Control of the Platinum(II) ligating properties of rigid 1,2-diamines: the case of trans-2,3-diaminonorbornane.

Guided by a simple predictive model, a norbornane-based trans-1,2-diamine was identified as a potential bridging ligand for di-nuclear platinum complex formation; efficient synthesis and product characterization confirmed this hypothesis

2-Aminobenzothiazole degradation by free and Ca-alginate immobilized cells of Rhodococcus rhodochrous

International audience2-Aminobenzothiazole (ABT) degradation was investigated using free and immobilized systems during photodegradation under solar light in the presence of Fe(III)-nitrilotriacetic acid (FeNTA), biodegradation by Rhodococcus rhodochrous, and during combined conditions. Ca-alginate hydrogel was chosen as a model matrix and some complementary studies were required to characterize this new system. R. rhodochrous metabolism in this type of environment was monitored by NMR spectroscopy. Neither change in intracellular pH values nor in ATP concentrations was observed by in vivo 31P NMR, showing that no metabolic modification occurred between free and immobilized cells. 1H NMR demonstrated that alginate was not used as carbon source by R. rhodochrous. After establishing the pre-treatment protocol by SPE to eliminate solubilised alginate, ABT adsorption on beads and degradation were studied. The same pathways of transformation were observed in suspended and immobilized cell systems. Considering the ABT adsorption phenomenon on alginate beads (8%), the efficiency of the two systems was found to be comparable although the degradation rate was slightly lower with immobilized cells. The most important result was the finding that the positive effect of FeNTA on ABT degradation with immobilized cells was similar to that observed previously with free cells. All these results show that mechanisms observed with free cells can be extrapolated to entrapped cells, i.e. under conditions much closer to those usually encountered in the environment

Cloud Microorganisms, an Interesting Source of Biosurfactants

A new scientific hypothesis states that biosurfactants from cloud microorganism origin could change the surface tension of aerosols and thus the mode of precipitations. In order to check this hypothesis, our team has screened a collection of 480 microbial strains isolated from cloud waters for the production of biosurfactants and showed that 42% of these strains were producing such molecules. In the present work, we isolated and identified by LC-MS-MS lipopeptides produced from three strains issued from this screening. Viscosin and massetolide E (cyclic lipopeptides) were produced by Pseudomonas sp. PDD-14b-2, and syringafactins (linear lipopeptides) were produced by Xanthomonas campestris PDD-32b-52 and Pseudomonas syringae PDD-32b-74. The critical micelle concentration (CMC) of these biosurfactants was determined using the pendant drop method. Finally, two approaches of molecular dynamics were used to model the conformation of viscosin and syringafactin A at the water-air interface: one is based on all-atoms simulation (CHARMM force field), while the other one on coarse-grain (CG) simulation (MARTINI force field). To conclude, this work shows how the biodiversity of the cloud microbiota can be explored to search and produce biosurfactants of interest both for atmospheric sciences and also for biotechnological applications

Ionic association and interactions in aqueous methylsulfate alkyl-imidazolium-based ionic liquids

International audienceSeveral experimental techniques were used to study ionic association and interactions in aqueous [C1C2Im][MeSO4], 1-ethyl-3-methylimidazolium methylsulfate, and [C1C4Im][MeSO4], 1-butyl-3-methylimidazolium methylsulfate. Two transport properties, viscosity and electrical conductivity, were determined for these two binary mixtures. For a better assessment of the ionic association and the perturbation of water into the molecular structure of the ionic liquid, diffusion coefficients of ions and water molecules were obtained by NMR spectroscopy while molecular interactions were probed by IR spectroscopy.The comparison of the two ionic liquids shows that for the shorter alkyl chain the viscosity was lower and the electrical conductivity was higher. While the viscosity of the mixture drops already with small additions of water, the electrical conductivity of the solution is only significantly increased for high water concentrations. A maximum is observed for compositions around xwater = (0.90 to 0.95). The SO3 asymmetric stretching band of the IR spectrum can be used as a probe to observe the evolution of the structure around the anion which was mainly occurring for high concentrations of water. Several experimental techniques show than the main change in the ionic association was only observed for high water contents (water mole fraction > 0.8)

Click glycoconjugation of per-azido- and alkynyl-functionalized beta-peptides built from aspartic acid

International audienceAzide- and alkynyl-containing homo-beta3-peptides, of up to six residues in length, were synthesised in solution from aspartic acid. Their subsequent conjugation with monosaccharides bearing an azide or a terminal alkyne function was efficiently achieved by copper-mediated cycloadditions leading to two novel families of small glycoclusters. These compounds represent ideal tools to explore carbohydrate-mediated multivalent interaction

Quantification of the impact of water as an impurity on standard physico-chemical properties of ionic liquids

International audienceThe objective of this work was to quantify the effect of the presence of water as impurity in ionic liquids. First, density and viscosity of five ionic liquids as well as their aqueous solutions were measured. For hydrophobic dried ionic liquids, traces of water (50 ppm) have measurable impact neither on the density nor on the viscosity values. In the concentration range studied (up to 5000 ppm), a linear evolution of the molar volume of the mixture with the mole fraction composition is observed. Practically, this allows to estimate the density of an neat ionic liquid provided (i) the water quantity and (ii) the density of the undried sample are known. This is particularly useful for hydrophilic ionic liquids that are difficult to dry. In the studied concentration range, a linear evolution of the relative viscosity was also depicted as a function of the mass fraction composition. It is thus possible to evaluate the viscosity of the pure ionic liquid knowing the water quantity and the viscosity of the undried sample. The comparison of the results obtained using two viscosimeters confirms that a Stabinger viscosimeter is appropriate to precisely measure ionic liquids viscosities. Second, NMR and IR spectroscopies were used to characterize the pure ionic liquids and their solutions with water. The sensitivity of IR spectroscopy does allow neither the quantification nor the detection of water below 1 mol%. With NMR spectroscopy, water can be quantified using either the intensity or the chemical shift of the water proton peak for mole fractions as low as 200 ppm. It is even possible to detect water in the dried hydrophobic ionic liquids, few ppm of water, as long as the water peak does not overlap the ionic liquid signal

Formation of unilamellar vesicles by repetitive freeze-thaw cycles: characterization by electron microscopy and 31 P-nuclear magnetic resonance

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Catabolism of L-Ascorbate by Lactobacillus rhamnosus GG

International audienceCatabolism of l-ascorbate by enteric bacteria is well documented, but no study has formally proved that bacteria of the Lactobacillus genus ferment this compound. However, some genes analogous to those of yiaK-S operon and ula regulon, which encoded proteins leading to l-ascorbate degradation by Escherichia coli and Klebsiella pneumoniae, have been identified in the recently sequenced Lactobacillus rhamnosus GG genome. Investigations by HPLC and in vivo 13C NMR using l-[1,6-13C]-ascorbate showed that L. rhamnosus GG, a common probiotic strain, has the ability to catabolize l-ascorbate under anaerobiosis. The main products of the ascorbate degradation have been identified as CO2, acetate, and lactate. These results are in accordance with the metabolic pathway proposed for the fermentation of l-ascorbate by E. col

Application of Quantitative 1H and 19F NMR to Organometallics

International audiencePurity assessment of organometallics is particularly important for catalytic applications. While quantitative NMR is a well-known method in pharmaceutic chemistry, the present work illustrates its usefulness for the determination of the ligands and organometallics purities using proton and fluorine NMR. This method is fast, straightforward and provides accuracy results

An Entry to 1,7-Dioxaspiro[5.6]dodecanes and 1,6-Dioxaspiro[4.6]undecanes

International audienceKetones 11a–c obtained by iterative alkylation of acetone N,N-dimethylhydrazone with iodides 6 and 8a,b or epoxide 9 followed by SiO2/H2O-induced cleavage of the hydrazone were quantitatively transformed into 1,6-dioxaspiro[4.6]undecanes 12a,c and 1,7-dioxaspiro[5.6]dodecanes 12b using Yb(OTf)3 in CH3CN