TOPICAL electron paramagnetic resonance

Information about RNA structure and movement is critical for our understanding of how RNA is able to carry out its multifaceted functions. One spectroscopic technique that has shown great promise to study RNA, as well as other biopolymers, is electron paramagnetic resonance (EPR) spectroscopy, also named electron spin resonance (ESR) spectroscopy. EPR is a magnetic resonance technique that monitors the behaviors of unpaired electrons, and has long been used to study structure and dynamics of biomolecules (see recent reviews by Klug and Feix, 2008 Sowa and Qin, 2008). Structural information can be obtained by distance measurements, that is, by determination of distances between two spin-centers, and is the topic of another chapter in this volume (see Chapter 16 in this volume). 

Saifutdinov, Rafik Galimzyanovich. Electron Paramagnetic Resonance in Biochemistry and Medicine. Topics in Applied Chemistry. New York Kluwer Academic/Plenum, 2001. 

The second volume of this new treatise is focused on the physicochemical properties and photochromic behavior of the best known systems. We have included chapters on the most appropriate physicochemical methods by which photochromic substances can be studied (spectrokinetic studies on photostationary states, Raman spectroscopy, electron paramagnetic resonance, chemical computations and molecular modeling, and X-ray diffraction analysis). In addition, special topics such as interactions between photochromic compounds and polymer matrices, photodegradation mechanisms, and potential biological applications have been treated. A final chapter on thermochromic materials is included to emphasize the chemical similarities between photochromic and thermochromic materials. In general, the literature cited within the chapters covers publications through 1995. However, in several cases, publications from as late as 1997 are included. 

Magnetic resonance plays a role in biophysical spectroscopy of ever increasing importance and diversity. The topic is conveniently and conventionally divided into three domains (1) nuclear magnetic resonance (NMR) spectroscopy, (2) Mdssbauer spectroscopy, and (3) electron paramagnetic resonance (EPR) spectroscopy. All three of these methods depend on the presence of a magnetic moment, either that of a nucleus or of an unpaired electron. This overview is confined to the topic of EPR as the biological applications of NMR are so extensive that they receive dedicated reviews (e.g.. Volume 239 in this series) and the biochemical applications of Mdssbauer spectroscopy have been reviewed elsewhere in this series. ... 

For the reader who is interested in further aspects of chemical modelling we mention that this field, of course, is not only of interest to theoreticians but also used in addressing problems in experimental studies. Thus, also other Specialist Periodical Reports on other topics contain contributions devoted to chemical modelling. This is, e.g., the case for vol. 27 of the Catalysis series and for vol. 24 of the Electron Paramagnetic Resonance series. 

A very interesting paper by Chesnut and Phillips (1961) represents almost a cross between the topics discussed in A and C above. They have studied the electron spin resonance spectra of single crystals containing the paramagnetic (doublet) radical anion of tetracyano-quinodimethane,... 

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