Physicochemical properties of Riboflavin (Vitamin B2) (RF), in Dextran 70 (Dx70) (a biological relevant glucidic type macromolecule) and Human Serum Albumin (HSA) (a carrier/transport protein) based system, have been studied by absorption, fluorescence, circular dichroism and electrochemistry. No significant changes on the fluorescence of RF in Dx70/HSA systems with and without the influence of temperature (30–60 °C range) were observed. No changes on the intrinsic Tryptophan fluorescence in Dx70/RF/HSA system, have been evidenced. HSA secondary structure when RF binds in Dx70/RF/HSA systems, with a renaturation effect of Dx70, was found. In Dx70/RF/HSA system the major process which RF undergoes is the proton transfer, Ered = ?0.43 V. Using the chemiluminescence method, an improvement of the antioxidant activity of RF into the Dx70/RF/HSA system, was also found. RF concentration in Dx70/RF/HSA systems is important in RF oxidative damages when it reacts with target molecules and thus promotes their oxidation. The results have relevance in the oxidative stress process and in pharmaceutical formulations containing RF. 相似文献
The present chain of five papers considers the concept of defect engineering in processing TiO2-based photosensitive semiconductors for solar-to-chemical energy conversion. The papers report the effect of chromium on the key performance-related properties of polycrystalline TiO2 (rutile), including (i) electronic structure, (ii) chromium-related photocatalytic properties, (iii) oxygen-related photocatalytic properties, (iv) electrochemical coupling and (v) surface versus bulk properties. The present work reports the effect of chromium on defect disorder and the related electronic structure of TiO2, including the band gap and mid-gap energy levels. It is shown that chromium incorporation into the TiO2 lattice results in a decrease of the band gap from 3.04 eV for pure TiO2 to 1.4 and 1.3 eV, for Cr-doped TiO2 (1.365 at% Cr) after annealing at 1373 K in the gas phase of controlled oxygen activity, 21 kPa and 10?10 Pa, respectively. The optical properties determined using the ultraviolet-vis spectroscopy (in the reflectance mode) indicate that chromium incorporation results in the formation of mid-band energy levels. In this work, we show that chromium at and above the concentrations levels of 0.04 and 0.376 at% results in the formation of acceptor-type energy levels at 0.57 and 1.16 eV (above the valence band), respectively, which are related to tri-valent chromium in titanium sites and titanium vacancies, respectively. Application of well-defined protocol leads to the determination of data that are well reproducible. The new insight involves the determination of the band gap of TiO2 processed in the gas phase of controlled oxygen activity.
