Biosynthèse de la farnésylacétone-(E,E) par les glandes androgènes du crabe carcinus maenas

Biosynthesis of E, E-farnesylacetone by the andogenic glands of the crab Carcinus maenas Using sodium acetate-1,2-[¹⁴C] or mevalonic acid-2-[¹⁴C], the biosynthesis of (E,E)-farnesylacetone 1 by the androgenic glands of the crab Carcinus maenas, kept as organ subculture is demonstrated. Ozonolysis of the NaBH₄ reduction product 3 leads to three fragments the radioactivity of which has been measured after isolation by GC. It is thus established that the biosynthesis of 1 proceeds through geranylgeraniol. The hexahydroderivative 2 is not labelled in the two experiments.     

Fine-tuning the transition temperature of a stimuli-responsive polymer by a simple blending procedure

Binary mixtures of well-defined, stimuli-responsive elastin-based side-chain polymers show a single transition temperature that depends on blend composition.     

Antioxidative effect of <Emphasis Type="Italic">Bacteroides thetaiotaomicron</Emphasis> extracts: superoxide dismutase identification

Bacteroides thetaiotaomicron, a bowel anaerobic commensal, seems to release enzymes detoxifying reactive oxygen species according to our recent work. This opportunistic pathogen would be beneficial in the case of an inflammatory process. To explore its role after an oxidative or nutritive stress, six to seven separate experiments were performed. The bacteria were grown on media restricted in growth factors or supplemented with bile. Their viability was checked after surface protein extraction. The extracts underwent 2D electrophoresis. Gel images were statistically analysed to construct “master” gels. Proteins were identified (peptide-mass fingerprinting technique). The effect of each extract on superoxide anions was evaluated (spectrophotometric method). Superoxide dismutase was identified and a major superoxide anion inhibition was shown by extracts obtained after a nutritive and oxidative stress without significant bacterial death. So, a therapeutic antioxidant potential is firmly hoped for. Figure These intestinal commensal Gram negative anaerobic bacilli are able to release a high level of functional superoxide dismutase when grown in minimal medium. Presented at the Annual French National Symposium on Mass Spectrometry, Electrophoresis and Proteomics, 17–20 September 2007 in Pau, France.     

Analysis of the importance of the metallo-beta-lactamase active site loop in substrate binding and catalysis

The role of the mobile loop comprising residues 60-66 in metallo-beta-lactamases has been studied by site-directed mutagenesis, determination of kinetic parameters for six substrates and two inhibitors, pre-steady-state characterization of the interaction with chromogenic nitrocefin, and molecular modeling. The W64A mutation was performed in IMP-1 and BcII (after replacement of the BcII 60-66 peptide by that of IMP-1) and always resulted in increased K(i) and K(m) and decreased k(cat)/K(m) values, an effect reinforced by complete deletion of the loop. k(cat) values were, by contrast, much more diversely affected, indicating that the loop does not systematically favor the best relative positioning of substrate and enzyme catalytic groups. The hydrophobic nature of the ligand is also crucial to strong interactions with the loop, since imipenem was almost insensitive to loop modifications.     

Lubricated squeezing flow of thin slabs of wheat flour dough: comparison of results at constant plate speed and constant extension rates

Lubricated squeezing flow experiments on wheat flour dough have, until now, mostly been performed in constant plate speed mode (CPS), i.e. at a permanently increasing extension rate. We have compared the results obtained under the CPS and constant extension rate (CER) modes using one of the very few commercial rheometers that allow operation in the CER mode. In both cases, and at any constant biaxial strain, a power law could be fitted to the stress versus extension rate data, the “consistency index” (K) increasing continuously with the strain and the “flow behaviour index” (n) being constant only up to a low strain value (≈0.25) and then decreasing. When compared to the CER mode, the CPS mode produced higher K and n values. For wheat flour doughs, an increase in K with extension may be associated to a strain-hardening phenomenon but the roles of viscoelasticity and lubricant thinning are discussed.     

Ultraviolet absorption spectra of chloramines and chlorine in carbon tetrachloride

In order to quantify mixtures of chloramines and chlorine in carbon tetrachloride, the ultraviolet spectra of monochloramine, dichloramine, trichloramine and chlorine were measured between 250 and 410 nm. Monochloramine and chlorine absorb at 259 nm (?=484.61 mol^?1 cm^?1 ) and 331 nm (?=95.7 l mol^?1 cm^?1), respectively, while dichloramine and trichloramine exhibit two peaks. For dichloramine, the maximum absorptions are observed at 255 nm (?=126.1 l mol^?1 cm^?1) and 301 nm (?=307.8 l mol^?1 cm^?1) and for trichloramine, at 262 nm (?=635.4 l mol^?1 cm^?1) and 344 nm (?=315.0 l mol^?1 cm^?1).     

Twenty-species and 15-species chemical kinetic mechanisms for cyclohexane using the local self-similarity tabulation method

The 1081 species cyclohexane-oxidation elementary reaction mechanism of Silke et al. (DOI: 10.1021/jp067592d ) is reduced in the number of species by a factor using the local self-similarity tabulation (LS2T) method. Reduced-species mechanisms of both 20 (R20) and 15 (R15) species are created in the high-pressure combustion regime typical of diesel engines. To evaluate the performance of R20 and R15 against the elementary kinetics, simulations are performed for cyclohexane/air mixtures at initial temperatures of 1150, 900, 750, and 680 K and constant pressures of 20 and 40 bar for a variety of equivalence ratios (, 1.0, and 2 for 1150 and 900 K; for 750 K; for 680 K). Very good agreement between R20 and R15 with the elementary kinetics mechanism is demonstrated at 1150 and 900 K for which the self-similarity is very well obeyed; however, only fair agreement is obtained at 750 and 680 K, a fact which is traced to the less faithful adherence to the self-similarity due to the one order of magnitude increase in ignition time over the range 750-680 K. These results are found to be quasi-independent of the tabulation grid. Future work is proposed to improve the reduction in the cold-ignition, high-pressure regime.     

Study of the electrochemical properties in substituted Li2Ti3O7 ramsdellite

Substituting the ramsdellite compound Li₂Ti₃O₇ has been considered in order to improve the structure stability and performances for its use as electrode material for Li-ion accumulators. Two substitutions have been carried out, Ti/Fe and (Ti, Li)/(Fe,Ni). The presence of ⁵⁷Fe as a local Mössbauer probe is interesting for studying its local environment and the electrochemical mechanisms induced by lithium insertion.