Nuclear overhauser effect NMR

In achiral media, different NMR spectra are expected for each of the four types of enantiomeric pairs and for the two meso compounds. In general, because of the synthetic approach, the ratio of cis- to /nmv-rcsiducs is about three, which, assuming that quaternisation at one tetrahydroisoquinoline residue does not affect quaternisation at the other, leads to proportions of cis-cis, cis-trans and trans-trans isomers in the approximate ratio of 11 6 1. The preference for cis-residues has been proved by using nuclear Overhauser effect NMR measurements and by X-ray crystallography on related substances [37,38]. The H NMR chemical shifts, principally of the H8 proton, can be affected not only by whether the C1-N2 configuration in the residue is cis or trans but also by the configuration of the remote tetrahydroisoquinoline unit. 

See also Drug Metabolism Studied Using NMR Spectroscopy NMR Applications, Solution State Hydrogen Bonding and other Physicochemical Interactions Studied By iR and Raman Spectroscopy Nitrogen NMR Nuclear Overhauser Effect NMR Proteins Studied Using NMR Spectroscopy. 

See also Chemical Shift and Relaxation Reagents in NMR Chiroptical Spectroscopy, General Theory Het-eronuclear NMR Applications (O, S, Se, Te) Liquid Crystals and Liquid Crystal Solutions Studied By NMR NMR Relaxation Rates Nuclear Overhauser Effect NMR Parameters in NMR Spectroscopy, Theory of Vibrational CD, Applications. 

Applications - Other Nuclei Isotopic Labelling in Biochemistry, NMR Studies Medical Applications of Mass Spectrometry Nuclear Overhauser Effect NMR Perfused Organs Studied Using NMR Spectroscopy. 

You can often use experimental data, such as Nuclear Overhauser Effect (NOE) signals from 2D NMR studies, as restraints. NOE signals give distances between pairs of hydrogens in a molecule. Use these distances to limit distances during a molecular mechanics geometry optimization or molecular dynamics calculation. Information on dihedral angles, deduced from NMR, can also limit a conformational search. 

Another technique often used to examine the stmcture of double-heUcal oligonucleotides is two-dimensional nmr spectroscopy (see AfAGNETiC SPIN resonance). This method rehes on measurement of the nuclear Overhauser effects (NOEs) through space to determine the distances between protons (6). The stmcture of an oligonucleotide may be determined theoretically from a set of iaterproton distances. As a result of the complexities of the experiment and data analysis, the quality of the stmctural information obtained is debated. However, nmr spectroscopy does provide information pertaining to the stmcture of DNA ia solution and can serve as a complement to the stmctural information provided by crystallographic analysis. 

Although experimental studies of DNA and RNA structure have revealed the significant structural diversity of oligonucleotides, there are limitations to these approaches. X-ray crystallographic structures are limited to relatively small DNA duplexes, and the crystal lattice can impact the three-dimensional conformation [4]. NMR-based structural studies allow for the determination of structures in solution however, the limited amount of nuclear overhauser effect (NOE) data between nonadjacent stacked basepairs makes the determination of the overall structure of DNA difficult [5]. In addition, nanotechnology-based experiments, such as the use of optical tweezers and atomic force microscopy [6], have revealed that the forces required to distort DNA are relatively small, consistent with the structural heterogeneity observed in both DNA and RNA. 

Figure 1. Pulse sequences of some typical 2D-NMR experiments. COSY = correlation SpectroscopY, DQFCOSY = Double Quantum Filtered COSY, RELAY = RELAYed Magnetization Spectroscopy, and NOESY = Nuclear Overhauser Effect SpectroscopY.

Gated decoupling The decoupler is gated during certain pulse NMR experiments, so spin decoupling occurs only when the decoupler is switched on and not when it is switched off used to eliminate either H- C spincoupling or nuclear Overhauser effect in a ID C spectrum, and employed as a standard technique in many other H-NMR experiments, such as APT and y-resolved. 

Keepers, J.W. and James, T.L., A theoretical smdy of distance determinations from NMR two-dimensional nuclear Overhauser effect spectra, J. Mag. Resort, 57, 404, 1984. Kemp, W., Organic Spectroscopy, 3rd ed., W.H. Ereeman, New York, 1991. Figueiredo, P. et al., New aspects of anthocyanin complexation intramolecular copigmentation as a means for colour loss Phytochemistry, 41, 301, 1996. 

Nuclear Overhauser effects (NOEs) cause changes in the intensity of NMR signals by through-space dipole iipole interactions [36]. The magnitude of an observed NOE between two magnetic nuclei gives useful information on the distances between them. The observed NOE is also related to Brownian... 

Inter-/intramolecular distances 0.1-1 nm Nuclear Overhauser effect (1-NMR), dipolar splittings (s-NMR)... 

The conformation of the mixed p agonist/5 antagonist H-Tyr-c[-D-Orn-2-Nal-D-Pro-Gly-] in comparison to that of H-Tyr-c[-D-Orn-Phe-D-Pro-Gly-] was studied in DMSO-d6 by NMR spectroscopy and by molecular mechanics calculations [62,64]. Neither peptide showed nuclear Overhauser effects between C H protons or chemical exchange cross peaks in spectra obtained by total correlation and rotating frame Overhauser enhance-... 

NOE stands for Nuclear Overhauser Effect. Probably only physicists understand the NOE fully, and we shall not go into the theory but only present the results. It is a phenomenon which is useful and important in the NMR of both small and large molecules. 

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