In Process Citation

Generation of ethoxide and hydroxide ions in aqueous ethanolic medium by controlled-current electrolysis is suggested for coulometric titration of 2-phenylpropionic acid derivatives. The electroreduction of the carboxylic hydrogen atom leads to the anion by elimination of a hydrogen radical. Potentiometric or conductimetric methods can be used for detection of the end-point.     

Characterization of nanoscale metal structures obtained by template synthesis

Generating submicron objects made of nanostructured materials is one of the challenges of nanotechnology. A method for producing micron-sized structures without the use of lithographic techniques has been developed. Electrochemical deposition of metals into nanometer-wide parallel pores of porous anodic oxide films on aluminium is used to produce micro- to nano-wires or -tip arrays. The nanoscale structures and the structuring procedure have been investigated by the examination of lateral and cross-sectional specimens by SEM, EDS and XPS. The investigations show the feasibility of generating films with a variety of different compositions, a high density of tips, and tip diameters in the range of 30–150 nm. Furthermore, impedance spectroscopy was used to characterize the properties of the nanostructured surface. The results show a structure and composition dependent behavior due to the large (electrochemically) active surface area.     

Understanding otolith biomineralization processes: new insights into microscale spatial distribution of organic and mineral fractions from Raman microspectrometry

It is generally accepted that the formation of otolith microstructures (L- and D-zones) and in particular the organic and mineral fractions vary on a daily basis. Raman microspectrometry provides a nondestructive technique that can be used to provide structural information on organic and mineral compounds. We applied it to thin otolith sections of hake in order to address the following issues: (1) the simultaneous characterization of variations in the organic and mineral fractions both in the core area and along successive otolith microstructures; (2) elucidation of significant differences between these fractions; (3) quantification of the effects of etching and staining protocols on otolith structures. The primordium appeared as a punctual area depicting higher luminescence and greater concentrations in organic compounds containing CH groups. Sulcus side showed similar composition suggesting that the contact of the otolith with the macula and its orientation in otosac occur rapidly (about 10 days). The characterization of L- and D-zones in the opaque zones indicated that both structures contained organic and aragonitic fractions with cyclic and synchronous variations. Contrary to the results obtained after EDTA etching, L-zones depicted greater concentrations in organic compounds containing CH groups, whereas D-zones appear richer in aragonite. This organic fraction seemed to be revealed by Mutvei’s staining and was affected by EDTA etching which suggests that it corresponds to the soluble fraction of organic matrix. Such results indicate that L- and D-zones differ in their respective organic constituents. Raman microspectrometry thus appears as a powerful technique to acquire quantitative information that is required for a better understanding of otolith biomineralization. Figure Raman microspectrometry is a powerful technique for studying otolith biomineralization     

Decarbonation and preservation method for the analysis of organic C and N contents and stable isotope ratios of low-carbonated suspended particulate material

The aim of this study was to determine a simple routine procedure to preserve, decarbonate and analyse low-carbonated filters of suspended particulate organic matter (POM) for particulate organic carbon and nitrogen content, and . Our goal was to analyse these four parameters from a single and entire filter of POM without altering the organic material.First, freezing (−20 °C) versus oven-drying (60 °C) were compared as the initial preservation step. Afterwards, non-acidified samples were compared to acid-treated samples using 0.12N HCl (diluted HCl rinsing at the end of the filtration) or 12N HCl (filters exposed to HCl fumes for 4 h in a dessicator). Regarding the preservation methods, our results indicate that freezing increases the uncertainty of measurements and, in combination with concentrated HCl treatment, leads to a loss of particulate nitrogen and an alteration of the signature. Consequently, we recommend drying to preserve filter samples. Regarding acid treatments, we found that (i) diluted HCl would not be sufficient to fully remove the carbonate from our samples, (ii) in contrast, a 4 h exposure of the filters to the HCl fumes was enough to remove all the inorganic carbon, and (iii) the concentrated HCl treatment did not alter the nitrogen measurements (only when drying without freezing is used to preserve the filters). Consequently, we propose that low-carbonated POM filters are preserved by drying and carbonates are removed by exposing the filters to HCl fumes (4 h) for the analysis of particulate organic C and N content and isotope ratios.     

Transpositions spinales in vitro en milieu acide—VII : Isomerisation d'hydroxy-17 steroïdes ethyleniques: possibilite d'un mecanisme concerte au niveau des cycles c et d

Synthesis and rearrangement of ethylenic 17-hydroxy steroids, with a cis or trans configuration of the 18-methyl and 17-hydroxy groups, is described. The cis compounds lead, in acidic media, to backbone-rearranged steroids, whereas the trans compounds lead to C-nor spiroketones. A concerted mechanism is postulated for the rearrangement of the C and D rings, in every case different from the one occurring for the transposition of ABC rings.