Continuous-wave electron paramagnetic resonance

D. Collison, M. Helliwell, V.M. Jones, F.E. Mabbs, E.J.L. Mclnnes, P.C. Riedi, G.M. Smith, R.G. Pritchard and W.I. Cross, Single and double quantum transitions in the multi-frequency continuous wave electron paramagnetic resonance (cwEPR) of three six-co-ordinate nickel(II) complexes ... 

Studying RNA Using Site-Directed Spin-Labeling and Continuous-Wave Electron Paramagnetic Resonance Spectroscopy... 

Zucchi MR, Nascimento OR, Faljoni-Alario A et al (2003) Modulation of cytochrome c spin states by lipid acyl chains a continuous-wave electron paramagnetic resonance (CW-EPR) study of haem iron. Biochem J 370 671-678... 

Hustedt EJ, Smirnov AI, Laub CE, Cobb CE, Beth AH. Molecular distances from dipolar coupled spin-labels the global analysis of multifrequency continuous wave electron paramagnetic resonance data. Biophys. J. 1997 74 1861-1877. 

Electron-nuclear double resonance (ENDOR) spectroscopy A magnetic resonance spectroscopic technique for the determination of hyperfine interactions between electrons and nuclear spins. There are two principal techniques. In continuous-wave ENDOR the intensity of an electron paramagnetic resonance signal, partially saturated with microwave power, is measured as radio frequency is applied. In pulsed ENDOR the radio frequency is applied as pulses and the EPR signal is detected as a spin-echo. In each case an enhancement of the EPR signal is observed when the radiofrequency is in resonance with the coupled nuclei. 

CW, continuous wave Cys, cysteine DFT, density functional theory ENDOR, electron nuclear double resonance ehba, 2-ethyl-2-hydroxybutanoate2 EPR, electron paramagnetic resonance Glc6P, D-glucose 6-phosphate GSH, reduced glutathione HEPES, 4-(2-hydroxyethyl)-l-piperazineethanesulfonic acid Hex, aldohexose ... 

Electron paramagnetic resonance spectroscopy, also known as electron spin resonance (ESR) spectroscopy, detects the excitation of electron spins in an applied external magnetic field.13 Conventional continuous-wave (CW) EPR is based on resonance of a fixed-frequency standing microwave to excite some of the electrons in Zeeman-split spin multiplets to undergo a transition from a lower Ms level to a higher... 

Altenbach C, Eroncisz W, Hyde JS, Hubbell WL (1989) Conformation of spin-labeled melittin at membrane surfaces investigated by pulse saturation recovery and continuous wave power saturation electron-paramagnetic resonance. Biophys J 56 1183-1191... 

Electron paramagnetic resonance (EPR) spectroscopy [1-3] is the most selective, best resolved, and a highly sensitive spectroscopy for the characterization of species that contain unpaired electrons. After the first experiments by Zavoisky in 1944 [4] mainly continuous-wave (CW) techniques in the X-band frequency range (9-10 GHz) were developed and applied to organic free radicals, transition metal complexes, and rare earth ions. Many of these applications were related to reaction mechanisms and catalysis, as species with unpaired electrons are inherently unstable and thus reactive. This period culminated in the 1970s, when CW EPR had become a routine technique in these fields. The best resolution for the hyperfine couplings between the unaired electron and nuclei in the vicinity was obtained with CW electron nuclear double resonance (ENDOR) techniques [5]. 

Because some of the forms of heme proteins are intrinsically paramagnetic, electron paramagnetic resonance (EPR) has been used extensively to study the stracture and structure-function relations of these proteins. By far the majority of these investigations are done using continuous-wave (cw) EPR at the conventional X-band microwave frequency ( 9.5 GHz), and these cw-EPR studies have formed the basis of many excellent reviews [4-6]. In the last two decennia, the field of EPR spectroscopy has, however, been revolutionized by many technical developments. Indeed, the construction of pulse-EPR spectrometers, die accompanying developments of the pulse-EPR methodology, and the (ongoing) development of... 

Jee B, Eisinger K, Gul-E-Noor F et al (2010) Continuous wave and pulsed electron spin resonance spectroscopy of paramagnetic framework cupric ion in the Zn(Il) doped porous coordination polymer Cu3 xZnx(btc)2. J Phys Chem C 114 16630-16639... 

Electron spin resonance (ESR) spectroscopy is a very powerful and sensitive method for the characterization of the electronic structures of materials with unpaired electrons. There is a variety of ESR techniques, each with its own advantages. In continuous wave ESR (CW-ESR), the sample is subjected to a continuous beam of microwave irradiation of fixed frequency and the magnetic field is swept. Different microwave frequencies may be used and they are denoted as S-band (3.5 GHz),X-band (9.25 GHz), K-band (20 GHz), Q-band (35 GHz) and W-band (95 GHz). Other techniques, such as electron nuclear double resonance (ENDOR) and electron spin echo envelope modulation (ESEEM) spectroscopies, record in essence the NMR spectra of paramagnetic species. 

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