Experimental and theoretical study for corrosion inhibition of mild steel in normal hydrochloric acid solution by some new macrocyclic polyether compounds

International audienceNew macrocyclic polyether compounds containing a 1,3,4-thiadiazole moiety have been prepared to study the corrosion inhibitive effect of mild steel in normal hydrochloric acid solutions. The salient features obtained from weight loss and electrochemical impedance spectroscopy (EIS) have been discussed. The results of these investigations have shown enhancement in inhibition efficiencies with the extent of the polyethylene glycol unit that forms a cavity. Data obtained from EIS show a frequency distribution and therefore a modelling element with frequency dispersion behaviour, a constant phase element (CPE) has been used

Structural insights into Lewis acid- and F4TCNQ-doped conjugated polymers by solid-state magnetic resonance spectroscopy

International audienceMolecular doping strategies facilitate orders of magnitude enhancement in the charge carrier mobility of organic semiconductors (OSCs). Understanding the different doping mechanisms and molecular-level constraints on doping efficiency related to the material energy levels is crucial to develop versatile dopants for OSCs. Given the compositional and structural heterogeneities associated with OSC thin films, insight into dopant–polymer interactions by long-range techniques such as X-ray scattering and electron microscopy is exceedingly challenging to obtain. This study employs short-range probes, solid-state (ss)NMR and EPR spectroscopy, to resolve local structures and intermolecular interactions between dopants such as F4TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane), Lewis acid BCF (tris[pentafluorophenyl] borane) and Lewis base conjugated polymer, PCPDTBT (P4) (poly[2,6-(4,4-bis(2-hexadecyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)]). Analysis of 1H and 13C ssNMR spectra of P4, P4 : F4TCNQ and P4 : BCF blends indicates that the addition of dopants induces local structural changes in the P4 polymer, and causes paramagnetism-induced signal broadening and intensity losses. The hyperfine interactions in P4 : BCF and P4 : F4TCNQ are characterized by two-dimensional pulsed EPR spectroscopy. For P4 : F4TCNQ, 19F ssNMR analysis indicates that the F4TCNQ molecules are distributed and aggregated into different local chemical environments. By comparison, BCF molecules are intermixed with the P4 polymer and interact with traces of water molecules to form BCF–water complexes that serve as Brønsted acid sites, as revealed by 11B ssNMR spectroscopy. These results indicate that the P4–dopant blends exhibit complex morphology with different distributions of dopants, whereby the combined use of ssNMR and EPR provides essential insights into how higher doping efficiency is observed with BCF and a mediocre efficiency is associated with F4TCNQ molecules

Complexes à transfert de charge entre l’iode et MOFs à base de titane MIL-125 et MIL-125(NH2)

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The influence of some new 2,5-disubstituted 1,3,4-thiadiazoles on the corrosion behaviour of mild steel in 1M HCl solution: AC impedance study and theoretical approach

International audienceThe new 2,5-disubstituted 1,3,4-thiadiazoles were investigated as corrosion inhibitors of mild steel in 1 M HCl using AC impedance technique. Four of these compounds exhibit good inhibition properties, while two of them, 2,5-bis(4-nitrophenyl)-1,3,4-thiadiazole and 2,5-bis(4-chlorophenyl)-1,3,4-thiadiazole, stimulate the corrosion process especially at low concentrations. The experimental data obtained from this method show a frequency distribution and therefore a modelling element with frequency dispersion behaviour, a constant phase element (CPE) has been used. Possible correlations between experimental inhibition efficiencies and quantum chemical parameters such as dipole moment (μ), highest occupied (EHOMO) and lowest unoccupied (ELUMO) molecular orbitals were investigated. The models of the inhibitors were optimised with the Density Functional Theory formalism (DFT) using hybrid B3LYP/6-31G (2d,2p) as a higher level of theory. The Quantitative Structure Activity Relationship (QSAR) approach has been used and composite index of some quantum chemical parameters were constructed in order to characterize the inhibition performance of the tested molecules

Induced effect of tungsten incorporation on the catalytic properties of CeVO 4 systems for the selective reduction of NO x by ammonia

International audienceThe SCR performances of aged W-doped CeVO4 catalysts were investigated in fast-, NO2- and standard conditions. Bulk CeV1-xWxO4 catalysts were prepared in soft conditions, according to a hydrothermal synthesis route at 180 °C leading to the ad hoc tetragonal structure. The aging procedure consisted in exposing the samples to 10 vol.% H2O diluted in air at 600 °C. The impact of this aging process was investigated as a function of tungsten loading, with x varying in the range 0.02–0.15. A clear beneficial effect is distinguishable at high temperature, i.e., above 300 °C, associated to a sharp selectivity enhancement irrespective of the operating conditions and tungsten loading. On the contrary, a slight detrimental effect on the reaction rate is clearly discernible in standard-conditions below 300 °C. It was found that the thermal aging induces more extensive diffusion of V5+ species assisted by the presence of substituted W6+. It was also demonstrated that tungsten diffuses more readily than V5+ leading ultimately to a significant surface enrichment and the formation of Ce4W9O33 mixed oxide evidenced from XRD and Raman spectroscopy. Hence, tungsten would rather act as a stabilizer than promoter avoiding the sintering of monomeric VOx species to more active polyvanadate species but also less selective. The gain observed in selectivity at high temperature can be equally explained by a greater stabilization of Brønsted acid sites and the preservation of the dispersion of monomeric vanadate species preventing the occurrence of ammonia oxidation

Understanding the adsorption of 4 H -1,2,4-triazole derivatives on mild steel surface in molar hydrochloric acid

International audienceThis study examines the use of some 4H-triazole derivatives, namely 3,5-diphenyl-4H-1,2,4-triazole (DHT), 3,5-bis(4-pyridyl)-4H-1,2,4-triazole (4-PHT) and 3,5-bis(4-methyltiophenyl)-4H-1,2,4-triazole (4-MTHT) for corrosion and dissolution protection of mild steel in normal hydrochloric acid solution. The inhibiting efficiency of the different additives is evaluated by means of weight loss and electrochemical techniques such as ac impedance measurements and polarisation curves. The experimental results obtained reveal that 4-MTHT is the best effective inhibitor and the inhibition efficiency is found to be in the following order: 4-MTHT > 4-PHT > DHT. The variation in inhibitive efficiency mainly depends on the type and nature of the substituents present in the inhibitor molecule. Polarisation curves show that theses triazoles are mixed-type inhibitors in 1 M HCl. The inhibition efficiency increases with 4H-triazole derivatives concentration and attains the maximum value of 99.6% in the case of 4-MTHT at 5 × 10−4 M. The results obtained from weight loss electrochemical studies were in reasonable agreement. The adsorption of 4H-triazole derivatives on the steel surface obeys to the Langmuir isotherm model. The thermodynamic data of adsorption and activation are determined and discussed. The fundamental thermodynamic functions were used to glean important information about the 4H-triazoles inhibitory behaviour. Molecular modeling was used to get better insight, about structural and electronic effects in relation to the inhibition efficiencies

Proanthocyanidin microcapsules: preparation, properties and free radical scavenging activity

International audienceMicrocapsules were prepared by interfacial cross-linking of grape proanthocyanidin (GPO) with terephthaloyl chloride (TC). Using 5% TC, 30-min reaction time and a stirring speed of 5000 rpm, batches were prepared from 10% GPO solutions in buffers pH 8, 9.8, and 11, respectively. Microcapsules were studied with respect to morphology (microscopy), size (laser diffraction technique), stability in water at 45°C and, for stable batches, IR spectroscopy, degradation in human plasma, and free radical scavenging activity studied by electron paramagnetic resonance (EPR) using both extinction of the stable radical DPPH (2,2-diphenyl-picryl-hydrazyl), and scavenging of OH° (evaluated using 5,5-dimethyl-pyrrolidine-N-oxide; DMPO). All particles had a mean size 5 months). Using a stirring speed of 3000 rpm at pH 11 provided 15-μm particles which gave a yellow supernatant after 3 weeks. The IR spectra of the two stable batches (pH 9.8 and 11) showed bands at 1736 and 1267 cm−1 reflecting the formation of esters. They were slowly degraded in plasma, and although less active than the initial GPO, they exhibited a significant antioxidant activity. The method appears to be an efficient means of stabilizing the polyphenol without suppressing the free radical scavenging activity

Impact of Thermal Aging on the SCR Performance of Tungsten Doped CeVO4 Mixed Oxides

International audienceThe development of more thermally stable vanadia-based SCR catalysts for combined end-of-pipe technologies, i.e. selective catalytic reduction catalysts wash-coated on a particulate filter, has been considered in this study. The impact of thermal aging at 850 °C in wet atmosphere has been investigated on bulk W-doped CeVO4 catalysts. Strong detrimental effect on the specific surface area was observed delayed by the presence of tungsten. However, they preserve a significant selective conversion depending on the surface composition with an optimal tungsten composition

The Camptothecin-Resistant Topoisomerase I Mutant F361S Is Cross-Resistant to Antitumor Rebeccamycin Derivatives. A Model for Topoisomerase I Inhibition by Indolocarbazoles

International audienceDNA topoisomerase I is a major cellular target for antitumor indolocarbazole derivatives (IND) such as the antibiotic rebeccamycin and the synthetic analogue NB-506 which is undergoing phase I clinical trials. We have investigated the mechanism of topoisomerase I inhibition by a rebeccamycin analogue, R-3, using the wild-type human topoisomerase I and a well-characterized recombinant enzyme, F361S. The catalytic activity of this mutant remains fully intact, but the enzyme is resistant to inhibition by camptothecin (CPT). Here we show that the mutated enzyme is cross-resistant to the rebeccamycin analogue. Despite their profound structural differences, CPT and R-3 interfere similarly with the activity of the wild-type and mutant topoisomerase I enzymes, and the drug-induced cleavable complexes are equally sensitive to the NaCl concentration. CPT and IND likely recognize identical structural elements of the topoisomerase I−DNA covalent complex; however, differences do exist in terms of sequence-specificity of topoisomerase I-mediated DNA cleavage. For the first time, a molecular model showing that CPT and IND share common steric and electronic features is proposed. The model helps to identify a specific pharmacophore for topoisomerase I inhibitors