Nuclear overhauser enhancement -based

The structure determination of organic molecules in solution — constitution, configuration and conformation — is probably the most important application of high-resolution NMR spectroscopy. Sophisticated methods based on classical NMR parameters like chemical shifts, /-couplings and nuclear Overhauser enhancement (NOE) have been developed for deriving structural models.1 2 The approach has been successfully applied to a vast number of molecules including thousands of biomacromolecules and uncountable natural and synthetic products. 

Intramolecular dynamics of 1,5-dihydronaphtho[l,8-(s/][l,2,3]trithiocine 16 in solutions was studied by 2-D nuclear Overhauser enhancement spectroscopy (NOESY) technique <2003AMR97> and interpreted based on the... 

Pulsed n.m.r. methods have been used to probe the conformations adopted by 2 -amino-2 -deoxyadenosine, 3 -amino-3 -deoxyadenosine, and puromycin. Longitudinal proton relaxation time and nuclear Overhauser enhancement measurements were carried out to characterize orientation of the base relative to ribose. The latter two compounds have a preferred N-anti-g+ conformation, while 2 -amino-2 -deoxyadenosine adopts the S-syn-g jt family of conformations. These findings corroborate the previous proposal relating the N state of ribose with a/t//-orientation of the base and the S state with syn orientation. Nuclear Overhauser enhancements have also been used to determine the site of glycosylation in nucleosides of -triazole the n.O.e. of H-r due to 3-Me or 5-Me showed that the structure of the major product of fusion of l-0-acetyl-2,3,5-tri-0-benzoyl-j8-D-ribofuranose with 3,5-dimethyl-1,2,4-triazole was (9) and that of the minor was (10). High resolution... 

CP measurements on static samples use of spectral simulation based on line shapes obtained from model compounds Optimization of sensitivity for analysis of coals, with judicious choice of pulse flip angles and use of a special pulse sequence to correct baseline problems Use of advanced NMR methods (nuclear Overhauser enhancement, DNP, 2D correlation and other 2D methods, spectral editing, etc.)... 

The numbering of atoms within the base and sugar moieties is according to the standard lUPAC/IUB rules [84S1]. The resonance positions of the imino protons incorporated in this survey are all based on one and/or two dimensional nuclear Overhauser enhancement spectroscopy. 

As a matter of fact, the vast majority of experimental studies focuses on a relatively well-defined set of parameters. Taking as an example the important case of NMR spectroscopy of organic molecules, the characterization is usually based on measurements of proton and carbon chemical shifts in solution, homonuclear (and possibly heteronuclear) coupling constants, and proton-proton nuclear Overhauser enhancements [or the corresponding rotating-frame effects (ROEs)]. This set of data is certainly reductive if compared with the information content potentially accessible by NMR measurements however, it does represent a reasonable balance of such factors as operator and instrument time, apparatus availabihty, costs, amounts of material required, completeness of information, and ease of interpretation. 

Judeinstein et al have conducted direct measurement of through-space NMR interactions that provide definitive evidence for spatial proximity of different species. Dipole-dipole interactions can be measured in principle between any NMR active nuclei with heteronuclear correlation experiments in the liquid or solid state." The dipole-dipole interactions decay quickly with the internuclear distances (r ), and are difficult to evaluate for long-range distances and even more difficult when exchange, conformation, or motion phenomena are present. However, the measurement of the nuclear Overhauser method" based on the dipole-dipole-induced crossrelaxation, was proposed to successfully measure intermolecular interactions" and the formation of ion pairs." " In agreement with recent studies, the pulsed field gradient enhanced inverse HOESY (heteronuclear Overhauser enhancement spectroscopy) sequence is usually preferred because it is more sensitive for isotope pairs H- Li and also improves the digital resolution in the H crowded spectrum." ... 

Techniques Based on Nuclear Overhauser Effect. A recently introduced C polarisation technique based on the nuclear Overhauser polarisation (NOP MAS) has been applied to uniformly C, N-labelled proteins. " NOP enhancement factors per scan of 1.5-2.0 were obtained, while that by CP was less than 1.0. It was shown that uniform enhancement of all C signals by CP is difficult to attain, while it is easily achieved by NOP, thus enabling quantitative comparison of signal intensities. In addition, NOP is easy to carry out under fast MAS and works well even for somewhat mobile molecules, for which CP does not work. Moreover, in labelled protein samples containing nonlabelled additives, NOP can be used to eliminate the signals of nonlabelled species. It was concluded that in the case of uniformly C labelled proteins NOP is superior to CP. 

Nuclear Overhauser experiments on purified synthetic 6 confirmed that it did have the E,E,E,E configuration. Irradiation at an olefinic methyl or methylene causes significant enhancement of an olefinic proton that is cis to it but not for one that is trans (5,11). Proton assignments were made based on double irradiation... 

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