Search results for "resonance spectroscopy"
showing 10 items of 1478 documents
Complete 1H and 13C NMR assignments of clerodane diterpenoids of Salvia splendens.
2006
Unambiguous and complete assignments of 1H and 13C NMR chemical shifts for five clerodane diterpenes, four of them isolated from Salvia splendens (salviarin, splendidin and splenolides A and B) and one obtained by acetylation of splenolide A, are presented. The assignments are based on 2D shift-correlated [1H,1H–COSY, 1H,13C-gHSQC–1J(C,H) and 1H,13C-gHMBC-nJ(C,H) (n = 2 and 3)] and nuclear Overhauser effect (NOE) experiments. The conformation of the rings of these compounds is supported by the 3J(H,H) values and NOE results. Copyright © 2006 John Wiley & Sons, Ltd.
Reversible coordination of dioxygen by tripodal tetraamine copper complexes incorporated in a porous silica framework.
2010
The present study reports the synthesis and rational design of porous structured materials by using a templating method. A tetraethoxysilylated tripodal tetraamine (TREN) was covalently incorporated in a silica framework with a double imprint: A surfactant template and a metal ion imprint. The presence of a cationic surfactant (CTAB) endowed the material with a high porosity, and the tripodal or square-pyramidal topology of the ligand was preserved thanks to the use of the silylated Cu(II) complex. After removal of the surfactant and de-metalation, the incorporated tetraamine was quantitatively complexed by CuCl(2) and the material has shown after thermal activation that a reversible bindin…
An ab initio study of the relation between NMR chemical shifts and solid-state structures: hexabenzocoronene derivatives
2000
The assignment of solid-state NMR spectra is studied by the use of model systems computed with ab initio methods. The investigated system is a hexabenzocoronene derivative, for which a T-like arrangement of dimer units is found in the solid-state structure. Here, a tetramer model is required to explain the intermolecular interactions influencing the spectrum, whereas a dimer model is found to be inadequate. For the tetramer model, agreement of the computed NMR spectrum with the experimental solid-state magic angle spinning MAS-NMR data is observed. This study implies that the combination of experimental NMR data with quantum chemical calculations can be employed as a useful tool in determin…
Everything you wanted to know about phase and reference frequency in one- and two-dimensional NMR spectroscopy
2019
The fundamental concept of phase discussed in this tutorial aimed at providing students with an explanation of the delays and processing parameters they may find in nuclear magnetic resonance (NMR) pulse programs. We consider the phase of radio-frequency pulses, receiver, and magnetization and how all these parameters are related to phases and offsets of signals in spectra. The impact of the off-resonance effect on the phase of the magnetization is discussed before presenting an overview of how adjustment of the time reference of the free induction decay avoids first-order correction of the phase of spectra. The main objective of this tutorial is to show how the relative phase of a pulse an…
The association between the Mediterranean diet and magnetic resonance parameters for knee osteoarthritis: data from the Osteoarthritis Initiative
2018
The Mediterranean diet appears to be beneficial for osteoarthritis (OA), but the few data available regarding the association between the diet and the condition are limited to X-ray and clinical findings. The current study aimed to investigate the association between adherence to the Mediterranean diet and knee cartilage morphology, assessed using magnetic resonance (MRI) in a cohort of North American participants. Seven hundred eighty-three participants in the Osteoarthritis Initiative (59.8% females; mean age 62.3 years) in possession of a MRI assessment (a coronal 3D FLASH with Water Excitation MR sequence of the right knee) were enrolled in our cross-sectional study. Adherence to the Me…
Resorcinarene Bis-Thiacrowns: Prospective Host Molecules for Silver Encapsulation
2012
Mixed-donor atom tetramethoxy resorcinarene bis-thiacrown hosts, in which the crown unit contains both hard oxygen and soft sulfur donor atoms, were synthesized for soft metal cation binding. The binding properties were investigated both in solution and in the solid state by NMR spectroscopy and X-ray crystallography. It was found that the resorcinarene bis-thiacrowns were able to complex silver cations with remarkable affinity forming readily 1:2 host–guest complexes in solution. The solid state structures also revealed that the bis-thiacrowns form silver complexes in an unanticipated endo- and exo-cavity fashion within the same host molecule. Both the solution and solid state studies indi…
Cyclic heptapeptides from the soil-derived fungus Clonostachys rosea
2019
Abstract Three new cyclic heptapeptides (1–3) together with three known compounds (4–6) were isolated from a solid rice culture of the soil-derived fungus Clonostachys rosea. Fermentation of the fungus on white beans instead of rice afforded a new γ-lactam (7) and a known γ-lactone (8) that were not detected in the former extracts. The structures of the new compounds were elucidated on the basis of 1D and 2D NMR spectra as well as by HRESIMS data. Compounds 1 and 4 exhibited significant cytotoxicity against the L5178Y mouse lymphoma cell line with IC50 values of 4.1 and 0.1 µM, respectively. Compound 4 also displayed cytotoxicity against the A2780 human ovarian cancer cell line with an IC50…
Antitumor effects of curcumin and structurally β-diketone modified analogs on multidrug resistant cancer cells
2007
Abstract Using concepts of bioisostery a series of curcumin analogs were synthesized: the diketonic system of the compound was elaborated into enaminones, oximes, and the isoxazole heterocycle. The cell growth inhibitory and apoptosis inducing effects of the new analogs were evaluated by in vitro assays in the hepatocellular carcinoma HA22T/VGH cells, as well as in the MCF-7 breast cancer cell line and in its multidrug resistant (MDR) variant MCF-7R. Increased antitumor activity on all cell lines was found with the isoxazole analog and especially with the benzyl oxime derivative; in the HA22T/VGH cell model, the latter compound inhibited constitutive NF-κB activation.
Characterization by solid-state NMR and selective dissolution techniques of anhydrous and hydrated CEM V cement pastes.
2010
International audience; The long term behaviour of cement based materials is strongly dependent on the paste microstructure and also on the internal chemistry. A CEM V blended cement containing pulverised fly ash (PFA) and blastfurnace slag (BFS) has been studied in order to understand hydration processes which influence the paste microstructure. Solid-state NMR spectroscopy with complementary X-ray diffraction analysis and selective dissolution techniques have been used for the characterization of the various phases (C3S, C2S, C3A and C4AF) of the clinker and additives and then for estimation of the degree of hydration of these same phases. Their quantification after simulation of experime…
The MC3 receptor binding affinity of melanocortins correlates with the nitric oxide production inhibition in mice brain inflammation model
2006
Melanocortins possess strong anti-inflammatory effects acting in the central nervous system via inhibition of the production of nitric oxide (NO) during brain inflammation. To shed more light into the role of melanocortin (MC) receptor subtypes involved we synthesized and evaluated some novel peptides, modified in the melanocyte-stimulating hormone (MSH) core structure, natural MCs and known MC receptor selective peptides - MS05, MS06. Since the study included both selective, high affinity binders and the novel peptides, it was possible to do the correlation analysis of binding activities and the NO induction-related anti-inflammatory effect of the peptides. beta-MSH, gamma1-MSH, gamma2-MSH…