Rotation echo double resonance REDOR

Rotational-echo double-resonance (REDOR)(75,79) is a new solid-state NMR technique which is sensitive to through-space carbon-nitrogen interactions between selectively 13C and 15N-enriched sites separated by up to 5A (20-22). The parameter directly measured in a REDOR experiment is the heteronuclear dipolar coupling constant DCN, which is in itself proportional to the inverse third power of the intemuclear distance, rCN. It is this dependence on (icn)3 which accounts both for REDOR s ability to accurately measure short distances and its insensitivity to longer-range interactions. As a technique which can probe, in detail, intermolecular interactions over a distance range of 5A, REDOR is well suited to studying the distribution of small selectively-labeled molecules in polymer delivery systems. 

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

Another study of the surface structure of CdSe NCs of 3.7 nm size used 31P MAS-NMR and 31P/77Se rotational-echo double-resonance (REDOR) to identify overlapping broad peaks from two surface species trioctylphosphine oxide (TOPO) at 29.3 ppm and trioctylphosphine selenide (TOPSe) at 22.2 ppm [343]. Both the isotropic chemical shift and CSA of the surface-bound TOPO were substantially different from those of the free ligand. Spin-echo experiments on 31P were stated to indicate an average P-P distance of 8-10 A at the surface, consistent with capping at alternate atomic sites (all Cd but not Se). 

Poly(benzyl ether) dendrimers synthesized by Frechet el al. have been studied with many techniques in order to reveal their conformational properties. Size exclusion measurements performed by Mourey et al. [154], rotational-echo double resonance (REDOR) NMR studies by Wooley et al. [155] and spin lattice relaxation measurements by Gorman et al. [156] reveal that back-folding takes place and the end-groups can be found throughout the molecule. The observed trends are in qualitative agreement with the model of Lescanec and Muthukumar [54],... 

Rotational-echo double resonance (REDOR), originally introduced by Gullion and Schaefer [102], is a method to recouple heteronuclear spin pairs. The sequence relies on a train of rotor-synchronized n pulses applied to the I spin to interrupt the spatial averaging of the heteronuclear dipolar coupling under MAS to give a nonvanishing dipolar Hamiltonian over a full rotor cycle (Fig. 11.8). Typically, REDOR data are collected by col-... 

The application of 31P-19F rotational echo double resonance (REDOR) measurements in structural studies of nucleic acids has been reviewed by Iuga et al.13 In recent years, this methodology has been further developed.85... 

The symmetric geometry of the TMEDA complex of 68 was also confirmed by using the Rotational-Echo Double Resonance (REDOR) method, and the position of the lithium cation was determined with an error of about 0.2 A127. However, the accuracy of the REDOR method could not be confirmed, because this complex has not been investigated by X-ray crystallography. 

Accurate 13C-15N interatomic distances have been measured by means of rotational echo double resonance (REDOR) experiments for oligopeptides [50]. The interatomic 13C-15N distance in the hydrogen bonded fragment was measured to be 4.5 0.1 A in five different samples studied. This finding is consistent with an a-helix structure, in agreement with conformation-dependent 13C chemical shift data. 

Since its introduction, several other coherence transfer pathways have been employed. The described FSLG-HETCOR and recently proposed MAS-J-HMQC pulse sequence uses heteronuclear dipolar couplings, while the REPT-HMQC employs the rotational-echo double resonance (REDOR) recoupling pulse sequence. 

Many multiple resonance methods such as cross-polarisation (CP), Rotational Echo Double Resonance (REDOR), and Transferred Echo Double Resonance (TEDOR) are available. Their application can be differentiated between systems involving exclusively spin- /2 nuclei and those containing quadrupolar nuclei. The presence of quadrupolar nuclei may prohibit straightforward application of these experiments and can affect the interpretation of the results. There are, however, benefits arising from the presence of quadrupolar nuclei, as illustrated by the Transfer of Populations by Double Resonance (TRAPDOR) experiment which will only work for quadrupolar nuclei. 

The synthesis of a range of silicon boron carbonitride ceramics can conveniently be carried out by thermal treatment of suitable amorphous precursor molecules in which the desired atomic linkages are already in place. A series of new amorphous precursor molecules has been investigated by "B MAS NMR and double resonance techniques such as Si- B) Rotational Echo Adiabatic Passage DOuble Resonance (REAP-DOR) and B-j Si) Rotational Echo DOuble Resonance (REDOR) (van Wiillen and Jansen 2001). The results indicate the presence of hexagonal BN and (3-Si3N4 in some... 

One of the important applications of butylcalix[4]arenes arises from their ability to trap alkali metal ions. In particular, Cs+-calixarene complexes have received much attention because of the need to remove the Cs radionucleotide from nuclear wastes. Benevelli et al. have used one-pulse solid state NMR experiments to directly observe Li, Na and Cs ions in the host cavity [52]. More advanced experiments, which allow the investigation of metal lattice interactions were also reported. Rotational-echo double resonance (REDOR) NMR is a useful tool for obtaining structural details of butylcalix[4]arene [53]. Gullion and coworkers used REDOR to determine the position of the... 

Because of the complex spin-dynamics of the CP transfer involving quadrupolar nuclei, CP-based methods may not be quantitative. An alternative approach to CP spectral editing, introduced by Fernandez et al. [70], combines MQMAS with (quadrupolar spin)-observe (spin l/2)-dephase Rotational Echo Double Resonance (REDOR) [90]. The method relies on reintroducing the het-... 

The rotational echo double resonance (REDOR) technique is essentially the MAS version of SEDOR, affording a site-resolved measurement of heteronu-clear dipolar coupling information on rotating samples. Figure 8 shows two commonly used pulse sequences [21-24]. 

Fluorine-probe protocol has been applied to solid-state magic-angle spinning (SSMAS) 19F NMR analysis with the radiofrequency-driven dipolar recoupling (RFDR) method to measure the F-F distance in the microtubule-bound conformation of F2-10-Ac-docetaxel (see Figure 1.29a) [167], Moreover, five intramolecular distances of the key atoms in the microtubule-bound l9I72II/l3(Mabeled paclitaxel were determined by the rotational echo double resonance (REDOR) method (see Figure 1.29b and c) [168, 169],... 

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