Nuclear Overhauser effect feature

The 1H-1H TOCSY and 1H-1H NOESY NMR studies of a series of substituted Ind titanium complexes using nuclear Overhauser effects have been used to investigate structural features of these derivatives.1123... 

Another conformational feature that could be deduced from H NMR studies of all cA-DDP-platinated oligonucleotides containing an embedded d(GpG) sequence is that both guanosine nucleosides retain the anti orientation of the base around the Cl -N9 glycosidic linkage (Figure 9.9). This result was deduced from the lack of a pronounced nuclear Overhauser effect (NOE) between H8 and the HI protons, such as would occur in the syn conformation. An NOE between H8 resonances on the two coordinated nucleosides was observed for... 

At least for the present, proton saturation transfer experiments will be the most tractable. For accurate measurement of the degree of saturation, adequate time must have elapsed for equilibrium to be established. This time is on the order of five times the relaxation time, or k. Hence, for the gated decoupling of the protons in (7) -allyl)Fe(CO)3l, decoupling must be carried out for 10-20 seconds before the 90° pulse to achieve reproducible results. A second feature, which can often be observed in syn and anti protons, is the signal enhancement arising from the nuclear Overhauser effect (NOE). Thus, the observed intensity is a function of both the NOE and the magnetization transferred into the site. Quantitative determinations must correct for the NOE enhancements. 

Even one-dimensional (ID) NMR spectra are often adequate to deduce some delicate configurational and conformational characteristics of a molecule. Such features are inferred from the chemical shifts and coupling constants of the respective protons as well as from the position of the easily detectable singlets of the C18 and C19 angular methyl groups. The use of the nuclear Overhauser effect (NOE) and various multipulse NMR techniques enable the solving of even more difficult problems. 

The most useful feature of the method is not so much the rate data, but that it tells us which protons are exchanging with which, and so allows us to solve some difficult mechanistic problems. In certain circumstances the nuclear Overhauser effect (NOE) (Section 10.7) can affect the experiment, and must also be taken into account. ... 

VcF, and Vff and couplings have been measured by Reiter et al for a series of 2-amino-4-phenylthiazoles and analysed together with nuclear Overhauser effects from the point of view of conformational preferences of these compounds. This was a part of their studies on molecular features crucial to the activity of pyrimidine benzamide-based thrombopoietin receptor agonists. 

The bound conformations of ligands determined by transferred-NOE (nuclear Overhauser effect) can also serve as templates for query formulation, even though this implicit approach cannot identify the spatial arrangement of site residue atoms. With these data, one proceeds with the analysis of the bound conformation as in the case of a co-determined complex (see above) however, the excluded volume constraints cannot be specified. One advantage of this data set is that multiple distance geometry solutions for the NOE-determined bound conformation can be used to define some initial tolerances for the distance, angle, and torsional 3D constraint features. 

The essential features of the Overhauser effect and related relaxation phenomena can be seen by considering the transitions between the energy levels of a two-spin system consisting of a nuclear spin I and an electron spin S. Although this may appear to be a drastic oversimplification for describing the interactions in a solution containing free radicals, the rapid random diffusion of the molecules ensures that the solvent molecules are near a free radical many times during the nuclear relaxation time, and therefore any nucleus in solution may be considered to be in continuous interaction with an electron. 

After having demonstrated that the spins were moving in undoped rrflU5-(CH)., the aim of the researchers was to characterize the motion. Use was made of various methods described in section III. At first, as suggested by the polymeric nature of (CH), the motion was expected to proceed essentially along the chains. Evidence for the 1-D feature of the motion was given from the tu dependence of the nuclear relaxation rate Ti (u It should be noted that such a frequency dependence could also be obtained in the case of nuclear relaxation induced by fixed electronic spins and transmitted by nuclear spin diffusion. However, this alternative explanation for TL 3c w was invalidated by the Overhauser effect, which proved that the electronic spins were not fixed. Let us stress that the same spins are responsible for both the Overhauser effect and the nuclear relaxation. Further data supported the 1-D nature of the motion (1) The w - dependence was also observed for the electronic spin relaxation [41] and (2) the ESR lineshape was shown to display 1-D features, namely the Fourier transform of G(t) exp [24,25,36]. 

---