Modified Ta/MCM-41 catalysts for enantioselective oxidation of thioanisole

Ta-MCM41 catalysts have been prepared by grafting of Ta(OEt)5 on MCM41, pre-calcined at three different temperatures (550, 650 and 750 °C). These solids have been modified with two chiral ligands: R-(+)-diethyl l-tartrate (DET) and R-(+)-diisopropyl l-tartrate (DIPT). The formation of the chiral tantalum species and their influence on the structure of MCM41 have been studied by several characterization techniques, such as XRD, FTIR, N2 adsorption isotherms and MAS NMR. The grafted tantalum species are always much less active than the homogeneous analogues in the oxidation of thioanisole (methyl phenyl sulfide) with either aqueous H2O2 or alkyl (tert-butyl, TBHP, or cumyl, CHP) hydroperoxides. The enantioselectivities obtained with the heterogeneous catalysts are also always lower than those obtained with the homogeneous ones under the same conditions, and the best results are obtained with the DIPT-modified solids, up to 25% ee. The calcination temperature of the support and the nature of the oxidant are also parameters that significantly affect the enantioselectivity. The recovered catalysts show an increase in the catalytic activity and a decrease in the enantioselectivity, in agreement with a loss of chiral tartrate, whereas the Si-O-Ta bond remains stable and recoverable.Financial support from the Spanish Ministerio de Economía y Competitividad (Project CTQ2011-28124) and the Diputación General de Aragón (E11 Group co-financed by the European Regional Development Funds) is gratefully acknowledged. M. F. thanks the Tunisien Ministère de l’Enseignement Supérieure et la Recherche Scientifique for a short-mobility grant (bourse d’alternance).Peer Reviewe

Enhanced group-based wireless ad-hoc sensor network protocol

[EN] Communication is the major energy consumption source in wireless ad-hoc sensor networks. Thus, an efficient tradeoff between the energy cost of the communication and network's performance is a key challenge in conceiving a wireless ad-hoc sensor network. In this article, we propose an improved group-based architecture for wireless ad-hoc sensor networks. An optimized group forming procedure and an efficient communication operation are introduced. In order to validate the proposed approach, we suggest a group-based strategy to monitor pharmaceutical drugs during transportation. Real measurements of temperature and vibration were performed to validate the effectiveness of our approach.Khedher, M.; Lloret, J.; Douik, A. (2016). Enhanced group-based wireless ad-hoc sensor network protocol. International Journal of Distributed Sensor Networks. 12(7):1-18. https://doi.org/10.1177/1550147716659427S118127Dargie, W., & Poellabauer, C. (2010). Fundamentals of Wireless Sensor Networks. doi:10.1002/9780470666388Singh, S. P., & Sharma, S. C. (2015). A Survey on Cluster Based Routing Protocols in Wireless Sensor Networks. Procedia Computer Science, 45, 687-695. doi:10.1016/j.procs.2015.03.133Liao, Y., Qi, H., & Li, W. (2013). Load-Balanced Clustering Algorithm With Distributed Self-Organization for Wireless Sensor Networks. IEEE Sensors Journal, 13(5), 1498-1506. doi:10.1109/jsen.2012.2227704Peng, I.-H., & Chen, Y.-W. (2013). Energy consumption bounds analysis and its applications for grid based wireless sensor networks. Journal of Network and Computer Applications, 36(1), 444-451. doi:10.1016/j.jnca.2012.04.014Lloret, J., Garcia, M., Tomás, J., & Boronat, F. (2008). GBP-WAHSN: A Group-Based Protocol for Large Wireless Ad Hoc and Sensor Networks. Journal of Computer Science and Technology, 23(3), 461-480. doi:10.1007/s11390-008-9147-6Lloret, J., García, M., Boronat, F., & Tomás, J. (s. f.). MANET Protocols Performance in Group-based Networks. IFIP International Federation for Information Processing, 161-172. doi:10.1007/978-0-387-84839-6_13Lloret, J., Garcia, M., & Tomas, J. (s. f.). Improving Mobile and Ad-hoc Networks performance using Group-Based Topologies. Wireless Sensor and Actor Networks II, 209-220. doi:10.1007/978-0-387-09441-0_18Lloret, J., Palau, C., Boronat, F., & Tomas, J. (2008). Improving networks using group-based topologies. Computer Communications, 31(14), 3438-3450. doi:10.1016/j.comcom.2008.05.030Garcia, M., Sendra, S., Lloret, J., & Canovas, A. (2011). Saving energy and improving communications using cooperative group-based Wireless Sensor Networks. Telecommunication Systems, 52(4), 2489-2502. doi:10.1007/s11235-011-9568-3Garcia, M., & Lloret, J. (2009). A Cooperative Group-Based Sensor Network for Environmental Monitoring. Cooperative Design, Visualization, and Engineering, 276-279. doi:10.1007/978-3-642-04265-2_41Shaikh, R. A., Jameel, H., d’ Auriol, B. J., Heejo Lee, Sungyoung Lee, & Young-Jae Song. (2009). Group-Based Trust Management Scheme for Clustered Wireless Sensor Networks. IEEE Transactions on Parallel and Distributed Systems, 20(11), 1698-1712. doi:10.1109/tpds.2008.258Chen, Y.-S., Hsu, C.-S., & Lee, H.-K. (2014). An Enhanced Group Mobility Protocol for 6LoWPAN-Based Wireless Body Area Networks. IEEE Sensors Journal, 14(3), 797-807. doi:10.1109/jsen.2013.2287895Yao-Chung Chang, Zhi-Sheng Lin, & Jiann-Liang Chen. (2006). Cluster based self-organization management protocols for wireless sensor networks. IEEE Transactions on Consumer Electronics, 52(1), 75-80. doi:10.1109/tce.2006.1605028Fazio, P., De Rango, F., Sottile, C., & Santamaria, A. F. (2013). Routing Optimization in Vehicular Networks: A New Approach Based on Multiobjective Metrics and Minimum Spanning Tree. International Journal of Distributed Sensor Networks, 9(11), 598675. doi:10.1155/2013/598675Saravanan, M., & Madheswaran, M. (2014). A Hybrid Optimized Weighted Minimum Spanning Tree for the Shortest Intrapath Selection in Wireless Sensor Network. Mathematical Problems in Engineering, 2014, 1-8. doi:10.1155/2014/71342

Enantioselective epoxidation of styrene with TBHP catalyzed by bis(oxazoline)–vanadyl–laponite materials

Bis(oxazoline)-vanadyl complexes have been prepared from two precursors, VO(acac)2 and VOSO4, and immobilized on laponite by cation exchange. These catalysts have been tested in the enantioselective epoxidation of styrene with TBHP. The catalytic activities are always much higher in the case of VO(acac)2. The ligand improves the catalytic activity, with similar or slightly better selectivity to styrene oxide (up to 42%) and up to 63% ee in solution. Laponite support is also beneficial in most cases, with selectivities to styrene oxide up to 60%. Moderate enantioselectivities are obtained, better with VOSO4 solids, up to 72% ee.This work was supported by the Spanish Ministerio de Economía y Competitividad (grant CTQ2014-52367-R) and the Diputación General de Aragón (E37_17R, Group co-financed by the European Regional Development Funds). M. F. thanks the Tunisien Ministère de l'Enseignement Supérieure et la Recherche Scientifique for a short-mobility grant (bourse d'alternance).Peer reviewe

Comparison of Ta–MCM-41 and Ti–MCM-41 as catalysts for the enantioselective epoxidation of styrene with TBHP

Chiral Ti–MCM-41 and Ta–MCM-41 catalysts have been prepared by grafting of Ti(OiPr)4 and Ta(OEt)5 and the modification with R-(+)-diethyl l-tartrate or R-(+)-diisopropyl l-tartrate. In general, the solid catalysts are more active and selective than their homogeneous counterparts in the epoxidation of styrene with tert-butyl hydroperoxide. The enantioselectivities depend on both the nature of the chiral ligand and the calcination temperature of the support, as it is supposed this controls the type of surface species that are formed. The best result of 71% ee is obtained with DIPT–Ta–MCM550 and is the first example of the use of a Ta catalyst for the enantioselective epoxidation of unfunctionalized alkenes. Nonetheless, the recovered Ta catalysts are less active and selective.This work was supported by the Spanish Ministerio de Economía y Competitividad (grant CTQ2014-52367-R) and the Diputación General de Aragón (E11 Group cofinanced by the European Regional Development Funds). M.F. thanks the Tunisian “Ministère de l’Enseignement supérieur et de la Recherche scientifique” for a short-mobility grant (bourse d'alternance).Peer reviewe

Modified Ti/MCM-41 catalysts for enantioselective epoxidation of styrene

Ti sites grafted on MCM-41, pretreated at different temperatures, have been modified with chiral tartrates, leading to different species. Those solids are active catalyst for the epoxidation of styrene with tert-butyl hydroperoxide, although their efficiency is not optimal, mainly due to the subsequent epoxide rearrangement to phenyl acetaldehyde and further oxidation of it. Styrene oxide is obtained with moderate enantioselectivity, in the range of 55-62% e.e., and the best overall results correspond to the use of MCM-41 calcined at the lowest temperature (550 °C). These results are much better with regard to styrene oxide selectivity than those obtained in homogeneous phase under the same conditions, whereas enantioselectivity is similar. The heterogeneous catalysts are recoverable, but only partially due to a loss in activity, although enantioselectivity is kept at similar levels, demonstrating the stability of the supported Ti-tartrate species.Financial support from the Spanish Ministerio de Economía y Competitividad (Project CTQ2014-52367-R) and the Diputación General de Aragón (E11 Group co-financed by the European Regional Development Funds) is gratefully acknowledged. M.F. thanks the Tunisien Ministère de l’Enseignement Supérieure et la Recherche Scientifique for a short-mobility grant (bourse d’alternance).Peer Reviewe

New bis(oxazoline)–vanadyl complexes, supported by electrostatic interaction in Laponite clay, as heterogeneous catalysts for asymmetric oxidation of methyl phenyl sulfide

Chiral bis(oxazoline) ligands are used for the first time to promote the enantioselective vanadium-catalyzed oxidation of sulfides with alkyl hydroperoxides. Several bis(oxazoline)-VO complexes have been prepared and supported by cation exchange in Laponite clay. The substituent in the oxazoline ring, and the type of hydroperoxide are relevant parameters that control the activity and selectivity of the resulting catalysts. Tert-butyl hydroperoxide is more reactive but less enantioselective than cumenehydroperoxide, both with the neat and supported VO-bis(oxazoline) complexes. Activities and enantioselectivities obtained with the heterogeneous catalysts are always lower than in solution, and in general better and more consistent results are obtained with box(Pr) ligand which seems to be also the best chiral auxiliary in homogeneous phase, leading to a modest but significant enantioselectivity of 20% ee in heterogeneous phase and of 28% in homogeneous phase. The recovered of the best catalyst shows a decrease in the catalytic activity and in the enantioselectivity, in agreement with some decomplexation of the chiral ligand, whereas the supported vanadium species remain stable and recoverable.Financial support from the Spanish Ministerio de Economía y Competitividad (Project CTQ2014-52367-R) and the Diputación General de Aragón (E11 Group co-financed by the European Regional Development Funds) is gratefully acknowledged. M. F. thanks theTunisien Ministère de l’Enseignement Supérieure et la Recherche Scientifique for a short-mobility grant (bourse d'alternance).Peer Reviewe

Cholinesterase activity as biomarker of neurotoxicity: utility in the assessment of aquatic environment contamination * Actividade da colinesterase como biomarcador de neurotoxicidade: avaliação da contaminação em ambientes aquáticos ** ** Portuguese Titl

AbstrAct Cholinesterase can take place in aquatic organisms under a series of environmental adverse conditions. The study of cholinesterases in these organisms can give important information about their physiological status and about environmental health. However, it is very important to know how the environmental factors such as fluctuation of physicochemical parameters associated to the presence of pollutants might affect these cholinesterase activities. We studied the response of cholinesterase activity in the caged cockle Cerastoderma glaucum. In addition, we evaluated the potential uses of cholinesterase activity in the common sole, which inhabit the Tunisian coast, subjected to different stress conditions, such as the exposure to different contaminants. This review summarizes the data obtained in some studies carried out in organisms from the Tunisian aquatic environment. Keyword

Effects of Zinc Supplementation on Oxidative Stress in Patients Undergoing Maintenance Hemodialysis

Introduction: The aim of this study was to examine the effects of Zn supplementation on oxidative stress by evaluating changes in serum Copper (Cu) to Zinc (Zn) ratio, homocysteine (hCys), Glutathione (GSH), Total Bilirubin (TB) and Catalase (CAT) activity in hemodialysis patients.Methods: Seventy-seven HD patients were enrolled in a multicenter simple-blind randomized clinical trial. Only 37 HD patients completed the study. They were randomly divided into two groups and supplemented with zinc sulfate (n = 17) or placebo (n = 20) for two months. Serum Zn and Cu were measured by atomic absorption spectrophotometry. Serum hCys was measured by immunology method, serum GSH and CAT activity were assessed by spectrophotometry method and TB was measured by colorimetric method. Determinations were performed before and after supplementation.Findings: After zinc supplementation, serum Zn, serum GSH, and Serum Total Bilirubin (STB) significantly increased. Serum Cu to Zn ratio, serum hCys, and CAT activity significantly decreased in the Zn Zn-supplemented group.Conclusion: Zinc supplementation increased serum antioxidant factors such as Zn, GSH, and bilirubin and decreased serum oxidative factors such as copper to zinc ratio, hCys, and decreased CAT activity. The study results suggest that zinc supplementation may be a useful tool for the improvement of oxidative stress in HD patients