Synthesis,proton NMR stereochemical study and diels-alder reaction of (E)-7-arylidene-2H,6H-naphtho[1,8-bc]furan-2,6-diones

7-Arylidene-2H,6H-naphtho[1,8-bc]furan-2,6-diones 3 were prepared by a retro-Diels-Alder reaction of the corresponding dihydro 1,3-oxazines 2 or in a one pot synthesis from 6-hydroxy-2H-naphtho[1,8-bc]furan-2-one 1 . Their E configuration was established from the chemical shift's values of the vinylic proton and by ¹H nmr NOE difference spectroscopy. Cycloadditions of 3b upon styrene or stilbene were catalyzed by boron trifluoride etherate. The cycloadducts were obtained with the relative trans configuration.     

Characterization of an Algerian diatomite by inverse gas chromatography: Specific and non-specific contribution and Lewis acid–base parameters

The fundamental understanding of the behavior of a solid is intimately related to the understanding of the interactions on the surface of the latter, a major challenge in particular if the material is natural and ecological. The infinite dilution-inverse gas chromatography was used to evaluate the surface thermodynamic properties of several phases (grafted and/or coated) diatomite. A series of non- or polar-solute probes were injected at temperatures of 45?°C and 90?°C. The dispersive surface free energies values of the supports decrease with increasing temperature and their active surface is amphoteric with predominantly acidic character.     

Comparison of multicomponent fuel droplet vaporization experiments in forced convection with the Sirignano model

The vaporization of multicomponent fuel droplets was studied experimentally in a heated flow and the results were compared to the model proposed by Abramzon and Sirignano. The droplet was suspended on a permanent holder which was set up in a thermal wind-tunnel. This wind-tunnel was fitted with a video recording system and an infra-red camera. The period during which the droplet was suspended on the holder before the opening of the hot air flow damper was recorded. This first sequence corresponds to the droplet vaporization in natural convection, whose initial experiment conditions, especially diameter, temperature, composition of the droplet, are well known. Then the damper was turn on, and the sequence of forced convection begun. The initial diameter of the droplet was recorded by the video system. The other initial conditions of this second sequence cannot be determined experimentally. The distribution of temperature in the droplet and the surface temperature, the mass fraction distribution in the droplet and the surface mass fraction were unknown. These unknown parameters were determined by coupling our experiment with a model using “the film concept” in natural convection. Experimental results were compared with the calculations and found satisfactory, in natural convection as well as in forced convection initiated by this method. The method was tested in the case of a fuel mixture droplets (heptane–decane) for different initial concentrations and variable durations of the sequence in natural convection.     

Influence of the anode material on an argon arc

The interaction between the arc and the anode was experimentally studied by means of a transferred arc burning in argon with copper, iron, or steel anodes. Depending on the rate of anode cooling, a stable plasma was obtained just above the anode, established either in pure argon (strong cooling) or in a mixture of argon with metal vapor. Temperature and metal concentration fields were deduced from spectroscopic measurements. Two important results were reached: the arc radius near the anode depends on the nature of the electrode, even without anode erosion; and the presence of metal vapor leads to a cooling of the plasma. The same arc configurations were theoretically simulated by a two-dimensional model. The comparison between experimental and numerical results allows a large proportion of the observed phenomena to be interpreted, in spite of partial discrepancies between predicted and measured values. The dimension of the arc root at the anode depends on the thermal conductivity of the solid metal, whereas the cooling effect due to metal vapor in the plasma is explained by the increases of electrical conductivity and of radiative losses in the presence of the vapor     

Intégrales orbitales sur les algèbres de Lie réductives

Sans résuméOblatum 28-I-1992 & 13-VII-1992     

Hydroxytyrosol Acyl Esters: Biosynthesis and Activities

We previously reported the production of high yields of hydroxytyrosol through the bioconversion of tyrosol. In the present work, hydroxytyrosol was subjected to the lipase catalyzed acylation aiming for the recovery of more lipophilic esters that might be easily incorporated in cosmetic and food preparations. Hydroxytyrosyl acetate and hydroxytyrosyl oleate were produced with respective molar esterification yields of 98% and 78%. DPPH free radical quenching potency demonstrated that the acylation of hydroxytyrosol did not alter its antioxidant activity. The acylated esters were shown to be more effective than the natural antioxidant: caffeic acid and two synthetic ones as BHA and BHT. Antiproliferative activity on human cervical cells (HeLa) resulted in IC₅₀ values of 0.46, 0.42 and 0.33 mM for hydroxytyrosol and its acetyl and oleyl esters, respectively. Additionally, when used at a non-cytotoxic concentration (100 μM), these compounds showed significant effectiveness in preventing iron-induced oxidative stress, resulting in a reduction of 30%, 36% and 38% in thiobarbituric acid-reactive substance production, respectively.     

Investigation of the dissociation pathways of metolachlor, acetochlor and alachlor under electron ionization - application to the identification of ozonation products

With the future aim of using gas chromatography coupled with mass spectrometry to characterize the transformation products of ozonated herbicides: metolachlor, acetochlor and alachlor, an interpretation of their electron ionization mass spectra is presented. Fragmentation mechanisms are proposed on the basis of isotopic labelling and multiple-stage mass spectrometry experiments carried out on an ion trap mass spectrometer. We also give examples in order to demonstrate how the elucidation of such fragmentation mechanisms for herbicides may simplify the characterization of their ozonation products.