An unexpected Diels-Alder type cycloaddition of cyclic enone ethylene ketals

The ethylene ketal of 2-cyelopentenone and 2-cyelohexenone in acetonitrile in thepresence of a trace of an acid rapidly undergoes the Diels-Alder type dimerization,Theproducts are regiospecific but not stereoselective and are hydrolysed sequentially to affordketo-ketals and diketones whose structures are determined by extensive applications of NMRspectroscopy.     

Microscopic modelling of bulk and quantum-well GaAs-based semiconductor lasers

The dynamical behaviour of Fabry-Perot type semiconductor lasers is modelled, including the relevant many-body Coulomb effects of the excited carriers. Conditions are given under which a parametrization of the full model is possible, allowing simple analytic relations for local gain, refractive index and linewidth enhancement factor. The parameters of the simplified model are uniquely determined by the microscopic theory and have to be optimized for the respective operating conditions. The theory is evaluated for bulk and quantum-well GaAs active material and a variety of laser structures, including strongly and weakly index-guided structures, as well as purely guided single-and twin-stripe lasers.     

Possibility of using laser-fibre optics as a fire detection system

Optical fibres together with a helium-neon laser is proposed to be used as a new fire detection system. This has been Investigated experimentally and reported in this paper. Results on the coupling loss, bending loss, extinction loss of the fibres due to smoke and refraction loss through hot air shimmer are described. Comparison with the performance of common optical and ionization detectors is made. Experimental results indicate that the optical signal would be significantly changed when there is smoke. Hence it is highly probable that a new fire detection system can be designed using laser-fibre optics.     

Electronic structure and dynamics of muonium in semiconductors

In this paper, a selection of recent results on muonium in semiconductors is presented. These are primarily taken from Si and GaAs and encompass the electronic structure of the diamagnetic centers, charge state cycling, spin‐exchange scattering and interconversion between muonium states. These experiments illustrate the power of μSR for investigating the behavior of muonium and, by analogy, the technologically relevant isolated hydrogen centers in semiconductors. This revised version was published online in August 2006 with corrections to the Cover Date.     

A versatile reagent to synthesize diverse ionic liquids ranging from small molecules and dendrimers to functionalized proteins

An ionic liquid "reagent" bearing a succinimidyl activated ester is reported that can be used to synthesize a variety of small molecule and macromolecular ionic liquids. In addition, the ionic liquid reagent was used to modify lysozyme, and the protein retained its structure and function after modification. This study describes a facile and reliable route to new ionic liquid compositions.     

Cyclometalated platinum(II) complexes as topoisomerase IIα poisons

A platinum(II)-based major groove binder [Pt(II)(C^N)(C≡NR)(2)](+) (HC^N = 2-phenylpyridine (phpy), R = 2-naphthyl) was identified as a potent human topoisomerase IIα poison. It stabilizes the covalent TopoIIα-DNA cleavage complex and induces cancer cell death with potency significantly higher than the widely clinically used TopoIIα poison Vp-16.     

Seasonal effects on bioactive compounds and antioxidant capacity of six economically important brassica vegetables

Research on natural and bioactive compounds is increasingly focused on their effects on human health, but there are unexpectedly few studies evaluating the relationship between climate and natural antioxidants. The aim of this study was analyze the biological role of six different Brassica vegetables (Brassica oleracea L. and Brassica rapa L.) as a natural source of antioxidant compounds. The antioxidant activity may be assigned to high levels of L-ascorbic acid, total phenolics and total flavonoids of each sample. The climate seasons affected directly the concentration of bioactive components and the antioxidant activity. Broccoli inflorescences and Portuguese kale showed high antioxidant activity in Spring-Summer whilst turnip leaves did so in Summer-Winter. The Brassica vegetables can provide considerable amounts of bioactive compounds and thus may constitute an important natural source of dietary antioxidants.     

Determining a synthetic approach to pierisformaside C

An efficient route detailing the construction of the central core of pierisformaside C, the first grayanane-type diterpene to possess three central double bonds, is reported.