Metal–metal bonding and structures of trinickel and tricobalt dipyridylamido complexes from surface‐enhanced Raman spectra

We recorded surface‐enhanced Raman scattering (SERS) spectra of metal‐string complexes Co₃(dpa)₄ Cl₂ [di(2‐pyridyl)amido (dpa)], Ni₃(dpa)₄ Cl₂ and the oxidized form of the Ni₃ complex to determine their vibrational wavenumbers and to investigate their structures. For SERS measurements these complexes were adsorbed on silver nanoparticles in aqueous solution to eliminate the constraint of a crystal lattice and the complexes remain in thermal equilibrium. From our analysis of the vibrational normal modes we assigned the SERS lines at 242 and 276 cm⁻¹ to Ni₃ and Co₃ symmetric‐stretching modes of the symmetric form. For Co₃ (dpa)₄Cl₂ a Raman line at 383 cm⁻¹ was assigned to the Co Co stretching mode of the unsymmetric form. The wavenumber of the Ni₃ symmetric‐stretching mode of the oxidized form [Ni₃(dpa)₄]³⁺ is 274 cm⁻¹, greater than that for neutral Ni₃(dpa)₄Cl₂, in agreement with a prediction of delocalized molecular‐orbital theory that an electron is removed from an antibonding orbital after oxidation. The experimental data show that the SERS technique serves as an excellent tool to observe the variation of metal–metal bonding during an oxidation or reduction reaction. Copyright © 2010 John Wiley & Sons, Ltd.     

Sol-gel prepared copper doped SiO2 glasses

SiO₂ glasses doped with nano-sized copper particles were prepared through sol-gel method. Samples with nominal composition xCu–(1–x)SiO₂ (x=0.02, 0.05, 0.1, 0.2, 0.4) were prepared by hydrolyzing tetraethylorthosilicate with various amounts of Cu(NO₃)₂. The dried gels were heat treated at 400, 500, 600, 700°C for 10 hrs under flowing 5% H₂-95% N₂ mixture gas to reduce Cu⁺² ions to metallic copper. The amorphous nature of the SiO₂ matrix was confirmed by powder X-ray diffraction. The size of particulate copper metal, which was determined by transmission electron microscopy, increases with the temperature of heat treatment and the copper content. The local structure of SiO₂ matrix was probed by FTIR. The silica matrix has no major structural change for gels heat treated at different temperatures and with different copper contents.     

MO imagery techniques using arrays of large aperture telescopes

Simultaneous multiple-path looks at a moving object (MO) of low signal to noise ratio (SNR) is proposed using an array of telescopes without using either interferometric or adaptive optics techniques. Instead, proper Affine overlays, of all looks through nonisoplanatic regions, give a better SNR and a better turning view in the real time and image plane, and can be furthermore integrated temporally using Affine transformation to yield new templates of a MO. Thereby a scheme of open, self-taught and therefore smart pattern recognition of MO's becomes possible. The system performance of a multi-opto-sensor-Affine (MOSA) system is generally derived in terms of system parameters and field conditions. Geometric constructions of Affine transformations are shown to be either area-ration preserving among three control picture elements (pixels), which are proved to be sufficient using Euler's theorem of solid body motion, or the first order moment of area-ratio preserving, when more than three pixels are needed due to poor SNR.     

Finite-depth and intrinsic losses in vertically etched two-dimensional photonic crystals

We address the issue of out-of-plane losses in two-dimensional (2D) photonic crystals (PC) etched through a GaAs monomode waveguide clad with standard GaAlAs alloys. We correlate experimental transmission of PCs with two kinds of loss simulation results. The first kind is 2D and introduces an ad hoc imaginary index in the air holes to account for the losses [see (Benisty et al. Appl. Phys. Lett. 76, 532, 2000)]. The second kind is a novel exact three-dimensional calculation inspired by grating-Fourier analysis that provides quantitatively unprecedented agreement with experimental measurements taking into account hole depth as a limiting parameter. We conclude that, in revision to the conclusions of the above reference, the experimental losses are not the intrinsic ones, being larger by a factor of 5 to 10 due to insufficient hole depth. The transition occurs at a critical etch depth shown to be here around 700 nm. We thus predict, for holes deeper than 700 nm, much improved crystals with very low transmission losses and microresonators with ultra-high quality factors.     

The role of new eudesmane-type sesquiterpenoid and known eudesmane derivatives from the red alga Laurencia obtusa as potential antifungal–antitumour agents

A new eudesmane sesquiterpenoid, eudesma-4(15),7-diene-5,11-diol (1) along with the known trinor-sesquiterene, teuhetenone (2), and a seco-eudesmane sesquiterpene, chabrolidione B (3), have been isolated from the Red Sea red alga Laurencia obtusa. The chemical structures were elucidated on the basis of extensive spectroscopic analysis. The antifungal and cytotoxic activities of the isolated metabolites were tested against several fungi, yeast and human mammary carcinoma cell line (MCF-7). Compounds 1 and 3 showed a much better activity [minimum inhibitory concentration (MIC): 2.9 μM] than that of amphotericin B (MIC: 4.6 μM). Interestingly, compound 2, the least active antifungal compound, retained the high anticancer activity against MCF-7 (22 μM) in comparison with cisplatin (59 μM), which was determined by employing lactate dehydrogenase assay. Compounds 1–3 are recorded here for the first time from algal flora. The chemotaxonomic importance of the isolated metabolites was discussed.     

Spectral Response of a Stochastic Oscillator under Impacts

An approximate analytical procedure is presented to estimate theresponse spectrum of an oscillator with elastic impacts under a Gaussian whitenoise excitation. The proposed approach is based on a perturbation analysis ofthe problem and on the use of the stochastic averaging principle. The basicidea is to replace the initial system by a more regular system obtained byapproximating the nonlinear restoring force by a Chebychev polynomial, and thento construct for this regular system two approximations: one for the flowand one for the stationary distribution of the response amplitude. Ananalytical approximation of the response spectrum can then be derived fromthese results. Predictions from this analytical approximation are compared with corresponding digital simulation estimates and with the ones obtained from theconventional equivalent linearization method.     

High‐Performance p‐Channel Organic Semiconducting Candidates Based on Benzo[1,2‐k;4,5‐k′]difluoranthene Derivatives

Orbital promises : Frontier orbital analyses showed that the small λ⁺ value of 8,17‐di‐n‐hexylbenzo[1,2‐k;4,5‐k′]difluoranthene (DH‐BDF) is owed to the nonbonding character of the BDF framework. The calculated adiabatic ionic potential and hole mobility indicates that this compound is a p‐type air‐stable organic field‐effect transistor, which promises to be a soluble, stable and high‐performance p‐type organic semiconductor.

     

Structure and Electronic Configuration of an Iron(II) Complex in a LIESST State: A Pump and Probe Method

Switchable molecules : The electronic configurations of the Fe center in trans‐[Fe(tzpy)₂(NCS)₂] in low‐spin, high‐spin, and LIESST states (LIESST=light‐induced excited spin‐state trapping) were confirmed by K‐ and L‐edge X‐ray absorption and magnetic measurements. The molecular structures at 40 K before and after irradiation are superimposed in the picture, which demonstrates a single‐crystal‐to‐single‐crystal transition by irradiation.