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.     

Influence of specific surface area of pyrogenic silicas on their heat of immersion in water and on their surface properties assessed using inverse gas chromatography

The heat of immersion and the surface properties of pyrogenic silicas were examined using microcalorimetry and inverse gas chromatography at finite concentration (FC-IGC). The microcalorimetric measurements showed a regular decrease of the heat of immersion, in water, per area unit with an increase in the surface areas. The desorption isotherms were established using FC-IGC. It is observed that BET constant value goes through a minimum, whereas the shapes of distribution function of the adsorption energies of isopropanol are changing. All results could be interpreted using a model of formation of the pyrogenic silica in the flame, which explains the change of surface functionality and geometry occurring around 200 m2/g.     

Collective behavior during the exit of a wetting liquid through a network of channels

The exit of a wetting fluid from a thin microchannel into a sudden expansion is studied experimentally. In the case of the exit from a single channel, the advancing interface converges to a parabolic shape after an initial transient, in accordance with the lubrication limit analysis of a spreading drop. The experiments are then repeated for the exit from two parallel channels. At early times, the two exiting drops behave independently and display the same evolution as a single exiting droplet, while at late times we recover a single parabolic profile. The transition between the early and late states is due to the merging of the two drops, which is associated with a sudden increase in the flow rate. This is the signature of a collective effect which acts to redistribute the fluid spatially. Finally, the experiment is generalized to the case of seven parallel channels where a cascade of two-by-two mergings is observed, indicating that local interactions dominate the dynamics which lead to the global state of the system.     

Multiresidue analytical methods for the ultra-trace quantification of 33 priority substances present in the list of REACH in real water samples

Innovative and simultaneous multiresidue analytical methods of 33 multi-class pollutants in wastewaters, surface and ground waters, using solid phase extraction (SPE) followed by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) are presented. Target compounds include several groups of emerging and persistent contaminants derived from the European priority list of the registration evaluation and authorisation of chemicals system (REACH): organochlorine (8) and organophosphorus (2) pesticides, carbamates (2), fungicides (8), phthalates (2), alkylphenols (10) and bisphenol A.The recovery rates of the SPE gave levels ranged from 84 to 118% with exception of some compounds that yielded lower (methamidophos (50%), p,p′-DDT (60%) and o,p′-DDT (72%)) but all recoveries were acceptable. Low limits of detection (LOD) varied between 0.2 and 88.9 ng L⁻¹ (except for HPTE and 4n-octylphenol giving 161 and 220 ng L⁻¹, respectively). A study of matrix effects was performed in order to evaluate the best and reliable calibration approach.The developed analytical method was successfully applied to the analysis of the 33 substances in wastewater effluents as well as surface and ground waters. The most frequently detected families were alkylphenols and industrial endocrine disrupting compounds (phthalates and bisphenol A).     

Formation of neutral methylcarbamic acid (CH3NHCOOH) and methylammonium methylcarbamate [CH3NH3+][CH3NHCO2-] at low temperature

We study low temperature reactivity of methylamine (CH3NH2) and carbon dioxide (CO2) mixed within different ratios, using FTIR spectroscopy and mass spectrometry. We report experimental evidence that the methylammonium methylcarbamate [CH3NH3(+)][C3NHCO2(-)] and methylcarbamic acid (CH3NHCOOH) are formed when the initial mixture CH3NH2:CO2 is warmed up to temperatures above 40 K. An excess of CH3NH2 favors the carbamate formation while an excess of CO2 leads to a mixture of both methylammonium methylcarbamate and methylcarbamic acid. Quantum calculations show that methylcarbamic acid molecules are associated into centrosymmetric dimers. Above 230 K, the carbamate breaks down into CH3NH2 and CH3NHCOOH, then this latter dissociates into CH3NH2 and CO2. After 260 K, it remains on the substrate a solid residue made of a well-organized structure coming from the association between the remaining methylcarbamic acid dimers. This study shows that amines can react at low temperature in interstellar ices rich in carbon dioxide which are a privileged place of complex molecules formation, before being later released into "hot core" regions.