Description de l'effet Overhauser dans les systèmes en échange: application à l'analyse conformationnelle d'aldéhydes hétérocycliques

1971 ◽  
Vol 49 (6) ◽  
pp. 904-913 ◽  
Author(s):  
S. Combrisson ◽  
B. Roques ◽  
P. Rigny ◽  
J. J. Basselier
Keyword(s):  
Ambient Temperature ◽  
Nuclear Overhauser Effect ◽  
Relaxation Times ◽  
Life Time ◽  
Relative Increase ◽  
Spatial Position ◽  
Conformational Preference ◽  
Overhauser Effect ◽  
Order Of Magnitude ◽  
Nuclear Overhauser

The equations of the nuclear Overhauser effect (n.O.e.) in exchanging systems predict relative increases for proton signals where the life times for exchange are of the same order of magnitude as the relaxation times. This method allows one to obtain structural informations. Hence, for a temperature sufficiently below that of the coalescence, it allows one to infer a conformational preference by an examination of the relative increase in intensity with respect to spatial position of exchange sites. We have hereby determined the conformations of formyl-2 bromo-4 thiophene and acetyl-2 dibromo-4,5 thiophene. The compounds show at ambient temperature a single rotamer OS-cis. Formyl-2 bromo-4 furan exists at −90 °C in an equilibrium between the rotamers OO-cis and OO-trans. In this case, the results of different irradiations show OO-cis to be the preferred rotamer. Moreover, this method is able to give indications of the life time on different sites. We also give an evaluation of the limits of the method.

Cross-linked polydimethylsiloxane colloid as novel contrast agent for gastrointestinal magnetic resonance imaging: Transient nuclear Overhauser effect within the interface

2020 ◽  
Vol 35 (2) ◽  
pp. 264-273
Author(s):  
Fu-Hu Su ◽  
Wang-Chuan Xiao ◽  
Sheann-Huei Lin ◽  
Qiyong Li
Keyword(s):  
Magnetic Resonance ◽  
Nuclear Overhauser Effect ◽  
Relaxation Times ◽  
Resonance Imaging ◽  
Transverse Relaxation ◽  
Overhauser Effect ◽  
Nuclear Magnetic Resonance Spectra ◽  
Relaxation Experiments ◽  
Longitudinal Relaxation ◽  
Nuclear Overhauser

With good contrast in T1 and T2 weighted imaging as well as low toxicity in 3- (4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, this work proposes the cross-linked polydimethylsiloxane colloids as a novel non-ionic contrast agent for gastrointestinal magnetic resonance imaging. The experiments of nuclear magnetic resonance spectra and relaxation show that within the interface of the colloids, there are nuclear Overhauser effect and transient nuclear Overhauser effect (cross-relaxation). Regarding the longitudinal relaxation experiments of CH2CH2O segments of Tween 80, a two spins system is found and modeled well by the equation [Formula: see text] which is deduced based on the transient nuclear Overhauser effect proposed by Solomon. The arbitrary constant X is additionally added with the initial conditions ( Iz −  I0) t=0 = −2 XS0 and ( Sz −  S0) t=0 = −2 S0. For the two spins system, D1 and T1 are corresponding to longitudinal relaxation times of the bound water and the CH2CH2O respectively. Concerning the transverse relaxation experiments of the CH2CH2O, they agree with the equation with three exponential decays, defined by three relaxation times, likely corresponding to three mechanisms. These mechanisms possibly are intramolecular and intermolecular dipole–dipole (DD) interactions and scalar coupling. Within the interface, hydrogen bonding causes the positive nuclear Overhauser effect of the CH2CH2O’s nuclear magnetic resonance spectra, the transient nuclear Overhauser effect of the CH2CH2O’s longitudinal relaxation experiments and the intermolecular dipole–dipole interactions of the CH2CH2O’s transverse relaxation experiments.

The conformational analysis of leukotriene D4 in aqueous solution based on high-field nuclear magnetic resonance measurements

1984 ◽  
Vol 62 (8) ◽  
pp. 1640-1645 ◽  
Author(s):  
Makiko Sugiura ◽  
Helmut Beierbeck ◽  
George Kotovych ◽  
Patrice C. Bélanger
Keyword(s):  
Conformational Analysis ◽  
Nuclear Overhauser Effect ◽  
Relaxation Times ◽  
Coupling Constants ◽  
Leukotriene D4 ◽  
Proton Proton ◽  
Proton Coupling ◽  
Overhauser Effect ◽  
Vicinal Proton ◽  
Nuclear Overhauser

The conformational analysis of LTD4 in D2O was carried out based on the analysis of vicinal proton–proton coupling constants, nonselective proton longitudinal relaxation times, and nuclear Overhauser effect data. The H6—C6 to C12 region of the molecule is transoid, the predominant rotamer about C5—C6 is gauche, and two rotamers can be used to describe the rotation about C12—C13. There are three rotamers that can be used to describe the rotation about the C21—C22 bond of cysteine. Finally, chelation between an Yb3+, shift reagents and LTD4 was not observed.

123Te and 125Te Fourier Transform NMR Investigations

1977 ◽  
Vol 32 (11) ◽  
pp. 1263-1265 ◽  
Author(s):  
K. U. Buckler ◽  
J. Kronenbitter ◽  
. Lutz ◽  
A. Nollle
Keyword(s):  
Fourier Transform ◽  
Nuclear Overhauser Effect ◽  
Chemical Shifts ◽  
Magnetic Moments ◽  
Relaxation Times ◽  
Dipole Interaction ◽  
High Accuracy ◽  
Overhauser Effect ◽  
Nuclear Overhauser ◽  
Nmr Signals

Abstract The NMR signals of 123Te and 125Te have been observed in solutions of K2TeO3 and Na2TeO3 in D2O. In these solutions the ratios of Larmor frequencies ν(125Te)/ν(123Te), ν(125Te)/v(2H) and ν(125Te)/ν(23Na) have been determined with high accuracy. With the measured chemical shifts of 2H, 23Na, 125Te relative to infinitely diluted solutions the ratios of the Larmor frequencies are extrapolated and values of the magnetic moments are given. The relaxation times T1 and T2 are very different for 125Te in TeO32-: a ratio T1/T2 of 8.2 ± 0.4 has been found. No nuclear Overhauser effect due to dipole-dipole interaction of 125Te with the water protons has been detected.

1H NMR studies of [N-MeAib1, Tyr(Me)4]ANGII and [N-MeAib1, Tyr(Me)4, Ile8]ANGII in dimethylsulfoxide by nuclear Overhauser effect (NOE) enhancement spectroscopy: cis-trans Isomerism of the His-Pro bond

1990 ◽  
Vol 55 (4) ◽  
pp. 1106-1111 ◽  
Author(s):  
John Matsoukas ◽  
Paul Cordopatis ◽  
Raghav Yamdagni ◽  
Graham J. Moore
Keyword(s):  
1H Nmr ◽  
Nuclear Overhauser Effect ◽  
Nmr Studies ◽  
Restricted Rotation ◽  
Overhauser Effect ◽  
Major Isomer ◽  
Conformational Properties ◽  
Nuclear Overhauser

The conformational properties of the Sarmesin analogues [N-MeAib1, Tyr(Me)4]ANGII and [N-MeAib1, Tyr(Me)4, Ile8]ANGII in hexadeutero-dimethysulfoxide were investigated by Nuclear Overhauser Effect (NOE) Enhancement Studies. Cis-trans isomers (ratio 1 : 6) due to restricted rotation of the His-Pro bond were observed. Interresidue interactions between the His Cα proton and the two Pro Cδ protons revealed that the major isomer was the trans.

scholarly journals Cylindromicin from Arctic-Derived Fungus Tolypocladium sp. SCSIO 40433

Molecules ◽  
2021 ◽  
Vol 26 (4) ◽  
pp. 1080
Author(s):  
Imran Khan ◽  
Jing Peng ◽  
Zhuangjie Fang ◽  
Wei Liu ◽  
Wenjun Zhang ◽  
...  
Keyword(s):  
Secondary Metabolites ◽  
Nuclear Overhauser Effect ◽  
Inhibition Activity ◽  
Tyrosinase Inhibition ◽  
Bioactive Natural Products ◽  
Chemical Structures ◽  
Overhauser Effect ◽  
Spectroscopic Analyses ◽  
Potential Resource ◽  
Nuclear Overhauser

The fungus strain SCSIO 40433 was isolated from an Arctic-derived glacier sediment sample and characterized as Tolypocladium cylindrosporum. A new compound, cylindromicin (1), and seven known secondary metabolites (2–8) were isolated from this strain. The chemical structures of these compounds were elucidated by comprehensive spectroscopic analyses. Cylindromicin (1) featured a 3,4-dihydro-2H-pyran skeleton. The absolute configuration of compound 1 was assigned via interpretation of key Nuclear Overhauser Effect Spectroscopy (NOESY) correlations and Electronic Circular Dichroism (ECD) calculation. Cylindromicin (1) exhibited significant tyrosinase inhibition activity. This study highlights Polar fungi as a potential resource for new bioactive natural products.

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