Application Of Electron Paramagnetic Resonance Spectroscopy Research Articles

Application of EPR Spectroscopy in TiO2 and Nb2O5 Photocatalysis

The interaction of light with semiconducting materials becomes the center of a wide range of technologies, such as photocatalysis. This technology has recently attracted increasing attention due to its prospective uses in green energy and environmental remediation. The characterization of the electronic structure of the semiconductors is essential to a deep understanding of the photocatalytic process since they influence and govern the photocatalytic activity by the formation of reactive radical species. Electron paramagnetic resonance (EPR) spectroscopy is a unique analytical tool that can be employed to monitor the photoinduced phenomena occurring in the solid and liquid phases and provides precise insights into the dynamic and reactivity of the photocatalyst under different experimental conditions. This review focus on the application of EPR in the observation of paramagnetic centers formed upon irradiation of titanium dioxide and niobium oxide photocatalysts. TiO2 and Nb2O5 are very well-known semiconductors that have been widely used for photocatalytic applications. A large number of experimental results on both materials offer a reliable platform to illustrate the contribution of the EPR studies on heterogeneous photocatalysis, particularly in monitoring the photogenerated charge carriers, trap states, and surface charge transfer steps. A detailed overview of EPR-spin trapping techniques in mechanistic studies to follow the nature of the photogenerated species in suspension during the photocatalytic process is presented. The role of the electron donors or the electron acceptors and their effect on the photocatalytic process in the solid or the liquid phase are highlighted.

Mitochondria respiratory chain studied by electron paramagnetic resonance spectroscopy

Aerobic respiration is the indispensable physiology of higher organism living on earth, since the required energy for biological activities is supplied mainly by this metabolism. It is well established that mitochondria plays an important role in converting the stable chemical energy stored in foods into the active and utilizable energy supplying to life activities. Upon the process, the energy conversion is carried out by the respiratory electron transport chain, which consists of five distinct and coupled protein complexes (termed complex I−V) embedded in the mitochondria intima. Among them, complex I (NADH-ubiquinone oxidoreductase), III (cytochrome bc 1) and IV (cytochrome c oxidase) are the electron-coupled proton-pumping enzymes. Except for the complex V (i.e., ATP synthase), each complex has several redox cofactors to promote the electron transfer within themselves, and the transfer from complex I and II to complex III is shuttled by membrane-embedded ubiquinones, from complex III to IV by the soluble cytochrome c . When the reductive electron is donated by the initial donors NADH or FADH2 to the final acceptor molecular oxygen O2, a transmembrane proton motive force is formed simultaneously. The latter is the driving force for the ATP synthesis via ATP synthase with a ratio of three protons per ATP. All the aforementioned processes are also known as oxidative phosphorylation, and the arrangement of the electron carriers therein is called as respiratory electron transport chain. In the stepwise electron relay, these carriers undergo the redox changes, giving rise to the respective paramagnetic and diamagnetic spin states. These single-electron relays are prone to the electron paramagnetic resonance spectroscopy (EPR), which is a powerful and noninvasive technique to monitor the unpaired electron in situ . As shown in the overwhelming literatures, EPR technique has been adopted to reveal the electron transfer pathway in different biological activities. Herein, the application of EPR to study the dynamic electron transfer in mitochondria is reviewed briefly. However, this conventional application required rather high concentration of the active center at a level of 1–10 µmol/L. Actually, most of the intermediates of the electron carriers are very active and short-life. In the human body, only a few tissues can accumulate such required concentration of paramagnetic substances, e.g., in blood, heart and liver. For the past decade, a more sensitive single-molecule magnetic resonance technique based on the nitrogen-vacancy (NV) center of diamond has been developing dramatically. In principle, this advanced EPR technique requires the less sample or concentration, even down to the single biomolecule, and provides the time-resolved dynamic information. Lately, the studies of single-biomolecule EPR at room temperature or in aqueous solution have been reported consecutively in single protein (MAD2/mitotic arrest deficient-2) and single DNA (tethered DNA duplexes). Finally, a perspective of single-biomolecule magnetic resonance technique is given for the further study on mitochondrion and relative physiological activities. The single molecule EPR technique is also helpful to unveil the other specific information of biological processes, for example, drug screening, personalized medicine and other major applications.

An electron paramagnetic resonance mobile universal surface explorer

Many samples cannot be studied by electron paramagnetic resonance (EPR) spectroscopy because they are too large to fit into the spectrometer and too precious to be destructively sampled for study. An EPR mobile universal surface explorer (MOUSE), also known as a unilateral EPR spectrometer, was constructed for studying this class of sample. The EPR MOUSE can nondestructively record a low frequency EPR (LFEPR) spectrum of a small region of any size object by placing the MOUSE against the object. The capabilities of the EPR MOUSE are demonstrated on paramagnetic paint pigments on canvas, magnetic ink on paper, and a ceramic candlestick. The mobile nature of the MOUSE will allow the spectrometer to be brought to the sample, thus opening new applications of EPR spectroscopy.

Free radical formation in chloramphenicol heated at different temperatures and the best thermal sterilization conditions – application of EPR spectroscopy and UV spectrophotometry

Free radicals in thermally treated chloramphenicol were examined by electron paramagnetic resonance (EPR) spectroscopy. The parameters and shape of EPR spectra were analysed and free radical concentrations were obtained in the tested drug samples. Chloramphenicol was thermally sterilized at pharmacopeia conditions: 100 °C (120 min). Sterilization was also carried out at different conditions, 110 °C (60 min) and 120 °C (30 min), for comparison with pharmacopeia settings. Microbiological analysis was performed on the samples to confirm sterility. The aim of this work was to determine the concentration of free radicals in chloramphenicol following thermal sterilization at pharmacopeia conditions and compare this with other sets of conditions [110 °C (60 min) and 120 °C (30 min)]. The best conditions of thermal sterilization are determined as those that kill microorganisms and produce the lowest amounts of free radicals in this drug. It was concluded that the optimal temperatures and times for the thermal sterilization of chloramphenicol are 100 °C and 120 min and 110 °C and 60 min. A temperature of 120 °C coupled with a heating time of 30 min was rejected for thermal sterilization because of the high amount of free radicals produced by the drug samples.

Applications of in vivo electron paramagnetic resonance (EPR) spectroscopy: measurements of pO 2 and NO in endotoxin shock

Recent developments of EPR instrumentation that allow the use of large tissue samples or whole animals and the ability to image spatially resolved EPR signals has led to novel applications of EPR spectroscopy in vivo. Utilising a 1 GHz EPR spectrometer with a 3.4-cm birdcage resonator, it was possible to detect and measure nitric oxide and oxygen in the livers of mice with lipopolysaccharide (LPS)-induced septic shock. Nitric oxide was detected as the nitric oxide (NO) complex of Fe–diethyldithiocarbamic acid (Fe–DETC) while pO 2 was measured from the EPR linewidth of the oxygen-sensitive coal material ‘gloxy’. LPS treatment stimulated the production of nitric oxide in the liver and the general circulation and the oxygenation of liver tissue was decreased. Selective placement of the EPR probes allowed images of nitric oxide and oxygen to be obtained in the liver. The spectral and spatial information obtained with this technique will allow improved understanding of the pathophysiology of such diseases.

Electron Paramagnetic Resonance Spectroscopic (EPR) Study of Copper Amine Treated Southern Pine in Wood Preservation

Summary The structure of copper complexes in copper amine treated wood samples were elucidated by the application of electron paramagnetic resonance spectroscopy (EPR). EPR axial spectra were observed for all Cu-amine treated samples irrespective of the formulations. The values of A∥ and g∥ of the axial spectra indicate that the stereo-structure of copper complexes in copper amine treated wood was either tetragonal-based octahedral or square-based pyramidal. Comparison of electronic parameters of A∥ and g∥ in Cu-amine treated wood with those of the Cu-amine treating solution and the values in literature suggests that the interaction of wood with copper amine is through complexation in which wood functional groups are complexed with copper amine perpendicularly. The copper complexes in both treating solution and treated wood are in the form of CuN2O2, where copper is ligated with 2 nitrogen and 2 oxygen.