Kinetics of the reactions of CH3O with Cl and CIO

The kinetics of the reactions CH₃O + Cl → H₂CO + HCl (1) and CH₃O + ClO → H₂CO + HOCl (2) have been studied using the discharge-flow techniques. CH₃O was monitored by laser-induced fluorescence, whereas mass spectrometry was used for the detection or titration of other species. The rate constants obtained at 298 K are: k₁ = (1.9 ± 0.4) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and k₂ = (2.3 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. These data are useful to interpret the results of the studies of the reactions of CH₃O₂ with Cl and ClO which, at least partly, produce CH₃O radicals. © 1996 John Wiley & Sons, Inc.     

Enzyme-catalyzed syntheses of poly(1,6-hexanediyl maleate) and poly(1,6-hexanediyl fumarate) in organic medium

The lipase-catalyzed preparation of poly(1,6-hexanediyl maleate) by transesterification of 1,6-hexanediol and dimethyl maleate is described. A configurationally pure poly(1,6-hexanediyl maleate) exhibiting exclusively cis structure was obtained. During the reaction, a substantial amount of macrolactones was formed. They were isolated, and the cyclic oligomer with y = 2 was found to predominate. Cycles are semi-crystalline, while no melting point was detected for the linear poly(1,6-hexanediyl maleate). We assume that the linear unsaturated polyester is completely amorphous owing to its cis configuration.     

A Constraint Programming Framework for Local Search Methods

We propose in this paper a novel integration of local search algorithms within a constraint programming framework for combinatorial optimization problems, in an attempt to gain both the efficiency of local search methods and the flexibility of constraint programming while maintaining a clear separation between the constraints of the problem and the actual search procedure. Each neighborhood exploration is performed by branch-and-bound search, whose potential pruning capabilities open the door to more elaborate local moves, which could lead to even better approximate results. Two illustrations of this framework are provided, including computational results for the traveling salesman problem with time windows. These results indicate that it is one order of magnitude faster than the customary constraint programming approach to local search and that it is competitive with a specialized local search algorithm.     

A Review of Manganese(III) (Oxyhydr)Oxides Use in Advanced Oxidation Processes

The key role of trivalent manganese (Mn(III)) species in promoting sulfate radical-based advanced oxidation processes (SR-AOPs) has recently attracted increasing attention. This review provides a comprehensive summary of Mn(III) (oxyhydr)oxide-based catalysts used to activate peroxymonosulfate (PMS) and peroxydisulfate (PDS) in water. The crystal structures of different Mn(III) (oxyhydr)oxides (such as α-Mn₂O₃, γ-MnOOH, and Mn₃O₄) are first introduced. Then the impact of the catalyst structure and composition on the activation mechanisms are discussed, as well as the effects of solution pH and inorganic ions. In the Mn(III) (oxyhydr)oxide activated SR-AOPs systems, the activation mechanisms of PMS and PDS are different. For example, both radical (such as sulfate and hydroxyl radical) and non-radical (singlet oxygen) were generated by Mn(III) (oxyhydr)oxide activated PMS. In comparison, the activation of PDS by α-Mn₂O₃ and γ-MnOOH preferred to form the singlet oxygen and catalyst surface activated complex to remove the organic pollutants. Finally, research gaps are discussed to suggest future directions in context of applying radical-based advanced oxidation in wastewater treatment processes.     

Helix‐Forming Oligoureas: Temperature‐Dependent NMR,Structure Determination,and Circular Dichroism of a Nonamer with Functionalized Side Chains

To further investigate the degree of structural homology between γ‐peptides A and N,N′‐linked oligoureas B , we prepared oligourea nonamer 2 containing Ala, Val, Leu, Phe, Tyr and Lys side chains. Oligomer 2 was synthesized on solid support from activated monomers, i.e., from enantiomerically pure succinimidyl {2‐{[(9H‐fluoren‐9‐ylmethoxy)carbonyl]amino}ethyl}carbamates 3a – f that are further substituted at C(2) of the ethyl moiety. These precursors were conveniently prepared from N‐Fmoc‐protected β³‐amino acids with corresponding side chains. Detailed NMR studies (DQF‐COSY, TOCSY, and ROESY) in (D₅)pyridine revealed that 2 adopts a regular (P)‐2.5 helical secondary structure very similar to that previously determined for oligourea heptamer 1 and closely related to the (P)‐2.6₁₄ helix of γ‐peptides. Temperature‐dependent NMR further demonstrated the conformational homogeneity and remarkable stability of the structure of 2 in pyridine. The CD spectrum of 2 (0.2 mM ) was recorded in MeOH with the aim to gain more information about the conformation of oligoureas. In contrast to 2.6‐helical γ‐peptides, which display only a weak or no Cotton effect, oligourea 2 exhibits an intense positive Cotton effect at ca. 203 nm ([Θ]=+373000 deg cm² dmol⁻¹) that decreases only slowly upon increasing the temperature.     

Enhanced Degradation of Paracetamol by the Fe(III)-Sulfite System under UVA Irradiation

The Fe(III)-S(IV) system used for advanced oxidation processes (AOPs) at acidic pH has just been proposed and demonstrated valid for very few contaminants in the last several years. In this work, we investigated the effect of ultraviolet A (UVA) radiation on the degradation efficiency of the Fe(III)/S(IV) system at near-neutral pH. Paracetamol (PARA) was selected as a model contaminant. The influencing factors, such as initial pH and Fe(III)/S(IV) molar ratio on chemical kinetics, and the mechanism of PARA degradation are investigated, with an emphasis on the determination of dominant oxidant species. Our results show that irradiation enhances the PARA degradation by accelerating the decrease of pH to acidic levels, and the optimal pH for the degradation of PARA in the Fe(III)/S(IV)/O₂ system was around 4.0. At near-neutral pH, more than 60% of PARA was decomposed within 40 min under irradiation, whereas no significant degradation of PARA was observed using Fe(III)/S(IV) at pH 7.0 without irradiation. Mechanism investigation revealed that sulfate radical (SO₄^•‒) is the main oxidant species generated and responsible for the PARA degradation under these conditions. This finding may have promising implications in developing a new degradation process for dealing with wastewater at near-neutral pH by the Fe(III)/S(IV)/O₂ system under UVA irradiation.     

Elucidating the Color of Rosé Wines Using Polyphenol-Targeted Metabolomics

The color of rosé wines is extremely diverse and a key element in their marketing. It is due to the presence of anthocyanins and of additional pigments derived from them and from other wine constituents. To explore the pigment composition and determine its links with color, 268 commercial rosé wines were analysed. The concentration of 125 polyphenolic compounds was determined by a targeted metabolomics approach using ultra high-performance liquid chromatography coupled to triple quadrupole mass spectrometry (UHPLC-QqQ-MS) analysis in the Multiple Reaction Monitoring (MRM) mode and the color characterised by spectrophotometry and CieLab parameters. Chemometrics analysis of the composition and color data showed that although color intensity is primarily determined by polyphenol extraction (especially anthocyanins and flavanols) from the grapes, different color styles correspond to different pigment compositions. The salmon shade of light rosé wines is mostly due to pyranoanthocyanin pigments, resulting from reactions of anthocyanins with phenolic acids and pyruvic acid, a yeast metabolite. Redness of intermediate color wines is related to anthocyanins and carboxypoyranoanthocyanins and that of dark rosé wines to products of anthocyanin reactions with flavanols while yellowness of these wines is associated to oxidation.     

Mise au point et caracterisation de mousses syntactiques

Syntactic foams are manufactured to provide buoyancy to submarine devices. Last investigations were realized to study new syntactic foams which can be employed until six thousand meters deep. The syntactic materials made by S.N.P.E. are used mainly to buoy submarine devices and so, have to withstand very high pressures. So their components have to be made of high performance elements, thus, we employ epoxy matrices who possess low viscosity for wetting and casting easier. Fillers are glass microspheres, the average diameter of which are in the range of 50 to 100 μm. In order to use syntactic materials for this application the thermal and mechanical behaviour of some syntactic foams was characterized. We show some results of the syntactic foams. An other group of tests has been done in order to study the damage of the materials during an increase of the hydrostatic pressure. These tests have been conducted in a qualitative way in order to show the different eventual damage mechanisms. Also in the future syntactic materials have common interests with structural composite materials, hence we can assess their importance in the future, particularly in submarine projects.