Advanced paramagnetic resonance spectroscopies of iron-sulfur proteins: Electron nuclear double resonance (ENDOR) and electron spin echo envelope modulation (ESEEM).

The advanced electron paramagnetic resonance (EPR) techniques, electron nuclear double resonance (ENDOR) and electron spin echo envelope modulation (ESEEM) spectroscopies, provide unique insights into the structure, coordination chemistry, and biochemical mechanism of nature's widely distributed iron-sulfur cluster (FeS) proteins. This review describes the ENDOR and ESEEM techniques and then provides a series of case studies on their application to a wide variety of FeS proteins including ferredoxins, nitrogenase, and radical SAM enzymes. This article is part of a Special Issue entitled: Fe/S proteins: Analysis, structure, function, biogenesis and diseases.

High-frequency and high-field electron paramagnetic resonance (HFEPR): a new spectroscopic tool for bioinorganic chemistry.

This minireview describes high-frequency and high-field electron paramagnetic resonance (HFEPR) spectroscopy in the context of its application to bioinorganic chemistry, specifically to metalloproteins and model compounds. HFEPR is defined as frequencies above ~100 GHz (i.e., above W-band) and a resonant field reaching 25 T and above. The ability of HFEPR to provide high-resolution determination of g values of S = 1/2 is shown; however, the main aim of the minireview is to demonstrate how HFEPR can extract spin Hamiltonian parameters [zero-field splitting (zfs) and g values] for species with S > 1/2 with an accuracy and precision unrivalled by other physical methods. Background theory on the nature of zfs in S = 1, 3/2, 2, and 5/2 systems is presented, along with selected examples of HFEPR spectroscopy of each that are relevant to bioinorganic chemistry. The minireview also provides some suggestions of specific systems in bioinorganic chemistry where HFEPR could be rewardingly applied, in the hope of inspiring workers in this area.

From spin-labeled proteins to in vivo EPR applications.

This is a historical overview of the advent of applications of spin labeling to biological systems and the subsequent developments from the perspective of a scientist who was working as a Ph.D. student when the technique was conceived and was fortunate enough to participate in its development. In addition, the historical development of in vivo applications of EPR on animals and other living systems is described from a personal perspective.

XIth EPR Workshop on Applications of EPR in Biology and Medicine.

We are pleased and honored to present this special issue for CBBI on the broad topic of biomedical EPR. The papers herein resulted from the most recent October 2019 EPR Workshop in Kraków that encompasses work from outstanding researchers in the field. Before describing the range of articles, we have briefly summarized the history of these workshops and the publications that resulted.

Recent advances and applications of site-directed spin labeling.

Site-directed spin labeling has become a popular biophysical tool for the characterization of protein structure, dynamics and conformational change. This method is well suited and widely used to study small soluble proteins, membrane proteins and large protein complexes. Recent advances in site-directed spin labeling methodology have occurred in two areas. The first involves an understanding of the conformations and local dynamics of the spin-labeled sidechain, including the features of proteins that influence electron paramagnetic resonance lineshape. The second advance is the application of pulse techniques to determine long-range distances and distance distributions in proteins. During the past two years, these technical developments have been used to address several important problems concerning the molecular function of proteins.

Pulse EPR in biological systems - Beyond the expert's courtyard.

Application of EPR to biological systems includes many techniques and applications. In this short perspective, which dares to look into the future, I focus on pulse EPR, which is my field of expertise. Generally, pulse EPR techniques can be divided into two main groups: (1) hyperfine spectroscopy, which explores electron-nuclear interactions, and (2) pulse-dipolar (PD) EPR spectroscopy, which is based on electron-electron spin interactions. Here I focus on PD-EPR because it has a better chance of becoming a widely applied, easy-to-use table-top method to study the structural and dynamic aspects of bio-molecules. I will briefly introduce this technique, its current state of the art, the challenges it is facing, and finally I will describe futuristic scenarios of low-cost PD-EPR approaches that can cross the diffusion barrier from the core of experts to the bulk of the scientific community.

What are the methodological and theoretical prospects for paramagnetic NMR in structural biology? A glimpse into the crystal ball.

NMR spectroscopy is very sensitive to the presence of unpaired electrons, which perturb the NMR chemical shifts, J splittings and nuclear relaxation rates. These paramagnetic effects have attracted increasing attention over the last decades, and their use is expected to increase further in the future because they can provide structural information not easily achievable with other techniques. In fact, paramagnetic data provide long range structural restraints that can be used to assess the accuracy of crystal structures in solution and to improve them by simultaneous refinements with the X-ray data. They are also precious for obtaining information on the conformational variability of biomolecular systems, possibly in conjunction with SAXS and/or DEER data. We foresee that new tools will be developed in the next years for the simultaneous analysis of the paramagnetic data with data obtained from different techniques, in order to take advantage synergistically of the information content of all of them. Of course, the use of the paramagnetic data for structural purposes requires the knowledge of the relationship between these data and the molecular coordinates. Recently, the equations commonly used, dating back to half a century ago, have been questioned by first principle quantum chemistry calculations. Our prediction is that further theoretical/computational improvements will essentially confirm the validity of the old semi-empirical equations for the analysis of the experimental paramagnetic data.

Joint International Conference on EPR Spectroscopy and wound healing.

The International Conference on Electron Paramagnetic Resonance Spectroscopy and Imaging of Biological Systems (EPR 2005) was held September 4 through 9, 2005, at Columbus, Ohio, U.S.A. Nearly 200 participants from 16 countries presented recent advances on the use of EPR technology to study biologic processes, with an emphasis on human health. For the first time, the EPR conference allied with the Wound Healing Conference, and the alliance opened an avenue for successful amalgamation of the basic biomedical and clinical aspects of wound healing with EPR technology and vice versa. This should lead to emerging applications of EPR technology in biomedical research and clinical practice.

The Third International Intercomparison on EPR Tooth Dosimetry: part 2, final analysis.

The objective of the Third International Intercomparison on EPR Tooth Dosimetry was to evaluate laboratories performing tooth enamel dosimetry <300 mGy. Final analysis of results included a correlation analysis between features of laboratory dose reconstruction protocols and dosimetry performance. Applicability of electron paramagnetic resonance (EPR) tooth dosimetry at low dose was shown at two applied dose levels of 79 and 176 mGy. Most (9 of 12) laboratories reported the dose to be within 50 mGy of the delivered dose of 79 mGy, and 10 of 12 laboratories reported the dose to be within 100 mGy of the delivered dose of 176 mGy. At the high-dose tested (704 mGy) agreement within 25% of the delivered dose was found in 10 laboratories. Features of EPR dose reconstruction protocols that affect dosimetry performance were found to be magnetic field modulation amplitude in EPR spectrum recording, EPR signal model in spectrum deconvolution and duration of latency period for tooth enamel samples after preparation.

ESR spectrometry: a future-oriented tool for dosimetry and dating.

ESR spectroscopy is currently taking root as a key technology in dosimetry, dating and imaging. In dosimetry, it competes with cytometry in the fields of biological dosimetry and retrospective dosimetry, leads in high-level reference and routine dosimetry, is high-ranking among the methods to identify radiation preserved foods, represents a method of choice to date geological, archaeological and paleontological materials back millions of years, and has demonstrated capacity for imaging. Further scientific and technological progress as predicted in the recent past (Appl. Radiat. Isot. 52 (2000) 1023) is reviewed here. Additionally, the review is expanded to include international reports and recommendations on ESR dosimetry and dose reconstruction, under way at the American Society for Testing and Materials (ASTM), the International Organisation of Standards (ISO), the International Atomic Energy Agency (IAEA) and the International Commission on Radiation Units and Measurements (ICRU). Emphasis is placed on interpretation of tooth enamel doses in terms of organ and effective doses, using CT-based virtual humans. The future of EPR spectroscopy for in situ dose measurements is noted, depicting a non-destructive in vivo dosimetry applicable directly to individuals, but also to hominid and animal fossils for direct dating.

Functional imaging of intratumoral hypoxia.

PURPOSE: Tumor hypoxia plays a fundamental role in tumor progression and treatment resistance. Recent evidence that hypoxia also influences the regulation and transcription of various genes involved in malignant growth and metastases, and promotes a more aggressive tumor phenotype makes its diagnosis even more important. PROCEDURES: The evidence for the biology of hypoxia in tumors, and imaging of hypoxia with different technologies was reviewed through literature review and Medline searches, and clinical studies with 18F-fluoromisonidazole (FMISO) Positron Emission Tomography (PET). RESULTS: Until recently, determination of the level of tumor oxygenation was only possible using invasive methods that limited its clinical application. Imaging techniques that have shown promise in assessing hypoxia include magnetic resonance imaging and spectroscopy, single photon emission computed tomography (SPECT) and PET. Quantitative hypoxia measurement with 18F-FMISO PET in patients with malignant gliomas and lung cancer have demonstrated intratumoural hypoxia and dissociation of glucose metabolism from hypoxia in some cases, indicating the complex nature of cellular metabolic response to stress. CONCLUSION: The emerging role of therapies that have improved efficacy in hypoxic conditions, and recent advances in the ability to noninvasively measure in vivo intratumoral hypoxia with functional imaging has renewed interest in the clinical measurement of tumor hypoxia and its impact on cancer treatment.

Recent progress in in vivo ESR spectroscopy.

The generation of free radicals and redox status is related to various diseases and injuries that are related to radiation, aging, ischemia-reperfusion, and other oxidative factors. In vivo electron spin resonance (ESR) spectroscopy is noninvasive and detects durable free radicals in live animals. ESR spectrometers for in vivo measurements operate at a lower frequency (approximately 3.5 GHz, approximately 1 GHz, 700 MHz, and approximately 300 MHz) than usual (9-10 GHz). Several types of resonators have been designed to minimize the dielectric loss of electromagnetic waves caused by water in animal bodies. In vivo ESR spectroscopy and its imaging have been used to analyze radical generation, redox status, partial pressure of oxygen and other conditions in various disease and injury models related to oxidative stress with probes, such as nitroxyl radicals. Through these applications, the clarification of the mechanisms related to oxidative diseases (injuries) and the accumulation of basic data for radiological cancer therapy are now ongoing. In vivo ESR measurement is performed in about 10 laboratories worldwide, including ours. To introduce in vivo ESR spectroscopy to life scientists, this article reviews the recent progress of in vivo ESR spectroscopy in instrumentation and its application to the life sciences.

From dating to biophysics--20 years of progress in applied ESR spectroscopy.

ESR spectroscopy represents a tool for quantitative radiation analysis that was developed somehow simultaneously for dating purposes in Japan and in Germany for high-level standardization, in the mid-seventies. Meanwhile, ESR dosimetry has reached an established metrology level. Present research fields of ESR dosimetry consider post-accident dose reconstruction in the environment, and biophysical dosimetry using human tissues. The latter promises a re-definition of radiation risk for chronicle exposure to be derived from individuals of the early nuclear facilities in Russia, and hopefully United States in the future. An attempt is made to sketch development and potential future of the ESR technique.

ESR dating: is it still an 'experimental' technique?

Nearly 25 years ago, Motoji Ikeya demonstrated the potential of ESR dating. From a single substance (stalagmitic carbonate) and a single site (Akiyoshi Cavern), the field has grown to include materials from all over the world and time periods from a few thousand years ago to several million years ago. A vigorous program of instrumentation development has increased the precision of measurements as well as opening up new ways of collecting and interpreting spectra. Yet there are still references to ESR dating as an 'experimental' technique, one which cannot be trusted to produce dates that are accurate or precise. This paper discusses areas for which this is true and suggests what should be done to convince skeptics. Other areas for which the evidence suggests that ESR is at least as reliable as 'standard' methods will also be covered.

[Progress and application of free radical determination techniques in the biological domain].

Seeking for convenient, rapid and highly effective techniques of free radical determination is a key point for studying the biologic mechanism of free radicals. This paper reviewed the progress of these techniques in biological domain and described the electron spin resonance imaging [correction of imagine] (ESRI) technique development since the 1990s.

The world as viewed by and with unpaired electrons.

Recent advances in electron paramagnetic resonance (EPR) include capabilities for applications to areas as diverse as archeology, beer shelf life, biological structure, dosimetry, in vivo imaging, molecular magnets, and quantum computing. Enabling technologies include multifrequency continuous wave, pulsed, and rapid scan EPR. Interpretation is enhanced by increasingly powerful computational models.

Fingernail dosimetry: current status and perspectives.

A summary of recent developments in fingernail EPR dosimetry is presented in this paper. Until 2007, there had been a very limited number of studies of radiation-induced signals in fingernails. Although these studies showed some promising results, they were not complete with regard to the nature of non-radiation signals and the variability of dose dependence in fingernails. Recent study has shown that the two non-radiation components of the EPR spectrum of fingernails are originated from mechanical stress induced in the samples at their cut. The mechanical properties of fingernails were found to be very similar to those of a sponge; therefore, an effective way to eliminate their mechanical deformation is by soaking them in water. Stress caused by deformation can also significantly modify the dose response and radiation sensitivity. Consequently, it is critically important to take into account the mechanical stress in fingernail samples under EPR dose measurements. Obtained results have allowed formulating a prototype of a protocol for dose measurements in human fingernails.

In vivo electron spin resonance: An effective new tool for reactive oxygen species/reactive nitrogen species measurement.

Reactive oxygen species are regarded as important factors in the initiation and progression of many diseases. Therefore, measurement of redox status would be helpful in understanding the "Redox Navigation" of such diseases. Because electron spin resonance (ESR) shows good signal responses to nitroxyl radical and various redox-related species, such as oxygen radicals and antioxidants, the in vivo ESR/nitroxyl probe technique can provide useful information on real-time redox status in a living body. ESR spectrometers for in vivo measurements can be operated at lower frequencies (approximately 3.5 GHz, 1 GHz, 700 MHz, and 300 MHz) than usual (9-10 GHz). Several types of resonators were also designed to minimize the dielectric loss of electromagnetic waves caused by water in animal bodies. In vivo ESR spectroscopy and its imaging have been used to analyze radical generation, redox status, partial pressure of oxygen and other conditions in various diseases. In addition, ESR has been used to analyze injury models related to oxidative stresses, such as nitroxyl radicals. The application of in vivo ESR for diseases related to oxidative injuries currently being investigated and the accumulation of basic data for therapy is ongoing. Recent progress in the instrumentation for in vivo ESR spectroscopy and its application to the life sciences are reviewed, because measurement of redox status in vivo is considered necessary to understand the initiation and progression of diseases.