Microscopic aspects of the effect of friction reducers at the lubrication limit

An attempt is made to analytically model the physicochemical properties of lubricants and their capacity to reduce friction. A technique of frozen fracturing of the lubricants was employed to study the dispersion of additives throughout a lubricant. Adsorption was observed at the liquid-solid interface, which was the region where the solid and lubricant met, and the molecular dispersion of the additive enhanced the effectiveness of the lubricant. The electrically conductive characteristics of the lubricant at the friction interface indicated the presence of tunneling effects. The Bethe model was used to examine the relationship between the coefficient of friction and the variation of interface thickness. The electron transport permitted an inelastic tunnel electron spectroscopic investigation of the molecular transformations undergone by the additive during friction episodes

alpha,beta-Unsaturated 2-Acyl-Imidazoles in Asymmetric Biohybrid Catalysis

International audienceα,β‐Unsaturated acylimidazoles have been used in a plethora of enantioselective transformations over the years and have unsurprisingly become privileged building blocks for asymmetric catalysis. Interestingly however, their use in asymmetric biohybrid catalysis as bidentate substrates able to interact with artificial metalloenzymes has only recently emerged, expanding considerably in the last few years. Easy to prepare and to post‐transform, α,β‐unsaturated acylimidazoles appear as leading synthons for the asymmetric construction of C−C and C−O bonds. This Minireview highlights the current and increasing interest of these key building blocks in the context of asymmetric biohybrid catalysis with the aim to stimulate further research into their still unexploited potential. The use of these α,β‐unsaturated acylimidazoles in metal‐catalyzed and organocatalyzed transformations will be covered in a back‐to‐back Minireview by Renata Marcia de Figueiredo, Jean‐Marc Campagne and co‐workers

DNA-Based Asymmetric Inverse Electron-Demand Hetero-Diels-Alder

International audienceWhile artificial cyclases hold great promise in chemical synthesis, this work presents the first example of a DNA-catalyzed inverse electron-demand hetero-Diels-Alder (IEDHDA) between dihydrofuran and various α,β-unsaturated acyl imidazoles. The resulting fused bicyclic O,O-acetals containing three contiguous stereogenic centers are obtained in high yields (up to 99 %) and excellent diastereo- (up to >99:1 dr) and enantioselectivities (up to 95 % ee) using a low catalyst loading. Most importantly, these results show that the concept of DNA-based asymmetric catalysis can be expanded to new synthetic transformations offering an efficient, sustainable, and highly selective tool for the construction of chiral building blocks

Tribological properties of room temperature fluorinated graphite heat-treated under fluorine atmosphere

This work is concerned with the study of the tribologic properties of room temperature fluorinated graphite heat-treated under fluorine atmosphere. The fluorinated compounds all present good intrinsic friction properties (friction coefficient in the range 0.05–0.09). The tribologic performances are optimized if the materials present remaining graphitic domains (influenced by the presence of intercalated fluorinated species) whereas the perfluorinated compounds, where the fluorocarbon layers are corrugated (armchair configuration of the saturated carbon rings) present higher friction coefficients. Raman analyses reveal that the friction process induces severe changes in the materials structure especially the partial re-building of graphitic domains in the case of perfluorinated compounds which explains the improvement of μ during the friction tests for these last materials

DNA‐Templated [2 2] Photocycloaddition: A Straightforward Entry into the Aplysinopsin Family of Natural Products

Biosynthetic considerations inspired us to harness the template properties offered by DNA to promote a [2+2] photo‐induced cycloaddition. The method was developed based on the dimerization of (E)‐aplysinopsin, which was previously shown to be unproductive in solution. In sharp contrast, exposure of this tryptophan‐derived olefin to light in the presence of salmon testes DNA (st‐DNA) reproducibly afforded the corresponding homo‐dimerized spiro‐fused cyclobutane in excellent yields. DNA provides unique templating interactions enabling a singular mimic of the solid‐state aggregation necessary for the [2+2] photo‐cycloaddition to occur. This method was ultimately used to promote the prerequisite dimerizations leading to both dictazole B and tubastrindole B, thus constituting the first example of a DNA‐mediated transformation to be applied to the total synthesis of a natural product.Agence Nationale de la Recherche for financial support (D-CYSIV project; ANR-2015-CE29-0021-01)

Contribution to the understanding of tribological properties of graphite intercalation compounds with metal chloride

Intrinsic tribological properties of lamellar compounds are usually attributed to the presence of van der Waals gaps in their structure through which interlayer interactions are weak. The controlled variation of the distances and interactions between graphene layers by intercalation of electrophilic species in graphite is used in order to explore more deeply the friction reduction properties of low-dimensional compounds. Three graphite intercalation compounds with antimony pentachloride, iron trichloride and aluminium trichloride are studied. Their tribological properties are correlated to their structural parameters, and the interlayer interactions are deduced from ab initio bands structure calculations

Effect of Operating and Sampling Conditions on the Exhaust Gas Composition of Small-Scale Power Generators

Small stationary diesel engines, like in generator sets, have limited emission control measures and are therefore responsible for 44% of the particulate matter (PM) emissions in the United States. The diesel exhaust composition depends on operating conditions of the combustion engine. Furthermore, the measurements are influenced by the used sampling method. This study examines the effect of engine loading and exhaust gas dilution on the composition of small-scale power generators. These generators are used in different operating conditions than road-transport vehicles, resulting in different emission characteristics. Experimental data were obtained for gaseous volatile organic compounds (VOC) and PM mass concentration, elemental composition and nitrate content. The exhaust composition depends on load condition because of its effect on fuel consumption, engine wear and combustion temperature. Higher load conditions result in lower PM concentration and sharper edged particles with larger aerodynamic diameters. A positive correlation with load condition was found for K, Ca, Sr, Mn, Cu, Zn and Pb adsorbed on PM, elements that originate from lubricating oil or engine corrosion. The nitrate concentration decreases at higher load conditions, due to enhanced nitrate dissociation to gaseous NO at higher engine temperatures. Dilution on the other hand decreases PM and nitrate concentration and increases gaseous VOC and adsorbed metal content. In conclusion, these data show that operating and sampling conditions have a major effect on the exhaust gas composition of small-scale diesel generators. Therefore, care must be taken when designing new experiments or comparing literature results

Quantitative study of irradiation damage in organo-metallic colloidal particles

Irradiation damage in colloidal particles of lead isooctanoate are investigated by means of time resolved low dose Electron Diffraction and Electron Energy Loss Spectroscopy. Both structural and chemical transformations are studied. The kinetic of the irradiation damage process is interpreted using a chemical type approach which allows us to deduce the partial orders relative to the lead isooctanoate concentration and electron dose rate.Une étude des dégâts d'irradiation subis par des particules colloidales d'isooctanoate de plomb est réalisée au moyen de la diffraction électronique et de la spectroscopie de pertes d'énergie d'électrons transmis résolues dans le temps. L'étude porte à la fois sur les transformations structurales et chimiques provoquées par le faisceau d'électrons. Les résultats sont interprétés en utilisant une approche de type cinétique chimique qui nous permet de déduire les ordres partiels de réaction relatifs à la concentration d'isooctanoate de plomb et au taux d'irradiation

I. Jubault In-situ Pressure Measurements Using Raman Microspectroscopy in a Rolling Elastohydrodynamic Contact

The physical conditions (pressure, shear stress, temperature