Atomistic modeling of segregation and bulk ordering in Ag-Au alloys

The bulk and surface properties of Ag-Au alloys, for the whole range of concentration and as a function of temperature, is studied by means of a simple modeling scheme using the Bozzolo-Ferrante-Smith method for alloys. Evidence for short-range order is found and explained, as well as its relationship with the experimentally observed segregation behavior.     

Surface functionalization of electro-deposited nickel

A new in situ electrochemical method of functionalizing an oxide-free Ni surface is demonstrated using octanethiol. Initial adsorption results in a multilayer molecular film, which blocks both the hydrogen evolution reaction (HER) and re-oxidation of the Ni by ambient oxygen. However, excess octanethiol can be removed by rinsing with ethanol, leaving behind a monolayer that continues to protect against re-oxidation but gives rise to an unexpected enhancement in the HER, with a greater enhancement for longer film formation times. The presence of an octanethiol monolayer on the surface was confirmed by spectroscopic observation of the CH(2), CH(3) and thiolate groups using infra red spectroscopy, while X-ray photo-electron spectroscopy demonstrated the effectiveness of the thiol layer as a barrier to surface oxidation. The electrochemically prepared octanethiol film impedes oxidation of the Ni in air more effectively than a film formed by immersion in a solution of octanethiol in ethanol.     

Solvation and aggregation of n,n'-dialkylimidazolium ionic liquids: a multinuclear NMR spectroscopy and molecular dynamics simulation study

The solvation and aggregation of the ionic liquid (IL) 1-n-butyl-3-methylimidazolium chloride ([C4mim]Cl) in water and dimethylsulfoxide (DMSO) were examined by analysis of (1)H and (35/37)Cl chemical shift perturbations and molecular dynamics (MD) simulations. Evidence of aggregation of the IL n-butyl chains in aqueous environments at IL concentrations of 75-80 wt% was observed both in the NMR experiments and in the MD simulations. The studies also show that [C4mim]Cl behaves as a typical electrolyte in water, with both ions completely solvated at low concentrations. On the other hand, the data reveal that the interactions between the [C4mim](+) and Cl(-) ions strengthen as the DMSO content of the solutions increases, and IL-rich clusters persist in this solvent even at concentrations below 10 wt%. These results provide an experimentally supported atomistic explanation of the effects that these two solvents have on some of the macroscopic properties of [C4mim]Cl. The implications that these findings could have on the design of IL-based solvent systems are briefly discussed.     

Classification of vegetable oils according to their botanical origin using amino acid profiles established by direct infusion mass spectrometry

Amino acid profiles, established by direct infusion mass spectrometry, have been used to classify vegetable oils according to their botanical origin. The proteins present in hazelnut, sunflower, corn, soybean, olive, avocado, peanut and grapeseed oils were precipitated with acetone, and the residue was hydrolyzed in acid medium, diluted in a hydrochloric acid/ethanol mixture, and infused into the mass spectrometer. The spectra of the hydrolyzed protein extracts showed [M+H]+ ions of the following amino acids: glycine, alanine, serine, proline, valine, threonine, cysteine, isoleucine + leucine, aspartic acid, lysine, glutamic acid, methionine, histidine, phenylalanine, arginine and tyrosine. These ions were used to construct linear discriminant analysis (LDA) models. The ratios of the ion signal intensities selected by pairs were used as predictors. With the sequential application of three LDA models, the eight botanical origin categories of the samples were well resolved.     

Two-photon absorption in aqueous micellar solutions

Addition of the surfactant sodium dodecyl sulfate at concentrations above the critical micelle concentration increases the fluorescence quantum yield and the two-photon absorption cross-section of charged [2.2]paracyclophane chromophores containing pairs of D-pi-D chromophores. The resulting spectra in the micellar solutions are very similar to those obtained for neutral isostructural analogues in toluene. The measured etadelta values are 1300 GM for 1C and 1920 GM for 2C, which are comparable or larger to those in toluene. These results highlight possible misleading interpretation of two-photon-induced emission for evaluating the concentration of labeled substrates used in two-photon microscopy and provide guidelines for designing molecular structures with optimized two-photon action cross-sections in water.     

Efficient synthesis of fluorinated α- and β-amino nitriles from fluoroalkylated α,β-unsaturated imines

A simple and efficient synthesis of fluoroalkylated α-amino nitrile (4) derivatives by regioselective 1,2-addition of trimethylsilyl cyanide to fluoroalkylated α,β-unsaturated imines (1) is described. Fluoroalkylated β-amino nitriles (7) are also prepared by regioselective 1,2-addition of α-carbanions derived from acetonitrile to fluoroalkylated α,β-unsaturated imines (1). Fluoroalkylated α-(4) and β-amino nitriles (7) are also prepared through an ‘one pot’ procedure by reaction of enaminophosphonate 2 with BuLi, addition of aldehydes and subsequent addition of either trimethylsilyl cyanide or α-carbanion derived from acetonitrile. Basic hydrolysis of α-(4) and β-amino nitriles (7) gives fluoroalkylated α-(5) and β-amino acids (8).     

Single and double metallic layer-containing ruthenium dendrimers. Synthesis and catalytic properties

The reaction of a series of phosphanyl-terminated carbosilane dendrimers displaying only one phosphorus ligand per arm with [RuCl(2)(p-cymene)](2) resulted in the grafting of RuCl(p-cymene) moieties on the periphery of the dendrimer. In these species, the chloride ligand is easily displaced by the organic bases pyridine, 4-cyanopyridine and 4,4[prime or minute]-bipyridine to afford new cationic metallodendrimers. NMR studies have confirmed the chirality of the ruthenium centre. The species containing 4,4[prime or minute]-bipyridine reacts through the uncoordinated pyridyl nitrogen with a new equivalent of [RuCl(2)(p-cymene)](2) or [RhCl(CO)(2)](2) to lead to homo- or hetero-bimetallic layer-containing dendrimeric systems. The ruthenodendrimers were tested as catalysts in the transfer hydrogenation of cyclohexanone by propan-2-ol and their activity compared with that of some analogous mononuclear ruthenium(ii) complexes.     

Alpha,omega-bis(thioacetyl)oligophenylenevinylene chromophores from thioanisol precursors

The selective cleavage of arylmethyl thioethers provides a convenient protocol for the synthesis of all-E isomers of alpha, omega-bis(thioacetyl)oligophenyenevinylene molecules (OPVs). The S-methyl group is tolerant of Wittig-type and Heck-type reactions for forming OPV structures and can be converted to the S-acetyl group by treatment with sodium thiomethoxide and acetyl chloride. The thermal conditions of the deprotection/reprotection step concurrently isomerize the conjugated chromophore to the all-E isomer, regardless of the stereochemistry of the starting olefins. This approach is demonstrated for a variety of linear and [2.2]paracyclophane containing OPVs, which have been characterized by electrochemical and spectroscopic techniques. Additionally, these S-acetyl-terminated OPVs self-assemble on gold surfaces. Monolayers containing these molecules were characterized by water contact angle measurements, ellipsometry, and X-ray photoelectron spectroscopy.     

Analytical potential of mid-infrared detection in capillary electrophoresis and liquid chromatography: a review

Literature published in the last decade concerning the use of mid-infrared spectrometry as a detection system in separation techniques employing a liquid mobile phase is reviewed. In addition to the continued use of isocratic liquid chromatographic (LC) techniques, advances in chemometric data evaluation techniques now allow the use of gradient techniques on a routine basis, thus significantly broadening the range of possible applications of LC-IR. The general trend towards miniaturized separation systems was also followed for mid-IR detection where two key developments are of special importance. Firstly, concerning on-line detection the advent of micro-fabricated flow-cells with inner volumes of only a few nL for transmission as well as attenuated total reflection measurements enabled on-line mid-IR detection in capillary LC and opened the path for the first successful realization of on-line mid-IR detection in capillary zone electrophoresis as well as micellar electrokinetic chromatography. Secondly, concerning off-line detection the use of micro-flow through dispensers now enables to concentrate eluting analytes on dried spots sized a few tens of micrometers, thus matching the dimensions for sensitive detection by mid-IR microscopy. Finally in an attempt to increase detection sensitivity of on-line mid-IR detection, mid-IR quantum cascade lasers have been used. Applications cover the field of food analysis, environmental analysis and the characterization of explosives among others. Best detection sensitivities for on-line and off-line detection have been achieved in miniaturized systems and are in the order of 50 ng and 2 ng on column, respectively.     

Ketene functionalized polyethylene: control of cross-link density and material properties

The functionalization and cross-linking of polyethylene is synthetically challenging, commonly relying on highly optimized radical based postpolymerization strategies. To address these difficulties, a norbornene monomer containing Meldrum's acid is shown to be effectively copolymerized with polyethylene using a nickel α-iminocarbaxamidato complex, providing high-melting, semicrystalline polymers with a tunable incorporation of the functional comonomer. Upon heating the copolymer to common polyethylene processing temperatures, the thermolysis of Meldrum's acid to ketene provides the desired reactive group. This simple and versatile methodology does not require small molecule radical sources or catalysts, and the dimerization of the in situ generated ketenes is shown to provide tunable cross-linking densities in polyethylene. Subsequent rheological and tensile experiments illustrate the ability to tune cross-linked polyethylene properties by comonomer incorporation and elucidate valuable structure/property relationships in these materials. This study illustrates the power of well-defined and synthetically accessible functional groups in polyolefin synthesis and functionalization.