Asymmetric hydrogenation of enol phosphinates by iridium catalysts having N,P ligands

[reaction: see text] Enol phosphinates, which are structural analogues of enol acetates, have for the first time been employed as substrates for Ir-catalyzed asymmetric hydrogenation. A number of enol phosphinates have been synthesized and reduced successfully with up to and above 99% ee.     

Bayesian stratified random sampling using auxiliary information

Summary Smith (1976,J. R. Statist. Soc., A,139, 183–204) has argued that survey statisticians should attempt to model finite population structures in the same way that statisticians in other disciplines have to provide models of finite or infinite populations. Following this argument, we suggest in this paper that an obvious model for a stratified population when auxiliary information regarding variate values is available, is the one way analysis of covariance model with unequal variances and we consider the problem of estimating the finite population mean. Finally a possible extension of this result is discussed.     

Idiosyncratic Ag7Pt2O7: An Electron Imprecise yet Diamagnetic Small Band Gap Oxide

The seminal qualitative concepts of chemical bonding, as presented by Walter Kossel and Gilbert Newton Lewis back in 1916, have lasting general validity. These basic rules of chemical valence still serve as a touchstone for validating the plausibility of composition and constitution of a given chemical compound. We report on Ag₇Pt₂O₇, with a composition that violates the basic rules of chemical valence and an exotic crystal structure. The first coordination sphere of platinum is characteristic of tetravalent platinum. Thus, the electron count corresponds to Ag₇Pt₂O₇*e⁻, where excess electrons are associated with the silver substructure. Such conditions given, it is commonly assumed that the excess electrons are either itinerant or localized in Ag−Ag bonds. However, the material does not show metallic conductivity, nor does the structure feature Ag-Ag pairs. Instead, the excess electrons organize themselves in 2e−4c bonds within the silver substructure. This subvalent silver oxide reveals a new general facet pertinent to silver chemistry.     

Synthesis of gold nanoparticles using herbal Acorus calamus rhizome extract and coating on cotton fabric for antibacterial and UV blocking applications

Gold nanoparticles (AuNPs) have been synthesized by greener method using chloroauric acid as precursor and extract of Acorus calamus rhizome as reducing agent. Formation of AuNP was confirmed by the presence of Surface Plasmon Resonance (SPR) peak in UV–Visible spectral analysis. XRD and FT-IR spectral analyses were performed for characterization. SEM images show spherical morphology and HR-TEM images reveal nanosize of AuNPs. The AuNPs were then coated on cotton fabric by pad-dry-cure method and characterized by SEM with EDAX technique. The results reveal the deposition of AuNPs on the surface of cotton fabric. Uncoated cotton, neat extract coated cotton and extract containing AuNPs coated cotton fabrics were then tested for antibacterial activity against Gram positive (Staphylococcus aureus) and Gram negative (Escherichia coli) bacterial strains by AATCC 100 test method. It showed that the extract containing AuNPs coated cotton fabric had higher antibacterial activity than other test samples against E. coli. UV-DRS analysis performed on extract containing AuNPs coated cotton fabric showed improved UV-blocking property than uncoated cotton fabric and neat extract coated cotton fabric.     

A source of screw dislocation in polyoxymethylene crystals

Polyoxymethylene crystallizes as hexagonal lamellar crystals accompanied by spiral growth from dilute bromobenzene solution. Spirals of this polymer are formed by several mechanisms. There is discussion of various origins of screw dislocation due to interlocking of two independently growing crystals with crevices. After entanglement, various growth stages of crystals have been observed.     

Etching and the morphology of branched and cross-linked polyethylene

A permanganic acid etching technique was used to characterize the genuine morphologies of bulk crystallized samples of linear, branched, and crosslinked polyethylene. Four different kinds of artifacts as large as 15–20 m were detected. It was also noted that artifact density could be drastically reduced by proper selection of etching conditions. The morphologies of artifacts were independent of specimen crystallinity and the orientation of lamellar crystals; however, their rate of production was susceptible to the crystallinity of samples. The formation of a fresh surface involved the preferential etching of edge-on and secondary lamellae. As the growth features of cross-linked polyethylene were less than 6 m and were mainly sheaf-like structures, growth features could be readily distinguished from the artifacts by transmission electron microscopy. Another type of artifact (globules morphology) produced at angstrom scale was found to depend on the crystallinity and the surface structure of lamellar crystals. It is demonstrated that the fine lamellar details of branched and cross-linked polyethylene can be observed using transmission electron microscopy. Increasing the number of cross-links in polyethylene, modifies the size and nature of supermolecular structures, the periodic twisting of lamellar crystals, and the nature of the nucleation process. The study of a blend of branched and cross-linked polyethylene showed that the structurally dissimilar molecules co-crystallized at low crystallization temperatures, while there is a tendency for molecular fractionation at higher crystallization temperatures.     

Rectangular single crystals of polyacrylonitrile

Rectangular single, multilayered and twinned crystals of polyacrylonitrile have been grown from the fractionated samples in propylene carbonate at different temperatures (140–150°) using Film Formation Method of crystal growth.     

Copper(II)‐Specific Fluorogenic Task‐Specific Ionic Liquids as Selective Fluorescence Probes and Recyclable Extractants

The designed synthesis of a series of copper(II) specific fluorogenic hydrophobic task‐specific ionic liquids (TSILs) from a new naphthalene‐based tetradentate ligand is reported. Absorption and fluorescence spectral studies reveal both the ligand and its derivative TSILs show exclusive selectivity towards copper(II) ions. The Stern–Volmer method for calculation of the detection limit for ligand and TSIL_1–3 shows values of 0.12, 20, 17, and 15 μM , respectively. Extraction and striping studies by doping these TSILs in [bmim][NTf₂] demonstrated that these TSILs are recyclable extractants for the selective recovery of Cu^II ions from a mixture of 14 relevant metal chloride aqueous solutions in biphasic liquid–liquid extraction with approximately 95 % recovery.     

Water-in-carbon dioxide emulsions stabilized with hydrophobic silica particles

W/C emulsions were stabilized using hydrophobic silica particles adsorbed at the interface, resulting in average droplet diameters as low as 7.5 microm. A porous cross-linked shell was formed about a hydrophilic (colloidal and fumed) silica core with a trifunctional silylating agent, (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethyoxysilane, to render the particles CO(2)-philic. The stability of emulsions comprising equal weights of CO(2) and water was assessed with visual observations of settling fronts and the degree of emulsion coalescence, and the average drop size was measured by optical microscopy. The effect of CO(2) density on both emulsion stability and droplet size was determined quantitatively. The major destabilizing mechanism of the emulsions was settling, whereas Ostwald ripening and coalescence were not visible at any density, even over 7 days. Flocculation of the settling droplets did not occur, although gelation of the emulsions through particle interactions resulted after longer periods of time. CO(2)-philic particles offer a new route to highly stable W/C emulsions, with particle energies of attachment on the order of 10(6)kT, even at CO(2) densities as low as 0.78 g ml(-1). At these low densities, surfactants rarely stabilize emulsions as the result of poor surfactant tail solvation.     

Recent developments on ion-exchange membranes and electro-membrane processes

Rapid growth of chemical and biotechnology in diversified areas fuels the demand for the need of reliable green technologies for the down stream processes, which include separation, purification and isolation of the molecules. Ion-exchange membrane technologies are non-hazardous in nature and being widely used not only for separation and purification but their application also extended towards energy conversion devices, storage batteries and sensors etc. Now there is a quite demand for the ion-exchange membrane with better selectivities, less electrical resistance, high chemical, mechanical and thermal stability as well as good durability. A lot of work has been done for the development of these types of ion-exchange membranes during the past twenty-five years. Herein we have reviewed the preparation of various types of ion-exchange membranes, their characterization and applications for different electro-membrane processes. Primary attention has been given to the chemical route used for the membrane preparation. Several general reactions used for the preparation of ion-exchange membranes were described. Methodologies used for the characterization of these membranes and their applications were also reviewed for the benefit of readers, so that they can get all information about the ion-exchange membranes at one platform. Although there are large number of reports available regarding preparations and applications of ion-exchange membranes more emphasis were predicted for the usefulness of these membranes or processes for solving certain type of industrial or social problems. More efforts are needed to bring many products or processes to pilot scale and extent their applications.