Bimetallic Ag‐Pt Sub‐nanometer Supported Clusters as Highly Efficient and Robust Oxidation Catalysts

A combined experimental and theoretical investigation of Ag‐Pt sub‐nanometer clusters as heterogeneous catalysts in the CO→CO₂ reaction (COox) is presented. Ag₉Pt₂ and Ag₉Pt₃ clusters are size‐selected in the gas phase, deposited on an ultrathin amorphous alumina support, and tested as catalysts experimentally under realistic conditions and by first‐principles simulations at realistic coverage. In situ GISAXS/TPRx demonstrates that the clusters do not sinter or deactivate even after prolonged exposure to reactants at high temperature, and present comparable, extremely high COox catalytic efficiency. Such high activity and stability are ascribed to a synergic role of Ag and Pt in ultranano‐aggregates, in which Pt anchors the clusters to the support and binds and activates two CO molecules, while Ag binds and activates O₂, and Ag/Pt surface proximity disfavors poisoning by CO or oxidized species.     

The development of information storage materials — How microscopy can help?

The response of giant magnetoresistance (GMR) devices depends critically on the film microstructure, with parameters such as layer thickness and interfacial abruptness being crucial. This paper presents results obtained using high resolution electron microscopy (HREM), chemical mapping and atom probe microanalysis. Local variations in the magnetic properties are induced by the microstructure and also when the films are patterned to form small elements. These lead to changes in the magnetization reversal mechanism. Some results of the studies of the magnetization reversal carried out using in situ in Lorentz transmission electron microscopy (LTEM) magnetizing experiments are also included.     

pH‐Triggered Sustained Drug Delivery from a Polymer Micelle having the β‐Thiopropionate Linkage

The synthesis, micellar aggregation, and pH‐triggered intracellular drug delivery ability of an amphiphilic statistical copolymer (P2) are studied. Two methacrylate derivatives, one containing a hydrophilic pendant and the other containing a hydrophobic pendant chain, are copolymerized to produce P2. The hydrophobic pendant chain is linked to the polymer backbone by a β‐thiopropionate linkage, known to undergo slow hydrolysis at mild acidic pH. P2 forms a multimicellar cluster in water with a critical aggregation concentration of 0.02 mg mL⁻¹ and encapsulates a hydrophobic guest such as pyrene, Nile red, or the anti‐cancer drug doxorubicin (Dox). Sustained release of the entrapped Dox (80% after 100 h) is noticed at pH 5.2, while release is significantly slower (35% after 100 h) at pH 7.4. Acidic hydrolysis of the β‐thiopropionate linkage leading to the reduction of the hydrophobicity is established as the cause for micellar disassembly and triggered drug release. Cell‐culture studies with the human breast cancer cell line, MCF‐7, reveal biocompatibility of P2 (below 150 μg mL⁻¹). It is further tested for intracellular delivery of Dox. MCF‐7 cells remain healthy at pH 7.4 but become unhealthy at pH 5.2 when treated with a Dox‐loaded P2 micelles.

     

Dynamic solvation in imidazolium-based ionic liquids on short time scales

Steady-state and time-resolved Stokes shift data for the probe coumarin 153 in two imidazoles, six imidazolium-based ionic liquids, and several other solvents are presented. These results are consistent with our original suggestion (J. Phys. Chem. B 2004, 108, 10245-10255) that initial solvation is dominated by the organic moiety of the ionic liquid, and they show that for the imidazole-based liquids initial solvation is in all cases very rapid. Solvation by methylimidazole and butylimidazole is complete in 100 ps, and all of the imidazolium ionic liquids demonstrate similarly rapid initial solvation. Owing to the importance of determining the amount of initial solvation that is missed in a given experiment with finite time resolution, we discuss a method of estimating the intramolecular contribution to the reorganization energy. This method yields 2068 cm(-1) and is compared with an alternative method.     

Peak effect studies in single crystals CeRu2 and 2H-NbS2

We have studied the peak effect (PE) phenomenon in single crystals of weakly pinned superconductors CeRu₂ and 2H-NbS₂. 2H-NbS₂ is iso-structural and iso-electronic to 2H-NbSe₂, whose similarity with CeRu₂ as regards the PE representing the order-to-disorder transformation of the flux line lattice was claimed some time ago. We report on the step change in equilibrium magnetization across the peak effect in CeRu₂. We also present the vortex phase diagram of 2H-NbS₂ obtained from the magnetization data, and compare the PE phenomenon in 2H-NbS₂ and 2H-NbSe₂.     

UV–Vis and NMR spectroscopic investigations on effective and selective non-covalent interactions between fullerenes and calix[6]arene

Ground state non-covalent interactions between a macro cyclic calixarene receptor, namely, 4-tert-butylcalix[6]arene (1), and fullerenes (C₆₀ and C₇₀) were studied in toluene medium by absorption spectrophotometric method. Absorption band due to the charge transfer (CT) transition have been observed in the visible region between fullerenes and 1. Utilizing the CT absorption bands, various important physicochemical parameters like oscillator strength, resonance energy, transition dipole strength of the fullerene-1 complexes and ionization potential of 1 is determined in present investigations. From Jobs method of continuous variation, it is observed that both C₆₀ and C₇₀ form stable 1:1 complexes with 1. The most fascinating feature of the present study is that 1 binds selectively C₇₀ compared to C₆₀ as obtained from binding constant (K) data of C₆₀–1 (K_C60–1) and C₇₀–1 (K_C70–1) complexes, i.e., K_C60–1 = 32,400 dm³·mol^? 1 and K_C70–1 = 110,000 dm³.mol^? 1 and selectivity (K_C70–1/K_C60–1) = 3.4. ¹H NMR analysis provides very good support in favor of strong binding between C₇₀ and 1.     

Elucidating the structure of surface acid sites on γ-Al2O3

Differential pair distribution function analysis was applied to resolve, with crystallographic detail, the structure of catalytic sites on the surface of nanoscale γ-Al(2)O(3). The structure was determined for a basic probe molecule, monomethylamine (MMA), bound at the minority Lewis acid sites. These active sites were found to be five-coordinate, forming distorted octahedra upon MMA binding. This approach could be applied to study the interaction of molecules at surfaces in dye-sensitized solar cells, nanoparticles, sensors, materials for waste remediation, and catalysts.     

Conformational supramolecular isomerism in one-dimensional silver(I) coordination polymer of a flexible bis(bidentate) N,N-donor ligand with p-xylyl spacer

The isolation and structural characterisation of three isomeric silver(I) complexes, 1a, 1b and 2 with the general formula {[AgL(1)]ClO(4)}(n) (where L(1) is a bis(bidentate) N,N-donor ligand derived from the Schiff-base condensation of α,α'-diamino-p-xylene and pyridine-2-carboxaldehyde) are discussed. Single-crystal X-ray structures reveal the polymeric nature for the complexes where all the silver ions are in pseudotetrahedral geometry with the AgN(4) coordination environment. Isomers 1a (Pc space group) and 1b (Cc space group) were crystallised from acetonitrile whereas 2 (C2/c space group) was crystallised during the synthesis from a solvent mixture of dicholormethane and methanol. The flexible ligand (L(1)) adopts only an anti conformation in 1b and the presence of two different anti conformations in the repeating unit results in the formation of a trapezoidal wave polymeric chain. However, both gauche and anti conformations of the ligand are found to be present in the polymeric chains of 1a. In the polymeric chain of 2, only one anti isomer of the ligand is present in the repeating unit resulting in a triangular wave chain. The structure of isomer 1a is solvent induced and solvent plays a major role in the crystal packing of this isomer. One-dimensional coordination polymers 1a, 1b and 2 are related to each other as conformational supramolecular isomers. Additionally, two independent polymeric chains parallel to each other: one triangular wave consisting of only an anti conformation and a trapezoidal wave chain consisting of alternate gauche and anti conformations of the ligand are observed in 1a. This is a rare example of two supramolecular isomers present in the same crystal. Six different conformers of the flexible ligand are observed in the crystals of coordination polymers.