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.     

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.     

Crystal Growth and Structural Characterization of a Thiocyanato-Bridged Copper(I/II) Mixed-Valence Coordination Polymer

Crystallography Reports - A new mixed-valence coordination polymer [Cu3(SCN)4(DMSO)2] n (SCN– = thiocyanato and DMSO = dimethyl sulfoxide) was prepared and characterized by single crystal...     

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.     

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.     

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.     

Adjacency based method for generating maximal efficient faces in multiobjective linear programming

Multiobjective linear optimization problems (MOLPs) arise when several linear objective functions have to be optimized over a convex polyhedron. In this paper, we propose a new method for generating the entire efficient set for MOLPs in the outcome space. This method is based on the concept of adjacencies between efficient extreme points. It uses a local exploration approach to generate simultaneously efficient extreme points and maximal efficient faces. We therefore define an efficient face as the combination of adjacent efficient extreme points that define its border. We propose to use an iterative simplex pivoting algorithm to find adjacent efficient extreme points. Concurrently, maximal efficient faces are generated by testing relative interior points. The proposed method is constructive such that each extreme point, while searching for incident faces, can transmit some local informations to its adjacent efficient extreme points in order to complete the faces’ construction. The performance of our method is reported and the computational results based on randomly generated MOLPs are discussed.     

Essential Spectra of a 3 × 3 Operator Matrix and an Application to Three-Group Transport Equations

In this paper we study spectral properties of a 3 × 3 block operator matrix with unbounded entries and with domain consisting of vectors which satisfy certain relations between their components. It is shown that, under certain conditions, this block operator matrix defines a closed operator, and the essential spectra of this operator are determined. These results are applied to a three-group transport equation.