Tayssir Hamieh

Chemical Composition, Antibacterial and Antioxidant Activities of Six Essentials Oils from the Alliaceae Family

Six essential oils (EOs) from the Alliaceae family, namely garlic (Allium sativum), onion (Allium cepa), leek (Allium porrum), Chinese chive (Allium tuberosum), shallot (Allium ascalonicum) and chive (Allium schoenoprasum) were characterized by GC and GC-MS and evaluated for their functional food properties. Antibacterial properties were tested on five food-borne pathogens: Two Gram-positive Staphylococcus aureus (ATCC 25923), Listeria monocytogenes (ATCC 19115) and three Gram-negative Salmonella Typhimurium (ATCC 14028), Escherichia coli (ATCC 8739) and Campylobacter jejuni (ATCC 33291) bacteria. Antioxidant and radical-scavenging properties were tested by means of Folin-Ciocalteu and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays. Garlic, Chinese chive and onion EOs had the highest antibacterial activity whereas shallot and leek EOs were the strongest antioxidants. Heating caused a decrease in the antioxidant activity of these Eos, as shown in the Total Polar Materials (TPM) test. Suggestions on relationships between chemical composition and biological activities are presented. Results show that the EOs could be of value in the food industry as alternatives to synthetic antioxidants.

New approach to characterise physicochemical properties of solid substrates by inverse gas chromatography at infinite dilution. II. Study of the transition temperatures of poly(methyl methacrylate) at various tacticities and of poly(methyl methacrylate) adsorbed on alumina and silica.

The determination of the temperature transitions in polymers and more particularly when polymers are adsorbed on oxides is very important in many industrial processes. In this second part, we used inverse gas chromatography (IGC) at infinite dilution to determine the second order transition temperatures of poly(methyl methacrylate) (PMMA) adsorbed (or not) on alumina or on silica. Three types of PMMA were used: atactic (a), syndiotactic (syndio) and isotactic (iso). The IGC technique allowed to obtain the net retention volume Vn and the dispersive component of the surface energy gamma(s)d for various theoretical models of molecules, using the results of Part I. By plotting RT ln Vn as a function of (1/T) or gamma(s)d as a function of the temperature T, we proved the presence of three particular temperatures that correspond respectively to the transition temperature relative to beta-relaxation (Tbeta), the glass transition temperature (Tg), and the liquid-liquid transition temperature or order-disorder transition (T1.1). Results obtained in this part allowed us to show the effect of the tacticity of PMMA and the recovery fraction of polymer adsorbed on alumina or silica on the transition temperatures.

New approach to characterise physicochemical properties of solid substrates by inverse gas chromatography at infinite dilution. I. Some new methods to determine the surface areas of some molecules adsorbed on solid surfaces.

This study was divided into three different parts that tried to give a new contribution to determine and quantify more precisely the superficial properties of solid substrates (polymers and/or oxides) obtained by inverse gas chromatography (IGC) at infinite dilution. It criticised certain of the classical methods and relationships used to determine some physico-chemical properties of a solid and gave new methods and equations that can be more precise and more realistic. Part I developed some new methods to determine the surface areas of some molecules adsorbed on solids. A theoretical calculation of surface areas of molecules adsorbed on solid substrates was proposed by using some theoretical models. Two new methods to determine the surface areas of polar molecules were developed. The first one consists of the determination of surface areas by coupling two classical methods, the dynamic contact angle and IGC techniques. The second new and general method, using the IGC technique, assumes that the specific interactions between a polar molecule and a solid proposed by Papirer and Schultz are the same. A new equation was obtained to determine the surface areas of polar molecules.

New approach to characterise physicochemical properties of solid substrates by inverse gas chromatography at infinite dilution. III. Determination of the acid-base properties of some solid substrates (polymers, oxides and carbon fibres): a new model.

In this paper, the inverse gas chromatography (IGC) technique was used to calculate the acid-base superficial characteristics of some solid substrates such as oxides, polymer and polymer adsorbed on oxide. The acid-base constants were calculated for many solids: Monogal, MgO, ZnO, SiO2 and Al2O3, four different carbon fibres and polymers such as poly(methyl methacrylate) (PMMA) at various tacticities adsorbed on alumina or silica. The determination, by IGC, of the specific free enthalpy deltaG(a)sp of adsorption corresponding to the specific interactions of polar molecules with the solid, as a function of the temperature, allowed to obtain the specific enthalpy deltaH(a)sp and specific entropy deltaS(a)sp. Knowing deltaH(a)sp of the various polar molecules, we were able to determine the acidic constant K(A) and basic constant K(D), the two constants characterizing solid substrates like PMMA, PMMA-SiO2 or PMMA-Al2O3, using the following classical expression: - deltaH(a)sp = K(A)DN + K(D)AN where DN and AN are respectively the electron donor and acceptor numbers of the solid substrates. This study showed an important effect of the tacticity on the acid-base properties. On the other hand, we proved that the previous relation was not correct in many cases and especially for some oxides (as MgO, ZnO and Monogal) and carbon fibres. We proposed a new relationship by adding a third parameter K reflecting the amphoteric character of the solid according to: - deltaH(a)sp = K(A)DN + K(D)AN - KDN x AN.

Study of acid-base interactions between some metallic oxides and model organic molecules

Abstract Inverse gas chromatography technique at infinite dilution was used to calculate the acidic and basic surface characteristics of three oxides (Monogal, MgO and ZnO). We determined the specific interactions between them and model organic molecules and showed the amphoteric feature of such oxides. It was observed that MgO is more basic than the others. We also proved that the usual relation giving the specific enthalpy of adsorption (Δ H sp ) of a polar molecule adsorbed on a solid: (−Δ H sp )=( K A DN+ K D AN) was not correct. We proposed a new relationship by adding a third parameter K reflecting the amphoteric character of the solid according to: (−ΔHsp)= K A DN+ K D AN− KANDN We proved that our model gives the best results relatively to those obtained by the classical equation. Another relationship was also proposed: (−Δ H sp)= w ( K A DN+ K D AN) where w is the weighing factor of the exchanging interactions between adsorbed molecule and solid substrate.

Effect of mineral impurities on the charge and surface potential of coal: Application to obtaining concentrated suspensions of coal in water

Abstract The surface charge of pulverized coal particles in water at different pH values was studied and the surface potential was shown to reach —50 mV at 20°C. The surface charge essentially originates from the presence of mineral impurities. The effect of these mineral impurities on the surface potential of the coals was then studied: the point of zero charge was a direct function of the SiO2/ Al2O3 molar ratio of the mineral impurities contained in the coal (linear dependency). These mineral impurities have a majority effect in creating an electric double-layer shell around the coal particles. Having found this, we were able to prepare stable, fluid concentrated suspensions (up to 72% coal by weight) in water in the presence of sodium tripolyphosphate and sodium lignosulfonate, which are also stabilizers and thinners of concentrated suspensions of clay (drilling muds, for example).

Copper photoredox catalysts for polymerization upon near UV or visible light: structure/reactivity/efficiency relationships and use in LED projector 3D printing resins

Copper complexes (CuCs) bearing pyridine–pyrazole ligands are synthesized and evaluated as new photoredox catalysts/photoinitiators in combination with an iodonium salt (Iod) for the free radical polymerization of (meth)acrylates and the cationic polymerization of epoxides upon visible light exposure using a Light Emitting Diode (LED)@405 nm. The structure/reactivity/efficiency relationships for the copper complexes are studied as well as the chemical mechanisms involved. The different substituents on the pyrazole moiety of the ligand allow tuning of the oxidation potential and the visible light absorbance of the complexes and to optimize the performance of the polymerization photoredox catalysts. The use of a novel additive (CARET) in a three-component system (CuC/Iod/CARET) highly improves the performance. Finally, the high performances of the Cu(I) complexes for the development of new 3D printing resins using an LED projector are demonstrated. Currently, LED projector printing is really advantageous in 3D printing i.e. this technology projects the profile of an entire layer at one time.

Photoinitiating systems of polymerization and in situ incorporation of metal nanoparticles into polymer matrices upon exposure to visible light: push–pull malonate and malononitrile based dyes

Novel push–pull dyes containing a (substituted) hydrocarbon moiety and a malonate (or a malononitrile) moiety are proposed as photoinitiators for the ring opening polymerization of epoxides as well as the synthesis of interpenetrated polymer networks (IPNs) upon exposure to visible light (laser diode, halogen lamp, etc.). Excellent polymerization profiles are obtained. The role of the acceptor and donor moieties in these dyes towards their light absorption properties, the associated photochemical processes and their photoinitiating ability is investigated. A very efficient dye has been selected for the reduction of Ag+ and the in situ formation of Ag(0) nanoparticles in the synthesized IPNs.

Adsorption kinetics and equilibrium of phenol drifts on three zeolites

In this study, the sorption of phenol drifts was studied by performing batch kinetic sorption experiments. The equilibrium kinetic data was analyzed using the pseudo-second-order kinetic model. Fowler-Guggenheim model gives a perfect fitting with the isotherm data. The influence of porous structure of a zeolite particle on phenol adsorption from aqueous solutions is analyzed and discussed. The adsorption for phenol drifts on zeolite was proved to be an exothermic process. Thus the solubility of the phenolic compound and the pH of the solution play also an important role in adsorption phenomena.The relative affinity of the phenolic compound toward the zeolite was related to the electron donor-acceptor complexes that were formed between the basic sites on the zeolite (oxygen) and hydrogens (acidic site) of the phenols. Finally zeolite seems to be an efficient adsorbent; it can be easily regenerated by methanol leaching.

Influence of Substrate Properties on the Dewetting Dynamics of Viscoelastic Polymer Films

We studied the dewetting process of thin polystyrene (PS) films on silicon substrates, coated with a thin, irreversibly adsorbed polydimethylsiloxane (PDMS) layer, by optical microscopy and atomic force microscopy. Besides demonstrating the exceptional potential of dewetting for a sensitive characterization of rheological properties of PS thin films, characterized by a stress-relaxation time, τ1, we focused on the influence of the frictional behaviour (energy dissipation mechanism) at the interface between the PDMS-coated silicon wafer and the PS film on the dewetting process. Our results show that the initial stages of dewetting depend sensitively on the thickness and the way the PDMS layer was adsorbed. The maximum width of the dewetting rim at τ1 increased with increasing PDMS layer thickness, which can be interpreted as an increase of the effective, velocity-dependent slippage length. Interestingly, τ1 was found to be almost independent of the substrate properties. Our results demonstrate that dewetting is a really powerful approach for rheological and frictional studies of thin polymer films.