Dependence of surface properties of silylated silica on the length of silane arms

Amorphous precipitated Zeosil 1165 MP silica was silylated with low grafting degrees of organosilicons bearing different alkoxy and hydrocarbon tails, like monomethoxy(dimethyl)octadecylsilane (DMODMS), monomethoxytrimethylsilane (TMMS), trimethoxymercaptopropylsilane (MPTS), and 3-octanoylthio-1-propyltriethoxysilane (NXT^?). Thermogravimetry and Elemental Analysis were used to determine the degree of silane grafting and the final number of free silanol OH groups/nm² on the modified Zeosil surface. Free energy, enthalpy and entropy of adsorption of hydrocarbon probes were determined by Inverse Gas Chromatography at infinite dilution and dispersive component, $\gamma_{s}^{d}$ , and specific interaction parameter, I ^sp , of the surface tension of the silica surface were calculated. Silylation changes the hydrophilic character of Zeosil silica to the hydrophobic one, on increasing the grafting degree and, mainly, the length of hydrocarbon tail of the silane molecule (DMODMS and NXT^?). The long hydrocarbon tails practically shield the silica particle surface and the adsorbed probes preferentially interact with them. In the case of TMMS-Zeosil the adsorbed probes practically interact with the silica surface, with loss of entropy well above that of the bare silica, while being equal the values of the enthalpy of adsorption. All the other modified silicas show loss of entropy lower than that of bare silica. Steric hindrance, played by the presence of methyl groups of TMMS, is suggested to reduce the freedom of translational and rotational movements of the adsorbed probe.     

Electrophoresis in gel channels

We describe a novel approach to generate dynamic pH gradients suited to fractionate or purify samples of biomolecules or particles such as proteins and viruses in tiny volumes. The method combines diffusion and electromigration between micro-scaled channels embedded in hydrogel. For the used geometry and in accordance with numerical calculations the gel-channel system reaches a tuneable, steady-state pH gradient after a few minutes. For quantification of experimentally generated pH-profiles, the concentration independent extinction ratio of phenol red at two wavelengths is used. The proposed electrophoretic flow-cell is simple and flexible since no Immobilines are required to establish the pH gradient.     

Outstanding Methane Oxidation Performance of Palladium‐Embedded Ceria Catalysts Prepared by a One‐Step Dry Ball‐Milling Method

By carefully mixing Pd metal nanoparticles with CeO₂ polycrystalline powder under dry conditions, an unpredicted arrangement of the Pd‐O‐Ce interface is obtained in which an amorphous shell containing palladium species dissolved in ceria is covering a core of CeO₂ particles. The robust contact that is generated at the nanoscale, along with mechanical forces generated during mixing, promotes the redox exchange between Pd and CeO₂ and creates highly reactive and stable sites constituted by PdO_x embedded into CeO₂ surface layers. This specific arrangement outperforms conventional Pd/CeO₂ reference catalysts in methane oxidation by lowering light‐off temperature by more than 50°C and boosting the reaction rate. The origin of the outstanding activity is traced to the structural properties of the interface, modified at the nanoscale by mechanochemical interaction.     

Investigation into the interactions between filler and elastomers used for tyre production

An investigation in the interactions between silica and elastomers used in the production of tyre treads was carried out. To achieve some knowledge on the interactions between reinforcing agent and elastomers, which are fundamental in determining the rubber reinforcement, inverse gas chromatography (IGC) at infinite dilution was used to evaluate surface properties of both unmodified and modified silica and to calculate the adsorption free energy and enthalpy of low molecular weight analogues of elastomers. The predictions derived from the thermodynamic study were compared with some of the results obtained by a morphological analysis of silica-filled compounds carried out by transmission electron microscopy (TEM) and automated image analysis (AIA).     

Vibration-inversion-rotation spectra of ammonia: A vibration-inversion-rotation Hamiltonian for NH2D and ND2H

The model Hamiltonian developed previously for ammonia NH₃ has been used to study the vibration-inversion-rotation energy levels of the isotopic species of ammonia NH₂D and ND₂H. In this model the inversion motion is removed from the vibrational problem by allowing the molecular reference configuration to be a function of the large amplitude motion coordinate.The ground state inversion-rotation energy levels of NH₂D and ND₂H have been calculated with the use of the zeroth-order inversion-rotation Hamiltonian, and the calculated transition frequencies have been compared with the experimental data.     

N,N'-dimethylformamide-derived products from catalytic oxidation of 3-hydroxyflavone

The biomimetic conversion of 3-hydroxyflavone in the presence of a copper(II) catalyst, dioxygen, and N,N'-dimethylformamide to oxidation products as well as two previously unreported solvent-derived products is seen. The two solvent-derived products were characterized, and their crystal structures were determined.