Perfluorocyclohexene bridges in inverse DiArylEthenes: synthesis through Pd-catalysed C-H bond activation, experimental and theoretical studies on their photoreactivity.

International audienceThe palladium-catalysed direct di-heteroarylation of 1,2-dichloroperfluorocyclohexene with a variety of heteroarenes gives rise in to a new family of 1,2-di(heteroaryl)perfluorocyclohexenes. These derivatives do not exhibit photoreactivity and this unexpected outcome is explained by calculations demonstrating the lack of reactive isomers

Temporal and spatial variations in nutrient stoichiometry and regulation of phytoplankton biomass in Hong Kong waters : influence of the Pearl River outflow and sewage inputs

Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Pollution Bulletin 57 (2008): 335-348, doi:10.1016/j.marpolbul.2008.01.020.In 2001, the Hong Kong government implemented the Harbor Area Treatment Scheme (HATS) under which 70% of the sewage that had been formerly discharged into Victoria Harbor is now collected and sent to Stonecutters Island Sewage Works where it receives chemically enhanced primary treatment (CEPT), and is then discharged into waters west of the Harbor. The relocation of the sewage discharge will possibly change the nutrient dynamics and phytoplankton biomass in this area. Therefore, there is a need to examine the factors that regulate phytoplankton growth in Hong Kong waters in order to understand future impacts. Based on a historic nutrient data set (1986-2001), a comparison of ambient nutrient ratios with the Redfield ratio (N:P:Si=16:1:16) showed clear spatial variations in the factors that regulate phytoplankton biomass along a west (estuary) to east (coastal/oceanic) transect through Hong Kong waters. Algal biomass was constrained by a combination of low light conditions, a rapid change in salinity, and strong turbulent mixing in western waters throughout the year. Potential stoichiometric Si limitation (up to 94% of the cases in winter) occurred in Victoria Harbor due to the contribution of sewage effluent with high N and P enrichment all year, except for summer when the frequency of stoichiometric Si limitation (48%) was the same as P, owing to the influence of the high Si in the Pearl River discharge. In the eastern waters, potential N limitation and N and P co-limitation occurred in autumn and winter respectively, because of the dominance of coastal/oceanic water with low nutrients and low N:P ratios. In contrast, potential Si limitation occurred in spring and a switch to potential N, P and Si limitation occurred in eastern waters in summer. In southern waters, there was a shift from P limitation (80%) in summer due to the influence of the N-rich Pearl River discharge, to N limitation (68%) in autumn, and to N and P co-limitation in winter due to the dominance of N-poor oceanic water from the oligotrophic South China Sea. Our results show clear temporal and spatial variations in the nutrient stoichiometry which indicates potential regulation of phytoplankton biomass in HK waters due to the combination of the seasonal exchange of the Pearl River discharge and oceanic water, sewage effluent inputs, and strong hydrodynamic mixing from SW monsoon winds in summer and the NE monsoon winds in winter.Financial support for this research was provided by the University Grants Council of Hong Kong AoE project (AoE/P-04/0401), and RGC project HKUST6478/05M. Support was also provided (to DMA) by U.S. National Science Foundation grants OCE-0402707 and OCE-0430724 and by NIEHS grant 1 P50-ES01274201

The stabilization and release performances of curcumin-loaded liposomes coated by high and low molecular weight chitosan

A comprehensive stability evaluation for curcumin-loaded liposomes (Cur-LP) coated by low (LCS) or high (HCS) molecular weight chitosan with three gradient concentrations (L: low; M: medium; H: high) was the main objective of this study. Apart from leading to a higher encapsulation efficiency (>90%), all chitosan-coated Cur-LP displayed an improved stability with respect to resistant to salt, sunlight, heat, accelerated centrifugation and long-term storage at 4 °C. Increasing the molecular weight and concentration of chitosan could effectively improve the stability of Cur-LP, in which HCS-H coatings displayed the best performance. According to the fluorescence probe analysis, the mechanical reinforcement of liposomes and the concomitant reduction in membrane fluidity accounts for the major contribution to vesicle stability. Secondly, a simulated digestion model was used to prove the applicability of sustained curcumin release, achieved by adjusting the molecular weight and concentration of the chitosan stabilizer for Cur-LP. The results of this study show that high molecular weight chitosan used at relatively high concentrations, is a promising coating material for improving the stability and sustained release of Cur-LP in vitro

Activations de liaisons C-H pallado-catalysées : Nouveaux accès à des diarylethenes et couplages désulfitatifs

Au cours de cette thèse, nous nous sommes intéressés à la synthèse de photo-interrupteurs organiques [DAE, di(hétéro)arylethenes] via activation de liaisons sp² C-H d'hétéroaromatiques catalysées par le palladium. Le système catalytique pour l'arylation directe précédemment établi, Pd(OAc)₂/KOAc/DMAc, s'est montré adapté aux nouvelles transformations souhaitées. Cette méthode permet l'accès direct à une grande variété de molécules photo-commutable en peu d'étapes. En outre, concernant le développement de nouvelles procédures de fonctionnalisation de liaisons C-H d'hétéroaromatiques, nous avons constaté que le système catalytique Pd(CH₃CN)₂Cl2/Li₂CO₃/dioxane, pour le couplage de thiophènes avec des chlorures d'arylsulfonyle conduit à des thiophènes β-arylés. Ce nouveau système catalytique peut également être utilisé dans une réaction d'addition conjuguée, en utilisant des énones et des chlorures d'arylsulfonyle en tant que partenaires de couplage. Enfin, nous avons décrit la formation de 4-aryl-1,2,3,4-tetrahydroquinolines via Heck/sp² C-H activation co-catalysée par PdCl₂/CuBr.During this thesis, we were interested in the synthesis of organic photo-switches [DAE, di(hetero)arylethenes] via palladium catalyzed sp2 C-H bond activation of heteroaromatics. The previously established catalysts system for direct arylation, Pd(OAc)₂/KOAc/DMA, was found to be suitable for the new desired transformations. This method allows the straightforward access to a wide variety of useful photo-switchable molecules in a few steps. Moreover, during the course of further developments of C-H bond functionalization of heteroaromatics, we found that a phosphine free catalytic system, Pd(CH₃CN)₂Cl2/Li ₂CO₃/dioxane, promotes the coupling of thiophenes and arylsulfonyl chlorides to afford unexpected β-arylated products. This new catalytic system can also be utilized in conjugate addition reaction by using enones and arylsulfonyl chlorides as coupling partners. Finally, we describe PdCl2/CuBr co-catalyzed formation of 4-aryl-1,2,3,4-tetrahydroquinolines via cascade desulfitative Heck/sp² C-H activation sequence

Activations de liaisons C-H pallado-catalysées : Nouveaux accès à des diarylethenes et couplages désulfitatifs

Au cours de cette thèse, nous nous sommes intéressés à la synthèse de photo-interrupteurs organiques [DAE, di(hétéro)arylethenes] via activation de liaisons sp² C-H d'hétéroaromatiques catalysées par le palladium. Le système catalytique pour l'arylation directe précédemment établi, Pd(OAc)₂/KOAc/DMAc, s'est montré adapté aux nouvelles transformations souhaitées. Cette méthode permet l'accès direct à une grande variété de molécules photo-commutable en peu d'étapes. En outre, concernant le développement de nouvelles procédures de fonctionnalisation de liaisons C-H d'hétéroaromatiques, nous avons constaté que le système catalytique Pd(CH₃CN)₂Cl2/Li₂CO₃/dioxane, pour le couplage de thiophènes avec des chlorures d'arylsulfonyle conduit à des thiophènes β-arylés. Ce nouveau système catalytique peut également être utilisé dans une réaction d'addition conjuguée, en utilisant des énones et des chlorures d'arylsulfonyle en tant que partenaires de couplage. Enfin, nous avons décrit la formation de 4-aryl-1,2,3,4-tetrahydroquinolines via Heck/sp² C-H activation co-catalysée par PdCl₂/CuBr.During this thesis, we were interested in the synthesis of organic photo-switches [DAE, di(hetero)arylethenes] via palladium catalyzed sp2 C-H bond activation of heteroaromatics. The previously established catalysts system for direct arylation, Pd(OAc)₂/KOAc/DMA, was found to be suitable for the new desired transformations. This method allows the straightforward access to a wide variety of useful photo-switchable molecules in a few steps. Moreover, during the course of further developments of C-H bond functionalization of heteroaromatics, we found that a phosphine free catalytic system, Pd(CH₃CN)₂Cl2/Li ₂CO₃/dioxane, promotes the coupling of thiophenes and arylsulfonyl chlorides to afford unexpected β-arylated products. This new catalytic system can also be utilized in conjugate addition reaction by using enones and arylsulfonyl chlorides as coupling partners. Finally, we describe PdCl2/CuBr co-catalyzed formation of 4-aryl-1,2,3,4-tetrahydroquinolines via cascade desulfitative Heck/sp² C-H activation sequence

Access to Alternative Regioisomers for Palladium-Catalysed Direct Arylations of (Benzo)thiophenes.

International audienceA review. Arylation of (benzo)thiophenes at the β-position is reviewed. Included is a description of the β-arylation of benzothiophene by aryl chlorides catalyzed by Pd/CuCl without the need for ligands. [on SciFinder(R)

Benzenesulfonyl chlorides: new reagents for access to alternative regioisomers in palladium-catalysed direct arylations of thiophenes

International audienceThe palladium-catalysed coupling of benzenesulfonyl chlorides with thiophene derivatives allows regioselective access to β-arylated thiophenes. The reaction proceeds with easily accessible catalyst, base and substrates, without oxidant or ligand and tolerates a variety of substituents on both the benzene and thiophene moieties

Double Maximum Ratios of Viruses to Bacteria in the Water Column: Implications for Different Regulating Mechanisms

The viruses play an important role in limiting bacterial abundance in oceans and, hence, in regulating bacterial biogeochemical functions. A cruise was conducted in September 2005 along a transect in the deep South China Sea (SCS). The results showed the double maxima in the ratio of viral to bacterial abundance (VBR) in the water column: a deep maximum at 800-1000 m coinciding with the oxygen minimum zone (OMZ) and a subsurface maximum at 50-100 m near the subsurface chlorophyll maximum (SCM) layer. At the deep maximum of VBR, both viral and bacterial abundances were lower than those in the upper layer, but the former was reduced less than the latter. In contrast, at the subsurface maximum of VBR, both viral and bacterial abundances increased to the maximum, with viral abundance increasing more than bacterial abundance. The results suggest that two VBR maxima were formed due to different mechanisms. In the SCM, the VBR maximum is due to an abundant supply of organic matter, which increases bacterial growth, and stimulates viral abundance faster. In contrast, in the OMZ, organic matter is consumed and limits bacterial growth, but viruses are less limited by organic matter and continue to infect bacteria, leading to the maximum VBR. The OMZ in the deep-water column of oceans is over hundreds of years old and receives a constant supply of organic matter from the water above. However, the oxygen level cannot be depleted to anoxia. Bacterial respiration is largely responsible for oxygen consumption in the OMZ; and hence, any process that limits bacterial abundance and respiration contributes to the variation in the OMZ. Viral control of bacterial abundance can be a potential mechanism responsible for slowing down oxygen consumption to anoxia in the OMZ. Our finding provides preliminary evidence that viruses are an important player in controlling bacterial abundance when bacterial growth is limited by organic matter, and thus, regulates the decomposition of organic matter, oxygen consumption and nutrient re-mineralization in deep oceans

Ruthenium-containing phosphinesulfonate chelate for the hydrogenation of aryl ketones.

International audienceVarious ruthenium(II) complexes that contain phosphinesulfonate chelate have been synthesized. Arene-free complexes were found to be efficient in the base-free hydrogenation of various aryl ketones, whereas the arene-containing precatalysts required the presence of an amine as an additive. The seminal asymmetric hydrogenation reaction by using the new Sulfo-Binepine ligand was also investigated for the possible intervention of a dihydride species