A cluster study of aluminum adsorption on Ga-rich GaAs(100)(2 × 1) and β (4 × 2) surfaces

Ab initio self-consistent total energy calculations using second order Møller-Plesset perturbation theory and Hay-Wadt effective core potentials with associated basis sets (HWECP’s) for gallium and arsenic have been used to investigate the chemisorption properties of atomic aluminum on the Ga-rich GaAs(100)-(2 × 1) and β(4 × 2) surfaces. Finite sized hydrogen saturated clusters with the experimental zinc-blende lattice constant of 5.654 Å and the energy optimized Ga dimer bond length of 2.758 Å have been used to model the semiconductor surface. To investigate the effects of the core electrons of aluminum in the adsorption process, we have represented the Al adatom with both HWECP’s and an all electron 6-311++G** basis set. Detailed energetics of chemisorption on the (100) surface, including chemisorption energies, nearest surface neighbor bond lengths, and Mulliken population analysis, have been reported for all considered sites of chemisorption.     

Probing Functional Heteromeric Chemokine Protein–Protein Interactions through Conformation‐Assisted Oxime Ligation

Protein–protein interactions (PPIs) govern most processes in living cells. Current drug development strategies are aimed at disrupting or stabilizing PPIs, which require a thorough understanding of PPI mechanisms. Examples of such PPIs are heteromeric chemokine interactions that are potentially involved in pathological disorders such as cancer, atherosclerosis, and HIV. It remains unclear whether this functional modulation is mediated by heterodimer formation or by the additive effects of mixed chemokines on their respective receptors. To address this issue, we report the synthesis of a covalent RANTES‐PF4 heterodimer (termed OPRAH) by total chemical synthesis and oxime ligation, with an acceleration of the final ligation step driven by PPIs between RANTES and PF4. Compared to mixed separate chemokines, OPRAH exhibited increased biological activity, thus providing evidence that physical formation of the heterodimer indeed mediates enhanced function.     

Synthesis of three putative kairomones of the beech leaf-mining weevil Orchestes fagi (L.)

The beech leaf-mining weevil, Orchestes fagi (L.), also known as the beech flea weevil, is a common and widespread pest of beech, Fagus sylvatica L., in its native Europe. It now appears to be well established in Nova Scotia, Canada. We report a novel synthesis of 9-geranyl-p-cymene and syntheses of 9-geranyl-α-terpinene and 1,1-dimethyl-3-methylene-2-vinylcyclohexane, making partial use of known methods. All three of these compounds are found in beech leaf volatiles and/or wood and are putative kairomones of the beech leaf-mining weevil.     

An integrated enzyme-linked immunosorbent assay system with an organic light-emitting diode and a charge-coupled device for fluorescence detection

A fluorescence detection system for a microfluidic device using an organic light-emitting diode (OLED) as the excitation light source and a charge-coupled device (CCD) as the photo detector was developed. The OLED was fabricated on a glass plate by photolithography and a vacuum deposition technique. The OLED produced a green luminescence with a peak emission at 512 nm and a half bandwidth of 55 nm. The maximum external quantum efficiency of the OLED was 7.2%. The emission intensity of the OLED at 10 mA/cm(2) was 13 μW (1.7 mW/cm(2)). The fluorescence detection system consisted of the OLED device, two band-pass filters, a five microchannel poly(dimethylsiloxane) (PDMS) microfluidic device and a linear CCD. The fluorescence detection system was successfully used in a flow-based enzyme-linked immunosorbent assay on a PDMS microfluidic device for the rapid determination of immunoglobulin A (IgA), a marker for human stress. The detection limit (S/N=3) for IgA was 16.5 ng/mL, and the sensitivity was sufficient for evaluating stress. Compared with the conventional 96-well microtiter plate assay, the analysis time and the amounts of reagent and sample solutions could all be reduced.     

Crystallization Elution Fractionation and Thermal Gradient Interaction Chromatography. Techniques Comparison

Summary: The chemical composition distribution has been shown to be the most critical and discriminating parameter in understanding the performance of industrial polyolefins with non homogeneous comonomer incorporation. The chemical composition distribution is being analyzed by well known techniques such as temperature rising elution fractionation, TREF, crystallization analysis fractionation, CRYSTAF and crystallization elution fractionation, CEF. These techniques separate according to crystallizability and provide a powerful and predictable separation of components based on the presence of branches, irregularities or tacticity differences, independently of the molar mass. TREF, CRYSTAF and CEF can not be used, however, for the separation of more amorphous resins, and may not always provide the best solution for complex multi-component resins due to the existence of some co-crystallization. The application of high temperature interactive HPLC to polyolefins opened a new route to characterize these types of polymers. The use of solvent gradient HPLC for separation of polyethylene and polypropylene and the developments in HPLC on carbon based columns extended further the application of high temperature HPLC in polyolefins. A new approach has been developed recently using the carbon based column but replacing solvent gradient by a thermal gradient which facilitates the analysis of polyethylene copolymers and provides a powerful tool for the analysis of elastomers. Thermal gradient interaction chromatography (TGIC) is being compared with TREF and CEF with the analysis of model samples. The advantages/disadvantages of each technique are being investigated and discussed. The combination of TGIC and TREF/CEF provides an extended range of separation of polyolefins.     

Analysis and interpretation of the first monochromatic X‐ray tomography data collected at the Australian Synchrotron Imaging and Medical beamline

The first monochromatic X‐ray tomography experiments conducted at the Imaging and Medical beamline of the Australian Synchrotron are reported. The sample was a phantom comprising nylon line, Al wire and finer Cu wire twisted together. Data sets were collected at four different X‐ray energies. In order to quantitatively account for the experimental values obtained for the Hounsfield (or CT) number, it was necessary to consider various issues including the point‐spread function for the X‐ray imaging system and harmonic contamination of the X‐ray beam. The analysis and interpretation of the data includes detailed considerations of the resolution and efficiency of the CCD detector, calculations of the X‐ray spectrum prior to monochromatization, allowance for the response of the double‐crystal Si monochromator used (via X‐ray dynamical theory), as well as a thorough assessment of the role of X‐ray phase‐contrast effects. Computer simulations relating to the tomography experiments also provide valuable insights into these important issues. It was found that a significant discrepancy between theory and experiment for the Cu wire could be largely resolved in terms of the effect of the point‐spread function. The findings of this study are important in respect of any attempts to extract quantitative information from X‐ray tomography data, across a wide range of disciplines, including materials and life sciences.     

BIPHASIC PHOTOCHEMISTRY: PHOTOCHEMICAL REGIOSPECIFICITY AND CRITICAL MICELLE CONCENTRATION DETERMINATION

Abstract— The irradiation of 3-n-butylcyclopentenone has been shown to give cyclobutane dimers, the ratio of head-to-head and head-to-tail isomers being solvent dependent. It is now shown that in aqueous medium this ratio is dependent on surfactant concentration both for charged and uncharged species. A very abrupt change in regiospecificity occurs at the critical micelle concentration, and c.m.c. values are obtained in which there is no ambiguity from extrapolation and which are in excellent agreement with values in the literature. This technique represents a new method for c.m.c. determination.