Deposit of UV- or γ-synthesized gold nanoparticles on TiO2 powder using lipid-based multilamellar vesicles

This article describes a general method for the deposition of gold nanoparticles onto solid support based on the use of multilamellar vesicles (MLVs). Gold nanoparticles (nps) synthesized within lipid-based MLVs by UV- or γ-irradiation were deposited onto TiO₂ powder support. The organic phase from MLVs was removed by calcination leading to high dispersion of naked Au nanoparticles. The resulting particles were investigated using spectrometry, electron microscopy and XPS. The gold nanoparticles were stable and well-separated on the titania surface. It was found that the metal nanoparticles produced by radiolysis have smaller average size and narrower size distribution than those synthesized by photochemical route. After calcinations, the particles tended to enlarge to reach c.a. 18 nm. The gold loading on the titania support could be controlled by changing the gold salt concentration and the MLV-to-TiO₂ weight ratio; values of Au-to-Ti ratio up to 44 % could be obtained.     

Top‐Down and Bottom‐Up Approaches in Engineering 1 T Phase Molybdenum Disulfide (MoS2): Towards Highly Catalytically Active Materials

The metallic 1 T phase of MoS₂ has been widely identified to be responsible for the improved performances of MoS₂ in applications including hydrogen evolution reactions and electrochemical supercapacitors. To this aim, various synthetic methods have been reported to obtain 1 T phase‐rich MoS₂. Here, the aim is to evaluate the efficiencies of the bottom‐up (hydrothermal reaction) and top‐down (chemical exfoliation) approaches in producing 1 T phase MoS₂. It is established in this study that the 1 T phase MoS₂ produced through the bottom‐up approach contains a high proportion of 1 T phase and demonstrates excellent electrochemical and electrical properties. Its performance in the hydrogen evolution reaction and electrochemical supercapacitors also surpassed that of 1 T phase MoS₂ produced through a top‐down approach.     

Syntheses of Lewis(x) and dimeric Lewis(x): construction of branched oligosaccharides by a combination of preactivation and reactivity based chemoselective one-pot glycosylations

Two asymmetrically branched oligosaccharides, LewisX and dimeric LewisX, were assembled in one pot with high yields and exclusive regio- and stereoselectivities. p-Tolyl thioglycosides were utilized as the sole type of building blocks, thus simplifying the overall synthetic design. The reactivity-independent nature of the preactivation based method allows modular assembly of the dimeric LewisX octasaccharide without the need for tedious protective group manipulation to achieve exact anomeric reactivities.     

Designing Organic/Inorganic Colloids by Heterophase Polymerization

Polymer/silica and polymer/Laponite nanocomposite colloids with various morphologies have been elaborated through emulsion polymerization using a polymerizable organosilane (route I) and a methyl methacrylate-terminated macromonomer (route II) as coupling agents. Depending on the synthetic strategy and on the nature of the mineral particles, either core-shell, raspberry-like, multipod-like, currant bun or inverted core-shell morphologies (the mineral forming the shell) were achieved. Beyond the control of particle shape, we have demonstrated that some of the polymerizations exhibited particular kinetics behaviors which could be correlated to the mechanism of formation of the composite particles. Interestingly, conversion versus time curves of a series of soap free polymerizations performed in the presence of the macromonomer showed a significant increase in the polymerization rate with increasing the inorganic particles concentration. Characterization of the composite latexes by transmission electron microscopy showed that the mineral was located at the surface of the latex spheres and participated therefore to their stabilization. The higher the amount of inorganic particles, the lower the particles size and the higher the polymerization rate.     

Orientation-dependent recovery in strongly deformed Al–0.1% Mn crystals

Single crystals of Al–0.1% Mn were channel-die compressed to a true strain of 2.3 and their recovery behaviour at 240–320°C investigated by microhardness measurements, electron backscatter diffraction (EBSD) microtexture mapping and X-ray line broadening analysis. The crystal orientations were the nominally stable Goss {110}?001?, brass {110}?112? and S {123}?634?. For all three orientations the microhardness decreases with a logarithmic time dependence but the instantaneous recovery rates of the brass oriented crystals are systematically lower than those of the other two orientations by a factor of about 2. The dislocation densities decrease rapidly in the first stages of recovery (<1?min) by dislocation dipole annihilation and more slowly thereafter. In the Goss and S orientations the later stage of recovery is due to sub-grain growth. The orientation dependence is ascribed to the relatively low misorientations developed by plastic straining in the brass crystals (average about 4°) compared with the Goss and S orientations (about 7–8°).     

A contrast estimator for completely or partially observed hypoelliptic diffusion

Parametric estimation of two-dimensional hypoelliptic diffusions is considered when complete observations–both coordinates discretely observed–or partial observations–only one coordinate observed–are available. Since the volatility matrix is degenerate, Euler contrast estimators cannot be used directly. For complete observations, we introduce an Euler contrast based on the second coordinate only. For partial observations, we define a contrast based on an integrated diffusion resulting from a transformation of the original one. A theoretical study proves that the estimators are consistent and asymptotically Gaussian. A numerical application to Langevin systems illustrates the nice properties of both complete and partial observations’ estimators.     

Bulk synthesis of polymer-inorganic colloidal clusters

We describe a procedure to synthesize colloidal clusters with polyhedral morphologies in high yield (liter quantities at up to 70% purity) using a combination of emulsion polymerization and inorganic surface chemistry. We show that the synthesis initially used for silica-polystyrene hybrid clusters can be generalized to create clusters from other inorganic and polymer particles. We also show that high yields of particular morphologies can be obtained by precise control of the inorganic seed particle size, a finding that can be explained using a hard-sphere packing model. These clusters can be further chemically modified for a variety of applications. Introducing a cross-linker leads to colloidal clusters that can be index matched in an appropriate solvent, allowing them to be used for particle tracking or optical studies of colloidal self-assembly. Also, depositing a thin silica layer on these colloids allows the surface properties to be controlled using silane chemistry.     

Strong ligand-protein interactions revealed by ultrafast infrared spectroscopy of CO in the heme pocket of the oxygen sensor FixL

In heme-based sensor proteins, ligand binding to heme in a sensor domain induces conformational changes that eventually lead to changes in enzymatic activity of an associated catalytic domain. The bacterial oxygen sensor FixL is the best-studied example of these proteins and displays marked differences in dynamic behavior with respect to model globin proteins. We report a mid-IR study of the configuration and ultrafast dynamics of CO in the distal heme pocket site of the sensor PAS domain FixLH, employing a recently developed method that provides a unique combination of high spectral resolution and range and high sensitivity. Anisotropy measurements indicate that CO rotates toward the heme plane upon dissociation, as is the case in globins. Remarkably, CO bound to the heme iron is tilted by ~30° with respect to the heme normal, which contrasts to the situation in myoglobin and in present FixLH-CO X-ray crystal structure models. This implies protein-environment-induced strain on the ligand, which is possibly at the origin of a very rapid docking-site population in a single conformation. Our observations likely explain the unusually low affinity of FixL for CO that is at the origin of the weak ligand discrimination between CO and O(2). Moreover, we observe orders of magnitude faster vibrational relaxation of dissociated CO in FixL than in globins, implying strong interactions of the ligand with the distal heme pocket environment. Finally, in the R220H FixLH mutant protein, where CO is H-bonded to a distal histidine, we demonstrate that the H-bond is maintained during photolysis. Comparison with extensively studied globin proteins unveils a surprisingly rich variety in both structural and dynamic properties of the interaction of a diatomic ligand with the ubiquitous b-type heme-proximal histidine system in different distal pockets.