Combined experimental and theoretical study on redox-active d8 metal dithione-dithiolato complexes showing molecular second-order nonlinear optical activity

Synthesis, characterization, NLO properties, and theoretical studies of the mixed-ligand dithiolene complexes of the nickel triad [M(II)(Bz(2)pipdt)(mnt)] (Bz(2)pipdt = 1,4-dibenzyl-piperazine-3,2-dithione, mnt = maleonitriledithiolato, M(II) = Ni, 1, Pd, 2, Pt, 3) are reported. Molecular structural characterization of 1-3 points out that four sulfur atoms are in a slightly distorted square-planar geometry. While the M-S bond distances are only slightly different, comparison of the C-C and C-S bonds in the C(2)S(2)MS(2)C(2) core allows us to point out a significant difference between the C-C and the C-S distances in Bz(2)pipdt and mnt. These findings suggest assigning a dithiolato character to mnt (pull ligand) and a dithione one (push ligand) to Bz(2)pipdt. Cyclic voltammetry of 1-3 exhibits two reversible reduction waves and a broad irreversible oxidation wave. These complexes are characterized in the visible region by a peak of moderately strong intensity, which undergoes negative solvatochromism. The molecular quadratic optical nonlinearities were determined by the EFISH technique, which provided the following values μβ(λ) (10(-48) esu) = -1436 (1), -1450 (2), and -1950 (3) converted in μβ(0) (10(-48) esu) = -463 (1), -684 (2), and -822 (3), showing that these complexes exhibit large negative second-order polarizabilities whose values depend on the metal, being highest for the Pt compound. DFT and TD-DFT calculations on 1-3 allow us to correlate geometries and electronic structures. Moreover, the first molecular hyperpolarizabilities have been calculated, and the results obtained support that the most appealing candidate as a second-order NLO chromophore is the platinum compound. This is due to (i) the most extensive mixture of the dithione/metal/dithiolato orbitals, (ii) the influence of the electric field of the solvent on the frontier orbitals that maximizes the difference in dipole moments between the excited and the ground state, and (iii) the largest oscillator strength in the platinum case vs nickel and palladium ones.     

A rapid multidimensional liquid-gas chromatography method for the analysis of mineral oil saturated hydrocarbons in vegetable oils

The present paper describes an investigation directed toward the development of a rapid heart-cutting LC-GC method for the analysis of mineral oil saturated hydrocarbons contained in vegetable oils. The automated LC-GC experiments were carried out by using a system equipped with a syringe-type interface, capable of both heart-cutting and comprehensive (LC × GC) two-dimensional analysis. The first dimension separation was achieved on a 100 mm × 3 mm ID × 5 μm d(p) silica column, operated under isocratic conditions (hexane). A single 30-s cut, corresponding to a 175 μL volume, was transferred to a programmed temperature vaporizer. After the large volume injection, the target analytes were separated in a rapid manner (~9 min) using a 15 m × 0.1mm ID × 0.1 μm micro-bore GC capillary. The overall LC-GC run time enables the analysis of ca. 4 samples/hour. Quantification was performed by using external calibration, in the 1-200 mg/kg range. The method was validated in terms of linearity, precision, limits of detection and quantification, and accuracy. A series of commercial samples were subjected to analysis. Various degrees of contamination were found in all samples, in the 7.6-180.6 mg/kg range.     

π-Electron manipulation of the 5,6-dihydroxyindole/quinone system by 3-alkynylation: mild acid-mediated entry to (cross)-conjugated scaffolds and paradigms for medium-tunable chromophores

5,6-Dihydroxyindole-based systems engender increasing interest for the design and implementation of new functional aromatic scaffolds and eumelanin-like materials with tailored absorption and electronic properties. However, studies aimed at elucidating the influence of external π-conjugating groups on the redox properties and acid-induced reactivity of these highly oxidizable indolic platforms are lacking. We report herein the synthesis (as acetyl derivatives) and chemical/quantum chemical characterization of the first π-extended 5,6-dihydroxyindole derivatives, 3-ethynyl-5,6-dihydroxyindole (1) and 3,3'-(1,2-ethynediyl)bis-5,6-dihydroxyindole (2), in order to understand whether and how β extension of the enamine-like pyrrole sector affects the absorption properties, redox behavior, and protonation equilibria at both the o-diphenol and quinone levels. Oxidation of 1 and 2 proceeded smoothly to generate dark insoluble materials with eumelanin-like UV properties. On exposure to phosphate buffer at pH 3, 1 was rapidly converted to 3-acetyl-5,6-dihydroxyindole (5) and, in the presence of 5,6-dihydroxyindole, to the cross-conjugated 3,3'-ethenylidenebis-5,6-dihydroxyindole (6). DFT calculations on 1 and 2 and their quinones in their pristine states and after protonation provided a mechanistic frame to rationalize the unusual acid-mediated chemistry of 1 and disclosed 2-quinone as the prototype of a novel class of medium-dependent chromophores. The ethynyl(ene) structural motif is thus proposed as the key to new tunable π-electron extended 5,6-dihydroxyindole/5,6-indolequinone paradigms for the rational design of alkyne-containing hybrid eumelanin-type polymers.     

Theoretical study and numerical simulation of textiles

We propose a new approach for developing continuum models fit to describe the mechanical behavior of textiles. We develop a physically motivated model, based on the properties of the yarns, which can predict and simulate the textile behavior. The approach relies on the selection of a suitable topological model for the patch of the textile, coupled with constitutive models for the yarn behavior. The textile structural configuration is related to the deformation through an energy functional, which depends on both the macroscopic deformation and the distribution of internal nodes. We determine the equilibrium positions of these latter, constrained to an assigned macroscopic deformation. As a result, we derive a macroscopic strain energy function, which reflects the possibly nonlinear character of the yarns as well as the anisotropy induced by the microscopic topological pattern. By means of both analytical estimates and numerical experiments, we show that our model is well suited for both academic test cases and real industrial textiles, with particular emphasis on the tricot textile.     

Nonperturbative entangling gates between distant qubits using uniform cold atom chains

We propose a new fast scalable method for achieving a two-qubit entangling gate between arbitrary distant qubits in a network by exploiting dispersionless propagation in uniform chains. This is achieved dynamically by switching on a strong interaction between the qubits and a bus formed by a nonengineered chain of interacting qubits. The quality of the gate scales very efficiently with qubit separations. Surprisingly, a sudden switching of the couplings is not necessary. Moreover, our gate mechanism works for multiple gate operations without resetting the bus. We propose a possible experimental realization in cold atoms trapped in optical lattices and near field Fresnel trapping potentials.     

Iridium/silicon multilayers for extreme ultraviolet applications in the 20-35 nm wavelength range

We have developed an Ir/Si multilayer for extreme ultraviolet (EUV) applications. Normal incidence reflectance measurements of a prototype film tuned to 30 nm wavelength show superior performance relative to a conventional Mo/Si multilayer structure; we also find good stability over time. Transmission electron microscopy and electron dispersive x-ray spectroscopy have been used to examine the microstructure and interface properties of this system: we find amorphous Si layers and polycrystalline Ir layers, with asymmetric interlayer regions of mixed composition. Potential applications of Ir/Si multilayers include instrumentation for solar physics and laboratory EUV beam manipulation.     

Optimization of organo‐layered double hydroxide dispersion in LDPE‐based nanocomposites

Low‐density polyethylene/layered double hydroxide (LDPE/LDH) nanocomposites were prepared via melt extrusion using organo‐LDH particles and maleic anhydride functionalized polyethylene as compatibilizer. Processing parameters, preparation method, and feed composition were properly modulated until obtaining nanocomposites with intercalated/exfoliated morphologies, and an uniform distribution of nanolayers, as evidenced by X‐ray diffraction and transmission electron microscopy analysis. These materials showed a significant improvement of the thermal‐oxidative stability, which increased of about 50°C during the first step of the degradation process. Moreover, a remarkable reduction of the oxygen permeability, proportional to the aspect ratio of LDH stacks dispersed in the polyolefin matrix was evidenced, indicating the possible application of nanocomposite films as food packaging materials. As highlighted by dynamic mechanical thermal analysis, interactions at the interface between LDH layers and polymer chains caused a shift of the LDPE β‐relaxation toward higher temperatures and a reduction of the peak intensity with respect to the matrix. It was also found that the storage modulus of the nanocomposites was lower in all the temperature range with respect to the reference samples. Finally, on‐line capillary rheometer measurements evidenced that the shear thinning behavior of the nanocomposites was dominated by the matrix so that the melt processability was not compromised by the presence of the filler. Copyright © 2010 John Wiley & Sons, Ltd.     

Electroactive multilayer assemblies of bilirubin oxidase and human cytochrome C mutants: insight in formation and kinetic behavior

Here, we report on cytochrome c/bilirubin oxidase multilayer electrodes with different cytochrome c (cyt c) forms including mutant forms of human cyt c, which exhibit different reaction rates with bilirubin oxidase (BOD) in solution. The multilayer formation via the layer-by-layer technique and the kinetic behavior of the mono (only cyt c) and biprotein (cyt c and BOD) multilayer systems are studied by SPR and cyclic voltammetry. For the layer construction, sulfonated polyaniline is used. The only cyt c containing multilayer electrodes show that the quantity of deposited protein and the kinetic behavior depend on the cyt c form incorporated. In the case of the biprotein multilayer with BOD, it is demonstrated that the catalytic signal chain from the electrode via cyt c to BOD and oxygen can be established with all chosen cyt c forms. However, the magnitude of the catalytic current as well as the kinetic behavior differ significantly. We conclude that the different cytochrome c forms affect three parameters, identified here, to be important for the functionality of the multilayer system: the amount of molecules per layer, which can be immobilized on the electrodes, the cyt c self-exchange rate, and the rate constant for the reaction with BOD.     

Chiral optical films based on achiral chromophore guests

Films constituted by an achiral host polymer and an achiral guest chromophore, which exhibit intense chiral optical responses for both host and guest peaks in the infrared as well as in the UV-visible regions, have been obtained. Such films can have any thickness from the nanoscale up to the macroscopic scale. This unexpected chiral optical behavior is easily achieved by crystallization of a robust commercial stereoregular host polymer (syndiotactic polystyrene, s-PS) from the amorphous phase as induced by a nonracemic guest, followed by exchange of the nonracemic guest with the achiral guest, leading to the formation of polymer-host/chromophore-guest cocrystalline phases. This finding opens the possibility to achieve s-PS-based films with chiral optical response at selected wavelengths. It has been also found that the chiral optical cocrystalline phase of s-PS with azulene exhibits a monoclinic δ-clathrate form with equal proportions of left- and right-handed helices. This confirms that the observed chiral optical behavior arises by the nonracemic native morphology of the crystalline regions, which has been induced by the temporary nonracemic guest.