Ti3SiC2-TiC-Si Antioxidant Coating Prepared on SiC coated MG Spheres of HTR Fuel Element by Molten Salt Technique

A Ti3SiC2-TiC-Si composite coating was prepared by molten salt technique on the surface of SiC coated matrix graphite (MG) spheres of HTR fuel element with different Ti content. The coating is composed of a transition layer, a SiC layer and an outer Ti- rich layer. When the content of Ti is 0.6g, the coating consists of Ti3SiC2, SiC, and TiC; when Ti content are 1.2g and 2.4g, the coating is composed of Ti3SiC2, SiC, TiC, and Si. Oxidation tests show that the kinetics of oxidation is parabolic at the beginning of oxidation; then it becomes linear after oxidation for 5h. The coating prepared with 0.6g Ti shows the best oxidation resistance, and the weight reduction of the coated MG spheres is only 0.33% after oxidation in static air at 1773K for 50h. These results show that Ti-based composites coating a kind of anti-oxidation coating system worth studying.

Kinetics and Mechanism of Catalyzed Oxidation of L-Cysteine by Salen Schiff Base Complexes of Co(III), Fe (III) and Cr(III)

Kinetics of oxidation of L-cysteine by new series of substituted ONNO-donor salen-type Schiff base complexes of general formula [MIII(L)Cl] (M = Co, Fe, Cr; L = Schiff base ligand) have been studied in aqueous solutions. Measurements were run at constant temperature (25º C), constant ionic strength (0.20 M), and constant pH (7.0) under pseudo-first order conditions, in which the concentration of cysteine is around two orders of magnitude greater than that of metal complex. The observed rate constant was determined by following the change in absorbance of reaction mixture at a predetermined wavelength with time. Results show that the rate of oxidation depends on the type of metal center, with Co(III) complexes were found to have the highest rates due to higher reduction potential of Co(III). The oxidation rate was also found to depend on steric factor and the electron withdrawing / releasing ability of the ligand bound to the metal ion.

Interactions between polyphenolic antioxidants quercetin and naringenin dictate the distinctive redox-related chemical and biological behaviour of their mixtures

Food synergy concept is suggested to explain observations that isolated antioxidants are less bioactive than real foods containing them. However, mechanisms behind this discrepancy were hardly studied. Here, we demonstrate the profound impact of interactions between two common food flavonoids (individual: aglycones quercetin—Q and naringenin—N− or their glycosides rutin—R and naringin—N+ vs. mixed: QN− and RN+) on their electrochemical properties and redox-related bioactivities. N− and N+ seemed weak antioxidants individually, yet in both chemical and cellular tests (DPPH and CAA, respectively), they increased reducing activity of mixtures synergistically. In-depth measurements (differential pulse voltammetry) pointed to kinetics of oxidation reaction as decisive factor for antioxidant power. In cellular (HT29 cells) tests, the mixtures exhibited properties of a new substance rather than those of components. Pure flavonoids did not influence proliferation; mixtures stimulated cell growth. Individual flavonoids tended to decrease global DNA methylation with growing concentration; this effect was more pronounced for mixtures, but not concentration-dependent. In nutrigenomic studies, expression of gene set affected by QN− differed entirely from common genes modulated by individual components. These results question the current approach of predicting bioactivity of mixtures based on research with isolated antioxidants.