The release of iron from ferritin is important in the formation of iron proteins and for the management of diseases in both animals and plants associated with abnormal accumulations of ferritin iron. Much more iron can be released experimentally by reduction of the ferric hydrous oxide core than by chelation of Fe3+ which has led to the notion that reduction is also the major aspect of iron release in vivo. Variations in the kinetics of reduction of the mineral core of ferritin have been attributed to the redox potential of the reductant, redox properties of the iron core, the structure of the protein coat, the analytical method used to detect Fe2+ and reactions at the surface of the mineral. Direct measurements of the oxidation state of the iron during reduction has never been used to analyze the kinetics of reduction, although Mössbauer spectroscopy has been used to confirm the extent of reduction after electrochemical reduction using dispersive X-ray absorption spectroscopy (DXAS). We show that the near edge of X-ray absorption spectra (XANES) can be used to quantify the relative amounts of Fe2+ and Fe3+ in mixtures of the hydrated ions. Since the nearest neighbors of iron in the ferritin iron core do not change during reduction, XANES can be used to monitor directly the reduction of the ferritin iron core. Previous studies of iron core reduction which measured by Fe2+.bipyridyl formation, or coulometric reduction with different mediators, suggested that rates depended mainly on the redox potential of the electron donor.(ABSTRACT TRUNCATED AT 250 WORDS)
In this study, we found that a photoelectric field in nematic liquid crystal (LC) cells that contains dyesensitized titania (TiO 2 ) layers leads to phase modulation of the LCs. When light is injected into the device, the Ru-dye is excited and electron-hole pairs are generated. The excited electrons then are transited to the conduction band of the TiO 2 and transported to the ITO electrode. The holes are transported to the opposite electrode, passing through the LCs and hole-transporting layers. This charge separation by the diffusion process induces a photoelectric field across the LC cells. The birefringence of the LCs was investigated using transmission ellipsometric methods in the absence of external applied voltage. In addition, the electro-optic properties with and without the photoelectric field were compared in twisted nematic LC cells. Furthermore, optically addressed spatial light modulation by the photoelectric field was confirmed using real-time optical images.
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