Synthesis and photoinitiated polymerization of diacrylate derivates of halobenzoates

The synthesis, characterization, mesomorphism and photoinitiated polymerization of new thermotropic derivatives of bis{4-[6-(acryloyloxy)hexyloxy]halobenzoate}-1,4-phenylene were studied. Halogen incorporation in the mesogenic unit decreases the stability of the mesophases of monomers containing three aromatic rings. The monomer MIII exhibits a nematic phase which has been macroscopically oriented by surface pre-treatment and fixed by photopolymerization in situ, yielding a uniaxially crosslinked network. The molecular ordering of liquid crystalline diacrylate films was visualized by examining the fracture surface by scanning electron microscopy. These films exhibit a fine texture, illustrating the presence of an oriented layered structure.     

Determination of the local electron number density in laser-induced plasmas by Stark-broadened profiles of spectral lines: Comparative results from Hα, Fe I and Si II lines

Measurements of the local electron density in laser-induced plasma have been carried out from the Stark-broadened profiles of three reference lines (H_α, Fe I and Si II). The plasma has been generated from a Fe–Si sample in air using a Nd:YAG laser. Compatible values of the local electron density have been obtained from the three lines. The experiment is based on the use of an imaging spectrometer, the capability for spatial resolution of a charge-coupled device and the application of a spatial deconvolution procedure to the spectra. Distributions of the emission coefficient have been obtained, showing that the three lines are emitted from different regions of the plasma. The implications in the apparent electron density values obtained in spatially-integrated measurements are discussed: similar values are obtained for the H_α and Si II lines, while the Fe I line leads to a 25% lower value.     

Titanocene-phosphine derivatives as precursors to cytotoxic heterometallic TiAu2 and TiM (M = Pd, Pt) compounds. Studies of their interactions with DNA

A series of tri- and bimetallic titanium-gold, titanium-palladium, and titanium-platinum derivatives of the general formulas [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)(AuCl)}(2)]·2THF [n = 0 (1); n = 2 (2); n = 3 (3)] and [TiCl(2){η(5)-C(5)H(4)κ-(CH(2))(n)PPh(2)}(2)(MCl(2))]·2THF [M = Pd, n = 0 (4); n = 2 (5); n = 3 (6) ; M = Pt, n = 0 (7); n = 2 (8); n = 3 (9)] have been synthesized and characterized by different spectroscopic techniques and mass spectrometry. The molecular structures of compounds 1-9 have been investigated by means of density functional theory calculations. The calculated IR spectra of the optimized structures fit well with the experimental IR data obtained for 1-9. The stability of the heterometallic compounds in deuterated solvents [CDCl(3), dimethyl sulfoxide (DMSO)-d(6), and mixtures 50:50 DMSO-d(6)/D(2)O and 1:99 DMSO-d(6)/D(2)O at acidic and neutral pH] has been evaluated by (31)P and (1)H NMR spectroscopy showing a higher stability for these compounds than for Cp(2)TiCl(2) or precursors [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)}(2)]. The new compounds display a lower acidity (1-2 units) than Cp(2)TiCl(2). The decomposition products have been identified over time. Complexes 1-9 have been tested as potential anticancer agents, and their cytotoxicity properties were evaluated in vitro against HeLa human cervical carcinoma and DU-145 human prostate cancer cells. TiAu(2) and TiPd compounds were highly cytotoxic for these two cell lines. The interactions of the compounds with calf thymus DNA have been evaluated by thermal denaturation (1-9) and by circular dichroism (1, 3, 4, and 7) spectroscopic methods. All of these complexes show a stronger interaction with DNA than that displayed by Cp(2)TiCl(2) at neutral pH. The data are consistent with electrostatic interactions with DNA for TiAu(2) compounds and for a covalent binding mode for TiM (M = Pd, Pt) complexes.     

The direct method in time-dependent bending of thermoelastic plates

The initial-boundary value problems with Dirichlet and Neumann boundary conditions arising in the theory of bending of thermoelastic plates with transverse shear deformation are reduced to time-dependent boundary integral equations by means of the Somigliana representation formulas. The solvability of these equations is then investigated in Sobolev-type spaces.     

Weak solutions for time‐dependent boundary integral equations associated with the bending of elastic plates under combined boundary data

The existence, uniqueness, stability, and integral representation of distributional solutions are investigated for the equations of motion of a thin elastic plate with a combination of displacement and moment‐stress components prescribed on the boundary. Copyright © 2004 John Wiley & Sons, Ltd.     

What are we determining using gas chromatographic multiresidue methods: tralomethrin or deltamethrin?

The analytical behaviour of the relatively new pyrethroid insecticide tralomethrin has been evaluated by using gas chromatography (GC) with electron-capture and mass spectrometry (MS) detectors, and liquid chromatography (LC)-atmospheric pressure ionization mass spectrometry with electrospray interfacing. Under the GC conditions commonly used in pesticide residue analysis, it was found that tralomethrin is transformed into deltamethrin (in a reproducible way) in the injector port of the GC system. Results obtained in this work indicate that the GC multiresidue methodologies routinely applied in the analysis of pyrethroid pesticides in foods cannot distinguish between these two pesticides, and the chromatographic signal obtained at the retention time of deltamethrin/tralomethrin can be really quantified as either deltamethrin or tralomethrin, including when it is confirmed as deltamethrin by MS. Under the LC-MS conditions assessed in this work, deltamethrin and the two diasteroisomers of tralomethrin were well separated and identified.