Ellipsometric study of thermally induced redistribution and crystallization of Ge in Ge:SiO2 mixture layers

Mixture layers of Ge:SiO₂ of 40:60 mol% respectively, have been prepared by co-sputtering. The thermally induced change of optical properties of the layers was studied by variable angle spectroscopic ellipsometry. The mixture was modelled as an unknown material with optical constants described by multiple oscillators. The optical parameters determined from ellipsometric measurements can be well correlated with structural changes in the mixture. The results indicate that Ge in the mixture deposited or annealed up to 600 °C is in an amorphous state and it redistributes with increase of temperature, changing refractive index through the layer. The crystallization starts between 600 and 650 °C, at first next to the substrate. Crystallites size grows with temperature. Results were compared with findings of grazing incidence wide angle X-ray scattering measurements and a good agreement was found. Ellipsometry has been shown to be an appropriate non-invasive technique for characterization of this kind of layers.     

The Intermolecular Pauson-Khand Reaction: Applications,Challenges, and Opportunities

The rapid assembly of complex organic molecules from simple and structurally diverse building blocks is a prevalent challenge in organic synthesis. The Pauson-Khand reaction (PKR) is a method of choice for the construction of five membered rings that has historically been popularized as a late-stage intramolecular cyclization method. The intermolecular version of the PKR, on the other hand, constitutes a powerful approach for the rapid assembly of densely functionalized cyclopentanic cores at early stages of a synthetic sequence. Despite its potential, the intermolecular PKR is much less prevalent in the organic synthesis literature due to several historical limitations, most importantly a reduced scope with respect to the alkene component of the reaction. The last decade has witnessed important developments in the area including a) experimental and theoretical studies that provide a good mechanistic understanding of the reaction and its selectivity, b) methodological developments that have broadened the scope of potential alkene partners, and c) the development of catalytic enantioselective versions that provide useful levels of enantioselectivity. In parallel, remarkable synthetic applications of the intermolecular PKR have emerged, including (enantioselective) total syntheses of complex natural products (polycyclic terpenes, alkaloids, prostanes) as well as examples of industrial relevance. A fundamental limitation of the PKR that needs to be addressed in the future is the current lack of a ligand-accelerated version of the reaction, which would be a promising advance towards developing more efficient and general catalytic (enantioselective) reactions.     

Reversible Photocontrol of Dopaminergic Transmission in Wild-Type Animals

Understanding the dopaminergic system is a priority in neurobiology and neuropharmacology. Dopamine receptors are involved in the modulation of fundamental physiological functions, and dysregulation of dopaminergic transmission is associated with major neurological disorders. However, the available tools to dissect the endogenous dopaminergic circuits have limited specificity, reversibility, resolution, or require genetic manipulation. Here, we introduce azodopa, a novel photoswitchable ligand that enables reversible spatiotemporal control of dopaminergic transmission. We demonstrate that azodopa activates D₁-like receptors in vitro in a light-dependent manner. Moreover, it enables reversibly photocontrolling zebrafish motility on a timescale of seconds and allows separating the retinal component of dopaminergic neurotransmission. Azodopa increases the overall neural activity in the cortex of anesthetized mice and displays illumination-dependent activity in individual cells. Azodopa is the first photoswitchable dopamine agonist with demonstrated efficacy in wild-type animals and opens the way to remotely controlling dopaminergic neurotransmission for fundamental and therapeutic purposes.     

Synthesis of Poly(p-Benzenesulphonamide) Part I. Preparation of Sulphanilic Acid Derivatives for Use as Intermediates

In view of the unique properties of poly (p-benzamide), particularly as a fibre, the synthesis of the structurally related poly (p-benzenesulphonamide) has been investigated. This first paper describes the preparation of two groups of possible precursors of the polymer starting with sulphanilic acid. The first group includes N-sulphinylaniline-4-sulphochloride, aniline-4-sulphochloride hydrochloride and aniline-4-sulphochloride. The key to the synthesis of these intermediates is the conversion of sulphanilic acid to N-sulphinylaniline-4-sulphochloride by reaction with thionyl chloride in the presence of a catalytic amount of dimethyl formamide. For the synthesis of poly (N-methyl-benzenesulphonamide), N-methylsulphanilic acid has been converted into N-methylaniline-4-sulphochloride hydrochloride by treatment with thionyl chloride. Some N-acetylated sulphanilic acid derivatives, CH₃CONH-C₆H₄-SO₂X, where X?OH, OEt, OC₆H₅ and Cl, and N-acetyl-1-naphthylamine-4-sulphochloride have also been prepared for evaluation as monomers in the synthesis of polysulphonamides by melt polymerisation.     

Biological and mechanical control of Sitophilus oryzae (Coleoptera: Curculionidae) in rice

The combination of mechanical and biological methods was evaluated in the laboratory to assess their impact on the rice weevil Sitophilus oryzae in rice. Mechanical methods comprising the conventional polishing process applied either before or after infestation, resulting in reduced nutritional quality plus the added effect of mechanical impact in the presence of the pest, biological methods including parasitism by the pteromalids Anisopteromalus calandrae and Lariophagus distinguendus, and combined methods (combinations of mechanical and subsequent biological treatments), were tested in the laboratory. All treatments significantly reduced the number of weevil progeny and individual weevil weight. Of the two parasitoids, L. distinguendus had the greater effect, reducing weevil populations by 98% in unpolished rice. In the combined treatments, parasitism increased the effect of mechanical methods. However, mechanical methods had a detrimental impact on parasitoid survival, especially in A. calandrae. Furthermore, in the presence of mechanical treatments, the sex ratio of A. calandrae was unbalanced in favour of males indicating the high vulnerability of females. The impact of both parasitoid species on weevils was attributed to successful parasitism as well as to aborted parasitism and host-feeding.     

Concentration changes of organochlorine compounds and polybromodiphenyl ethers during metamorphosis of aquatic insects

The role of insect larvae and pupae as sources of organochlorine compounds (OCs) and polybromodiphenyl ethers (PBDEs) in freshwater food webs for high predators such as fish is evaluated. Trichoptera and diptera have been taken as organisms of choice for such comparison because they are common in benthic aquatic habitats and accumulate substantial amounts of these compounds. Hexachlorobenzene, hexachlorocyclohexanes,4,4'-DDE,4,4'-DDT, polychlorobiphenyls, and PBDEs have been measured. The results show a nonselective enrichment of OCs and PBDEs from larvae to pupae. These concentration increases may result from the weight loss of pupae during metamorphosis as a consequence of mainly protein carbon respiration and lack of feeding. Despite the lack of change in total amount, the concentration increases from larvae to pupae are very relevant for the pollutant ingestion of the higher predators. The intakes of OCs and PBDEs by trout are between 2- and 5-fold higher per calorie gained when predating on pupae than on larvae. Since pollutant concentration, energy reward, predation susceptibility, and duration of life stage are very different between these two insect stages, and none of them is irrelevant for the incorporation of OCs or PBDEs to higher levels, bioaccumulation food-web models should distinguish between the two sources.