Directing Reaction Pathways through Controlled Reactant Binding at Pd–TiO2 Interfaces

Recent efforts to design selective catalysts for multi-step reactions, such as hydrodeoxygenation (HDO), have emphasized the preparation of active sites at the interface between two materials having different properties. However, achieving precise control over interfacial properties, and thus reaction selectivity, has remained a challenge. Here, we encapsulated Pd nanoparticles (NPs) with TiO₂ films of regulated porosity to gain a new level of control over catalyst performance, resulting in essentially 100 % HDO selectivity for two biomass-derived alcohols. This catalyst also showed exceptional reaction specificity in HDO of furfural and m-cresol. In addition to improving HDO activity by maximizing the interfacial contact between the metal and metal oxide sites, encapsulation by the nanoporous oxide film provided a significant selectivity boost by restricting the accessible conformations of aromatics on the surface.     

Electrochemical determination of reduction potentials in glass-forming melts

Square-wave voltammetry (SWV) has been used to determine the reduction potentials of several multivalent elements in situ in an alkali borosilicate melt. Such reduction potentials measured at melt temperature were found to be proportional to the relative reduction potentials obtained from analyses of the quenched glasses. Accordingly, the redox state of the glass typically reflects the redox state of the melt. Although SWV is a sensitive tool for monitoring the total concentration of specific multivalent elements in the melt, the method does not directly monitor the redox state of the melt.     

Differential inhibition of postnatal brain,spinal cord and body growth by a growth hormone antagonist

Background  

Growth hormone (GH) plays an incompletely understood role in the development of the central nervous system (CNS). In this study, we use transgenic mice expressing a growth hormone antagonist (GHA) to explore the role of GH in regulating postnatal brain, spinal cord and body growth into adulthood. The GHA transgene encodes a protein that inhibits the binding of GH to its receptor, specifically antagonizing the trophic effects of endogenous GH.     

Adsorption and reaction of 1-epoxy-3-butene on Pt(111): implications for heterogeneous catalysis of unsaturated oxygenates

High-resolution electron energy loss spectroscopy (HREELS), temperature-programmed desorption (TPD), and density functional theory (DFT) calculations were used to study the adsorption and reaction of 1-epoxy-3-butene (EpB) on Pt(111). These investigations were conducted to help elucidate mechanisms for improving olefin hydrogenation selectivity in reactions of unsaturated oxygenates. EpB dosed to Pt(111) at 91 K adsorbs molecularly on the surface through the vinyl group with apparent rehybridization to a di-sigma-bound state. By 233 K, however, EpB undergoes epoxide ring opening to form an aldehyde intermediate, which further decomposes upon heating to yield gas phase products CO, H2, and propylene. Comparison of the HREELS and TPD data to experiments performed with 2-butenal (crotonaldehyde) shows that EpB and 2-butenal decompose through related pathways. However, the EpB-derived aldehyde intermediate clearly has a unique structure, features of which have been elucidated by DFT calculations. In conjunction with previous surface science studies of EpB chemistry, these results can help explain selectivity trends for reactions of EpB on Pt catalysts and bimetallic PtAg catalysts, with indications that the enhanced olefin hydrogenation selectivity of PtAg catalysts likely originates from a bifunctional effect.     

Transfer measurements for the Ti+Ni systems at near barrier energies

Large enhancements have been observed in the sub-barrier fusion cross sections for Ti+Ni systems in our previous studies. Coupled channel calculations incorporating couplings to 2⁺ and 3⁻ states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer were carried out for ^46,48Ti+⁶¹Ni systems. The present paper gives the results of these studies.     

Using FTIR spectroscopy to detect sericin on historic silk

Silks represent some of the most precious ancient and historic textile artefacts in collections worldwide.Their optimum preservation demands an appreciation of their characteristics.One important concern,especially with regard to ancient Chinese silks,is whether the fabrics have been degummed.Silks with remnant sericin gum coating the fibroin fibres would require different conservation protocol.In previous research on aged silks,the presence of sericin has been inferred from amino acid analysis of hydrolysa...     

Theoretical study of the adsorption and dissociation of oxygen on Pt(111) in the presence of homogeneous electric fields

The effect of homogeneous electric fields on the adsorption energies of atomic and molecular oxygen and the dissociation activation energy of molecular oxygen on Pt(111) were studied by density functional theory (DFT). Positive electric fields, corresponding to positively charged surfaces, reduce the adsorption energies of the oxygen species on Pt(111), whereas negative fields increase the adsorption energies. The magnitude of the energy change for a given field is primarily determined by the static surface dipole moment induced by adsorption. On 10-atom Pt(111) clusters, the adsorption energy of atomic oxygen decreased by ca. 0.25 eV in the presence of a 0.51 V/A (0.01 au) electric field. This energy change, however, is heavily dependent on the number of atoms in the Pt(111) cluster, as the static dipole moment decreases with cluster size. Similar calculations with periodic slab models revealed a change in energy smaller by roughly an order of magnitude relative to the 10-atom cluster results. Calculations with adsorbed molecular oxygen and its transition state for dissociation showed similar behavior. Additionally, substrate relaxation in periodic slab models lowers the static dipole moment and, therefore, the effect of electric field on binding energy. The results presented in this paper indicate that the electrostatic effect of electric fields at fuel cell cathodes may be sufficiently large to influence the oxygen reduction reaction kinetics by increasing the activation energy for dissociation.     

Iron-catalyzed Doyle-Kirmse reaction of allyl sulfides with (trimethylsilyl)diazomethane

[formula: see text] Iron salts efficiently catalyze the Doyle-Kirmse reaction of allyl sulfides with (trimethylsilyl)diazomethane and ethyl diazoacetate in dichloroethane at 83 degrees C. Competitive dimerization is less of a problem with (trimethylsilyl)diazomethane than with ethyl diazoacetate. Good results are obtained using only 1.5 equiv of (trimethylsilyl)diazomethane, even without slow addition. Phosphine ligands affect the kinetics, but not the diastereoselectivity. Dppe and BINAP lead to higher yields than dppp, but no enantioselection was detected with R-(+)-BINAP.