A pressure-jump EPR system to monitor millisecond conformational exchange rates of spin-labeled proteins.

Site-directed spin labeling electron paramagnetic resonance (SDSL-EPR) using nitroxide spin labels is a well-established technology for mapping site-specific secondary and tertiary structure and for monitoring conformational changes in proteins of any degree of complexity, including membrane proteins, with high sensitivity. SDSL-EPR also provides information on protein dynamics in the timescale of ps-μs using continuous wave lineshape analysis and spin lattice relaxation time methods. However, the functionally important time domain of μs-ms, corresponding to large-scale protein motions, is inaccessible to those methods.

Asymmetric spin echo multi-echo echo planar imaging (ASEME-EPI) sequence for pre-clinical high-field fMRI.

In functional magnetic resonance imaging (fMRI) of the blood oxygen level-dependent (BOLD) contrast, gradient-recalled echo (GRE) acquisitions offer high sensitivity but suffer from susceptibility-induced signal loss and lack specificity to microvasculature. In contrast, spin echo (SE) acquisitions provide improved specificity at the cost of reduced sensitivity. This study introduces Asymmetric Spin Echo Multi-Echo Echo Planar Imaging (ASEME-EPI), a technique designed to combine the benefits of both GRE and SE for high-field preclinical fMRI.

A pressure-jump EPR system to monitor millisecond conformational exchange rates of spin-labeled proteins.

Site-directed spin labeling electron paramagnetic resonance (SDSL-EPR) using nitroxide spin labels is a well-established technology for mapping site-specific secondary and tertiary structure and for monitoring conformational changes in proteins of any degree of complexity, including membrane proteins, with high sensitivity. SDSL-EPR also provides information on protein dynamics in the time scale of ps-µs using continuous wave lineshape analysis and spin lattice relaxation time methods. However, the functionally important time domain of µs-ms, corresponding to large-scale protein motions, is inaccessible to those methods.

A personal account on 25 years of scientific literature on [FeFe]-hydrogenase.

[FeFe]-hydrogenases are gas-processing metalloenzymes that catalyze H oxidation and proton reduction (H release) in microorganisms. Their high turnover frequencies and lack of electrical overpotential in the hydrogen conversion reaction has inspired generations of biologists, chemists, and physicists to explore the inner workings of [FeFe]-hydrogenase. Here, we revisit 25 years of scientific literature on [FeFe]-hydrogenase and propose a personal account on 'must-read' research papers and review article that will allow interested scientists to follow the recent discussions on catalytic mechanism, O sensitivity, and the in vivo synthesis of the active site cofactor with its biologically uncommon ligands carbon monoxide and cyanide.

Milliwatt three- and four-pulse double electron electron resonance for protein structure determination.

Electron paramagnetic resonance (EPR) experiments for protein structure determination using double electron-electron resonance (DEER) spectroscopy rely on high-power microwave amplifiers (>300 W) to create the short pulse lengths needed to excite a sizable portion of the spectrum. The recently introduced self-resonant microhelix combines a high conversion efficiency with an intrinsically large bandwidth (low -value) and a high absolute sensitivity. We report dead times in 3-pulse DEER experiments as low as 14 ± 2 ns achieved using less than 1 W of power at X-band (nominally 9.

Dispersion EPR: Considerations for Low-Frequency Experiments.

The hypothesis is made that the dispersion electron paramagnetic resonance (EPR) spectrum can yield a higher signal-to-noise ratio than the absorption spectrum in diagnostic examinations if phase noise in the bridge is under control. The rationale for this hypothesis is based on the observation that the dispersion spectrum becomes more intense than the absorption spectrum at high incident powers. The rationale is dependent on optimization of high microwave efficiency (Λ; mT/W) and low quality factor (Q-value) resonators as well as the use of microwave sources with reduced phase noise.

Extending electron paramagnetic resonance to nanoliter volume protein single crystals using a self-resonant microhelix.

Electron paramagnetic resonance (EPR) spectroscopy on protein single crystals is the ultimate method for determining the electronic structure of paramagnetic intermediates at the active site of an enzyme and relating the magnetic tensor to a molecular structure. However, crystals of dimensions typical for protein crystallography (0.05 to 0.

Rutile dielectric loop-gap resonator for X-band EPR spectroscopy of small aqueous samples.

The performance of a metallic microwave resonator that contains a dielectric depends on the separation between metallic and dielectric surfaces, which affects radio frequency currents, evanescent waves, and polarization charges. The problem has previously been discussed for an X-band TE cylindrical cavity resonator that contains an axial dielectric tube (Hyde and Mett, 2017). Here, a short rutile dielectric tube inserted into a loop-gap resonator (LGR) at X-band, which is called a dielectric LGR (dLGR), is considered.

Photobleaching of pheomelanin increases its phototoxic potential: Physicochemical studies of synthetic pheomelanin subjected to aerobic photolysis.

Although melanin is a photoprotective pigment, its elevated photochemical reactivity could lead to various phototoxic processes. Photoreactivity of synthetic pheomelanin, derived from 5-S-cysteinyldopa (5SCD-M) and its photodegradation products obtained by subjecting the melanin to aerobic irradiation with UV-visible light, was examined employing an array of advanced physicochemical methods. Extensive photolysis of 5SCD-M was accompanied by partial bleaching of the melanin, modification of its paramagnetic properties, and significant increase in the ability to photogenerate singlet oxygen.

Uniform Field Resonators for EPR Spectroscopy: A Review.

Cavity resonators are often used for electron paramagnetic resonance (EPR). Rectangular TE and cylindrical TE are common modes at X-band even though the field varies cosinusoidally along the Z-axis. The authors found a way to create a uniform field (UF) in these modes.

Uniform Field Re-entrant Cylindrical TE[Formula: see text] Cavity for Pulse Electron Paramagnetic Resonance Spectroscopy at Q-band.

Uniform field (UF) resonators create a region-of-interest, where the sample volume receives a homogeneous microwave magnetic field ([Formula: see text]) excitation. However, as the region-of-interest is increased, resonator efficiency is reduced. In this work, a new class of uniform field resonators is introduced: the uniform field re-entrant cylindrical TE[Formula: see text] cavity.

Uniform field loop-gap resonator and rectangular TE for aqueous sample EPR at 94GHz.

In this work we present the design and implementation of two uniform-field resonators: a seven-loop-six-gap loop-gap resonator (LGR) and a rectangular TE cavity resonator. Each resonator has uniform-field-producing end-sections. These resonators have been designed for electron paramagnetic resonance (EPR) of aqueous samples at 94GHz.

Broadband W-band Rapid Frequency Sweep Considerations for Fourier Transform EPR.

A multi-arm W-band (94 GHz) electron paramagnetic resonance spectrometer that incorporates a loop-gap resonator with high bandwidth is described. A goal of the instrumental development is detection of free induction decay following rapid sweep of the microwave frequency across the spectrum of a nitroxide radical at physiological temperature, which is expected to lead to a capability for Fourier transform electron paramagnetic resonance. Progress toward this goal is a theme of the paper.

Extruded dielectric sample tubes of complex cross section for EPR signal enhancement of aqueous samples.

This paper builds on the work of Mett and Hyde (2003) and Sidabras et al. (2005) where multiple flat aqueous sample cells placed perpendicular to electric fields in microwave cavities were used to reduce the RF losses and increase the EPR signal. In this work, we present three novel sample holders for loop-gap resonators (LGRs) and cylindrical cavity geometries.

MRI surface-coil pair with strong inductive coupling.

A novel inductively coupled coil pair was used to obtain magnetic resonance phantom images. Rationale for using such a structure is described in R. R.

Axially uniform magnetic field-modulation excitation for electron paramagnetic resonance in rectangular and cylindrical cavities by slot cutting.

In continuous-wave (CW) Electron Paramagnetic Resonance (EPR) a low-frequency time-harmonic magnetic field, called field modulation, is applied parallel to the static magnetic field and incident on the sample. Varying amplitude of the field modulation incident on the sample has consequences on spectral line-shape and line-height over the axis of the sample. Here we present a method of coupling magnetic field into the cavity using slots perpendicular to the sample axis where the slot depths are designed in such a way to produce an axially uniform magnetic field along the sample.

POSSIBLE NATURE OF THE RADIATION-INDUCED SIGNAL IN NAILS: HIGH-FIELD EPR, CONFIRMING CHEMICAL SYNTHESIS, AND QUANTUM CHEMICAL CALCULATIONS.

Exposure of finger- and toe-nails to ionizing radiation generates an Electron Paramagnetic Resonance (EPR) signal whose intensity is dose dependent and stable at room temperature for several days. The dependency of the radiation-induced signal (RIS) on the received dose may be used as the basis for retrospective dosimetry of an individual's fortuitous exposure to ionizing radiation. Two radiation-induced signals, a quasi-stable (RIS2) and stable signal (RIS5), have been identified in nails irradiated up to a dose of 50 Gy.

Dielectric-Backed Aperture Resonators for X-Band in vivo EPR Nail Dosimetry.

A new resonator for X-band in vivo EPR nail dosimetry, the dielectric-backed aperture resonator (DAR), is developed based on rectangular TE geometry. This novel geometry for surface spectroscopy improves at least a factor of 20 compared to a traditional non-backed aperture resonator. Such an increase in EPR sensitivity is achieved by using a non-resonant dielectric slab, placed on the aperture inside the cavity.

Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy. II. Broadband characterization.

Experimental results have been reported on an oversize rectangular waveguide assembly operating nominally at 94 GHz. It was formed using commercially available WR28 waveguide as well as a pair of specially designed tapers with a hyperbolic-cosine shape from WR28 to WR10 waveguide [R. R.

Restoring susceptibility induced MRI signal loss in rat brain at 9.4 T: A step towards whole brain functional connectivity imaging.

The aural cavity magnetic susceptibility artifact leads to significant echo planar imaging (EPI) signal dropout in rat deep brain that limits acquisition of functional connectivity fcMRI data. In this study, we provide a method that recovers much of the EPI signal in deep brain. Needle puncture introduction of a liquid-phase fluorocarbon into the middle ear allows acquisition of rat fcMRI data without signal dropout.

Spin-label W-band EPR with seven-loop-six-gap resonator: Application to lens membranes derived from eyes of a single donor.

Spin-label W-band (94 GHz) EPR with a five-loop-four-gap resonator (LGR) was successfully applied to study membrane properties (L. Mainali, J.S.

A microwave resonator for limiting depth sensitivity for electron paramagnetic resonance spectroscopy of surfaces.

A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarter-wave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz.

Development and validation of an ex vivo electron paramagnetic resonance fingernail biodosimetric method.

There is an imperative need to develop methods that can rapidly and accurately determine individual exposure to radiation for screening (triage) populations and guiding medical treatment in an emergency response to a large-scale radiological/nuclear event. To this end, a number of methods that rely on dose-dependent chemical and/or physical alterations in biomaterials or biological responses are in various stages of development. One such method, ex vivo electron paramagnetic resonance (EPR) nail dosimetry using human nail clippings, is a physical biodosimetry technique that takes advantage of a stable radiation-induced signal (RIS) in the keratin matrix of fingernails and toenails.