Restoring symmetry in two-dimensional solid-state NMR correlation spectra

International audienc

The “Wine-T1” NMR experiment for novel wine-metabolome fingerprinting with nuclear-spin relaxation

In agreement with the draft resolution OENO-SCMA 17-618 at step 5 “Quantitation of glucose, malic acid, acetic acid, fumaric acid, shikimic acid and sorbic acid in wine using proton nuclear magnetic resonance spectroscopy (1H NMR)” said technique has been recently accepted within the OIV chair as a primary quantitative analytical technique for beverage analysis such as wine. However, poor chemical shift dispersion in 1H NMR spectra severely penalizes quantification within overlapped or crowded regions. To outflank said penalization and quantify metabolites in signal overcrowding situations, the novel “Wine-T1” experiment is proposed. The novel scheme comprises the addition of a second dimension, wherein the proton spin-lattice relaxation times (T1-{1H}) of each metabolite's spin-system is correlated to a chemical-shift dimension. The new experiment includes a water and ethanol signal pre-saturation module, prior to the T1 saturation-inversion recovery dimension in order to maximize signal-to-noise ratio of wine metabolome NMR spectra. “Wine-T1” pulse sequence can be adapted to all commercial spectrometers (Bruker, Varian/Agilent, Jeol) and with acquisition times in the order of minutes, it should be considered as a fast repetition method to produce a robust metabolome fingerprint that has not been described before, to the best of our knowledge

Probing Structural and Motional Features of the C-Terminal Part of the Human Centrin 2/P17-XPC Microcrystalline Complex by Solid-State NMR Spectroscopy

International audienceAn insight into structural and motional features of the C-terminal part of the Human Centrin 2 in complex with the peptide P17-XPC was obtained by using complementary solid-state NMR methods. We demonstrate that the experimental conditions and procedures of sample crystallization determine not only the quality of solid-state NMR spectra but can also dramatically modify the dynamic state of water molecules and the internal mobility of the protein. Two-dimensional (2D) 13C - 13C and 15N - 15N correlation spectra reveal intra- and inter-residue dipolar connectivities and provide partial, site-specific assignments of 13C and 15N resonance signals. The secondary structure of the C-ter HsCen2 /P17-XPC complex in a microcrystalline state appears similar to that found in solution. Conformational flexibility is probed through relaxation-compensated measurements of dipolar order parameters that exploit the dynamics of cross-polarization in multidimensional experiments. The extracted dipolar coupling constants and relevant order parameters reveal increased backbone flexibility of the loops except for residues involved in coordination with the Ca2+ cation that stabilizes the hydrophobic pocket containing the peptide P17-XPC

Silicone-specific identification of trace polydimethylsiloxanes in wines with 2D-diffusion-ordered nuclear magnetic resonance spectroscopy (DOSY-NMR)

Present work stresses a novel analytical approach for increasing the specificity of standard NMR approaches for identifying polydimethylsiloxane (PDMS) and further silicone moieties in wines’ organic extracts, by including a second dimension that correlates chemical shifts with diffusion coefficients by means of pulsed-field gradient diffusion ordered spectroscopy (DOSY-NMR). Each silicone source in wines is unambiguously assigned by correlation of both local chemical environments and by a unique diffusion coefficient value, in turn related to a hydrodynamic radius (RH) that can be obtained with respect proper internal standards. Obtained PDMS diffusion coefficient values and hydrodynamic radii in wines’ extracts, in agreement with expected values, present a selectivity and specificity so far not reported, that positions DOSY-NMR spectroscopy as an alternative in oenology for controlling PDMS limits

Revealing full chemical forms of lead in wine with combined XRF-NMR technologies

Since 1953, The World Organization of Vine and Wine (OIV) Member States have reduced the lead maximum limits (ML) in wines, down to 0.05 mg/L (2018). Evidently, this ML value is too restrictive for wine industry as it excludes from international market a significant portion of wine production. Currently, the Codex Committee on Contaminants in Foods and OIV had recognized the value of gathering robust and novel data to better assess the best lowest ML for wine industry. Currently, there is not a direct statement within international reference documents, of which chemical form of lead must be controlled and/ or reduced. This work presents for the first time a method combining Energy Dispersive X-Ray analysis (EDAX) and Nuclear Magnetic Resonance (NMR) spectroscopies in order to determine presence and concentrations of major and trace elements of lead and other element moieties in wine that can allow to better redefine lead's ML. By identification of K, L, M, radiation shells with additional αβi labelling of lead's major and minor components with semi-quantitative XRF, combined with chemical-shift analysis of inorganic Pb4+, Pb2+ and/or organo-lead within wine samples, we propose a full discrimination framework to disentangle and quantify different chemical forms of lead

Deciphering the Conformational Choreography of Zinc Coordination Complexes with Standard and Novel Proton NMR Techniques Combined with DFT Methods

International audienceThe presence of water has been shown to deeply impact thestability and geometry of Zn complexes in solution. Evidencefor tetra- and penta-coordinated species in a pyridylmethylamine–ZnII model complex is presented. Novel 1H NMR toolssuch as T1-filtered selective exchange spectroscopy and pureshifted gradient-encoded selective refocusing as well as classical2D (1H–1H) exchange spectroscopy, diffusion-ordered spectroscopyand T1(1H) measurements, in combination with densityfunctional theory methods allow the full conformational dynamicsof a pyridylmethylamine–ZnII complex to be revealed.Four conformers and two families of complexes depending onthe hydration states are elucidated