Spatial Distribution Of Free Radicals Research Articles

Chemical properties of superfine pulverized coal particles. Part 1. Electron paramagnetic resonance analysis of free radical characteristics

Superfine pulverized coal combustion is a new pulverized coal combustion technology with lots of advantages. A mechanochemical effect exists during the comminution process, which changes the chemical properties of coal significantly. Free radical concentrations and certain functional groups would increase with the decrease of particle sizes. In this paper, we combined electron paramagnetic resonance (EPR) and 13C solid-state nuclear magnetic resonance (NMR) techniques to study the free radical characteristics of superfine pulverized coal thoroughly. The final results indicate that the EPR spectra of coal are the superimpositions of several lines induced by different paramagnetic centers, which can be fitted by 1 Gaussian and 3 Lorentzian lines. The influences of coal maturities and particle sizes on EPR parameters, such as g-values, linewidths, and spin concentrations, are analyzed in detail. It is shown that with the decrease of particle sizes, more free radicals are induced through bond cleavages. Mechanical forces initiate the accumulation of free radicals in the fractures and inner pore surfaces of coal. Furthermore, the influence of particle sizes on oxygen-containing radicals (i.e., Lorentzian 1 types) is the greatest. This work provides a primary picture of the occurrence modes and spatial distributions of free radicals in superfine pulverized coal. The findings will help form the basis and provide guidance for further studies on revealing the correlations between the free radical reaction pathways and NOx formation mechanisms.

Fast gated EPR imaging of the beating heart: Spatiotemporally resolved 3D imaging of free-radical distribution during the cardiac cycle

In vivo or ex vivo electron paramagnetic resonance imaging (EPRI) is a powerful technique for determining the spatial distribution of free radicals and other paramagnetic species in living organs and tissues. However, applications of EPRI have been limited by long projection acquisition times and the consequent fact that rapid gated EPRI was not possible. Hence in vivo EPRI typically provided only time-averaged information. In order to achieve direct gated EPRI, a fast EPR acquisition scheme was developed to decrease EPR projection acquisition time down to 10-20 ms, along with corresponding software and instrumentation to achieve fast gated EPRI of the isolated beating heart with submillimeter spatial resolution in as little as 2-3 min. Reconstructed images display temporal and spatial variations of the free-radical distribution, anatomical structure, and contractile function within the rat heart during the cardiac cycle.

Analysis of the Spatial Distribution of Free Radicals in Ammonium Tartrate by Pulse EPR Techniques

Using pulse electron paramagnetic resonance (EPR) on a series of l(+)-ammonium tartrate (AT) dosimeters exposed to radiations with different linear energy transfer (LET), we assessed the ability of pulse EPR spectroscopy to discriminate the quality of various radiation beams such as (60)Co gamma-ray photons, protons and thermal neutrons at various doses by analyzing the local radical distributions produced by the different beams. We performed two types of pulse EPR investigations: two-pulse electron spin echo decay obtained by varying the microwave power, and a double electron-electron resonance (DEER) study. Both methods provide information about the dipolar interactions among the free radicals and about their spatial distributions. The first method provided information on the instantaneous diffusion and hence the microscopic concentration of the radicals that is compared with the macroscopic one obtained by CW-EPR. The DEER spectra yielded the distributions of distances between pairs of radicals two to five crystal cells apart produced by the same radiation event, a result reported here for the first time. The inter-radical distributions given by the DEER results have been simulated by modeling the radical distributions according to the details of the matter-radiation interactions for the various beams. The results of both types of pulse experiments are strongly dependent on the radiation quality. This was also observed for samples giving indistinguishable CW-EPR spectral profiles. We conclude that the pulse EPR measurements can be valuable tools for distinguishing the LET of the radiation beams, an important parameter for radiobiological considerations.

Measurements of UV-generated free radicals/reactive oxygen species (ROS) in skin

Free radicals/reactive oxygen species (ROS) generated in skin by UV irradiation were measured by electron spin resonance (ESR). To increase the sensitivity of measurement the short life free radicals/ROS were scavenged and accumulated by using the nitroxyl probe 3-carboxy-2,2,5,5-tetrametylpyrrolidine-1-oxyl (PCA). The spatial distribution of free radicals/ROS measured in pig skin biopsies with ESR imaging after UV irradiation corresponds to the intensity decay of irradiance in the depth of the skin. The main part of free radicals/ROS were generated by UVA (320–400 nm) so that the spatial distribution of free radicals reaches up to the lower side of the dermis. In vivo measurements on human skin were performed with a L-band ESR spectrometer and a surface coil integrating the signal intensities from all skin layers to get a sufficient signal amplitude. Using this experimental arrangement the protection of UVB and UVA/B filter against the generation of free radicals/ROS in skin were measured. The protection against ROS and the repair of damages caused by them can be realized with active antioxidants characterized by a high antioxidative power (AP). The effect of UV filter and antioxidants corresponding to their protection against free radicals/ROS in skin generated by UVAB irradiation can be quantified by the new radical sun protection factor (RSF). The RSF indicates the increase of time for staying in the sun to generate the same number of free radicals/ROS in the skin like for the unprotected skin. Regarding the amount of generated free radicals/ROS in skin as an biophysical endpoint the RSF characterizes both the protection against UVB and UVA radiation.

Free radicals and oxidative stress: targeted ESR measurement of free radicals

The detection of free radicals generated within the body may contribute to clarifying the pathophysiological role of free radicals in disease processes. As an appropriate procedure to examine the generation of free radicals in a biological system, electron spin resonance (ESR) has emerged as a powerful tool for detection and identification. A method for determination of oxygen radical scavenging activity using ESR and the spin trapping technique was developed. Oxygen radicals were trapped by 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) or alpha-phenyl-N-t-butylnitrone (PBN), and the DMPO or PBN spin adduct signal was measured quantitatively by an ESR spectrometer. The spin trapping method using ESR has also been reported for not only in vitro and ex vivo measurements but also in vivo measurements. In in vivo ESR, nitroxyl radical is being used as a spin trap well. ESR signal intensities of nitroxyl radical are measured after administration to animals and the signal decay rates of nitroxyl radical have reported to be influenced by various types of oxidative stress. With this method, it is possible to specify the type of radical or the location at which the free radicals are produced. The spin trapping method by in vivo ESR is an effective procedure for giving non-invasive measurements in animals. ESR imaging in the organs of live animals can also be obtained after injection of nitroxyl radicals as an imaging agent using ESR-computed tomography. In vivo ESR imaging has been established as a powerful technique for determining the spatial distribution of free radicals in living organs and tissues.

In vivo imaging of spin-trapped nitric oxide in rats with septic shock: MRI spin trapping.

This paper reports the first in vivo NMR image of the distribution of NO using the "MRI spin-trapping" technique. NO was complexed with the Fe(II)-chelate spin trap, N-methyl-D-glucamine dithiocarbamate (MGD), verified as (MGD)(2)-Fe(II)-NO by EPR, and the radical distribution was "visualized" by MR images. In rats, the (MGD)(2)-Fe(II)-NO complex was concentrated in the liver displaying significantly enhanced contrast in the vascular structure such as hepatic vein and inferior vena cava. Nitric oxide synthase was verified as the source of NO in rats with septic shock by pre-administration of the competitive inhibitor N-monomethyl-L-arginine, resulting in reduced enhancement. The NO complex was more stable in vivo and a more effective MRI contrast agent than other stable nitrogen containing radicals, such as nitroxides. The MRI spin-trapping method should be a powerful tool for visualizing spatial distributions of free radicals in pathologic organs and tissues when combined with the appropriate radical complexing agent, such as (MGD)(2)-Fe(II) used in these studies. Magn Reson Med 42:235-239, 1999.

Electron Paramagnetic Resonance Imaging of the Spatial Distribution of Free Radicals in PMR-15 Polyimide Resins

Prior studies have shown that free radicals generated by heating polyimides above 300 C are stable at room temperature and are involved in thermo-oxidative degradation in the presence of oxygen gas. Electron Paramagnetic Resonance Imaging (EPRI) is a technique to determine the spatial distribution of free radicals. X-band (9.5 GHz) EPR images of PMR-15 polyimide were obtained with a spatial resolution of about 0.18 mm along a 2 mm dimension of the sample. In a polyimide sample that was not thermocycled, the radical distribution was uniform along the 2 mm dimension of the sample. For a polyimide sample that was exposed to thermocycling in air for 300 one-hour cycles at 335 C, one-dimensional EPRI showed a higher concentration of free radicals in the surface layers than in the bulk sample. A spectral-spatial two-dimensional image showed that the EPR lineshape of the surface layer remained the same as that of the bulk. These EPRI results suggest that the thermo-oxidative degradation of PMR-15 resin involves free radicals present in the oxygen-rich surface layer.

ESR imaging of the rat brain with a nitroxide radical perfused by in vivo microdialysis

We report here our investigation of the spatial distribution of free radicals using an electron spin resonance (ESR)-imaging system combined with an in vivo brain microdialysis method, which was performed in the resonator of the ESR-imaging system. A nonmagnetic cannula, newly developed in this study, was used for the perfusion of the exogenous free radicals agent. A nitroxide, 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl (carbamoyl PROYXL), was used as the imaging agent in saline solution at a concentration of 0.3 M, which was perfused into the right caudate putamen of the rat at 2 μl/min by a microinfusion pump. Two-dimensional ESR projection of the Z- X plane, which was clearly distinguished (about φ 10 mm) from the nonperfused brain area, was obtained 6 h after the beginning of perfusion of carbamoyl PROXYL. The present method is considered to be a useful tool to introduce stable free radicals into a specific area of the brain.

Three-dimensional gated EPR imaging of the beating heart: time-resolved measurements of free radical distribution during the cardiac contractile cycle.

In vivo or ex vivo EPR imaging, EPRI, has been established as a powerful technique for determining the spatial distribution of free radicals and other paramagnetic species in living organs and tissues. While instrumentation capable of performing EPR imaging of free radicals in whole tissues and isolated organs has been previously reported, it was not possible to image rapidly moving organs such as the beating heart. Therefore instrumentation was developed to enable the performance of gated-spectroscopy and imaging on isolated beating rat hearts at L-band. A synchronized pulsing and timing system capable of gated acquisitions of up to 256 images per cycle, with rates of up to 16 Hz was developed. The temporal and spatial accuracy of this instrumentation was verified using a specially designed beating heart-shaped isovolumic phantom with electromechanically driven sinusoidal motion at a cycle rate of 5 Hz. Gated EPR imaging was performed on a series of isolated rat hearts perfused with nitroxide spin labels. These hearts were paced at a rate of 6 Hz with either 16 or 32 gated images acquired per cardiac contractile cycle. The image enabled visualization of the time-dependent alterations in the free radical distribution and anatomical structure of the heart that occur during the cardiac cycle.

Spatial distribution of free radicals in .gamma.-irradiated alcohol matrixes determined by the 2+1 electron spin echo method

Spatial distribution of free radicals in .gamma.-irradiated alcohol matrixes determined by the 2+1 electron spin echo method

Electron-electron double resonance in electron spin echo: Model biradical systems and the sensitized photolysis of decalin

Model systems, comprising frozen glassy solutions of stabilized radicals and biradicals of the nitroxyl type, have been used to test the applicability of electron-electron double resonance in electron spin echo (ELDOR ESE) in studies of the spatial distributions of free radicals arranged in groups in solids. The method was used to investigate the spatial distribution of alkyl radicals generated by the sensitized photolysis of glassy naphthalene solutions in decalin at 77 K. and detected radical pairs.

ESR study on the spatial distribution of radicals trapped in the heavy ion-irradiated n-eicosane single crystal

Single crystals of n−eicosane were subjected to the irradiation of helium, carbon, and nitrogen ions accelerated with the cyclotron, and the results were compared with those obtained by 60Co γ-ray irradiation. Irradiation was carried out at 77 °K. The nature and the spatial distribution of free radicals produced in the crystals were investigated by an ESR technique. The principal radical is –CH2ĊHCH2– (I) and the minor one, CH3ĊHCH2– (II); the linewidth and decay of these radicals were found to be LET-dependent. The ESR results indicate that radicals are trapped in two regions closely and sparsely; the relative distribution in the two regions is dependent on the LET of radiations used. The mean separation between the radicals trapped in the close proximity was estimated to be approximately 16 Å.

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With 60Co γ-rays and 210Po α-particles as examples the effect of linear energy transfer has been studied on accumulation, yields and spatial distribution of free radicals in glassy 5 mol dm −3 aqueous solutions of HClO 4 and H 2SO 4 and in glassy 10 mol dm −3 aqueous solution of KOH at 77 K. In both cases the same free radicals are formed (H and OH in HClO 4 solution; H, OH and SO 4 − in H 2SO 4 solution; e tr −, O − and H in KOH solution). Compared to γ-radiolysis the initial yields of free radicals (especially for alkaline “glass”) are shown to decrease appreciably on α-radiolysis. The spatial distribution of H atoms in acid solutions at low doses is found to be non-uniform in the case of α-radiolysis and uniform in the case of γ-radiolysis. At high doses (⩾3 × 10 20 eV/cm 3) the distribution is uniform. In alkaline “glass” the distribution is non-uniform for both types of radiation. The effects obtained are explained on the basis of the radical diffusion model in water radiolysis. The radii of cylindrical tracks of α-particles in acid solutions are equal to ≈80–100 Å for 5mol dm −3 solution of HClO 4 and ≈ 45–90 Å for 5 mol dm −3 solution of H 2SO 4.

Spatial Distribution of Free Radicals as studied by Electron Spin Resonance

THE spatial distribution of free radicals produced by irradiation is of interest in radiation chemistry and radiation biology. Although there have been many theoretical treatments of this problem, direct experimental evidence has so far been lacking. Electron spin resonance spectroscopy provides a means of measuring the distribution of free radicals; and we report here a preliminary investigation by this method.