Experimental assessment of the effective friction at the base of granular chute flows on a smooth incline.

We report on direct measurements of the basal force components for granular material flowing down a smooth incline. We investigate granular flows for a large range of inclination angles from θ=13.4^{∘} to 83.

Low temperature kinetics and theoretical studies of the reaction CN + CHNH: a potential source of cyanamide and methyl cyanamide in the interstellar medium.

The reaction between cyano radicals (which are ubiquitous in interstellar clouds) and methylamine (a molecule detected in various interstellar sources) has been investigated in a synergistic experimental and theoretical study. The reaction has been found to be very fast in the entire range of temperatures investigated (23-297 K) by using a CRESU apparatus coupled to pulsed laser photolysis - laser induced fluorescence. The global experimental rate coefficient is given by In addition, dedicated electronic structure calculations of the underlying potential energy surface have been performed, together with capture theory and RRKM calculations.

Uniform Supersonic Chemical Reactors: 30 Years of Astrochemical History and Future Challenges.

The interstellar medium is of great interest to us as the place where stars and planets are born and from where, probably, the molecular precursors of life came to Earth. Astronomical observations, astrochemical modeling, and laboratory astrochemistry should go hand in hand to understand the chemical pathways to the formation of stars, planets, and biological molecules. We review here laboratory experiments devoted to investigations on the reaction dynamics of species of astrochemical interest at the temperatures of the interstellar medium and which were performed by using one of the most popular techniques in the field, CRESU.

Mechanical Properties of Membranes Composed of Gel-Phase or Fluid-Phase Phospholipids Probed on Liposomes by Atomic Force Spectroscopy.

In many liposome applications, the nanomechanical properties of the membrane envelope are essential to ensure, e.g., physical stability, protection, or penetration into tissues.

Reactivity of Functionalized Ynamides with Tetracyanoethylene: Scope, Limitations and Optoelectronic Properties of the Adducts.

The reactivity of functionalized ynamides and arylynamines with tetracyanoethylene at room temperature was evaluated. In most cases, the corresponding 1,1,4,4-tetracyanobutadienes (TCBDs) were obtained in good to excellent yields through a [2+2]-cycloaddition/[2+2]-retro-electrocyclization sequence. The influence of diverse functional groups on the yield of the reaction was investigated, in particular concerning multiple ynamides.

Interactions of Organics within Hydrated Selective Layer of Reverse Osmosis Desalination Membrane: A Combined Experimental and Computational Study.

In this work we have examined a computational approach in predicting the interactions between uncharged organic solutes and polyamide membranes. We used three model organic molecules with identical molecular weights (100.1 g/mol), 4-aminopiperidine, 3,3-dimethyl-2-butanone (pinacolone) and methylisobutyl ketone for which we obtained experimental data on partitioning, diffusion and separation on a typical seawater reverse osmosis (RO) membrane.

Physics behind Water Transport through Nanoporous Boron Nitride and Graphene.

In this work, molecular dynamics simulations were used to determine the surface tension profile of water on graphene and boron nitride (BN) multilayers and to predict water permeation through nanoporous graphene and BN membranes. For both graphene and BN multilayers, a decrease in surface tension (γ) was evidenced as the number of layers increased. This lessening in γ was shown to result from a negative surface tension contribution due to long-range wetting of water, which also contributes to lower water permeation through a two-layer membrane with respect to permeation through a monolayer.

Low-Temperature Reactivity of C2n+1N(-) Anions with Polar Molecules.

Following the recent discovery of molecular anions in the interstellar medium, we report on the kinetics of proton transfer reactions between cyanopolyynide anions C2n+1N(-) (n = 0, 1, 2) and formic acid HCOOH. The results, obtained from room temperature down to 36 K by means of uniform supersonic flows, show a surprisingly weak temperature dependence of the CN(-) reaction rate, in contrast with longer chain anions. The CN(-) + HCOOH reaction is further studied theoretically via a reduced dimensional quantum model that highlights a tendency of the reaction probability to decrease with temperature, in agreement with experimental data but at the opposite of conventional long-range capture theories.

Ultrafast diffusion of Ionic Liquids Confined in Carbon Nanotubes.

Over the past decade many works have focused on various aspects of the dynamics of liquids confined at the nanoscale such as e.g. water flow enhancement through carbon nanotubes (CNTs).

Pressure dependent low temperature kinetics for CN + CH3CN: competition between chemical reaction and van der Waals complex formation.

The gas phase reaction between the CN radical and acetonitrile CH3CN was investigated experimentally, at low temperatures, with the CRESU apparatus and a slow flow reactor to explore the temperature dependence of its rate coefficient from 354 K down to 23 K. Whereas a standard Arrhenius behavior was found at T > 200 K, indicating the presence of an activation barrier, a dramatic increase in the rate coefficient by a factor of 130 was observed when the temperature was decreased from 168 to 123 K. The reaction was found to be pressure independent at 297 K unlike the experiments carried out at 52 and 132 K.

Synthesis, Chemistry, and Photochemistry of Methylcyanobutadiyne in the Context of Space Science.

An alternative preparation of methylcyanobutadiyne (MeC5N), a molecule present in the interstellar medium, was established in order to circumvent tedious steps from previous methods. The possibility of forming methylcyanoacetylene and MeC5N by gas-phase photolysis was evaluated from relevant acetylene derivatives in the context of space science. The reactivity of MeC5N toward simple nucleophiles was investigated.

Self-Organization of Quantum Rods Induced by Lipid Membrane Corrugations.

Self-organization of fluorescent nanoparticles, using biological molecules such as phospholipids to control assembly distances, is a promising method for creating hybrid nanostructures. We report here the formation of hybrid condensed phases made of anisotropic nanoparticles and phospholipids. Such structure formation is driven by electrostatic interaction between the nanoparticles and the phospholipids, and results in the formation of a 2D rectangular liquid crystal, as confirmed by high-resolution Small-Angle X-ray Scattering (SAXS).

The Electronic Structure of Some Cyanohydrins-A Spectroscopically Under-Investigated Family of Compounds.

Cyanohydrins are usually formed by addition of hydrogen cyanide to aldehydes or ketones while the elimination of HCN from cyanohydrins is easily observed upon heating. The low thermal stability of these highly boiling compounds leads to difficult studies in the gas phase where partial or complete decomposition is usually observed. Consequently, the reported physicochemical properties of such compounds in the gas phase are still scarce.

Product Branching in the Low Temperature Reaction of CN with Propyne by Chirped-Pulse Microwave Spectroscopy in a Uniform Supersonic Flow.

A new chirped-pulse/uniform flow (CPUF) spectrometer has been developed and used to determine product branching in a multichannel reaction. With this technique, bimolecular reactions can be initiated in a cold, thermalized, high-density molecular flow and a broadband microwave spectrum acquired for all products with rotational transitions within a chosen frequency window. In this work, the CN + CH3CCH reaction was found to yield HCN via a direct H-abstraction reaction, whereas indirect addition/elimination pathways to HCCCN, CH3CCCN, and CH2CCHCN were also probed.

Cholesterol strongly affects the organization of lipid monolayers studied as models of the milk fat globule membrane: Condensing effect and change in the lipid domain morphology.

The biological membrane that surrounds the milk fat globules exhibits phase separation of polar lipids that is poorly known. The objective of this study was to investigate the role played by cholesterol in the organization of monolayers prepared as models of the milk fat globule membrane (MFGM). Differential scanning calorimetry and X-ray diffraction experiments allowed characterization of the gel to liquid crystalline phase transition temperature of lipids, Tm ~35°C, in vesicles prepared with a MFGM lipid extract.

Superpermittivity of nanoconfined water.

Nowadays, it is well established that the physical properties of confined liquids strongly differ from those in bulk phase. While dynamical and structural properties were strongly explored, dielectric properties are poorly studied despite their importance in the understanding and the modelling of molecular mechanism in a number of nano-applications such as nanofluidics, nanofiltration, and nanomedicine. Among them, the dielectric permittivity is probably one of the most important.

Development of a pulsed uniform supersonic gas expansion system based on an aerodynamic chopper for gas phase reaction kinetic studies at ultra-low temperatures.

A detailed description of a new pulsed supersonic uniform gas expansion system is presented together with the experimental validation of the setup by applying the CRESU (French acronym for Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in a Uniform Supersonic Flow) technique to the gas-phase reaction of OH radicals with 1-butene at ca. 23 K and 0.63 millibars of helium (carrier gas).

Tunable dielectric constant of water at the nanoscale.

Using molecular dynamics simulations, the influence of the surface charge density of a nanotube on the static dielectric permittivity ε of confined water was reported. Whereas the dielectric anisotropy between the radial and axial directions of water confined in hydrophilic and hydrophobic membranes and the increase in axial dielectric permittivity with respect to the bulk value have previously been described, we found that an increase in the surface charge density leads to a drastic decrease in ε into the axial direction. The decrease in ε is accompanied by a strong slowdown in the rotational dynamics of water molecules.

Theoretical investigation of the ionic selectivity of polyelectrolyte multilayer membranes in nanofiltration.

Polyelectrolyte multilayer membranes have proven to be promising materials for ion nanofiltration. In this work, we implement a continuum mesoscopic transport model developed in previous works (Szymczyk, A.; Zhu, H.

A chirped-pulse Fourier-transform microwave/pulsed uniform flow spectrometer. II. Performance and applications for reaction dynamics.

This second paper in a series of two reports on the performance of a new instrument for studying chemical reaction dynamics and kinetics at low temperatures. Our approach employs chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy to probe photolysis and bimolecular reaction products that are thermalized in pulsed uniform flows. Here we detail the development and testing of a new K(a)-band CP-FTMW spectrometer in combination with the pulsed flow system described in Paper I [J.

Becker muscular dystrophy severity is linked to the structure of dystrophin.

In-frame exon deletions of the Duchenne muscular dystrophy (DMD) gene produce internally truncated proteins that typically lead to Becker muscular dystrophy (BMD), a milder allelic disorder of DMD. We hypothesized that differences in the structure of mutant dystrophin may be responsible for the clinical heterogeneity observed in Becker patients and we studied four prevalent in-frame exon deletions, i.e.

A chirped-pulse Fourier-transform microwave/pulsed uniform flow spectrometer. I. The low-temperature flow system.

We report the development of a new instrument that combines chirped-pulse microwave spectroscopy with a pulsed uniform supersonic flow. This combination promises a nearly universal detection method that can deliver isomer and conformer specific, quantitative detection and spectroscopic characterization of unstable reaction products and intermediates, product vibrational distributions, and molecular excited states. This first paper in a series of two presents a new pulsed-flow design, at the heart of which is a fast, high-throughput pulsed valve driven by a piezoelectric stack actuator.

Kinetics and mechanism of the tropospheric reaction of 3-hydroxy-3-methyl-2-butanone with Cl atoms.

The relative rate coefficient for the gas-phase reaction of 3-hydroxy-3-methyl-2-butanone (3H3M2B) with Cl atoms was determined under atmospheric conditions (298 ± 2 K, 720 ± 2 Torr). The products of the reaction were identified and quantified. This work provides the first kinetic and mechanistic determinations of the gas-phase reaction of Cl atoms with 3H3M2B.

Foam drainage control using thermocapillary stress in a two-dimensional microchamber.

We investigate the drainage of a 2D microfoam in a vertical Hele-Shaw cell, and show that the Marangoni stress at the air-water interface generated by a constant temperature gradient applied in situ can be tuned to control the drainage. The temperature gradient is applied in such a way that thermocapillarity and gravity have an antagonistic effect. We characterize the drainage over time by measuring the liquid volume fraction in the cell and find that thermocapillarity can overcome the effect of gravity, effectively draining the foam towards the top of the cell, or exactly compensate it, maintaining the liquid fraction at its initial value over at least 60 s.

Peptidic ligands to control the three-dimensional self-assembly of quantum rods in aqueous media.

The use of peptidic ligands is validated as a generic chemical platform allowing one to finely control the organization in solid phase of semiconductor nanorods originally dispersed in an aqueous media. An original method to generate, on a macroscopic scale and with the desired geometry, three-dimensional supracrystals composed of quantum rods is introduced. In a first step, nanorods are transferred in an aqueous phase thanks to the substitution of the original capping layer by peptidic ligands.