Self-organization processes and synthesis of nanostructured silver microparticles in AgNO<Subscript>3</Subscript> solutions with variable pH values

The morphology of micrometer-sized silver particles obtained by liquid-phase chemical reduction of silver nitrate with ascorbic acid depends appreciably on the solution pH. The synthesis carried out at 100°C for 20 min at pH < 4 or pH > 9 yields anisotropic faceted nanocrystalline particles, while the synthesis at pH = 5–8 results in self-assembly to give microspheres representing close-packed aggregates of a huge number of silver nanoparticles with a cauliflower structure.     

Effect of hydrogen adsorption on the x-ray absorption spectra of small Pt clusters

Hydrogen adsorption on Pt(6)H(n) clusters leads to striking changes in the Pt L(2,3) x-ray absorption spectra. These effects are interpreted using a self-consistent real space Green's function approach. Calculations show that they are due largely to changes in the atomic background contribution to x-ray absorption (i.e., atomic x-ray absorption fine structure) and to reduced Pt-Pt scattering at the edge, while Pt-H multiple scattering is relatively weak. The origin of both effects is traced to the change in the local Pt potential due to Pt-H bonding.     

Mathematical model of a kinetic boundary layer

The two-dimensional (plane) problem of a hypersonic kinetic boundary layer developing on a thin body in the case of a homogeneous polyatomic gas flow with no dissociation or electron excitation is considered assuming that energy exchange between translational and internal molecular degrees of freedom is easy. (The approximation of a hypersonic kinetic boundary layer arises from the kinetic theory of gases and, within the thin-layer model, takes into account the strong nonequilibrium of the hypersonic flow with respect to translational and internal degrees of freedom of the gas particles.) A method is proposed for constructing the solution of the given kinetic problem in terms of a given solution of an equivalent well-studied classical Navier-Stokes hypersonic boundary layer problem (which is traditionally formulated on the basis of the Navier-Stokes equations).     

The modes of combustion of copper nanopowders

It was shown that the synthesis of Cu nanopowder by thermal decomposition afforded chemically purer (without oxides) and finer (specific surface value ～45 m2 g^?1) product than the synthesis by chemical reduction. The latter method leads to pyrophoric nanopowders containing detectable amounts of copper oxides.     

Optical characterization of synthetic opals

The results of a structural-optical characterization of synthetic opals are presented. Information on the growth-induced features of the opal structure was derived from an analysis of the position and width of the one-dimensional photonic band gap. The structure of the samples was found to vary substantially along the growth axis coinciding with the [111] direction of the fcc lattice. It was shown that the regions corresponding to early stages in the opal structure growth are typically strongly disordered, which manifests itself, in particular, in the crystallites being misoriented relative to the sample growth axis. It was concluded that the regions of synthetic opals most suitable for application as photonic crystals are those corresponding to later growth stages.     

Dependence of the atomic structure and surface relief of platinum foils on the annealing and rolling conditions

The effect of cold rolling, polishing, and thermal annealing conditions on the atomic structure and surface geometry of platinum foils has been studied. The surface morphology has been analyzed using low-energy electron diffraction, atomic force microscopy, and scanning tunneling microscopy. The chemical composition of the surface has been evaluated by Auger electron spectroscopy. It has been demonstrated that a variation in the conditions used for the preparation of the samples makes it possible to produce surfaces with different degrees of perfection from atomically smooth to rippled, fractal, and diffraction-disordered surfaces.     

Planar Chiral Rhodium Complexes of 1,4-Benzoquinones

Diene rhodium complexes are important catalysts in modern organic synthesis. Herein, we report a new approach to such complexes with the uncommon planar chirality. The synthesis is achieved by face-selective coordination of the prochiral 2,5-disubstituted-1,4-benzoquinones (R₂-Q) with rhodium precursors containing the chiral auxiliary ligand S-salicyl-oxazoline (S-Salox). Such coordination leads to the formation of (R,R-R₂-Q)Rh(S-Salox) complexes in high yields and with exceptional diastereoselectivity (d. r.>20 : 1). Subsequent replacement of the auxiliary ligand provides various benzoquinone rhodium complexes with retention of the planar chirality. Combined theoretical and experimental studies show that due to their electron-withdrawing nature benzoquinones bind metals stronger than the related 1,4-cyclohexadiene, but weaker than other common diene ligands, such as cyclooctadiene.     

Modeling Flow in a Shock Viscous Layer

This paper considers the two-dimensional problem of the theory of viscous hypersonic flows formulated for the high-velocity translational-nonequilibrium flow of a monatomic gas past a surface based on macrokinetic 13-moment Grad equations using the model of a two-layer thin viscous shock layer (TVSL) near non-thin bodies. A class of similarity variables is proposed that allows the kinetic problem of the TVSL to be reduced to the well-studied Navier–Stokes problem of the TVSL.     

A Planar‐Chiral Rhodium(III) Catalyst with a Sterically Demanding Cyclopentadienyl Ligand and Its Application in the Enantioselective Synthesis of Dihydroisoquinolones

The rapid development of enantioselective C?H activation reactions has created a demand for new types of catalysts. Herein, we report the synthesis of a novel planar‐chiral rhodium catalyst [(C₅H₂^tBu₂CH₂^tBu)RhI₂]₂ in two steps from commercially available [(cod)RhCl]₂ and tert‐butylacetylene. Pure enantiomers of the catalyst were obtained through separation of its diastereomeric adducts with natural (S)‐proline. The catalyst promoted enantioselective reactions of aryl hydroxamic acids with strained alkenes to give dihydroisoquinolones in high yields (up to 97 %) and with good stereoselectivity (up to 95 % ee).