Search results for "Nuclear Overhauser effect"
showing 10 items of 18 documents
27Al NMR Study of the pH Dependent Hydrolysis Products of Al2(SO4)3 in Different Physiological Media
2018
Soluble inorganic aluminium compounds like aluminium sulfate or aluminium chloride have been challenged by the European Chemical Agency to induce germ cell mutagenicity. Before conducting mutagenicity tests, the hydrolysis products in water and in physiological solutions should be determined as a function of the concentration and pH. We used different 27Al NMR spectroscopic techniques (heteronuclear Overhauser effect spectroscopy (HOESY), exchange spectroscopy (EXSY), diffusion ordered (DOSY)) in this work to gain the information to study the aluminium species in solutions with Al2(SO4)3 concentrations of 50.0, 5.0, and 0.5 g/L and their pH and time dependent transformation. At low pH, thre…
Solution NMR structure of aD,L-alternating oligonorleucine as a model of ?-helix
2001
beta-Helix structures are of particular interest due to their capacity to form transmembrane channels with different transport properties. However, the relatively large number of beta-helices configurations does not allow a direct conformational analysis of beta-helical oligopeptides. A synthetic alternating D,L-oligopeptide with twelve norleucines (XIIMe) has been used as a model to get insight in the conformational features of beta-helix structures. The spatial configuration of XIIMe in solution has been determined by NMR. An extensive set of distances (nuclear Overhauser effect) and dihedral (J coupling constants) constraints have been included in molecular dynamics calculations. The NMR…
An Efficient and Simple Entry to N-Substituted beta-Enamino Acid Derivatives from 2-Alkyl-2-oxazolines and 2-Alkyl-2-thiazolines.
1996
Reaction of azaenolates of 2-alkyl-oxa(thia)zolines 6 with imidoyl chlorides 7 as electrophiles to furnish masked N-substituted beta-enamino acid derivatives 1-2 in 70-90% yield is described. Alternative routes are discussed. Compounds 1-2 generally appear in one tautomeric form, imino or enamino, depending on the nature of the imidoyl chloride. The configuration of the enamino moiety (Z) and the conformation (s-cis) of compounds 1-2 obtained were established by an NMR study and unequivocally set by nuclear Overhauser effect difference experiments. An X-ray structure of compound 1e is also reported, showing a strong intramolecular NH.N hydrogen bond. Ab initio calculations (HF/3-21G and HF/…
A truncated driven Overhauser effect study of Adriamycin in water: Conformation of the glycosidic linkage
1991
Abstract Truncated driven nuclear Overhauser effect difference spectra have been used to ascertain the conformational characteristics of the glycosidic linkage of Adriamycin in aqueous solution. The “two-spin approximation” has been employed to evaluate the cross-relaxation rates between nearby protons and to obtain the relative internuclear distances. The rotational angles φ1 = C(7)−O(7)−C(1′)−(H1′) and φ2 = H(7)−C(7)−O(7)−C(1′) have also been calculated.
Structural characterization of polysaccharides of a productive strain of the culinary-medicinal king oyster mushroom, pleurotus eryngii (Agaricomycet…
2018
A preliminary biological investigation of the dry basidiomata of strain C-142-c of Pleurotus eryngii has shown significant antioxidant activity. Two different polysaccharides (PEPS-A1 and PEPS-A2) were isolated from the cultivated edible mushroom, P. eryngii C-142-c strain. Based on acid hydrolysis, methylation analysis, and nuclear magnetic resonance experiments (1H, 13C, distortionless enhancement by polarization transfer, double quantum filtered correlation spectroscopy, total correlation spectroscopy, nuclear Overhauser effect spectroscopy, heteronuclear singlequantum correlation spectroscopy, and heteronuclear multiple-bond correlation spectroscopy), the structures of the repeating uni…
Diels-alder reactions of methyl- and π-acceptor-substituted 2-vinylindoles with dimethyl acetylenedicarboxylate and tetracyanoethylene: Novel functio…
1991
The Diels-Alder reactions of the 2-vinylindoles 1a-1d, which are now readily accessible, with dimethyl acetylenedicarboxylate and tetracyanoethylene give rise to the novel 1,2-dihydro- and 1,2,3,4-tetrahydrocarbazoles 2, 4, and 5 as well as the fully aromatized carbazoles 3. With regard to the product spectrum, the mechanistic rationale comprises a Diels-Alder step, formal 1,3-hydrogen shift, ene reaction, and dehydrogenation. Conformational aspects of the 1,2-dihydrocarbazoles 2b and 2c are also discussed.
Investigating Intermolecular Interactions in a DME-Based Hybrid Ionic Liquid Electrolyte by HOESY NMR
2019
The intermolecular interactions in a hybrid electrolyte based on various compositions of the ionic liquid N-methyl-N-propyl pyrrolidinium bis-fluorosulfonylimide (C3mpyrFSI), LiFSI salt and an ether-based additive, 1,2-dimethoxy ethane (DME), have been investigated using the HOESY (Heteronuclear Overhauser Effect SpectroscopY) NMR experiment. This NMR technique allows a quantification of the intermolecular interactions in ionic liquids (ILs) by measuring the cross-relaxation rate (σ) between different pairs of nuclei. Thereby, we compare the cross-relaxation rates between the cations, anions and DME in these hybrid electrolyte systems using 1H-7Li and 1H-19F HOESY experiments, and interpret…
13C spin-lattice relaxation study of chlorinated alkanes
1987
The spin-lattice relaxation of ten polychloroalkanes (ethanes to pentanes) have been studied both neat and in a 50% solution in CDCl3. The T1 values for the CH2, CH2Cl and CHCl2 carbons decrease with increasing molecular weight in accordance with a dipolar-dominated mechanism, whereas those of the CCl3 carbons showed no dependence on molecular weight. In chloropentanes, with chlorine substitution at one end only, the frequency of segmental motion begins to compete with that of overall tumbling of the molecule. Consequently, the T1 minimum is shifted from the middle towards the heavier end of the molecule, and also a relatively large T1 for the terminal methyl is observed. It was also demons…
A topology-constrained distance network algorithm for protein structure determination from NOESY data.
2005
This article formulates the multidi- mensional nuclear Overhauser effect spectroscopy (NOESY) interpretation problem using graph theory and presents a novel, bottom-up, topology-con- strained distance network analysis algorithm for NOESY cross peak interpretation using assigned resonances. AutoStructure is a software suite that implements this topology-constrained distance net- work analysis algorithm and iteratively generates structures using the three-dimensional (3D) protein structure calculation programs XPLOR/CNS or DY- ANA. The minimum input for AutoStructure in- cludes the amino acid sequence, a list of resonance assignments, and lists of 2D, 3D, and/or 4D-NOESY cross peaks. AutoStru…
13C NMR of carbonyl compounds -4. Solution conformation of β-ionone and related dienones
1986
Abstract The steric factors relevant for the conformations of β-ionone and structurally related compounds were studied by dynamic n.m.r. and 1 H, 1 H-NOE measurements.