Nuclear quadrupole double-resonance

With its natural abundance of 93.1% and a relative receptivity of its central transition comparable to that of C, K appears to be a suitable nucleus for solid state NMR. These factors are to some extent offset by its small magnetic moment and quadrupolar characteristics which have limited the number of solid-state NMR studies to date. An early study demonstrated the success of the nuclear quadrupole double resonance... 

With the use of nuclear quadrupole resonance (NQR) and nuclear quadrupole double resonance techniques,83,92 94 the temperature dependence of 35C1,14N and 170 frequencies was measured at 77-289 K for a series of salicylideneanilines. All the experimental results agree with a model in which the exchange between the low-energy enol form and the high-energy tautomeric keto form is fast and reflects a dynamic equilibrium between the two forms. 

D. T. Edmonds, "Nuclear quadrupole double resonance," Phys. Rep. 29C, 233-290 (1977). 

R 302 R. Blinc, T. Apih and J. Seliger, Nuclear Quadrupole Double Resonance Techniques for the Detection of Explosives and Drugs , Appl.Magn.Reson., 2004,25,523... 

Edmonds DT (1977) Nuclear quadrupole double resonance. Physics Reports (Section C of Physics Letters) 29 233-290. 

To resolve hf and nuclear quadrupole interactions which are not accessible in the EPR spectra, George Feher introduced in 1956 a double resonance technique, in which the spin system is simultaneously irradiated by a microwave (MW) and a radio frequency (rf) field3. This electron nuclear double resonance (ENDOR) spectroscopy has widely been applied in physics, chemistry and biology during the last 25 years. Several monographs2,4 and review articles7 11 dealing with experimental and theoretical aspects of ENDOR have been published. 

DPPH = 2,2-diphenyl-1-picrylhydrazyl ENDOR= electron-nuclear double resonance EPR = electron paramagnetic resonance ESE = electron spin echoes ESEEM = electron spin echo envelope modulation EFT = fast fourier transformations FWHM = fidl width at half maximum HYSCORE = hyperfine sublevel correlation nqi = nuclear quadrupole interaction TauD = taurme/aKG dioxygenase TWTA = traveling wave tube amphfier ZFS = zero field sphtting. 

In the double resonance experiments, the effect of the deuterium nuclear quadrupole transitions on the NMR signal50 or the NQR signal42 of another nucleus is observed. For example, an ingenious method of detecting pure quadrupole transitions by nuclear double resonance was suggested by Schwab and Hahn.50 In their experiment, the quadrupole transitions of deuterium in a 12 percent deuterium-enriched sample of p-dichlorobenzene were excited, and the effect on the proton resonance signal through dipolar cross relaxation was detected. The 35 Cl spins served to establish and monitor an ordered metastable spin state of the protons. 

Deuterium quadrupole coupling constants can also be obtained from electron nuclear double resonance (ENDOR).19 30 An observation of the hyperfine structure caused by quadrupole coupling in the electron paramagnetic resonance (EPR) spectrum, as for many lanthanide complexes, has not been reported for deuterium. The determination of nuclear quadrupole coupling constants from Mossbauer spectroscopy is not applicable to the deuterium nucleus. 

Electron-nuclear double resonance (ENDOR) is able to recover hyperfine and quadrupole information from incompletely resolved EPR-spectra. It was applied to native, azido- and cyano-derivatives of bovine Cu Zn superoxide dismutase . The ENDOR response of azido-SOD has led to the suggestion, that four nearly equivalent nitrogens surround the copper. The response of the native form was too complex for interpretation. The ENDOR response of the cyano form revealed that... 

Lunsford [3b] and Hoffman and Nelson [23] first reported the ESR spectra for adsorbed NO molecules. Then, Kasai [4b] revealed that ESR spectra of NO probe molecules are very sensitive to the interaction with metal ions and Lewis acid sites in zeolites. The earlier ESR studies of the NO/zeolite system have been summarized in several review papers [3a, 4a, 8]. A number of ESR studies have been also carried out for NO adsorbed on metal oxides such as MgO and ZnO as reviewed by Che and Giamello [5]. Modern ESR techniques such as pulsed ESR [25-27], ENDOR (Electron Nuclear Double Resonance) [26], and multi-frequency (X-, Q-, and W-band) ESR [28] are especially useful for an unambiguous identification of the ESR magnetic parameters (g, hyperfine A, and quadrupole tensors, etc.) and, consequently, for a detailed characterization of structural changes and motional dynamics involved. Some recent advancements in ESR studies on NO adsorbed on zeolites are presented in this section. 

In another related article Jerschow has reviewed new high-resolution NMR techniques for the study of quadrupolar nuclei. This article also includes theoretical description of the NMR techniques. A number of topics that are often left out in other review articles, such as nuclear quadrupole resonance, overtone spectroscopy and the ionic model for the calculation of electric field gradients, have also been considered. In addition, high-resolution techniques, such as double rotation, dynamic-angle spinning, MQ MAS, and satellite transition MAS have also been reviewed. 

From the experimental standpoint, a system such as is well parameterized because there will, in principle, be three spectroscopic transitions from which it will be possible to determine the two NQI parameters, e Qq and q. Other spin systems, such as 0 (/ = S ), S, and Cl (/= 3/1) are more difficult to parameterize because there are fewer spectroscopic transitions than theoretical parameters, but techniques such as double resonance enable one to get the requisite information (Semin et al, 1975 Lucken, 1969b). Simple orbital descriptions of the nuclear quadrupole coupling parameters and orbital hybridization have been reported (Cotton Harris, 1966), and measures of the nuclear quadrupole interaction parameters and their tensor orientation can therefore be applied to solving problems of molecular structure and reactivity. 

Continuous Wave Electron Magnetic Resonance Electron-Nuclear Double Resonance Electron Spin Echo Envelope Modulation Nuclear Quadrupole Interaction Nuclear Quadrupole Resonance Zero Field... 

Two of the three constants eqQaa, eqQbb id eqC c were determined from microwave optical double resonance (MODR) spectra of NH2 [1 to 4], microwave absorption spectra of ND2 [5], and by ab initio (UHF) calculations [6]. The third constant follows from eqQaa+ eqQbb + QQcc = 0 [3]- The nuclear quadrupole coupling constants listed in the following table are given in terms of the principle axis system (b C2, c 1 molecular plane). 

The effective ESR Hamiltonian, including also contributions from the nuclear spins and nuclear quadrupole moments (the latter primarily observable in electron-nuclear double resonance -ENDOR - spectroscopy), maybe written as (Harriman 1978) ... 

Blinc R (1975) Double resonance detection of nuclear quadrupole resonance spectra. In Smith JA (ed) Advances in Nuclear Quadrupole Resonance, Vol 2, pp 71-90. London Heyden. 

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