable tags. Cleavage of the peptide bond following electrochemical oxidation of Tyr or Trp results in a spirolactone moiety at the newly formed C-terminus offering a handle for chemical labeling. In this work, we developed a highly efficient and selective chemical labeling approach based on spirolactone chemistry.

NMR-Based Chemosensing via p-H2 Hyperpolarization: Application to Natural Extracts.

When dealing with trace analysis of complex mixtures, NMR suffers from both low sensitivity and signal overlap. NMR chemosensing, in which the association between an analyte and a receptor is "signaled" by an NMR response, has been proposed as a valuable analytical tool for biofluids and natural extracts. Such chemosensors offer the possibility to simultaneously detect and distinguish different analytes in solution, which makes them particularly suitable for analytical applications on complex mixtures.

Determination of long-range scalar (1)H-(1)H coupling constants responsible for polarization transfer in SABRE.

SABRE (Signal Amplification By Reversible Exchange) nuclear spin hyperpolarization method can provide strongly enhanced NMR signals as a result of the reversible association of small molecules with para-hydrogen (p-H2) at an iridium metal complex. The conversion of p-H2 singlet order to enhanced substrate proton magnetization within such complex is driven by the scalar coupling interactions between the p-H2 derived hydrides and substrate nuclear spins. In the present study these long-range homonuclear couplings are experimentally determined for several SABRE substrates using an NMR pulse sequence for coherent hyperpolarization transfer at high magnetic field.

Human ISPD Is a Cytidyltransferase Required for Dystroglycan O-Mannosylation.

A unique, unsolved O-mannosyl glycan on α-dystroglycan is essential for its interaction with protein ligands in the extracellular matrix. Defective O-mannosylation leads to a group of muscular dystrophies, called dystroglycanopathies. Mutations in isoprenoid synthase domain containing (ISPD) represent the second most common cause of these disorders, however, its molecular function remains uncharacterized.

2D NMR Trace Analysis by Continuous Hyperpolarization at High Magnetic Field.

Nuclear magnetic resonance is often the technique of choice in chemical analysis because of its sensitivity to molecular structure, quantitative character, and straightforward sample preparation. However, determination of trace analytes in complex mixtures is generally limited by low sensitivity and extensive signal overlap. Here, we present an approach for continuous hyperpolarization at high magnetic field that is based on signal amplification by reversible exchange (SABRE) and can be straightforwardly incorporated in multidimensional NMR experiments.

Application of the π-accepting ability parameter of N-heterocyclic carbene ligands in iridium complexes for signal amplification by reversible exchange (SABRE).

The new π-accepting ability parameter (PAAP) appears to be the best tool to analyse the electronic properties of NHC ligands in [Ir(H)2(NHC)(Py)3](+) complexes for SABRE. Together with the buried volume, the efficiency of hyperpolarisation transfer in SABRE, depending on the exchange rate of pyridine, can be described.

Computational (DFT) and Experimental (EXAFS) Study of the Interaction of [Ir(IMes)(H)2 (L)3 ] with Substrates and Co-substrates Relevant for SABRE in Dilute Systems.

Signal amplification by reversible exchange (SABRE) is an emerging hyperpolarization method in NMR spectroscopy, in which hyperpolarization is transferred through the scalar coupling network of para-hydrogen derived hydrides in a metal complex to a reversibly bound substrate. Substrates can even be hyperpolarized at concentrations below that of the metal complex by addition of a suitable co-substrate. Here we investigate the catalytic system used for trace detection in NMR spectroscopy with [Ir(IMes)(H)2 (L)3 ](+) (IMes=1,3-dimesitylimidazol-2-ylidene) as catalyst, pyridine as a substrate and 1-methyl-1,2,3-triazole as co-substrate in great detail.

Enzymatic preparation of multimilligram amounts of pure single-stranded DNA samples for material and analytical sciences.

We present a method for high-yield production of multimilligram amounts of pure single-stranded DNA employing rolling circle amplification (RCA) and processing by restriction enzymes. Pure and homogeneous samples are produced with minimal handling time, reagents, and waste products. The RCA method is more than twice as efficient in dNTP incorporation than conventional polymerase chain reaction in producing end product.

Quantitative trace analysis of complex mixtures using SABRE hyperpolarization.

Signal amplification by reversible exchange (SABRE) is an emerging nuclear spin hyperpolarization technique that strongly enhances NMR signals of small molecules in solution. However, such signal enhancements have never been exploited for concentration determination, as the efficiency of SABRE can strongly vary between different substrates or even between nuclear spins in the same molecule. The first application of SABRE for the quantitative analysis of a complex mixture is now reported.

Toward nanomolar detection by NMR through SABRE hyperpolarization.

SABRE is a nuclear spin hyperpolarization technique based on the reversible association of a substrate molecule and para-hydrogen (p-H2) to a metal complex. During the lifetime of such a complex, generally fractions of a second, the spin order of p-H2 is transferred to the nuclear spins of the substrate molecule via a transient scalar coupling network, resulting in strongly enhanced NMR signals. This technique is generally applied at relatively high concentrations (mM), in large excess of substrate with respect to metal complex.