Evaluation des conséquences économiques et administratives d'un prix élevé du baril de pétrole Région de Bruxelles-Capitale

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Revisiting the assembly of amino ester-based benzene-1,3,5-tricarboxamides: chiral rods in solution

International audienceSome benzene-1,3,5-tricarboxamide (BTA) monomers derived from (L) α−amino esters self-assemble into long rods at millimolar concentrations, and display a strong chiral amplification effect. These rods are in competition with dimeric species

How Spherical Are Gaseous Low Charged Dendrimer Ions: A Molecular Dynamics/Ion Mobility Study?

International audienceThe globular shape of gaseous ions, resulting from the ionization of large molecules such as polymers and proteins, is a recurring subject that has undergone a renewed interest with the advent of ion mobility spectrometry (IMS), especially in conjunction with theoretical chemistry techniques such as Molecular Dynamics (MD). Globular conformations result from a fine balance between entropy and enthalpy considerations. For multiply charged ions isolated in the gas phase of a mass spectrometer, the Coulombic repulsion between the different charges tends to prevent the ions from adopting a compact, and folded 3D structure. In the present paper, we closely associate data from IMS experiments and MD simulations to unambiguously access the conformations of dendrimer ions in the gas phase with special attention paid to the dendrimer structure, the generation, and the charge state. By doing so, we here combine a set of structural tools able to evaluate the (non)globular shape of ions based on both experimental and theoretical results

Two-Dimensional Self-Assemblies of Thiophene−Fluorenone Conjugated Oligomers on Graphite: A Joint STM and Molecular Modeling Study

International audienc

Stabilization of Supramolecular Polymer Phase at High Pressures

We utilize dynamic light scattering (DLS) and passive microrheology to examine the phase behavior of a supramolecular polymer at very high pressures. The monomer, 2,4-bis(2-ethylhexylureido)toluene (EHUT), self-assembles into supramolecular polymeric structures in the nonpolar solvent cyclohexane by means of hydrogen bonding. By varying the concentration and temperature at atmospheric pressure, the formation of the viscoelastic network (at lower temperatures) and predominantly viscous phases, based on self-assembled tube and filament structures, respectively, has been established. The associated changes in the rheological properties have been attributed to a structural thickness transition. Here, we investigate the effects of pressure variation from atmospheric up to 1 kbar at a given concentration. We construct a temperature–pressure diagram that reveals the predominance of the viscoelastic network phase at high pressures. The transition from the viscoelastic network organization of the tubes to a weaker viscous-dominated structure of the filaments is rationalized by using the Clapeyron equation, which yields an associated volume change of about 8 Å3 per EHUT molecule. This change is further explained by means of Molecular Dynamics simulations of the two phases, which show a decrease in the molecular volume at the filament-tube transition, originating from increased intermolecular contacts in the tube with respect to the filament. These findings offer insights into the role of pressure in stabilizing self-assemblies

Tuning the structure of 1,3,5-benzene tricarboxamide self-assemblies through stereochemistry

International audienceA heterochiral 1,3,5-benzene tricarboxamide (BTA) monomer, derived from valine dodecyl ester, forms long rods in cyclohexane whilst its homochiral analogue assembles into dimers only at the same concentration. This highly original assembly behaviour is related to the destabilization of the dimeric structure containing the two heterochiral monomers as corroborated by a combined experimental and computational study

Asymmetric stereodivergent catalysis achieved by means of a switchable asymmetric catalyst built on supramolecular helices

Despite recent developments on the design of dynamic catalysts, none of them have been exploited for the in-situ control of multiple stereogenic centers in a single molecular scaffold. We report herein that it is possible to select one major amongst four possible stereoisomers of an amino alcohol by means of a switchable asymmetric catalyst built on supramolecular helices. Hydrogen-bonded assemblies between a benzene-1,3,5-tricarboxamide (BTA) achiral phosphine ligand coordinated to copper and an enantiopure BTA monomer are engaged in a concomitant copper-hydride catalyzed hydrosilylation and hydroamination process, yielding mainly one of the possible stereoisomers in good yield. The nature of the product stereoisomer is related to the handedness of the helices and can thus be directed in a predictable way by the nature of the major enantiopure BTA present in the assemblies. Accordingly, a sequential reaction, during which the handedness of the supramolecular helices is switched in between the hydrosilylation and hydroamination steps, mainly yields the diastereoisomer that cannot be obtained in the aforementioned concomitant process. The strategy allows all stereoisomers to be obtained with similar selectivities. This work paves the way for the development of supramolecular helical catalysts as a platform to readily access molecules embedding several stereogenic centers

About the use of PCL/clay nanohybrid masterbatches

Présentation par affiche à la 4th International Conference Nanofun-Poly à Rome du 16 au 18 avril 200