Organocatalyzed Aldol Reaction between Pyridine‐2‐carbaldehydes and α‐Ketoacids: A Straightforward Route towards Indolizidines and Isotetronic Acids

Enantioselective aldol reactions between substituted pyridine carbaldehydes and α‐ketoacids were shown to provide isotetronic acids or their corresponding pyridinium salts, depending on the nature of the substituents on the pyridine ring. The pyridinium salts were generated through nucleophilic attack of the pyridine nitrogen atom onto the reactive keto functional group. Moderate‐to‐good yields of both compounds were typically obtained and high levels of enantioselectivity were observed by using benzimidazole pyrrolidine I as a catalyst. Hydrogenation of the resulting pyridinium salts led to new indolizidines with high ee values and diastereocontrol. X‐ray diffraction studies allowed the determination of the relative configuration of the products. Finally, DFT calculations were performed to rationalize the divergent pathway as a function of the pyridine substituents.     

Thermal yellowing sensitised by pre-photo-oxidation of non-deacidified paper

Characterization of oxidation products responsible for yellowing of paper through absorption and through emission is presented using independently UV-visible absorption spectrophotometry and microspectrofluorimetry to survey the thermal oxidation at 100 °C and the photo-oxidation at λ ≥ 340 nm and at 60 °C of the three types of paper containing low amount of ligneous residues (SA papers) or not (WH and C papers). It was shown that due to secondary oxidation yellowing of product is favoured in the dark. It was shown that pre-photo-oxidation largely increased the yellowing in the dark. The effect of pre-photo-oxidation on yellowing through absorption and on yellowing through emission was shown to be different.     

Combined XRD and infrared studies of pyridinium species in (PyH)(3)[PW(12)O(40)] single crystals

The pyridinium salts of 12-tungstophosphoric acid (PyH)(3)[PW(12)O(40)]·2CH(3)CN (1) and (PyH)(3)[PW(12)O(40)] (2) have been prepared and studied by single crystal and powder X-ray diffraction (XRD) in order to characterize the crystallographic sites occupied by the pyridinium species. The three PyH(+) species are located on two unequivalent sites. Two species are linearly H-bonded to the oxygen atoms of the Keggins unit (α species), whereas the third one (β) forms a bent H-bond. In order to determine the infrared bands characterizing each type of pyridinium species in the 1650-1300 cm(-1) range, infrared spectra have been recorded from room temperature to 100 K. They reveal that only α pyridinium species give rise to the unusual splitting of the PyH(+)ν8b and ν19b modes, whereas β pyridinium species lead to a classical pyridinium spectrum.     

Hydrogen oxidation reaction at the Ni/YSZ anode of solid oxide fuel cells from first principles

By means of ab initio simulations we here provide a comprehensive scenario for hydrogen oxidation reactions at the Ni/zirconia anode of solid oxide fuel cells. The simulations have also revealed that in the presence of water chemisorbed at the oxide surface, the active region for H oxidation actually extends beyond the metal/zirconia interface unraveling the role of water partial pressure in the decrease of the polarization resistance observed experimentally.     

Tunable magnetic properties of nanoparticle two-dimensional assemblies addressed by mixed self-assembled monolayers

Assemblies of magnetic nanoparticles (NPs) are intensively studied due to their high potential applications in spintronic, magnetic and magneto-electronic. The fine control over NP density, interdistance, and spatial arrangement onto substrates is of key importance to govern the magnetic properties through dipolar interactions. In this study, magnetic iron oxide NPs have been assembled on surfaces patterned with self-assembled monolayers (SAMs) of mixed organic molecules. The modification of the molar ratio between coadsorbed 11-mercaptoundecanoic acid (MUA) and mercaptododecane (MDD) on gold substrates is shown to control the size of NPs domains and thus to modulate the characteristic magnetic properties of the assemblies. Moreover, NPs can be used to indirectly probe the structure of SAMs in domains at the nanometer scale.     

Influence of nitrogen implantation on thermoluminescence of synthetic quartz

Thermoluminescence (TL) of synthetic quartz exposed to beta irradiation following implantation with 60?keV N⁺ ions at fluences ranging between 1?×?10¹⁴ and 5?×?10¹⁵?ions/cm² is reported. The glow curve measured at 5°C/s typically consists of a prominent peak near 110°C, studied in this work, and minor glow peaks at around 130°C and 190°C. The TL intensity of the main peak increased both with implantation and with fluence of implantation. The dependence of the intensity on heating rate and fluence suggests that the implantation introduces new defects that may possibly act as recombination centres. The increase in TL intensity with the heating rate exhibited by implanted samples has been observed in other luminescence materials. This anti-quenching phenomenon has been described as a competition effect between multiple luminescence pathways in luminescence materials. Kinetic analysis of the main glow peak using the initial rise, various heating rate and glow curve deconvolution methods shows that the activation energy of the main peak is about 0.7?eV with no systematic change due to ion fluence.     

Frottement interne dans le zirconium irradie aux neutrons A 77 K

Abstract

Le zirconium présente après irradiation neutronique à 77 K sept pics de frottement interne. Les deux premiers correspondent à la réorientation complexe de [icaron]interstitiel libre migrant à trois dimensions en fin de stade I. Le dipole élastique créé par cet interstitiel est monoclinique et sa réorientation complexe donne lieu à un pic dissocié conforme aux prévisions de Nowick. Ce défaut disparait par migration tridimensionnelle en fin de stade I et annihilation correlée puis non correlée. Les autres pics correspondent à des processus intrinsèques (réorientation de petits amas ?interstitiels, bilacune) ou extrinsèques avec intervention ?impuretés ou dc dislocations.

Ces pics ne sont pas fortement affectés par les impuretés.

Seven internal friction peaks are found in 77 K neutron irradiation zirconium. The first and second peaks correspond to the free interstitial reorientation and migration at the end of stage I. The elastic dipole created by this interstitial is monoclinic and its complex reorientation gives rise to “frozen free split” phcnomena predicted by Nowick. This defect disappears by correlated and uncorrelated annihilation after tridimensional migration at the end of stage I. The other peaks correspond either to intrinsic phenomena (interstitial loops, divacancies) or extrinsic processcs involving impurity or dislocation.

These peaks are not strongly affected by impurities.