Effect of ultrasound pretreatment on the hydrothermal synthesis of SSZ-13 zeolite.

SSZ-13 zeolite has been identified as effective material for catalysts and membranes for years because of its structure, but the long crystallization time is the main obstacle for the industry application. The sonochemical-assisted method was identified as one of the potential pre-treatment methods which could reduce the formation duration of zeolites as well as other microporous and mesoporous materials. In this work, zeolite SSZ-13 was prepared by ultrasound pretreatment prior to hydrothermal crystallization. For comparison, samples by the conventional pretreatment and hydrothermal method were also prepared. The synthesized powders were characterized by XRD, SEM, BET, FTIR, NMR and TGA. The results showed that the complete crystallization of SSZ-13 synthesized by the ultrasound-assisted hydrothermal method was achieved within 72h, and much faster than conventional hydrothermal synthesis (120h). Furthermore, the ultrasound pretreatment showed very little effect on the structure properties of the final product compared with the conventional aging method.

Effects of different selenium levels on gene expression of a subset of selenoproteins and antioxidative capacity in mice.

This study aimed to evaluate how excess selenium induces oxidative stress by determining antioxidant enzyme activity and changes in expression of selected selenoproteins in mice. BALB/c mice (n = 20 per group) were fed a diet containing 0.045 (Se-marginal), 0.1 (Se-adequate), 0.4 (Se-supernutrition), or 0.8 (Se-excess) mg Se/kg. Gene expression was quantified in RNA samples extracted from the liver, kidney, and testis by real-time quantitative reverse transcription-polymerase chain reaction. We found that glutathione peroxidase (GPx) and catalase activities decreased in livers of mice fed the marginal or excess dose of Se as compared to those in the Se-adequate group. Additionally, superoxide dismutase and glutathione reductase activities were significantly reduced only in mice fed the excess Se diet, compared to animals on the adequate Se diet. Se-supernutrition had no effect on hepatic mRNA levels of GPx isoforms 1 and 4 (GPx1 and GPx4), down-regulated GPx isoform 3 (GPx3), and upregulated selenoprotein W (SelW) mRNA expression. The excess Se diet led to decreased hepatic mRNA levels of GPx1, GPx3 and GPx4 but no change in testicular mRNA levels of GPx1, GPx3 or SelW. Dietary Se had no effect on testicular mRNA levels of GPx4. Thus, our results suggest that Se exposure can reduce hepatic antioxidant capacity and cause liver dysfunction. Dietary Se was found to differentially regulate mRNA levels of the GPx family or SelW, depending on exposure. Therefore, these genes may play a role in the toxicity associated with Se.