Spectroscopies and Electron Microscopies Unravel the Origin of the First Colour Photographs

The first colour photographs were created by a process introduced by Edmond Becquerel in 1848. The nature of these photochromatic images colours motivated a debate between scientists during the XIX^th century, which is still not settled. We present the results of chemical analysis (EDX, HAXPES and EXAFS) and morphology studies (SEM, STEM) aiming at explaining the optical properties of the photochromatic images (UV-visible spectroscopy and low loss EELS). We rule out the two hypotheses (pigment and interferences) that have prevailed since 1848, respectively based on variations in the oxidation degree of the compound forming the sensitized layer and periodically spaced photolytic silver planes. A study of the silver nanoparticles dispersions contained in the coloured layers showed specific localizations and sizes distributions of the nanoparticles for each colour. These results allow us to formulate a plasmonic hypothesis on the origin of the photochromatic images colours.     

Methods to Study Naphthenate Formation in w/o Emulsions by the Use of a Tetraacid Model Compound

Precipitation of naphthenate salts is normally a problem in the processing of acidic crude oils. In this study, the goal was to find suitable methods to investigate the interfacial reaction between tetraacid and calcium under emulsified conditions. Two different systems have been studied depending on composition and applied shear. The influence of inhibitors has been investigated and the same inhibitor was found to be the most effective one regardless of the system. Depletion of tetraacid in the oil phase was analyzed with UV-vis and HPLC. Interfacial area and droplet size in the emulsions were measured with fluorescence microscope and pulse-field gradient NMR. Since this reaction takes place over the interface, the investigation clearly documents, the importance of the total interfacial area of the emulsified system.     

Paper strengthening by polyaminoalkylalkoxysilane copolymer networks applied by spray or immersion: a model study

Two di-alkoxysilanes, with (AMDES, aminopropylmethyldiethoxysilane) or without (DMDES, dimethyldiethoxysilane) an amine function, and a tri-alkoxy aminosilane (APTES, aminopropyltriethoxysilane) as well as their mixtures were introduced in paper as fiber strengthening agents. The polymerization and copolymerization of these polysiloxanes in the paper were investigated. In all the cases where APTES was present, the formation of networks was established by measuring the soluble fraction amount extracted from the treated papers. A slight decrease of the opacity of the paper sheets when AMDES was part of the treatment was noted. The presence of APTES reduced this opacity loss. The study of the physicochemical properties of the treated paper (mechanical strength and alkalinity) demonstrated that, besides the required deacidification feature, the different treatments allowed an efficient strengthening of the cellulose fibers to various extents. Contact angle measurements indicated a decrease of the hydrophilic character of papers treated with the mixture APTES/AMDES and the occurrence of a hydrophobic character of the papers treated with APTES alone. These results were consistently obtained for both spray and immersion treatment processes.     

Ketopiperazines: Conformationally Constrained Peptidomimetic of Arginine Amides

We have synthesized guanidine‐containing ketopiperazines designed to be conformational mimics of peptidomimetic arginine amides. D‐Allylglycine was converted by an efficient approach to give enantiopure ketopiperazines in which the trans stereochemistry of the C‐substituents resulted from stereospecific enolate alkylation.     

Spectroscopies and Electron Microscopies Unravel the Origin of the First Colour Photographs

The first colour photographs were created by a process introduced by Edmond Becquerel in 1848. The nature of these photochromatic images colours motivated a debate between scientists during the XIX^th century, which is still not settled. We present the results of chemical analysis (EDX, HAXPES and EXAFS) and morphology studies (SEM, STEM) aiming at explaining the optical properties of the photochromatic images (UV‐visible spectroscopy and low loss EELS). We rule out the two hypotheses (pigment and interferences) that have prevailed since 1848, respectively based on variations in the oxidation degree of the compound forming the sensitized layer and periodically spaced photolytic silver planes. A study of the silver nanoparticles dispersions contained in the coloured layers showed specific localizations and sizes distributions of the nanoparticles for each colour. These results allow us to formulate a plasmonic hypothesis on the origin of the photochromatic images colours.     

Synthèse et étude de modèles de NADH à noyaux accolés en série pyrrolo[2,3-b] et [3,2-b]pyridines

Pyrrolo[2,3-b] and [3,2-b]pyridines derivatives, precursors for annealated NADH models have been prepared. Several methods for building a pyridinic annealates ring have been used starting from 2- or 3-aminopyrrole. The corresponding dihydropyridine structure leads to highly reactive NADH models compounds and are very much more stable than common models.     

Powder preparation and UV absorption properties of selected compositions in the CeO2-Y2O3 system

Several approaches have been investigated to prepare fluorite-type compositions within the (1−x) CeO₂-xYO_1.5 system. The optical properties of the resulting modified-ceria materials have been characterized in order to evaluate their potential abilities as inorganic UV absorbers. Diffuse reflectance analyses reveal a strong optical absorption between 390 and 400 nm for all substituted compositions and the spectral selectivities are estimated suitable for the targeted application. Additionally, time resolved microwave conductivity (TRMC) and phenol photodegradation analyses do not indicate any photocalatytic activity for these compositions. Aqueous colloidal suspensions of the Ce_0.7Y_0.3O_1.85 UV absorber have been carried out.     

State-specific reactions and autoionization dynamics of Ar produced by synchrotron radiation

The long-lived excited states of doubly charged rare gases can markedly affect their reactivity. In this paper we demonstrate the presence of strong state-specific effects in the charge exchange of Ar²⁺ (³P, ¹D and ¹S) with several neutral targets (He, Ne, Kr, Xe, D₂, and CH₄). State sensitive measurements have been performed by producing the different Ar²⁺ electronic states via tunable synchrotron radiation (Elettra-Trieste, Italy and SuperACO-Orsay, France). From the product ion yield data of charge transfer, state-selected total cross-sections have been deduced. Using the state-specific reactivity of Ar²⁺ towards different neutral targets, it has been possible to extract the photon-energy-dependent production branching of the three doubly charged states and to investigate the autoionization dynamics of neutral or singly charged Ar in the vicinity of the double ionization threshold.