Kinetics and mechanisms of gas‐phase elimination of 2,2‐diethoxyethyl amine and 2,2‐diethoxy‐N,N‐diethylethanamine

The gas‐phase elimination kinetics of 2,2‐diethoxyethyl amine and 2,2‐diethoxy‐N,N‐diethylethanamine (320–380 °C; 40–150 Torr) in a seasoned reaction vessel are homogeneous, unimolecular and obey a first‐order rate law. These elimination processes involve two parallel reactions. The first gives ethanol and the corresponding 2‐ethoxyethenamine. The latter compound further decomposes to ethylene, CO and the corresponding amine. The second parallel reaction produce ethane and the corresponding ethyl ester of an α‐amino acid. The following Arrhenius expressions are given as: For 2,2‐diethoxyethyl amine For 2,2‐diethoxy‐N,N‐diethylethanamine Comparative kinetic and thermodynamic parameters of the overall, the parallel and the consecutive reactions lead to consider two types of mechanisms in terms of a concerted polar cyclic transition state structures. Copyright © 2008 John Wiley & Sons, Ltd.     

Photoluminescence characterization of silicon nanostructures embedded in silicon oxide

This paper describes a simple method to analyze the photoluminescent characteristics of materials based on embedded light-emitting nanoclusters. Photoluminescence spectra of deposited silicon sub-oxide layers with the same composition and different thicknesses have been obtained. A saturation of the total luminescence intensity is observed with increase in thickness. By analyzing the photoluminescence spectra several optical and structural parameters can be evaluated. We thus propose a model in which the absorption of light from a nanostructure layer implies the possibility of subsequent luminescence and affects the underlying layers as well. By fitting the data to the developed model, two fundamental parameters are extracted: nanostructures absorption probability, which is independent of the emission energy and the spectra of emission probability of an excited nanostructure which fits a Gaussian shape.     

A finiteness theorem for transitive foliations and flat vector bundles

In this paper we prove a finiteness theorem for the spectral sequence (E _i(∇), (d _∇)_i) associated to a transitive foliation on a compact manifoldM, and to a flat vector bundleE overM with flat connection ∇. we also compute some examples of homogeneous Lie foliations on compact connected homogeneous spaces.     

Full-field photonic biosensors based on tunable bio-doped sol-gel glasses

A full-field generic photonic biosensor approach, which relies on a bio-doped polymeric strip waveguide configuration, is described. We show the potential of tailor-made hybrid polymeric materials prepared by sol-gel technology for the fabrication of ultra-compact biosensor devices, where both the transducer and the recognition elements are merged into one single microstructure. Such devices were fabricated by micromolding in capillaries (MIMIC) soft lithographic technique. In contrast to evanescent field sensors, the sensor response does not only rely on the interaction of the evanescent wave with the recognition element, but on the interaction of the whole field, thus enabling a reduction of the sensor dimensions and/or a decrease of its limit of detection (LOD). The potential of this generic approach was demonstrated by developing a biosensor for the detection of H(2)O(2) using horseradish peroxidase (HRP) as the doping agent. Solutions containing 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic) acid (ABTS) and different concentrations of H(2)O(2) were dispensed over the waveguide and the green-coloured cation radical ABTS*(+) product was mainly obtained inside the photonic structure, resulting in a maximum absorption increase of 2.5 a.u. at a set working wavelength of 670 nm over the H(2)O(2) concentration range studied. The sensor exhibited a sensitivity of (3.1+/-0.2) x 10(3) a.u./mol L(-1) and a limit of detection (LOD) of 4.4 x 10(-5) mol L(-1) H(2)O(2). These results anticipate that full-field waveguide microstructures based on bio-doped sol-gel polymers will enable the fabrication of cost-effective photonic biosensors. Moreover, the ease of fabrication by a soft lithography technique and the use of such polymeric materials are fully compatible with their integration in compact automatic analysis systems.     

Sub-monolayer assemblies of octanethiol and octadecylthiol at gold electrodes for the direct analysis of 4,4'-oxydianiline in wastewaters and shoe-dyeing samples

Self-assembled monolayers (SAMs) of di-n-octadecyldisulphide (C(18)) and n-octanethiol (C(8)) were prepared on gold electrodes. From the studies carried out by cyclic voltammetry and square wave voltammetry, it was observed that the electrochemical behaviour of 4,4'-oxydianiline on these electrodes is affected by the length chain of the alkanethiol. After the optimization of all the variables involved in the electrochemical response of 4,4'-oxydianiline by square wave voltammetry employing the modified electrodes, it is possible the determination of 4,4'-oxydianiline with a detection limit of 0.04microg/mL (C(18)) and 0.06microg/mL (C(8)) and determination limits of 0.12 and 0.22microg/mL, respectively. The calculated Er (%)(n=10) and R.S.D.(%)(n=10) values were minor than 2.2% and 3.7%. The proposed methods were successfully applied to the analysis of oxydianiline in wastewater and shoe-dyeing samples.     

Determination of Pd, Pt and Rh in vehicles escape fumes by GF-AAS and ICP-OES

Automotive exhaust gases from vehicles using catalytic converters were filtered through cellulose filter papers to collect suspended particles expulsed along with the engine's escape fumes. A specially designed sample collector was used for supporting the filter papers during collection. The collector was manufactured from a new car's exhaust pipe. A cellulose circular paper filter, 11 cm diameter, was attached to one end of the pipe and kept centered by pressing it against the borders of the pipe by means of a perforated aluminum cap, slightly wider than the pipe, used to cover this end of the collector. Filter papers loaded with the solid particles were acid-digested using a modified domestic microwave oven to bring the solid material into solution. The resulting solutions were analyzed for Pt by graphite furnace atomic absorption spectrometry (GF-AAS) and for Pd and Rh by inductively coupled plasma (ICP-OES). Results indicate that concentration of these analytes in the particulate is higher for new vehicles, having new catalytic converters, than for old ones. Maximum Pd, Pt and Rh in the samples analyzed were found to be 5.36, 12.60 and 1.03 microg g(-1), respectively.     

Force balance of particles trapped at fluid interfaces

We study the effective forces acting between colloidal particles trapped at a fluid interface which itself is exposed to a pressure field. To this end, we apply what we call the "force approach," which relies solely on the condition of mechanical equilibrium and turns to be in a certain sense less restrictive than the more frequently used "energy approach," which is based on the minimization of a free energy functional. The goals are (i) to elucidate the advantages and disadvantages of the force approach as compared to the energy approach, and (ii) to disentangle which features of the interfacial deformation and of the capillary-induced forces between the particles follow from the gross feature of mechanical equilibrium alone, as opposed to features which depend on the details of, e.g., the interaction of the interface with the particles or the boundaries of the system. First, we derive a general stress-tensor formulation of the forces at the interface. On that basis we work out a useful analogy with two-dimensional electrostatics in the particular case of small deformations of the interface relative to its flat configuration. We apply this analogy in order to compute the asymptotic decay of the effective force between particles trapped at a fluid interface, extending the validity of the previous results and revealing the advantages and limitations of the force approach compared to the energy approach. It follows the application of the force approach to the case of deformations of a nonflat interface. In this context, we first compute the deformation of a spherical droplet due to the electric field of a charged particle trapped at its surface and conclude that the interparticle capillary force is unlikely to explain certain recent experimental observations within such a configuration. We finally discuss the application of our approach to a generally curved interface and show as an illustrative example that a nonspherical particle deposited on an interface forming a minimal surface is pulled to regions of larger curvature.