Une généralisation de la théorie de brönsted en chimie analytique

The proposal is made that all reactions be considered as corresponding to the exchange of particles (particules).1. Exchange of electrons between an oxidising agent and a reducing agent. This is the classical conception of oxidation-reduction reactions.2. Exchange of ions (or of polar molecules) between an “acceptor” of the ion and a “donor” of the same ion. In the case of exchange of protons the reaction is one between acids and bases, according to Brönsted.The majority of reactions concern the exchange of different ions. It is proposed to apply to these reactions, and that for each type of particle exchanged, the type of reasoning which Brönsted has used for the exchange of protons.The analogy thus created between the different types of reactions leads to a considerable simplification. It allows identical reasoning and the use of similar formulations for all reactions.Further, the distinction between reactions in terms of the nature of the particle exchanged permits recognition of the respective influence of the factors which are available for controlling the reactions.It is suggested that the use of this conception is advantageous in teaching analytical chemistry.     

Holographic variable attenuators for high-power Nd:YAG lasers

Within the framework of the Eureka project EU-226: High Power Solid-State Lasers, we have investigated the possibility of making variable attenuators for industrial Nd:YAG lasers using holographic optical elements. Holographic variable attenuator (HVA) demonstrators were realized in fused silica for compatibility with multi-kilowatt Nd:YAG lasers. They were 40 mm long and 13 mm wide with transmission varying from 67% to 98%. Using two cascaded HVA, it was possible to vary the transmission from 44% to 97% using a probe beam of 850 m. Moreover, no noticeable apodization was found on a 5-mm-diameter laser beam.     

Multidimensional solid‐state NMR studies of the structure and dynamics of pectic polysaccharides in uniformly 13C‐labeled Arabidopsis primary cell walls

Plant cell wall (CW) polysaccharides are responsible for the mechanical strength and growth of plant cells; however, the high‐resolution structure and dynamics of the CW polysaccharides are still poorly understood because of the insoluble nature of these molecules. Here, we use 2D and 3D magic‐angle‐spinning (MAS) solid‐state NMR (SSNMR) to investigate the structural role of pectins in the plant CW. Intact and partially depectinated primary CWs of Arabidopsis thaliana were uniformly labeled with ¹³C and their NMR spectra were compared. Recent ¹³C resonance assignment of the major polysaccharides in Arabidopsis thaliana CWs allowed us to determine the effects of depectination on the intermolecular packing and dynamics of the remaining wall polysaccharides. 2D and 3D correlation spectra show the suppression of pectin signals, confirming partial pectin removal by chelating agents and sodium carbonate. Importantly, higher cross peaks are observed in 2D and 3D ¹³C spectra of the depectinated CW, suggesting higher rigidity and denser packing of the remaining wall polysaccharides compared with the intact CW. ¹³C spin–lattice relaxation times and ¹H rotating‐frame spin–lattice relaxation times indicate that the polysaccharides are more rigid on both the nanosecond and microsecond timescales in the depectinated CW. Taken together, these results indicate that pectic polysaccharides are highly dynamic and endow the polysaccharide network of the primary CW with mobility and flexibility, which may be important for pectin functions. This study demonstrates the capability of multidimensional SSNMR to determine the intermolecular interactions and dynamic structures of complex plant materials under near‐native conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

FAS grafted superhydrophobic ceramic membrane

The hydrophobic properties of γ-Al₂O₃ membrane have been obtained by grafting fluoroalkylsilane (FAS) on the surface of the membrane. The following grafting parameters were studied: the eroding time of the original membrane, the grafting time, the concentration of FAS solution and the multiplicity of grafting. Hydrophobicity of the membranes was characterized by contact angle (CA) measurement. The thermogravimetric analysis (TGA) was used to investigate the weight loss process (25–800 °C) of the fluoroalkylsilane grafted on Al₂O₃ powders under different grafting conditions. The morphologies of the membranes modified under different parameters were examined by field emission scanning electron microscopy (FE-SEM) and the surface roughness (Ra) was measured using white light interferometers. A needle-like structure was observed on the membrane surface after modification, which causes the change of Ra. On the results above, we speculated a model to describe the reaction between FAS and γ-Al₂O₃ membrane surface as well as the formed surface morphology.     

Sm5Ga3

Single crystals of penta­samarium trigallium, Sm₅Ga₃, display tetra­gonal symmetry. The crystal structure was solved and refined in space group P4/ncc. The present work does not confirm the space group I4/mcm previously deduced from powder data measurements. One Sm atom is in a general position, and the other Sm atom and one of the Ga atoms are at sites with fourfold symmetry. The remaining Ga atom is at a site with twofold symmetry.