Membrane protein selectively oriented on solid support and reconstituted into a lipid membrane

Mimetic functional membranes on solid support are now emerging for the development of membrane biosensor or for the study of membrane-mediated processes and should have an important impact on biodiagnostics. We established a method to reconstitute a membrane protein into a lipid membrane in a selective orientation on a solid support. Membrane protein OprM, a component of OprM-MexA-MexB multidrug efflux pump, solubilized in detergent was immobilized via its extracellular domain on aminosilane-modified silica surface. The oriented protein was reconstituted into a lipid membrane by detergent removal. The membrane protein reconstitution process carried out on silica nanoparticles and on planar silica surfaces was followed by cryo-electron microscopy (cryo-EM) and quartz crystal microbalance with dissipation monitoring (QCM-D) respectively. The selective protein orientation on aminosilane-modified silica surface was assessed by cryo-EM and was compared to the nonspecific protein deposition on silica surface. Finally, the binding of MexA, a periplasmic component of the tripartite efflux complex, was monitored with QCM-D on the oriented OprM protein monolayer. The large adsorbed mass gave a direct evidence of the high affinity of MexA with the periplasmic helical part of OprM.     

Efficient synthesis and astonishing supramolecular architectures of several symmetric macrolactams

The synthesis of four C(n) symmetric macrocyclic lactams cyclo-[NH-CH(2)-CH=CH-CH(2)-CO](n) (1, n=2; 2, n=3; 3, n=4) and cyclo-[NH-CH(2)-CH(2)-CH=CH-CO](3) (4) has been achieved by two approaches. A linear route leads to precursors that are subsequently macrocyclized in a separate step. The second, convergent approach relies on the symmetry of the targets: it includes suitably activated subunits, which are subjected to macrocyclization conditions. The subunits first oligomerize, then cyclize to form either pure macrolactams or mixtures. The macrolactam units 1, 2 and 4 stack on top each other through weak interactions (hydrogen bond and van der Waals), to form endless square, rectangular and triangular prisms, respectively. These stacks are further packed side by side in crystals grown from isotropic media. The overall dipoles in the crystals from lactams 1 and 4, which result mostly from the alignment of amide groups, are zero and large, respectively. Macrolactam 2 displays an astonishing isomorphism when allowed to cool down in anisotropic liquid crystal solutions. Large hollow hexagonal tubes are then obtained through a fractal process. Contrary to the three previous rings, 3 yields crystals where prisms of any shape are absent.     

Solid phase synthesis of highly substituted tetrahydropyrans by tandem ene-reaction/intramolecular Sakurai cyclization

A solid-phase tandem ene-reaction/intramolecular Sakurai cyclization sequence has been developed to synthesize highly substituted tetrahydropyran derivatives in two steps from aldehydes and with complete control of the relative stereochemistry of the three newly formed stereocenters. The compounds are obtained with high purity after release from the solid support and can be easily isolated in multimilligram amounts. Moreover, we have shown that asymmetric induction is possible on solid phase and that enantiomerically pure tetrahydropyrans containing four stereocenters can be effectively synthesized with this method.     

Short enantioselective syntheses of trans-5-alkylprolines from new functionalized amino alcohols

Amino alcohols, having an enol ether function, cyclized in acidic medium to give quantitatively diastereosomerically pure bicyclic compounds that were transformed in five steps in enantiopure trans-5-alkylproline derivatives.     

Gas-phase basicity of methionine

Proton affinity and protonation entropy of methionine (Met) were determined by the extended kinetic method from ESI-Q-TOF tandem mass spectrometry experiments. The values, PA(Met) = 937.5 +/- 2.9 kJ mol(-1) and Delta(p)S degrees (Met) = - 22 +/- 5 J mol(-1) K(-1), lead to gas-phase basicity GB(Met) = 898.2 +/- 3.2 kJ.mol(-1). Quantum chemical calculations using density functional theory confirm that the proton affinity of Met is indeed in the 940 kJ mol(-1) range and that a significant entropy loss, of at least - 25 J mol(-1) K(-1), occurs upon protonation. This last point is evidenced here for the first time and suggests revision of the tabulated protonation thermochemistry of Met. A comparison with previous experimental data allows us to propose the following evaluated thermochemical values: PA(Met) = 943 +/- 4 kJ mol(-1) and Delta(p)S degrees (Met) = - 35 +/- 15 J mol(-1) K(-1) and GB(Met) = 900 +/- 2 kJ mol(-1).     

Iterative Cr-mediated catalytic asymmetric allylation to synthesize syn/syn- and anti/anti-1,3,5-triols

Iterative use of Cr-mediated catalytic asymmetric allylation could give a simple access to 1,3-polyols. Using syn/syn- and anti/anti-1,3,5-triols as representative examples, the feasibility of this approach is studied, thereby demonstrating that (1) the pre-existing TMS-protected alcohol at the beta-position does not give a significant effect on the Cr-mediated catalytic asymmetric allylation and (2) this synthetic route furnishes the expected syn/syn- and anti/anti-1,3,5-triols at the useful level of asymmetric induction and yield.     

Investigation of the adsorption behaviour of acetone at the surface of ice. A grand canonical Monte Carlo simulation study

The adsorption isotherm of acetone at the surface of I(h) ice has been determined by a set of grand canonical Monte Carlo simulations at 200 K, by varying the chemical potential of acetone in the simulations. The obtained isotherm can be described by the Langmuir theory up to a certain relative pressure value (i.e., about 0.07); above which the isotherm increasingly deviates from the Langmuir form. This deviation mainly originates from the increasing importance of the lateral dipolar interactions. Further, above this pressure the adsorption sites are no longer equivalent: the adsorbed acetone molecules are aligned in three different ways. In one of these orientations the acetone molecule forms two, while in another one it forms one hydrogen bond with the surface waters, whereas in the third preferred orientation no hydrogen bonding occurs between the adsorbed molecule and the ice surface.     

Copper-catalyzed alkene aziridination with N-tosyloxycarbamates

Pyridine copper complexes were found as active catalysts for the intramolecular aziridination of allylic N-tosyloxycarbamates and the intermolecular aziridination of styrenes with trichloroethyl N-tosyloxycarbamates. Free aziridines were easily obtained by basic deprotection of the trichloroethyl group.     

Relaxation of residual stress and reentanglement of polymers in spin-coated films

Performing detailed studies of viscoelastic dewetting of thin polystyrene films on solid substrates, we demonstrate the existence of residual stress due to strongly out of equilibrium chain conformations and a reduced entanglement density resulting from film preparation by spin coating. The ratio of stress over elastic modulus was found to increase strongly with decreasing film thickness and increasing chain length. Full equilibration of chain conformations required long times comparable to bulk reptation times. However, for chains longer than about 3000 monomers, the residual stress relaxed faster, at a rate independent of chain length.     

A homogenised vibratory model for predicting the acoustic properties of hollow brick walls

The prediction and the physical understanding of sound transmission through masonry walls made of hollow bricks remain an open question. To solve this problem a semi-analytical approach is proposed. The inhomogeneous structures of the brick wall are homogenised and a simplified analytical model is established to calculate the transmission loss of an equivalent finite and multilayered anisotropic plate. An efficient numerical homogenisation technique is derived to define the equivalent anisotropic brick. This process only needs the knowledge of the elastic tensor of the brick material that has been determined using ultrasonic measurements. The features of the simplified brick wall have been then investigated through Lamb waves dispersion curves. Finally, the model has been used to explain the transmission loss curve of a wall and a good agreement between predictions and test data is obtained.