Optimal stopping problems by two or more decision makers: a survey

A review of the optimal stopping problem with more than a single decision maker (DM) is presented in this paper. We classify the existing literature according to the arrival of the offers, the utility of the DMs, the length of the sequence of offers, the nature of the game and the number of offers to be selected. We enumerate various definitions for this problem and describe some dynamic approaches. Fouad Ben Abdelaziz is on leave from the Institut Superieur de Gestion, University of Tunis, Tunisia e-mail: foued.benabdelaz@isg.run.tn.     

Structural and optical characterizations of rare earth pentaphosphates LnP5O14 (Ln = La, Gd) synthesized by the sol–gel process

The sol–gel chemistry route has successfully been used to prepare samples of LnP₅O₁₄ (Ln = La, Gd) pentaphosphates from lanthanides chlorides and phosphorous pentoxide dissolved in isopropanol. Crystallized powders of single phase were obtained after calcination of gels at 350 °C. The structural characterizations of materials were investigated by means of X-ray diffraction as well as infrared and Raman spectroscopies, whereas their thermal behavior has been studied by differential thermal analyse and thermogravimetric analyses. Powders morphology was analyzed by means of scanning electron microscopy and laser granulometry. The photoluminescence properties of the Eu³⁺ ions in sol–gel derived LaP₅O₁₄ and GdP₅O₁₄ samples were investigated and compared with homologous samples synthesized by the conventional solid state reaction.     

An Enhanced Process for the Production of a Highly Purified Extracellular Lipase in the Non-conventional Yeast <Emphasis Type="Italic">Yarrowia lipolytica</Emphasis>

Yarrowia lipolytica LgX64.81 is a non-genetically modified mutant that was previously identified as a promising microorganism for extracellular lipase production. In this work, the development of a fed-batch process for the production of this enzyme in this strain was described. A lipolytic activity of 2,145 U/mL was obtained after 32 h of batch culture in a defined medium supplemented with 10 g/L of tryptone, an enhancer of lipase expression. To maximize the volumetric productivity, two different fed-batch strategies had been investigated. In comparison to batch process, the intermittent fed-batch strategy had not improved the volumetric lipase productivity. In contrast, the stepwise feeding strategy combined with uncoupled cell growth and lipase production phases resulted in a 2-fold increase in the volumetric lipase productivity, namely, the lipase activity reached 10,000 U/mL after 80 h of culture. Furthermore, this lipase was purified to homogeneity by anion exchange chromatography on MonoQ resin followed by gel filtration on Sephacryl S-100. This process resulted in an overall yield of 72% and a 3.5-fold increase of the specific lipase activity. The developed process offers a great potential for an economic production of Lip2 at large scale in Y. lipolytica LgX64.81.     

Enantioselective ketoester reductions in water: a comparison between microorganism- and ruthenium-catalyzed reactions

In the search for green chemistry methods for the enantioselective reduction of ketoesters Saccharomyces cerevisiae- and ruthenium-catalyzed reactions in water have been investigated. The highest enantiomeric excesses for the reduction of α- and β-ketoesters have been obtained by S. cerevisiae. Chiral ruthenium catalysts are active for the reduction of all ketoesters with low to moderate enantioselectivities depending on the nature of the substrate and ligand. Interestingly, for several substrates both enantiomers of the hydroxyesters have been obtained according either to the catalytic method or to the structure of the ligand.     

Chemical composition and antioxidant activity of essential oil from aerial parts of Teucrium flavum L. subsp. flavum growing spontaneously in Tunisia

The objectives of this study were to chemically characterise and evaluate the antioxidant potential of the essential oil from Teucrium flavum L. subsp. flavum growing spontaneously in Tunisia. The volatile oil was extracted by hydrodistillation of the aerial parts in a Clevenger type apparatus. Forty constituents were identified via GC and GC-MS analysis. β-caryophyllene (32.5%) and α-humulene (17.8%) were the most abundant components. The evaluation of free radical scavenging activity using stable DPPH free radical showed that the volatile oil exhibits a moderate antioxidant activity and reduces DPPH to 50% at EC₅₀ value of 1230 μg mL^? 1.     

Synthesis and structure of the unsymmetrical β-diimine precursor: The β-iminoamine

The reaction of benzoylacetone with ortho-substituted aniline derivatives gives the unsymmetrical β-iminoamine ligands (5–8) with high yields. A convenient synthesis is described. These compounds have been characterized by NMR and IR spectroscopies. The structure of the β-iminoamine 5, 3-N-(2,6-diisopropylphenylamino)-1-phenyl-1N-(2,6-diisopropylphenylimino)but-2-ene, was solved by X-ray diffraction methods.     

Echiofruzine, a novel naringenin diglycoside from Echiochilon fruticosum growing in Tunisia

The aerial parts of the Tunisian plant Echiochilon fruticosum yielded a novel flavonol diglycoside: naringenin-5-O-beta-D-glycopyranoside-3-O-alpha-L-rhamnopyranoside, named Echiofruzine (1), together with the known compounds vomifoliol-9-O-beta-D-glucopyraroside (2), 1-oxo-alpha-ionyl-9-O-beta-D-glucopyranoside (3) and 1-O-[beta-D-xylopyranosyl(1 --> 6)-beta-D-glucopyranosyl] eugenol (4), described for the first time in the indicated plant. The structures of the four isolated compounds were established on the basis of chemical and spectroscopic evidence.     

The effect of conjugation length distribution on the properties of modified PPV

The aim of this work was to demonstrate the optical properties of a copolymer involving alternating poly(para-phenylene–vinylene) and ether groups derived from the conjugation length distribution. For this, the time-dependent density functional theory (TD-DFT) was used. Thus, different conjugation lengths were considered, where the correlation of the corresponding theoretical spectra, including Raman, optical absorption and photoluminescence, allows us to conclude that the conjugation length distribution is caused by a random distribution of the ether blocks. The weight of each conjugation length representing its contribution is shown by the use of the Raman spectra. Furthermore, the theoretical spectra arising from the response of different conjugation lengths are obtained and compared with the experimental ones.     

Switchable Lipids: Conformational Change for Fast pH‐Triggered Cytoplasmic Delivery

We report the use of switchable lipids to improve the endosomal escape and cytosolic delivery of cell‐impermeable compounds. The system is based on a conformational reorganization of the lipid structure upon acidification, as demonstrated by NMR spectroscopic studies. When incorporated in a liposome formulation, the switchable lipids triggered bilayer destabilization through fusion even in the presence of poly(ethylene glycol). We observed 88 % release of sulforhodamine B in 15 min at pH 5, and the liposome formulations demonstrated high stability at pH 7.4 for several months. By using sulforhodamine B as a model of a highly polar drug, we demonstrated fast cytosolic delivery mediated by endosomal escape in HeLa cells, and no toxicity.