University of Rennes

About: University of Rennes is a education organization based out in Rennes, France. It is known for research contribution in the topics: Population & Catalysis. The organization has 18404 authors who have published 40374 publications receiving 995327 citations.

Transformations in oxides induced by high-energy ball-milling

Abstract: This paper, by no means exhaustive, focuses on high-energy ball-milling of oxides, on their mechanically induced changes and on the consequences of such changes on their physical and chemical properties. High-energy ball-milling offers a fortunate combination of technical simplicity and of complexity both of physical mechanisms which act during milling and of mechanosynthesized materials. Its basic interest, which stems from the large diversity of routes it offers to prepare oxides either directly or indirectly, is illustrated with various families of oxides. The direct path is to be favoured when as-milled oxides are of interest per se because of their nanocrystalline characteristics, their defects or their modified structures which result from mechanically driven phase transformations. The indirect path consists of a sequence of steps starting with mechanically activated oxides which may be subsequently just annealed or submitted to a combination of thermal treatments, with the possible occurrence of various chemical reactions, to prepare the sought-after materials with potential gains in processing temperatures and times. High energy ball-milling of oxides is more and more currently used to activate powders and to prepare nano-oxides at moderate temperatures. The interest of an activation step is well illustrated by the broad development of doped titania powders, synthesized by heat treatment of pre-ground reactants, for photocatalytic applications or to develop antibacterial materials. Another important class of applications of high-energy ball-milling is the formation of composites. It is exemplified here with the case of oxide-dispersed strengthened alloys whose properties are considerably improved by a dispersion of ultra-stable nanosized oxides whose formation mechanisms were recently described. The basic understanding of the mechanisms by which oxides or oxide mixtures evolve by high-energy ball-milling appears to be less advanced than it is for metallic materials essentially because of the overall complexity of the oxide structures, of their surfaces, of their defects and of their mechanical behavior.

Involvement of gelatinases (MMP-2 and MMP-9) in the development of airway inflammation and pulmonary fibrosis.

Abstract: Pulmonary fibrosis has an aggressive course and is usually fatal an average of 3 to 6 years after the onset of symptoms Pulmonary fibrosis is associated with deposition of extracellular matrix (ECM) components in the lung interstitium Matrix metalloproteinases (MMPs) are a major group of proteinases known to regulate the ECM remodeling and so they are hypothesized to be important in the process of lung fibrosis These led to the concept that modulation of airway remodeling including excessive proteolytic damage of the tissue may be of interest for future treatment The excessive airway remodeling as a result of an imbalance in the equilibrium of the normal processes of synthesis and degradation of extracellular matrix components could argue in favor of antiprotease treatments Moreover, these observations emphasize that effective therapies for these disorders must be given early in the natural history of the disease, prior to the development of expensive lung destruction and fibrosis

Polynuclear carbon-rich organometallic complexes: clarification of the role of the bridging ligand in the redox properties.

Abstract: In this Perspective, we highlight the non-innocent behaviour of the bridging ligand in organometallic polynuclear metallic complexes displaying metal-carbon σ bonds between the metallic units and a strongly coupled conjugated carbon-rich bridging ligand. With the help of representative experimental and theoretical studies on polymetallic systems, but also on monometallic complexes, we point out that the level of implication of the carbon rich ligand in the redox processes is very sensitive to the nature of (i) the metal(s), (ii) the ancillary ligands and (iii) the carbon-rich ligand itself, and that this participation is frequently found to be major. Consequently, the general denomination M((n + 1)) that is usually used for oxidized species gives the picture that only the metal density is affected, which is misleading. Moreover, for polymetallic species, these elements make the mixed valence denomination and the use of standard methodologies to rationalize intramolecular electron transfer, such as the Hush model inaccurate. Indeed, these theoretical treatments of mixed-valent complexes have at their core the assumption of metal-based redox state changes. Quantum mechanical calculations, coupled with spectroscopic methods, such as EPR spectroscopy, turn out to be a valuable suite of tools to both identify and better describe those systems with appreciable ligand redox non-innocent character. Finally, some examples and perspectives of applications for this carbon-rich type of complexes that take advantage of their peculiar electronic structure are presented.