Chimie
Computational insights about the dynamic behavior for the inclusion process of deprotonated and neutral aspirin in β-cyclodextrin
Molecular dynamics was used to study the inclusion of neutral and deprotonated aspirin into the β-cyclodextrin (β-CD) cavity. The molecular dynamic simulation allows following the time dependent behavior of the formation of the inclusion complex. For both complexes, we find a reasonable and a realistic pattern of the complexation. The calculations show a single pathway consisting of a no reversible binding process leading to the complexation of aspirin. Whereas for deprotonated aspirin it has been observed a reversible binding, in which one way leads to the binding form, and the reverse way to the unbinding form. Throughout the simulation, the penetration of aspirin (ASA) or deprotonated aspirin (ASA−) inside the cavity occurs only with a phenyl ring entering first through the wider or narrower rim. The determination of free energy using unbiased and biased simulations of the corresponding inclusion processes gives more favorable inclusion process of aspirin than deprotonated aspirin. The inclusion of the guest molecule is found deeply embedded within ASA:β-CD complex whereas it is partial in ASA−:β-CD complex. Also, the orientation A of both complexes is found more favorable of ca. 1.9 kcal/mol, and of ca. 0.8 kcal/mol, respectively for neutral and deprotonated complex. Aspirin molecule establish one H-bond between the hydrogen carboxylic atom and one oxygen atom of primary hydroxyl group of β-CD; this H-bond is detected during about 20% of the simulation period. In addition, we found that water molecules in the first solvation layer are implied with hydrogen carboxylic atom and the keto oxygen atoms within H-bonds. While, water molecules of the second solvation layer is in interact with the O1 and O2 oxygen atoms of aspirin. Accordingly, based on the obtained results we can consider that the hydrophobic/hydrophilic interactions are the most important driving forces of the complexation assisted by stabilizing H-bonds. Voir les détails
Mots clés : Aspirin, Cyclodextrin, Inclusion complexes, Molecular dynamic simulation, Umbrella sampling, Hydrogen bonding
Core-rim structure formation in TiC-Ni based cermets fabricatedby a combined thermal explosion/hot-pressing process
TiC-Ni-based cermets were obtained by thermal explosion from different elemental mixtures(Ti, C, Ni and X, where X = Cr, Mo or W) and subsequently densified by hot-pressing under acyclic load. The whole process was performed in a single stage in the same experimentaldevice according to the following thermal and pressure procedure: a heating rate ramp up to1573 K without applying any load followed by an isothermal dwelling under a compressivecyclic load of 32 MPa. The thermal explosion synthesis occurred during the heating ramp at atemperature close to 1273 K that was practically independent of the starting nominalcomposition. The influence of different refractory elements on the chemical composition andmicrostructure of cermets was studied. SEM characterization showed that only with Mo andW, the cermets developed the characteristic core-rim structure. A high densification wasachieved, but decreased when the refractory elements were added. Nevertheless, in thesecases higher hardness values were obtained. Voir les détails
Mots clés : Cermets, Thermal explosion, Core-rim microstructure, Solid-solution carbides
Photocatalytically-assisted electrooxidation of herbicide fenuron usinga new bifunctional electrode PbO2/SnO2-Sb2O3/Ti//Ti/TiO2
The degradation of the herbicide fenuron was investigated using a new porous bifunctional electrodewhere the electrooxidation takes place on one side and the photocatalysis on the other side. The characterizationof the synthetized bifunctional electrode (PbO2/SnO2-Sb2O3/Ti//Ti/TiO2) was performed byscanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction analysis andshowed that the anodic side (Ti/SnO2-Sb2O3/PbO2) is covered with a tetragonal b-PbO2 film and that thephotocatalytic side (Ti/TiO2) consists of an anatase phase of TiO2. The single application of electrooxidationachieved 87.8% fenuron degradation and 84.1% chemical oxygen demand (COD) removal whileheterogeneous photocatalysis resulted in only 59.2% and 39.7% fenuron concentration decay and CODremoval, respectively. On the other hand, the photocatalytically-assisted electrooxidation (photo-electrooxidation)performed on the bifunctional electrode provided higher performances of fenurondegradation (97.5%) and mineralization (97.4%). Investigation of operating parameters highlighted thepositive effect of increase in current density. Conversely, an increase in fenuron concentration led to adecrease in degradation rate and COD removal. It was also found that the COD removal and mineralizationefficiency are higher in a neutral medium. Voir les détails
Mots clés : Fenuron Bifunctional electrode Lead dioxide anode Electrooxidation Photo-electrooxidation
ZnO nanoparticles and biocidal effect of nanostructured ZnO filmson Escherichia coli
The biocidal effect of ZnO nanostructured films was studied using Escherichia coli ATCC 43897. TheZnO nanoparticles were synthesized in diethylene glycol by using zinc acetate forced hydrolysis.X-ray diffraction analysis confirmed the formation of single wurtzite-type ZnO phase with a crystallitesize of 20.59 nm. Transmission electron microscopy observations revealed spherical-shaped particlesin the nanoscale regime with a mean particle size of 21.96 nm. It was found that the addition oftrioctylphosphine during synthesis favored much improved dispersion of ZnO nanoparticles, withsmaller particle size; that is, 16.28 nm. Meanwhile, ZnO film grown onto glass substrate by spin-coatingrevealed single phase with the formation of aggregates (≈700) having mushroom-like morphologyformed of very fine particles in the nanoscale regime. The as-deposited nanostructured films exhibiteda hydrophilic character. The classical bacteriological and electrochemical impedance spectroscopymeasurements enabled the biocidal effect of ZnO nanostructured films with 94% inactivation efficiencyafter 90 min of contact time. Voir les détails
Mots clés : ZnO; Spin-coating; Nanostructured film; Biocide effect; E. coli; EIS
Study of thin Films of Nickel Oxide (NiO) Deposited bythe Spray Pyrolysis Method
Abstract: In this work, thin films of nickel oxide (NiO) were deposited by a simple and inexpensive technique, which is spraypyrolysis on ordinary glass substrates heated to a fixed temperature of 500 °C, from a solution containing nickel nitrate hexahydrateas a precursor dissolved in distilled water with deferent values of concentrations. The NiO thin films obtained were characterized todetermine the structure with X-ray diffraction technique (XRD), the absorption domain (UV-Visible Spectroscopy), and the surfacemorphology (SEM). The X-ray diffraction patterns confirm the presence of NiO phase with preferential orientation along the (111)direction. The optical gap for nickel oxide calculated with a concentration of 0.1 M from the measurement of optical absorption is 3.6eV, which is quite comparable to the value of the ratio. Voir les détails
Mots clés : NiO, Thin films, Spray pyrolysis
Electrochemical behavior, characterization and corrosion protection properties of poly(bithiophene + 2-methylfuran) copolymer coatings on A304 stainless steel
Polybithiophene (PBTh), poly(2-methylfuran) (PMeFu) and poly(bithiophene + 2-methylfuran) noted poly(BTh + MeFu) copolymer films were synthesized by electrochemical deposition on 304-stainless steel, from an acetonitrile (ACN) solution containing 10−2 m bithiophene, 10−2 m 2-methylfuran and 10−1 m lithium perchlorate (LiClO4), by cyclic voltammetry (CV) between 0 V and 2 V vs. SCE, with a scan rate of 50 mV · s−1. The copolymers coated were studied in a corrosive sulfuric acid medium (H2SO4 1 N) using the potensiodynamique polarization method and the electrochemical impedance spectroscopy (EIS). Copolymers coated characterization was performed using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The polarization curves show that the copolymer film formed on A304, shifts the corrosion potential towards more positive potentials. The presence of the poly(BTh + MeFu) improves the corrosion resistance of the metal in a corrosive medium, H2SO4. This protection against corrosion is caused by the barrier effect of the layer of copolymer, which covers the surface of the A304 stainless steel against the aggressive ions of the corrosive medium. Voir les détails
Mots clés : 2-methylfuran, bithiophene, copolymers, protection against corrosion, stainless steel.
Simulation and Modeling of Uncertainties in the Calibration
Sensitivity analysis and uncertainty estimation are ofmajor importance for the declaration of conformity of finishedproducts. Models must be sought to analyze the test data. Themain objective of this work is to establish reliable models toanalyze our experimental data and validate them. So we havestudied and used the Monte Carlo and Bootstrap simulationmethods, we have been able to realize programs that calculate theuncertainty according to the ISO 8466 standard on X-rayfluorescence spectrometer samples from the URASM CRTIchemical analysis laboratory. Programs and interfaces are madewith Matlab (GUI). Voir les détails
Mots clés : simulation, Uncertainties, Monte Carlo, Bootstrap, calibration
Elaboration and characterization of ITO electrode modi?ed bytransition metal dispersed into polyaniline thin ?lms
This work presents the characteristics of composite materials thin ?lms of polyaniline (PAni) andnickel (Ni) particles deposited onto indium tin oxide (ITO) substrate. The electropolymerizationof aniline was performed in acidic medium by potentiodynamic methods. The nickel particleswere electrochemically deposited on the surface of PAni/ITO by reducing metal ions (Ni) usinga potentiostatic method from a separate solution. The e?ect of applied potential as well as immersingtime of complexation on the amount of nickel dispersed was investigated. Di?erentcharacterization techniques were employed to study the electrochemical behavior and surfacecharacteristics of the Ni-PAni/ITO thin ?lms such as Electrochemical Impedance Spectroscopy(EIS), Cyclic Voltammetry, Fourier Transform Infrared Spectroscopy (FTIR), UV–visSpectroscopy, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM).The morphology of the obtained composites shows a uniform dispersion of nickel particlesonto the polyaniline matrix and reveals that the immersing times of complexation has a signi?cante?ect on the amount of incorporated particles. The impedance spectroscopy study revealsthat the conductivity of the composite ?lm increases with the amount of nickel incorporated.UV–vis and FTIR results con?rm the presence of PAni and Ni particles on theelectrode surface. Voir les détails
Mots clés : polyaniline, Electro-polymerization, Nickel particles, Chronoamperometry, Materials composites
Synthèse, caractérisation et analyse des propriétés électrochimique et spectroscopiques des films de copolymères issus du : bithiophène et methyl-2furanne
Ce travail porte sur la synthétisé et la caractérisation électrochimique et spectroscopique des films de copolymère obtenus à partir de deux monomères conjugués; le bithiophène et le mèthyl-2furanne. L’électrocopolymérisation a été effectuée par voltampérométrie cyclique (cyclage), sur des électrodes (platine, ITO, acierA304), en milieu acétonitrile/LiClO4, contenant les deux monomères. Les films obtenus sont caractérisés par voltampérométrie cyclique(VC), spectroscopie d’impédance électrochimique (SIE), MEB, EDX, UV-visible et par photoélectrochimie.L’analyse des films obtenus par voltampérométrie cyclique montre des pics anodiques et cathodiques caractéristiques de l’oxydation et de la réduction des copolymères formés. L’étude par spectroscopie d’impédance montre que les propriétés électriques du film varient avec la concentration des deux monomères présents en solution. Les films de copolymère électrodéposé sur l’acier A304 ont été testés comme revêtement protecteurs, dans deux milieux corrosifs (H2SO4 et NaCl).Un déplacement du potentiel de corrosion vers des valeurs positives par rapport à celui de l’acier est observé. Ceci indique que le copolymère obtenu est de type anodique. L’efficacité inhibitrice de ce revêtement a été montrée par le tracé des courbes de Tafel, par une diminution de courant de corrosion, attestant que la présence de ce copolymère sur l’acier A304 améliore sa tenue à la corrosion. Voir les détails
Mots clés : bithiophène, methyl-2furanne, copolymère, électropolymérisation, photocourant, tenue à la corrosion
Etude des propriétés thermodynamiques des fluides pures
notre travail d'étude des propiétés thermodynamiques des fluides pures dans la région critique s'est porté sur le (propane, n-heptane, et l'Argon)pour leurs importances technologques et industrielles.nous appliquons lemodéle de Crossoversur les données expérimentales, pression, température et masse volumique(Ρ,ρ,Τ).les analyses nous ménent a la détermination d'un systéme de paramétre dépendant de chaque substance a fin d'établire une équation d'état.l'ajustement des paramétres éxperimentales de chaleure spécifique isochorique et isobarique(Cv et Cp), permet de déterminer les paramétres calorifiques pour l'obtention d'une équation fondamentale, la fiabilité du modéle de Crossover est vérifiée par la comparaison avec des mesures expérimentales, notre travail s'étend aussi a l'étude de la coexistence liquide vapeur des fluides étudiés,un programme de calcul sur ordinateur, basé sur un langage FORTRON est utilisé. Voir les détails
Mots clés : équation d'état, modéle de crossover, coexistence, fluides pures