Hydrogen activation on Mo-based sulfide catalysts,a periodic DFT study

Hydrogen adsorption on Mo[bond]S, Co[bond]Mo[bond]S, and Ni[bond]Mo[bond]S (10 1 macro 0) surfaces has been modeled by means of periodic DFT calculations taking into account the gaseous surrounding of these catalysts in working conditions. On the stable Mo[bond]S surface, only six-fold coordinated Mo cations are present, whereas substitution by Co or Ni leads to the creation of stable coordinatively unsaturated sites. On the stable MoS(2) surface, hydrogen dissociation is always endothermic and presents a high activation barrier. On Co[bond]Mo[bond]S surfaces, the ability to dissociate H(2) depends on the nature of the metal atom and the sulfur coordination environment. As an adsorption center, Co strongly favors molecular hydrogen activation as compared to the Mo atoms. Co also increases the ability of its sulfur atom ligands to bind hydrogen. Investigation of surface acidity using ammonia as a probe molecule confirms the crucial role of sulfur basicity on hydrogen activation on these surfaces. As a result, Co[bond]Mo[bond]S surfaces present Co[bond]S sites for which the dissociation of hydrogen is exothermic and weakly activated. On Ni[bond]Mo[bond]S surfaces, Ni[bond]S pairs are not stable and do not provide for an efficient way for hydrogen activation. These theoretical results are in good agreement with recent experimental studies of H(2)[bond]D(2) exchange reactions.     

Specific fibre composition and metabolism of the <Emphasis Type="Italic">rectus abdominis</Emphasis> muscle of bovine Charolais cattle

Background  

An important variability of contractile and metabolic properties between muscles has been highlighted. In the literature, the majority of studies on beef sensorial quality concerns M. longissimus thoracis. M. rectus abdominis (RA) is easy to sample without huge carcass depreciation and may appear as an alternative to M. longissimus thoracis for fast and routine physicochemical analysis. It was considered interesting to assess the muscle fibres of M. rectus abdominis in comparison with M. longissimus thoracis (LT) and M. triceps brachii (TB) on the basis of metabolic and contractile properties, area and myosin heavy chain isoforms (MyHC) proportions. Immuno-histochemical, histochemical, histological and enzymological techniques were used. This research concerned two populations of Charolais cattle: RA was compared to TB in a population of 19 steers while RA was compared to LT in a population of 153 heifers.     

Electronic structures of electron-rich octahedrally condensed transition-metal chalcogenide clusters

The electronic structures of some electron-rich octahedrally condensed transition-metal chalcogenide clusters are analyzed with the aid of extended Hückel and density functional molecular orbital calculations. A simple orbital approach is developed to analyze the electron counts of these clusters, which do not obey any existing electron-counting rules. Different electron counts are allowed, depending upon the nature of the metal. Optimal counts are discussed. Metal-metal bonding is generally weak in these species. Consequently, their structural arrangements are mainly governed by metal-ligand interactions.     

Retrosynthetic analysis of fullerene C(60): structure, stereochemistry, and calculated stability of C(30) fragments.

The total number of possible retrosynthetic bisections of C(60) leads to nine different isometric C(30) fragments. These molecules include five chiral units, four of which derive from partitions corresponding to four distinct "Coupes du Roi". The energies, curvatures, and homodesmotic stabilization energies of the C(30) fragments are evaluated at the ab initio 6-31G level.     

α'β-Elimination and wittig rearrangement of the carbanion from benzyl cyclooctyl ether

Beside the Wittig rearrangement and the migration of the cyclooctyl radical to the para position, the title carbanion gives rise to an elimination in a syn process.     

Théorie des processus stochastiques généraux applications aux surmartingales

Sans résuméCe nous est un très agréable devoir d'adresser ici nos plus vifs remerciements à Monsieur J. Paris qui a bien voulu, avec une bienveillance toute particulière, veiller au meilleur déroulement de ce travail, partie de notre thèse de doctorat défendue à l'Université Catholique de Louvain.Nous sommes également très reconnaissants à Monsieur P.A. Meyer, qui nous a signalé la seconde partie du théorème 12.     

The electronic structure of sulphur chloride penta-fluoride

The electronic structure of SCIF₅ is computed within the framework of the CNDO/2 approximation on the basis of Kewley's microwave geometrical data and is compared with our previous results on SF₆. The charge distribution and the value of the dipole moment are discussed as a function of the F-S-F_ax angle and an inversion of the net charge on Cl is observed when passing through the 95° value for (F-S-F_ax) angle.     

Simple enantiospecific syntheses of the C(2)-diastereomers of omuralide and 3-methylomuralide

[reaction: see text] Syntheses of two novel omuralide derivatives are described.