Solid-echo double resonance

Solid-echo double resonance (SEDOR) and rotational-echo double resonance (REDOR) techniques can be used to determine the proximity of the two types of nuclei, e.g., to determine which Na ions are closest to A1 atoms in the framework of a zeolite, or to determine internuclear distances, or to help locate the position of a guest molecule relative to the host framework. ... 

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. 

The REDOR experiment has formed the basis for a large number of ideal pulse type recoupling experiments, and later finite pulse variants, for heteronuclear dipolar recoupling. These include experiments such as frequency selective REDOR (FS-REDOR) [80], TEDOR (Transferred Echo DOuble Resonance) [25], and 3D variants of TEDOR [81, 82], which have found important applications, e.g., for measurement of intemuclear 13C-15N distances in biological solids. We should also mention that rotor-encoded variants of TEDOR, such as REPT, HDOR [83], and REREDOR [84], have been proposed for 1H13C dipolar recoupling under high-speed MAS conditions. 

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

Y. Pan, P- F rotational-echo double resonance nuclear magnetic resonance experiment on fluoridated hydroxyapatite. Solid State Nucl. Magn. Reson. 5 (1995) 263-268. L. Wu, W. Forsling, P.W. Schindler, Surface complexation of calcium mineral in aqueous solution, surface protonation at fluorapatite surface, J. Colloid Interface Sci. 147 (1991) 178-185. 

NMR-spectroscopic investigations of dendrimers can provide comparable information. Thus Wooley et al. used REDOR (Rational Echo Double-Resonance) solid state NMR experiments for the study of the density distribution and back-folding of terminal groups in fifth-generation poly(benzyl ether) dendrimers... 

N.M.R. STUDIES of ADSORBED ETHYLENE We have also investigated the reaction of C ethylene with colloidal palladium. Our initial intent was to attempt to observe the formation of ethylidyne from ethylene on the surface of the colloidal palladium particles, a reaction which is known to occur readily on the surface of supported palladium and on palladium single crystals (17). Such a reaction has been identified for ethylene on supported platinum by magnetic resonance experiments in which spin echo double resonance techniques were used to characterize the organic species (18,19), but direct observation of resonances for adsorbed ethylene or ethylidyne was not possible in the highly inhomogeneous solid samples used. The chemical shift differences... 

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... 

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],... 

Mani, R., Tang, M., Wu, X., et al. (2006) Membrane-bound dimer structure of a beta-hairpin antimicrobial peptide from rotational-echo double-resonance solid-state NMR. Biochemistry, 45(27), 8341-8349. 

Various ID and 2D high-resolution solid-state NMR techniques have been applied to hydrous silicate and aluminosilicate glasses simple acquisition, CPMAS, HETCOR, dipolar dephasing, spin counting, DQ correlation, and rotational echo double resonance (REDOR). ... 

As mentioned above, the determination of atomic level structure, i.e., the backbone torsion angles for an oriented protein fiber, is possible by using both solid-state NMR method described here and specifically isotope labeling. This is basically to obtain the angle information. Another structural parameter is distance between the nuclei for atomic coordinate determination. The observation of Nuclear Overhauser Enhancements (NOEs) between hydrogen atoms is a well known technique to determine the atomic coordinates of proteins in solution [14]. In the field of solid-state NMR, REDOR (rotational echo double resonance) for detection of weak heteronuclear dipole interactions, such as those due to C and N nuclei [15, 16] or R (rotational resonance) for detection of the distance between homonuclei, are typical methods for internuclear distance determination [17,18]. The REDOR technique has been applied to structure determination of a silk fibroin model compound [19]. In general, this does not require orientation of the samples in the analysis, but selective isotope labeling between specified nuclear pairs in the samples is required which frequently becomes a problem. A review of these approaches has appeared elsewhere [16]. 

For this purpose, it has been demonstrated that the high resolution solid-state NMR approach provides one with an alternative and convenient means to distinguish a variety of crystalline polymorphs and to reveal the secondary structures of biological macromolecules, because the chemical shifts of backbone carbons are displaced (up to 8 ppm) [1, 2] depending on their respective conformations. In addition, it is emphasized that this type of empirical approach can be used as a very valuable constraint to construct the three-dimensional structure of biological molecules, such as peptides and proteins, based on a set of accurately determined interatomic distances measured by a partial dipolar recoupling method, such as REDOR (rotational echo double resonance) [3-6]. 

As with the 2DTOSS studies, Munson and co-workers showed that solid-state NMR can provide important information on the structures of polymorphs and solvates whose crystal structure is not known. As we seek more detailed structural information of drugs in order to understand more about solid-state behavior, these 2D techniques will no doubt become more and more important. Additional 2D techniques have been utilized to study DNA complexes (104) and perform distance measurements (105), specifically using the rotational-echo double-resonance (REDOR) sequence (106,107). 

Having demonstrated the achievement of high-resolution sohd state NMR capability, the authors describe experiments that combine the high-resolution aspect of MAS NMR with methods that retain the structure and/or dynamic information inherent in the anisotropic interactions. Rotational-echo double resonance (REDOR) allows the determination of D between isolated heteronuclear spin pairs. D is related simply and without approximation to intemuclear separation. Hence, REDOR makes possible the unambiguous direct determination of intemuclear distance between the labeled spin pair, independent of pair orientation, i. e., in amorphous and /or microaystaUine solids, and extends our abihty to quantitatively explore complex materials. It is also possible to extract intemuclear distance from homonuclear dipolar coupled spin pairs, and these experiments are also reviewed. 

The silk I structure (the structure of Bombyx mori silk filroin before spiimiiig in the solid state) was detenxiined with two-dimensional (2D) spin-dffiision solid-state NMR, rotational echo double resonance (REDOR) and quantitative use of CP/MAS NMR chemical shifis. We used double labeled and double labeled model... 

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