Articles you may be interested inA kilowatt pulsed 94 GHz electron paramagnetic resonance spectrometer with high concentration sensitivity, high instantaneous bandwidth, and low dead time Rev. Sci. Instrum. A quasioptical transient electron spin resonance spectrometer operating at 120 and 240 GHz Rev. Sci. Instrum. 76, 074101 (2005);High-field/high-frequency electron spin resonance ͑ESR͒ offers improved sensitivity and resolution compared to ESR at conventional fields and frequencies. However, most high-field/high-frequency ESR spectrometers suffer from limited mm-wave power, thereby requiring long mm-wave pulses. This precludes their use when relaxation times are short, e.g., in fluid samples. Low mm-wave power is also a major factor limiting the achievable spectral coverage and thereby the multiplex advantage of Fourier transform ESR ͑FTESR͒ experiments. High-power pulses are needed to perform two-dimensional ͑2D͒ FTESR experiments, which can unravel the dynamics of a spin system in great detail, making it an excellent tool for studying spin and molecular dynamics. We report on the design and implementation of a high-power, high-bandwidth, pulsed ESR spectrometer operating at 95 GHz. One of the principal design goals was the ability to investigate dynamic processes in aqueous samples at physiological temperatures with the intent to study biological systems. In initial experiments on aqueous samples at room temperature, we achieved 200 MHz spectral coverage at a sensitivity of 1.1ϫ10 10 ͱs spins and a dead time of less than 50 ns.2D-electron-electron double resonance experiments on aqueous samples are discussed to demonstrate the practical application of such a spectrometer.

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A three-dimensional (3D) electron spin resonance (ESR) microimaging system, operating in pulse mode at 9GHz is presented. This microscope enables the acquisition of spatially resolved magnetic resonance signals of free-radicals in solid or liquid samples with a resolution of up to ∼3.5×7×11.4μm in 20min of acquisition. The detection sensitivity at room temperature is ∼1.2×109spins∕√Hz, which enables the measurement of ∼2×107 spins in each voxel after 60min of acquisition. The resolution and detection sensitivity are the best obtained so far for ESR at ambient conditions of temperature and pressure. This ESR microscope can be employed in the investigation of a variety of samples in the fields of botany, life sciences, and materials science.

Articles you may be interested inHigh-sensitivity Q-band electron spin resonance imaging system with submicron resolution Rev. Sci. Instrum. 82, 043708 (2011);A broadband pulsed radio frequency electron paramagnetic resonance spectrometer for biological applications Rev.An electron spin resonance (ESR) imaging system, capable of acquiring three-dimensional (3D) images with a resolution of ϳ10ϫ 10ϫ 30 m in a few minutes of acquisition, is presented. This ESR microscope employs a commercial continuous wave ESR spectrometer, working at 9.1 GHz, in conjunction with a miniature imaging probe (resonator+ gradient coils), gradient current drivers, and control software. The system can acquire the image of a small ͑ϳ1.5ϫ 1.5ϫ 0.25 mm͒ sample either by the modulated field gradient method, the projection reconstruction method, or by a combination of the two. A short discussion regarding the resolution of the modulated field gradient method in two-dimensional (2D) and 3D imaging is given. Detailed descriptions of the various system components are provided, along with several examples of 2D and 3D images that demonstrate the capabilities of the system.

The development, applications, and current challenges of the pulsed ESR technique of two-dimensional Electron-Electron Double Resonance (2D ELDOR) are described. This is a three-pulse technique akin to 2D Exchange Nuclear Magnetic Resonance, but involving electron spins, usually in the form of spin-probes or spin-labels. As a result, it required the extension to much higher frequencies, i.e., microwaves, and much faster time scales, with π/2 pulses in the 2-3 ns range. It has proven very useful for studying molecular dynamics in complex fluids, and spectral results can be explained by fitting theoretical models (also described) that provide a detailed analysis of the molecular dynamics and structure. We discuss concepts that also appear in other forms of 2D spectroscopy but emphasize the unique advantages and difficulties that are intrinsic to ESR. Advantages include the ability to tune the resonance frequency, in order to probe different motional ranges, while challenges include the high ratio of the detection dead time vs. the relaxation times. We review several important 2D ELDOR studies of molecular dynamics. (1) The results from a spin probe dissolved in a liquid crystal are followed throughout the isotropic → nematic → liquid-like smectic → solid-like smectic → crystalline phases as the temperature is reduced and are interpreted in terms of the slowly relaxing local structure model. Here, the labeled molecule is undergoing overall motion in the macroscopically aligned sample, as well as responding to local site fluctuations. (2) Several examples involving model phospholipid membranes are provided, including the dynamic structural characterization of the boundary lipid that coats a transmembrane peptide dimer. Additionally, subtle differences can be elicited for the phospholipid membrane phases: liquid disordered, liquid ordered, and gel, and the subtle effects upon the membrane, of antigen cross-linking of receptors on the surface of plasma membrane, vesicles can be observed. These 2D ELDOR experiments are performed as a function of mixing time, Tm, i.e., the time between the second and third π/2 pulses, which provides a third dimension. In fact, a fourth dimension may be added by varying the ESR frequency/magnetic field combination. Therefore, (3) it is shown how continuous-wave multifrequency ESR studies enable the decomposition of complex dynamics of, e.g., proteins by virtue of their respective time scales. These studies motivate our current efforts that are directed to extend 2D ELDOR to higher frequencies, 95 GHz in particular (from 9 and 17 GHz), in order to enable multi-frequency 2D ELDOR. This required the development of quasi-optical methods for performing the mm-wave experiments, which are summarized. We demonstrate state-of-the-art 95 GHz 2D ELDOR spectroscopy through its ability to resolve the two signals from a spin probe dissolved in both the lipid phase and the coexisting aqueous phase. As current 95 GHz experiments are restricted by limited spectral coverage of the π/2 pulse, as well as the...