Diffraction et mesure de Palm des processus ponctuels

Using the notion of Palm measure, we prove the existence of the diffraction measure of all stationary and ergodic point processes. We get precise expressions of those measures in the case of specific processes: stochastic subsets of $\text{Z}{}^{\mathrm{d}}$, sets obtained by the “cut-and-project” method. To cite this article: J.-B. Gouéré, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

Steroids as organising elements in anion receptors

The steroid nucleus has proved useful in various areas of supramolecular chemistry, acting as a building-block for extended, well-defined molecular architectures, and a scaffold for preorganised arrays of functionality. This article discusses its applications in the area of anion recognition, where cholic acid (2) has been especially valuable. The three secondary hydroxyl groups on 2 are nicely arranged for H-bond donation to a single anion, and may be converted into stronger neutral or positively-charged H-bond donors. Macrocyclic and acyclic receptors derived from 2 have been used to bind inorganic anions, carboxylates and nucleic acids.     

Electrochemical quantification of high-affinity halide binding by a steroid-based receptor

The strength of binding between a cholapod receptor and halide anions is quantified using voltammetry at the liquid/liquid interface, revealing very high affinities and size-selectivity peaking at chloride.     

Cycloruthenated primary and secondary amines as efficient catalyst precursors for asymmetric transfer hydrogenation

[reaction: see text] Ruthenacycles obtained by cyclometalation of enantiopure aromatic primary or secondary amines with [(eta6-benzene)RuCl2]2 or with [(eta6-p-cymene)RuCl2]2 are efficient catalysts for asymmetric transfer hydrogenation (TOF up to 190 h(-1) at room temperature). Enantioselectivities in the transfer hydrogenation of acetophenone ranged from 38% to 89%. It is possible to prepare the catalysts in situ, which allows the use of high throughput experimentation.     

PHOTOCLEAVAGE OF DNA IN THE PRESENCE OF SYNTHETIC WATER-SOLUBLE PORPHYRINS

In the presence of oxygen and visible light, various synthetic water-soluble porphyrins cleave pBR 322 plasmid supercoiled DNA (form I) producing relaxed (form II) and linear (form III) DNA corresponding to single-strand and double-strand breaks respectively. Large variations are observed in the efficiency of the porphyrins containing a diamagnetic metal or no metal at all. Singlet oxygen (¹O₂) seems to be involved in the mechanism of cleavage consistent with the inhibitory effect of the azide anion, N^–₃. The higher efficiency of cationic porphyrins (as compared to anionic ones) is due to their greater affinity for DNA as shown by experiments carried out at either high ionic strength or in the presence of the surfactant, sodium dodecyl sulfate.     

1,3-Diborata-2,4-diphosphoniocyclobutane-1,3-diyls communicate through a para-phenylene linker

The presence of a second 1,3-diborata-2,4-diphosphoniocyclobutane-1,3-diyl in the para-position of a phenylene linker favors the diradical form over the 1,3-diborata-2,4-diphosphoniobicyclo[1.1.0]butane bond stretch isomer, as long as the two planar diradical units are coplanar with the linker. This demonstrates that two BPBP diradicals communicate through the phenyl ring.     

Evolution of the surface polar character of pyrogenic silicas, with their grafting ratios by dimethylchlorosilane, studied by microcalorimetry

The interactions of water, hexamethyldisiloxane, and dodecane with pyrogenic silica samples, modified by a controlled partial silylation with dimethyldichlorosilane, were studied by microcalorimetry and wettability measurements. The samples, having a coverage ratio lower than dimethylsilyl (DMS) monolayer capacity ( approximately 2.6 DMS/nm(2)), show a regular and linear decrease of their heat of immersion into water with the coverage ratio and correlate with the increase of residual silanol groups. Two critical coverage ratios were evidenced at about 25 and 50% of the DMS monolayer capacity, the grafted silica remaining hydrophilic, below 25% being strongly hydrophobic beyond. The heat of immersion into hexamethyldisiloxane decreases until 50% of the DMS monolayer whereas that of dodecane remains independent of the grafting ratio. This study demonstrates that the water/residual free silica surface plays the main role in the stabilization of the W/O Pickering's emulsions.