Search results for "Nuclear magnetic resonance"

Brain lateralization probed by water diffusion at the atomic to micrometric scale

2019

International audience; Combined neutron scattering and diffusion nuclear magnetic resonance experiments have been used to reveal significant interregional asymmetries (lateralization) in bovine brain hemispheres in terms of myelin arrangement and water dynamics at micron to atomic scales. Thicker myelin sheaths were found in the left hemisphere using neutron diffraction. 4.7 T dMRI and quasi-elastic neutron experiments highlighted significant differences in the properties of water dynamics in the two hemispheres. The results were interpreted in terms of hemisphere-dependent cellular composition (number of neurons, cell distribution, etc.) as well as specificity of neurological functions (s…

Oligoamide Foldamers as Helical Chloride Receptors-the Influence of Electron-Withdrawing Substituents on Anion-Binding Interactions.

2019

The anion-binding properties of three closely related oligoamide foldamers were studied using NMR spectroscopy, isothermal titration calorimetry and mass spectrometry, as well as DFT calculations. The 1 H NMR spectra of the foldamers in [D6 ]acetone solution revealed partial preorganization by intramolecular hydrogen bonding, which creates a suitable cavity for anion binding. The limited size of the cavity, however, enabled efficient binding by the inner amide protons only for the chloride anion resulting in the formation of a thermodynamically stable 1:1 complex. All 1:1 chloride complexes displayed a significant favourable contribution of the entropy term. Most likely, this is due to the …

Polarisation dependent Raman study of single-crystal nickel oxide

2011

Abstract The magnetic domain structure and Raman scattering have been studied in NiO single-crystals with three different (100), (110) and (111) orientations. Twin-domain structure was observed in NiO(100) and NiO(110) single-crystals using cross-polarized optical microscopy. We found that the ratio of the two-magnon (at 1500 cm−1) to the two-phonon (2LO, at 1100 cm−1) Raman bands intensity is sensitive in a particular way to the type of the twin-domain pattern.

Secondary metabolites of the lichen-associated fungus Apiospora montagnei

2017

Abstract The endolichenic fungus Apiospora montagnei isolated from the lichen Cladonia sp. was cultured on solid rice medium, yielding the new diterpenoid libertellenone L (1), the new pyridine alkaloid, 23-O-acetyl-N-hydroxyapiosporamide (2) and the new xanthone derivative 8-hydroxy-3-hydroxymethyl-9-oxo-9H-xanthene-1-carboxylic acid methyl ether (3) together with 19 known compounds (4–22). The structures of the new compounds were elucidated by 1D and 2D NMR spectra as well as by HRESIMS data. The absolute configuration of the new 6,7-seco-libertellenone derivative 1 was determined by single-crystal X-ray diffraction. Four additional known compounds 23–26 were isolated when NaCl or NH4Cl w…

Cytotoxic eudesmane sesquiterpenes from Crepis sancta

2019

Abstract Chemical exploration of Crepis sancta (L.) Bornm. (Asteraceae) aerial parts afforded two new eudesmane sesquiterpenes (1 and 2) together with three known congeners (3-5) and two known methylated flavonoids (6 and 7). Structure elucidation of the new compounds was unambiguously performed based on HRESIMS, 1D and 2D NMR spectroscopic analyses. All isolated compounds were subjected to an in vitro cytotoxicity assay against mouse lymphoma (L5178Y) cells, revealing moderate activities with IC50 ranging from 7.9 to 21.0 μM.

New umbelliferone sesquiterpene ethers from roots ofLigularia persica

1991

An extract of roots of Ligularia persica yielded thirteen umbelliferone sesquiterpene ethers, among them the new ones ligupersin A (11) and ligupersin B (13).

COBALT SUBSTITUTED PROTEINS

1995

Cobalt(II) has been extensively used as a spectroscopic probe in many proteins, mainly replacing zinc, but also substituting iron, manganese and copper ions. The relatively short electronic relaxation times of high spin cobalt(II) makes this ion suitable as a paramagnetic probe for Nuclear Magnetic Resonance spectroscopy. A survey of the NMR studies performed in cobalt substituted proteins is shown. In the zinc enzymes Carboxypeptidase A, Carbonic Anhydrase and Superoxide Dismutase the implications of these studies on their catalytic mechanisms are commented. Finally, a further insight in the research of the blue copper protein Azurin by applying NMR to its cobalt derivative is also reporte…

Chapter 6 Contribution of NMR Spectroscopy to Flavour Release and Perception

2008

Abstract The control of flavouring of a food product as well as the flavour perception during consumption is a great challenge for improving food quality. However, the various ingredient composition and the different textural properties of foods can significantly affect the release of aroma compounds or sapid molecules. It is thus of major importance to determine physicochemical factors that govern diffusion and binding phenomena of these small solutes in food products. In this way, NMR spectroscopy is an efficient tool to characterize these mechanisms at a molecular scale. Diffusion rates of small solutes in aqueous, viscous and gel solutions can be extracted from relaxation or diffusion N…

New Porphycene Ligands: Octaethyl- and Etioporphycene(OEPc and EtioPc)—Tetra- and Pentacoordinated Zinc Complexes of OEPc

1993

1H 2D-NMR characterization of Ni(II)-substituted azurin fromPseudomonas aeruginosa

1993

1 H two-dimemional NMR experiments on nickel(II)-substituted azurin have been succesfully applied. Despite the short relaxation time of the hyperfine-shifted resonances, the combined use of NOESY and COSY spectra allowed the alignment of 15 resonances belonging to the metal-coordinated residues Gly-45, His-46, His-117 and Met-121. Even in the case of the two broad and furthest downfield resonances, the NOESY spectra were successful in assigning these signals to the β-CH 2 protons of Cys-112. The protons of the non-coordinated residues Met-13, Phe-15 and Trp-48 were also assigned via NOESY, COSY and TOCSY experiments