Double resonance, application

A wide variety of ID and wD NMR techniques are available. In many applications of ID NMR spectroscopy, the modification of the spin Hamiltonian plays an essential role. Standard techniques are double resonance for spin decoupling, multipulse techniques, pulsed-field gradients, selective pulsing, sample spinning, etc. Manipulation of the Hamiltonian requires an external perturbation of the system, which may either be time-independent or time-dependent. Time-independent... 

The development of a wide range of special forms of EPR was initiated when the idea of double resonance (using simultaneous irradiation by two different sources) was cast in 1956 by G. Feher at Bell Telephone Labs in his seminal paper on ENDOR, electron nuclear double resonance (Feher 1956). BioEPR applications of ENDOR were later developed on flavoprotein radicals in a collaboration of A. Ehrenberg and L. E. G. Eriksson in Stockholm, Sweden, and J. S. Hyde at Varian in Palo Alto, California (Ehrenberg et al. 1968), and on metalloproteins in a joint effort of the groups of R. H. Sands in Ann Arbor, I. C. Gunsalus in Urbana, Illinois, and H. Beinert in Madison (Fritz et al. 1971). 

The main application of double resonance is the resolution of hyperfine and particularly superhyperfine interactions that are not extractable from regular EPR spectra because they are lost in the inhomogeneous line. The biological relevance is in otherwise unavailable detailed information on the electronic structure and the coordination of active sites and their interaction with reactants, such as enzyme substrates. To be well prepared, check off the items in the following list. 

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. 

Numerous new developments and applications of solid state NMR techniques have emerged. Multidimensional NMR methods are able to probe connectivity patterns of zeolite framework structures and solve ambiguities in line assignments [27], high-resolution techniques for quadrupolar nuclei have been developed [31-34], and powerful double-resonance methods permit the study of spatial... 

The already known geissoschizol (7, C19H24N20, MP 224-226°C, [a]D -70°) 184) and its 10-hydroxy derivative (8, C19H24N202, MP 264°C) (184), were isolated from the roots of T. bufalina (Ervatamia hainanensis) (53). The detailed analysis of the H-NMR spectra of 7 and 8 diacetate were reported (Table III) and the assignment of all of the protons was made by application of consecutive double-resonance experiments. 

K. O. Douglass, J. E. Johns, P. M. Nair, G. G. Brown, F. S. Rees, and B. H. Pate, Applications of Fourier transform microwave (FTMW) detected infrared microwave double resonance spec troscopy to problems in vibrational dynamics. J. Mol. Spectrosc. 239, 29 40 (2006). 

Kurreck, H., Kirste, B. and Lubitz, W. (1988) Electron Nuclear Double Resonance Spectroscopy of Radicals in Solution - Application to Organic and Biological Chemistry. Weinheim, Germany VCH. 

With this procedure, as with the double-resonance methods in atomic physics, Zeeman and Stark splittings, hyperfine structures and A doublings in molecules can be measured with high precision, even if the observed level splittings are far less than the optical dopp-ler width. From the width of the rf resonance and from the time response of the pumped systems, orientation relaxation rates can be evaluated for individual v J") levels. Other possible applications of this promising technique have been outlined by Zare 30) Experiments to test some of these proposals are currently under investigation and their results will be reported elsewhere. 

NMR and EPR techniques provide unique information on the microscopic properties of solids, such as symmetry of atomic sites, covalent character of bonds, strength of exchange interactions, and rates of atomic and molecular motion. The recent developments of nuclear double resonance, the Overhauser effect, and ENDOR will allow further elucidation of these properties. Since the catalytic characteristics of solids are presumably related to the detailed electronic and geometric structure of solids, a correlation between the results of magnetic resonance studies and cata lytic properties can occur. The limitation of NMR lies in the fact that only certain nuclei are suitable for study in polycrystalline or amorphous solids while EPR is limited in that only paramagnetic species may be observed. These limitations, however, are counter-balanced by the wealth of information that can be obtained when the techniques are applicable. 

Hoffman s group for electron nuclear double resonance (El OR) spectroscopy). This paper will review how the application of spectroscopy in conjunction with chemical and biochemical data has resulted in an increasingly more sophisticated, and one assumes increasingly accurate, picture of the active site of aconitase. 

A technique related to EPR, electron nuclear double resonance (ENDOR), allows the assignment of the individual hfcs to particular nuclei and, with reasonable assumptions, will also identify the sign of the interaction. The only obvious drawback of this technique lies in the fact that it requires sophisticated instrumentation, which is, so far, available in only a few laboratories. Applications to strained ring systems, viz., cyclobutene, bicyclobutane, or a tricyclic derivative, have been reported. Howcvct, applications to simple cyclopropane systems have not been reported to date. 

Thus the response of a spatially uniform system in thermodynamic equilibrium is always characterized by translationally invariant and temporaly stationary after-effect functions. This article is restricted to a discussion of systems which prior to an application of an external perturbation are uniform and in equilibrium. The condition expressed by Eq. (7) must be satisfied. Caution must be exercised in applying linear response theory to problems in double resonance spectroscopy where non-equilibrium initial states are prepared. Having dispensed with this caveat, we adopt Eq. (7) in the remainder of this review article. 

Milov, A. D., Salikhov, K. M., and Shchirov, M. D. (1981). Application of the double resonance method to electron spin echo in a study of the spatial distribution of paramagnetic centers in sohds. Soviet. Phys. Solid State 23, 565—569. 

Milov, A. D., Maryasov, A. G., and Tsvetkov, Y. D. (1998). Pulsed electron double resonance (PELDOR) and its applications in ffee-radicals research. Appl. Magn. Reson. 15, 107—143. 

Nearly all the efforts toward the application of double-resonance NQR to explosives detection have been driven by the problem of TNT detection [91,96,97], although reports on its application to RDX [98] and PETN [99] detection have appeared recently. Both of the double-resonance detection schemes described earlier have been applied to TNT detection, as it does not fit neatly into either category around the H frequency of 1 MHz, the proton and nitrogen T1 s are similar, with the proton T1 becoming much longer at higher frequencies there are multiple 14N NQRs the proton line width is greater than 10 000 Hz. 

J. Brossel and F. Bitter, A new "double resonance" method for investigating atomic energy levels. Application to Hg 3PX, Phys. Rev. 86 308 (1952). 

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