Deracemization by enantioselective protonation IV an improved method for the enantiomeric enrichment of α-aminoacids using metalation by means of chiral amides

Optically active α-aminoesters are obtained by metalation of the corresponding Schiff bases by chiral lithium amide followed by protonation by an achiral or a chiral acid. 70 % e.e. can be obtained.     

Experimental study of the gravity influence on the periodic thermocapillary convection around a bubble

The 3D periodic state, following the steady thermocapillary convection state, around an air bubble immersed in a low-Prandtl-number silicone oil layer under a heated wall was experimentally investigated on the ground and during parabolic flights. This oscillation was observed under reduced gravity conditions for the first time. Consequently, the initiation of this oscillation seems to be independent of gravity and so of buoyancy convection. The reduced and increased gravity conditions showed that the gravity level modifies the oscillation. Its frequency increases with the gravity level. The comparison with the results obtained on the ground shows the bubble aspect ratio is not a relevant parameter when the gravity varies. Received: 27 November 2000/Accepted: 25 May 2001     

Etude photoelectronique de la separation du plomb et du cadmium par echange ionique sur le phosphate de hafnium: X-ray photoelectronic study of the separation of lead and cadmium ions on crystalline hafnium phosphate used as a cation exchanger

X-ray photoelectronic study of the separation of lead and cadmium ions on crystalline hafnium phosphate used as a cation exchanger.Crystalline hafnium monohydrogenphosphate monohydrate [Hf(HPO₄)₂·H₂O] is a useful cationic exchanger for separating lead(II) and cadmium(II) ions. Studies have been carried out at various pH and in the presence of various ligands. X-ray photoelectron spectroscopy has shown that lead diffuses into the deeper layers of the exchanger while cadmium remains near the surface. This property can be used to improve the selectivity of the method by masking cadmium with a large ligand (1,10-phenanthroline), which prevents the metal from adsorbing without any effect on lead fixation.     

Selective internal manipulation of a single molecule by scanning tunneling microscopy

We have studied the adsorption of the polyaromatic molecule 1,4"-paratriphenyldimethylacetone, which we have nicknamed Trima. The originality of this linear molecule is that it was designed and synthesized to have two functionalities. First, chemisorb itself to the surface by its two ends rather like a bridge. Second, the central part of the molecule could then be rotated by injecting electrons with the tip of the scanning tunneling microscope (STM). The length of the molecule corresponds exactly to the spacing between five dimers in a row on the Si(100)-2 x 1 surface. We found that the molecule adsorbs as expected on the clean silicon surface by using complementary STM and synchrotron radiation studies. Manipulation of individual molecules with the STM tip showed selective internal modifications that were highly voltage dependent. These manipulations were found to be compatible with an electronic excitation of the pi-pi* transition of the molecule.     

Migration du carbonyle : Obtention d'homologues du glyoxal à fonction cétonique protégée

Substituted glyoxals with protected ketogroup $\text{3}$ were obtained by reaction of α-chloro-α-(aryl- or alkyl-thio)ketones $\text{1}$ with sodium methylate in methanol.     

α-Cétoaldéhydes à groupement aldéhydique ou cétonique protégé

α-Ketoaldehydes with protected ketogroup 2 or protected aldehydrogroup 3 are obtained by reaction of thiophenol or methanol with α-chloro-α-(phenylthio)aldehydes 7.