REDOR spectroscopy

The dipolar interaction Hamiltonian under the conditions of MAS NMR is given as 

The acquired signal intensity then is only attenuated by transverse relaxation and therefore 

the heteronuclear dipolar information has been reintroduced into the MAS spin-echo experiment. The signal intensity follows from 

Since in the case of an isolated pair of spin nuclei the dipolar dephasing, and hence the REDOR evolution curve, is exclusively governed by the dipolar Hamiltonian, the data analysis proves to be straightforward employing a universal REDOR curve, in which the normalised difference intensity AS/Sq is plotted as a function of the dimensionless product NTRxd.2  

Approximate solutions derive from a series expansion of the cos-term in Equation (10), producing 

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Key Words Heteronuclear dipolar couplings, REDOR spectroscopy, Structure, Second moments. Constant time, SIMPSON... 

Rotational echo double resonance (REDOR) [86] is one of the most important techniques developed for solid-state NMR spectroscopy. The theory of REDOR is... 

FIGURE 23. Stereoview of the position of the lithium cation relative to the fluorenyl system in the TMEDA complex of fluorenyUithium as determined by REDOR NMR spectroscopy... 

CT-VPP-REDOR) or the pulse duration fp (CT-VPD-REDOR) then produces CT-REDOR curves, from which the second moment may be evaluated with distinctively superior accuracy as compared to the values obtained from a parabolic fit to the conventional REDOR data. When restricting the experiment to short dipolar evolution times, the two-spin approximation may be applied for the data analysis, which proves to be especially attractive for amorphous solids, for which the exact spin geometry is unknovm. The data presented on the model compoimds illustrate the various facets of CT-REDOR NMR spectroscopy. First application examples, namely, the evaluation of the heteronuclear Li-Ti dipolar couplings within the garnet structure of Li5La3Nb20i2, the determi-nation of the intemuclear B- P distance in frustrated Lewis pairs, the analysis of Na- F dipolar interaction in fluormica or Na- P... 

REDOR rotational echo double resonance (NMR spectroscopy)... 

The nonpolar conformation, also termed the extended conformation, was established on the basis of NMR data of paclitaxel and docetaxel in nonpolar solvent such as chloroform, as well as crystallographic data of docetaxel. Its presence was experimentally confirmed by fluorescence and solid-state NMR spectroscopies (REDOR). Wang et al. selected 20 amino acid residues and paclitaxel conformation in CDCI3 as a starting point to construct a mini-receptor model for both paclitaxel and epothilone, a family of macrocyclic antimitotic agents that was assumed to bind to the same site on tubulin as paclitaxel. This model has been... 

Measurement of the heteronuclear dipolar couplings defines the use of solid-state NMR spectroscopy for determination of intemuclear distances. The main part of such experiments involves refocusing of the heteronuclear dipolar couplings. The REDOR experiment has been used extensively to determine the intemuclear distances ( C N, C- P... 

Each of these experiments has pros and cons. The SEDOR experiment is easiest to set up but lacks the resolution since it is made on a static sample, and is often limited in the range of accessible dipolar couplings by T2. The REDOR experiment is more elaborate to set up and requires stable spinning, but its increased resolution enables multisite systems to be explored, while the longer T2 enables longer distances to be determined. TEDOR is less sensitive than REDOR as it involves a transfer step with a theoretical maximum efficiency of 50 percent. However, it is not a difference experiment, and is therefore less prone to experimental errors. An important application of TEDOR is its use in 2D-correlation spectroscopy. 

At the qualitative level, NMR studies devoted to this issue exploit heteronuclear dipolar recoupling to correlate resolved MAS NMR signals of the nuclear species associated with different network formers. This information comes from the dephasing of the observe nuclei in REDOR, TRAPDOR, or REAPDOR experiments, or from one- or two-dimensional correlation spectroscopy involving coherence transfer via TEDOR (transferred echo double resonance) or... 

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