A general procedure for the synthesis of stereochemically pure conduritol derivatives practical also for solid-phase chemistry

A straightforward synthetic protocol apt to synthesize a library constituted by all conduritol stereoisomers in solution phase is described and successfully applied to some polymer-supported substrates. During the solid-phase sequence, an unprecedented rearrangement of a resin-bound sulfone performed under the Ramberg-B?cklund conditions appears of particular interest. Upon treatment with Me(3)Si-I, thiepanes supported on resin are found to undergo regio- and stereospecific ring contraction to a six-membered ring system with traceless cleavage from the solid support.     

Flow injection-mini-column technique with ICP-AES detection for the isolation and preconcentration of the fast reactive aluminium fraction in waters

A flow injection mini-column system based on short reaction times with 8-hydroxyquinoline (oxine) with ICP-AES detection is described for the isolation and preconcentration of the “fast reactive” or “toxic” aluminium fraction in water samples. Using a 3 s reaction time with oxine (5 × 10^–4 mol/l) at pH 5.0, the “fast reactive” aluminium fraction is shown not to include the non-toxic AlF²⁺ species at low F^–: Al³⁺ molar ratios (0.3 : 1). The complexed aluminium is isolated in a stable and recoverable form on mini-columns of Amberlite XAD-2 (0.3 cm × 5.0 cm, resin particle size range 0.08 mm–0.16 mm)). The retained aluminium is recovered by “back-flushing” the analytical column with 1 mol/l HCl for final element specific detection by ICP-AES. Detection limits (after preconcentration) of 2 μg/l, a linear range of 0–500 μg/l, and possible preconcentration factors of up to 18 times are demonstrated with the present system. Implications for the possible solution of sample stability problems encountered with labile aluminium species analysis and the development of a “field sampling” technique are discussed, where the desired Al fraction is quantitatively retained in a stable form on mini-columns.     

Photocytotoxicity of a new Rh2(II,II) complex: increase in cytotoxicity upon irradiation similar to that of PDT agent hematoporphyrin

A new type of heteroleptic dirhodium complex cis-[Rh(2)(mu-O2CCH3)2-(bpy)(dppz)]2+ (3) was synthesized and its potential as a photodynamic therapy (PDT) agent was investigated. Although 27% hypochromicity of the absorption of 3 in the near-UV and visible regions is observed in the presence of duplex DNA, relative viscosity measurements reveal that the complex does not intercalate between the DNA bases. The DNA photocleavage with visible light by 3 proceeds via both oxygen dependent and independent mechanisms, and it is more efficient than that of related complexes. The increase in the cytotoxicity of 3 towards human skin cells is similar to that of hematoporphyrin, a key ingredient in a PDT drug currently in use. This feature makes this complex a useful candidate for further PDT studies.     

Turbulent Flow and Dispersion of Inertial Particles in a Confined Jet Issued by a Long Cylindrical Pipe

In this work we examine first the flow field of a confined jet produced by a turbulent flow in a long cylindrical pipe issuing in an abrupt angle diffuser. Second, we examine the dispersion of inertial micro-particles entrained by the turbulent flow. Specifically, we examine how the particle dispersion field evolves in the multiscale flow generated by the interactions between the large-scale structures, which are geometry dependent, with the smaller turbulent scales issued by the pipe which are advected downstream. We use Large-Eddy-Simulation (LES) for the flow field and Lagrangian tracking for particle dispersion. The complex shape of the domain is modelled using the immersed-boundaries method. Fully developed turbulence inlet conditions are derived from an independent LES of a spatially periodic cylindrical pipe flow. The flow field is analyzed in terms of local velocity signals to determine spatial coherence and decay rate of the coherent K–H vortices and to make quantitative comparisons with experimental data on free jets. Particle dispersion is analyzed in terms of statistical quantities and also with reference to the dynamics of the coherent structures. Results show that the particle dynamics is initially dominated by the Kelvin–Helmholtz (K–H) rolls which form at the expansion and only eventually by the advected smaller turbulence scales.     

Comparison of vacancy and antisite defects in GaAs and InGaAs through hybrid functionals

The formation energies and charge transition levels of vacancy and antisite defects in GaAs and In(0.5)Ga(0.5)As are calculated through hybrid density functionals. In As-rich conditions, the As antisite is the most stable defect in both GaAs and InGaAs, except for n-type GaAs for which the Ga vacancy is favored. The Ga antisite shows the lowest formation energy in Ga-rich conditions. The As antisite provides a consistent interpretation of the defect densities measured at mid-gap for both GaAs/oxide and InGaAs/oxide interfaces.     

An FDTD approach to the simulation of quantum-well infrared photodetectors

A Finite Difference Time Domain approach is used to design and to optimize quantum-well based infrared photodetectors. Results showing the influence of some parameters on the performance of these devices are presented and discussed.     

An inflationary bianchi V model with shear and rotation

A Bianchi V model, in the presence of a fluid with shear and rotation, is investigated. Asymptotic solutions are worked out, showing that shear and rotation may give rise to a conflict with present day observations, a problem that can be solved with the help of an inflationary solution.     

On elliptic equations with piecewise constant coefficients

In this work we prove an existence and uniqueness theorem for solutions in ²(R^t) of second order elliptic equations with coefficients that are constant on the half-spaces R+ⁿ and R ?ⁿ