Nuclear Overhauser effect measurement

Data of the XH-NMR spectra for the E- and Z-isomers of representative 3-substituted 3-aminoacrylonitriles (483)159 appear in Table 27. Nuclear Overhauser-effect measure-... 

It is understandable that in the early days the x/rr distinction was neglected, because no general method of distinguishing between isomeric N - and N -substituted structures in histidine derivatives was available. It is still the case that this distinction is nontrivial, but the problem has been solved in specific cases by crystallography, chemical degradation, or nuclear Overhauser effect measurements, and no exception to the cross-ring coupling constant criterion of Matthews and Rapoport ° is known. 

The stereochemistry of the resulting 2-methylbut-2-enylsilanes is elucidated to be exclusively Z on the basis of NOE (Nuclear Overhauser Effect) measurements , thus the hydrosiiyiation of isoprene with the palladium catalyst is found to be regio- and stereoselective. 

Conformations of Nicotinamide Coenzymes Bound to Active Sites OF A- AND B-Side Dehydrogenases/Reductases, as Determined by X-Ray Crystallography and Nuclear Overhauser Effect Measurements... 

A particularly elegant method has recently been devised for the stereoselective synthesis of (/ -methyl)- and (S-methyl)-yV -[merAy/- H, H, H]tetrahydro-folate (N -CHa-THF) for examining the stereochemistry of THF-dependent enzymes (344). For example, synthesis of the former substrate first involves reduction of Af, A -methenyl-THF with NaB Ha, demonstrated to be approximately 80% stereoselective on the basis of proton nuclear Overhauser effect measurements on the product (346) [Eq. (63)] ... 

Ferrage F, Cowbum D, Ghose R (2009) Accurate sampling of high-frequency motions in proteins by steady-state (15)N- (1)H nuclear Overhauser effect measurements in the presence of cross-correlated relaxation. J Am Chem Soc 131 6048-6049... 

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. 

One-dimensional nuclear Overhauser effect (NOE), relaxation measurements in native D. gigas Fdll, and analysis of temperature depen-... 

The aim of this work was to find out how to get more information about stereochemistry and molecular motion of polymer methyl- and methyl-phenyl-siloxanes by measuring longitudinal relaxation times, Tj, and nuclear Overhauser effects, NOE, of the individual building blocks. 

Key Words Carbon-13 spin relaxation, T, Measurements, Nuclear Overhauser effect, Rotation-diffusion tensor, HOESY experiments... 

The principle source of experimental conformational data in an NMR structure determination is constraints on short interatomic distances between hydrogen atoms obtained from NMR measurements of the nuclear Overhauser effect (NOE). NOEs result from cross-relaxation mediated by the dipole-dipole interaction between spatially proximate nu-... 

Exchange of magnetization due to cross-relaxation (NOE, nuclear Overhauser effect) does lead to intensity changes of individual resonances which provide valuable information about spatial and motional characteristics of the spins involved [4, 5]. It is currently mostly measured in two-dimensional NMR, where the NOE is measured as cross-peak intensity. Cross-relaxation is caused by mutual spin flips in dipolar coupled spin pairs. 

Since the discovery of the nuclear Overhauser effect (NOE, see previous section) [4, 5] and scalar coupling constants [36, 37] decades ago, NMR-derived structure calculations of biomolecules largely depended on the measurement of these two parameters [38]. Recently it became possible to use cross-correlated relaxation (CCR) to directly measure angles between bond vectors [39] (see also Chapt 7). In addition, residual dipolar couplings of weakly aligned molecules were discovered to measure the orientation of bond vectors relative to the alignment tensor (see Sect 16.5). Measurement of cross-correlated relaxation was described experimentally earlier for homonuclear cases [40, 41] and is widely used in solid-state NMR [42 14]. 

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