Impact of phosphate factory on the biological characteristics of North Lebanon surface sediments (Levantine Basin)

11 p.This study aims to analyse the surface sediment of Batroun coastal area in North Lebanon in order to reveal the integrating impact of Selaata chemical plant on its biological properties. Sediment samples were collected with cores by diving at 12 stations in summer period between mid July and beginning of August 2003. The values of the hydobiological parameters in the first 3 cm were ranging respectively between: 4.17 to 7.9 for pH, 0 to 171 mV for Eh,, 0 to 0.94 µg.g-1 for chlorophyll a and 24 to 4166 ind.10 cm-2 for meiofauna. The results showed that there was a reverse relationship between chlorophyll a and meiofauna and that Batroun marine area could be separated in two main areas of influence The first area includes the stations located in front of the main north-western emissary and where the sediments were more acid and less oxygenated with strong odour of hydrogen sulphide accompanied with high chlorophyll a contents and low numbers of meiofauna. The second area is consisted of stations located to the south or far offshore from the plant and where the sediments are characterized by lower acidity and higher redox potential with low chlorophyll a concentrations and higher population of meifauna. Exception could be found in some stations like M8 and M 13 that presented particular cases. The impact on the biological indices was limited to plant proximity where conditions were more perturbing and the variability in the concentrations of chlorophyll a and the numbers of meiofauna were not depending on sediments compositions but on the nature and toxicity of particulate matters rejected out of plant's emissaries such as the phosphogypsum

Basal interaction of the orphan receptor GPR101 with arrestins leads to constitutive internalization.

peer reviewedGPR101 is an orphan G protein-coupled receptor that promotes growth hormone secretion in the pituitary. The microduplication of the GPR101 gene has been linked with the X-linked acrogigantism, or X-LAG, syndrome. This disease is characterized by excessive growth hormone secretion and abnormal rapid growth beginning early in life. Mechanistically, GPR101 induces growth hormone secretion through constitutive activation of multiple heterotrimeric G proteins. However, the full scope of GPR101 signaling remains largely elusive. Herein, we investigated the association of GPR101 to multiple transducers and uncovered an important basal interaction with Arrestin 2 (β-arrestin 1) and Arrestin 3 (β-arrestin 2). By using a GPR101 mutant lacking the C-terminus and cell lines with an Arrestin 2/3 null background, we show that the arrestin association leads to constitutive clathrin- and dynamin-mediated GPR101 internalization. To further highlight GPR101 intracellular fate, we assessed the colocalization of GPR101 with Rab protein markers. Internalized GPR101 was mainly colocalized with the early endosome markers, Rab5 and EEA-1, and to a lesser degree with the late endosome marker Rab7. However, GPR101 was not colocalized with the recycling endosome marker Rab11. These findings show that the basal arrestin recruitment by GPR101 C-terminal tail drives the receptor constitutive clathrin-mediated internalization. Intracellularly, GPR101 concentrates in the endosomal compartment and is degraded through the lysosomal pathway. In conclusion, we uncovered a constitutive intracellular trafficking of GPR101 that potentially represents an important layer of regulation of its signaling and function

Dihydrogen generation from amine/boranes: synthesis, FT-ICR, and computational studies.

International audienceA Fourier transform ion cyclotron resonance spectrometry (FT-ICR) study of the gas-phase protonation of ammonia-borane and sixteen amine/boranes R(1)R(2)R(3)N-BH(3) (including six compounds synthesized for the first time) has shown that, without exception, the protonation of amine/boranes leads to the formation of dihydrogen. The structural effects on the experimental energetic thresholds of this reaction were determined experimentally. The most likely intermediate and the observed final species (besides H(2)) are R(1)R(2)R(3)N-BH(4)(+) and R(1)R(2)R(3)N-BH(2)(+), respectively. Isotopic substitution allowed the reaction mechanism to be ascertained. Computational analyses ([MP2/6-311+G(d,p)] level) of the thermodynamic stabilities of the R(1)R(2)R(3)N-BH(3) adducts, the acidities of the proton sources required for dihydrogen formation, and the structural effects on these processes were performed. It was further found that the family of R(1)R(2)R(3)N-BH(4)(+) ions is characterized by a three-center, two-electron bond between B and a loosely bound H(2) molecule. Unexpected features of some R(1)R(2)R(3)N-BH(4)(+) ions were found. This information allowed the properties of amine/boranes most suitable for dihydrogen generation and storage to be determined

The Stability of Bridgehead Carbocations

The gas-phase stability of bridgehead carbocations has been determined by Fourier transform ion cyclotron resonance spectroscopy (FT ICR) based on dissociative proton attachment (DPA) of bridgehead bromides, chlorides, and alcohols. When appropriate leaving group corrections are applied, the relative ion stabilities obtained from these precursors are identical. The relative rate constants (log k) for solvolysis of bridgehead derivatives correlate with the stabilities of the cations over the entire reactivity range. Theoretical calculations of the stabilities of the ions relative to those of the respective hydrocarbons at the MP2/6-311G** level agree fully with the experimental data

Small molecule ligands for the orphan GPR27

Background G protein-coupled receptors (GPCRs) are involved in many physiological processes and constitute the target of around 30% of marketed therapies. Nonetheless, ~100 human GPCRs have no known ligand and are designated as "orphan". This project focuses on GPR27, a rhodopsin-like alpha orphan of the SREB family (Super conserved Receptors Expressed in the Brain), presumably involved in the regulation of insulin secretion [1]. Methods In order to identify small molecules activating GPR27, we developed a firefly luciferase complementation assay (based on [2]) to assess the binding of ß-arrestin2 to the activated GPCR. To increase the affinity for and strengthen the interaction with ß-arrestin2, a GPR27-V2R chimera has been used for library screening. Results Small molecules activating GPR27-V2 have been identified in the DiverSetTM library (ChemBridge). After exclusion of non-specific activities using another unrelated GPCR, two compounds sharing a common scaffold with activity in the low micromolar range were selected for further investigations. We confirmed their agonist profile by performing complete concentration-response curves on our arrestin complementation assay as well as orthogonal assays. These compounds show good specificity being inactive on GPR85-V2 and GPR173-V2 (the two other SREB members). With these original tools, we characterized the recruitment of ß-arrestin2 to activated GPR27 WT. Conclusion We identified small molecule ligands for GPR27 that will serve as valuable tools for studying the pharmacology of GPR27 as well as its physiological roles, for example in insulin secretion. 1 Ku G.M., Pappalardo Z., Luo C.C., German M.S., McManus M.T. An siRNA Screen in Pancreatic Beta Cells Reveals a Role for Gpr27 in Insulin Production. PLoS genetics. 2012, 8, e1002449. 2 Takakura H., Hattori M., Takeuchi M., Ozawa T. Visualization and Quantitative Analysis of G Protein-Coupled Receptor−β-Arrestin Interaction in Single Cells and Specific Organs of Living Mice Using Split Luciferase Complementation. ACS Chem. Biol. 2012, 7, 901−910

Performance improvement with non-alloyed ohmic contacts technology on AlGaN/GaN High Electron Mobility Transistors on 6H-SiC substrate

International audienceABSTRACT In this paper, non-alloyed ohmic contacts regrown by molecular beam epitaxy (MBE) are fabricated on AlGaN/ GaN high-electron-mobility transistors on 6H-SiC substrate. Low ohmic contact resistance of 0.13 Ω.mm is obtained. This paper demonstrates the high frequency and high power performance improvements thanks to this technology regarding conventional technology based on alloyed ohmic contacts. The fabricated device with a 75- nm-T-shaped gate demonstrates a maximum drain current density of 1.1 A/mm at VGS = 1 V and a peak transconductance gm of 464 mS/mm. A current gain cut-off frequency fT of 110 GHz and a maximum oscillation frequency fMAX of 150 GHz are achieved. At VDS = 25 V, continuous-wave output power density of 3.8 W/mm is achieved at 40 GHz associated with 42.8% power-added efficiency and a linear power gain of 6 dB. A maximum power-added efficiency of 55% is also obtained at VDS = 20 V