Electron spin-echo resonance

Electron Spin Resonance Spectroscopy. Several ESR studies have been reported for adsorption systems [85-90]. ESR signals are strong enough to allow the detection of quite small amounts of unpaired electrons, and the shape of the signal can, in the case of adsorbed transition metal ions, give an indication of the geometry of the adsorption site. Ref. 91 provides a contemporary example of the use of ESR and of electron spin echo modulation (ESEM) to locate the environment of Cu(II) relative to in a microporous aluminophosphate molecular sieve. 

Riedel A, S Fetzner, M Rampp, F Lingens, U Liebl, J-L Zrmmermann, W Nitschke (1995) EPR, electron spin echo envelope modulation, and electron nuclear double resonance studies of the 2Ee-2S centers of the 2-halobenzoate 1,2-dioxygenase from Burkholderia (Pseudomonas) cepacia 2CBS. J Biol Chem 270 30869-30873. 

G.R. Eaton and S.S. Eaton, Electron-nuclear double resonance spectroscopy and electron spin echo envelope modulation spectroscopy, Comprehensive Coordination Chemistry II, Elsevier, Boston, 2004, 49. 

J. McCracken, Electron spin echo modulation, in Handbook of Electron Spin Resonance, ed. C.P. Poole and H.A. Farach, Springer-Verlag, New York, 1999, vol. 2. 

Double-resonance spectroscopy involves the use of two different sources of radiation. In the context of EPR, these usually are a microwave and a radiowave or (less common) a microwave and another microwave. The two combinations were originally called ENDOR (electron nuclear double resonance) and ELDOR (electron electron double resonance), but the development of many variations on this theme has led to a wide spectrum of derived techniques and associated acronyms, such as ESEEM (electron spin echo envelope modulation), which is a pulsed variant of ENDOR, or DEER (double electron electron spin resonance), which is a pulsed variant of ELDOR. The basic principle involves the saturation (partially or wholly) of an EPR absorption and the subsequent transfer of spin energy to a different absorption by means of the second radiation, leading to the detection of the difference signal. The requirement of saturability implies operation at close to liquid helium, or even lower, temperatures, which, combined with long experimentation times, produces a... 

Since the phenoxyls possess an S = ground state, they have been carefully studied by electron paramagnetic spectroscopy (EPR) and related techniques such as electron nuclear double resonance (ENDOR), and electron spin-echo envelope modulation (ESEEM). These powerful and very sensitive techniques are ideally suited to study the occurrence of tyrosyl radicals in a protein matrix (1, 27-30). Careful analysis of the experimental data (hyperfine coupling constants) provides experimental spin densities at a high level of precision and, in addition, the positions of these tyrosyls relative to other neighboring groups in the protein matrix. 

Mims, W. B. Electron spin echoes in Electron Paramagnetic Resonance, ed. Geschwind, S., New York Plenum Press (1972), chapt. 4... 

Electron Nuclear Double Resonance (ENDOR) and Electron Spin-Echo Envelope Modulation (ESEEM)... 

Electron nuclear double resonance (ENDOR) and electron spin-echo envelope modulation (ESEEM) are two of a variety of pulsed EPR techniques that are used to study paramagnetic metal centers in metalloenzymes. The techniques are discussed in Chapter 4 of reference la and will not be discussed in any detail here. The techniques can define electron-nuclear hyperfine interactions too small to be resolved within the natural width of the EPR line. For instance, as a paramagnetic transition metal center in a metalloprotein interacts with magnetic nuclei such as H, H, P, or these... 

An Electron Paramagnetic Resonance and Electron Spin Echo Study... 

Figure 19 Schematic representation of [VO(H20) +] and average intemuclear distances (A) from electron spin echo modulation (ESEM), electron nuclear double resonance (ENDOR) and X-ray diffraction studies4 ...

EPR, Electron paramagnetic resonance ESEEM, Electron spin-echo envelope modulation EXAFS, Extended X-ray absorption fine structure... 

A prototypical example of a molecular probe used extensively to study the mineral adsorbent-solution interface is the ESR spin-probe, Cu2+ (Sposito, 1993), whose spectroscopic properties are sensitive to changes in coordination environment. Since water does not interfere significantly with Cu11 ESR spectra, they may be recorded in situ for colloidal suspensions. Detailed, molecular-level information about coordination and orientation of both inner- and outer-sphere Cu2+ surface complexes has resulted from ESR studies of both phyllosilicates and metal oxyhydroxides. In addition, ESR techniques have been combined with closely related spectroscopic methods, like electron-spin-echo envelope modulation (ESEEM) and electron-nuclear double resonance (ENDOR), to provide complementary information about transition metal ion behaviour at mineral surfaces (Sposito, 1993). The level of sophistication and sensitivity of these kinds of surface speciation studies is increasing continually, such that the heterogeneous colloidal particles in soils can be investigated ever more accurately. 

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., Ponomarev, A. B., and Tsvetkov, Y. D. (1984). Electron—electron double resonance in electron spin echo Model biradical systems and the sensitized photolysis of decalin. Chem. Phys. Lett. 110, 67—72. 

Mims WB (1972) Electron spin echo. In Geschwind S (ed) Electron paramagnetic resonance. Plenum. New York, p 263... 

Aznar CP, Britt RD. Simulations of the 111 electron spin echo-electron nuclear double resonance and 2H electron spin echo envelope modulation spectra of exchangeable hydrogen nuclei coupled to the S2-state photosystem II manganese cluster. Phil Trans R Soc B. 2002 357(1426) 1359-66. 

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