The electrical double layer charge and associated dimensional changes of high surface area electrodes as detected by more deflectometry

Due to the high surface to volume ratio, the interfacial tension of porous solids affects their outer dimensions by a minute, but detectable amount. Changes in the interfacial tension of a high surface area graphite electrode could be monitored adopting the moire deflectometry, a new optical technique for ray deflection mapping, by which the resolution in relative length changes of th e electrode was less than 1 microstrain.The strain vs. potential curves are typically pseudo-parabolic. Within the double layer potential range, their slope is a linear function of the electronic charge delivered to the electrode. Unlike the double layer charge, faradaic currents are not recognized as a strain change of the electrode, thus the method may serve to distinguish between faradaic and double layer processes. Hysteresis takes place in curves of charge or strain vs. electrode potential, but not for charge vs. strain curves. The minimum in the strain-potential plot, attributed to the potential of zero charge occurs at about –350 mV vs. SCE, corresponding to a surface group free carbon (or graphite) electrode.     

Three-dimensional colloidal crystals with a well-defined architecture

Monodisperse silica spheres with diameters of 220-1100 nm were prepared by hydrolysis of tetraethyl orthosilicate (TEOS) in an alcoholic medium in the presence of water and ammonia. By grafting vinyl or amino groups onto silica surfaces using the coupling agents allyltrimethoxysilane and aminopropyltriethoxysilane, respectively, amphiphilic silica spheres were obtained and could be organized to form a stable Langmuir film at the air-water interface. The controlled transfer of this monolayer of particles onto a solid substrate gave us the ability to build three-dimensional regular crystals with a well-defined thickness and organization. These colloidal crystals diffract light in the UV, the visible, and the near-infrared (NIR) spectral regions, depending on the size of the silica spheres and according to Bragg's law. The depth of the photonic stop band can be tuned by varying the number of deposited layers of particles. By using successive depositions, we could prepare multilayered films with silica spheres of different sizes. The thickness of each slab in the binary crystals can be tuned at the layer level, while the crystalline order of each layer is well preserved.     

The unusual formation of pyrrolo[1,2-a]pyrazines in the reaction of alkylpyrazine anions with trans-1,2-dichloroethylene

The reaction of alkylpyrazine anions with trans-1,2-dichloroethylene produces pyrrolo[1,2-a]pyrazines in low yields.     

Determination of the performance of glass electrodes in aqueous solutions in the physiological ph range and at the physiological sodium ion concentration

A method for testing glass electrodes in the physiological pH range (6.4–7.6) and at the physiological sodium ion concentration (0.15 mol l^-1), based on indirect comparison of potentials with the hydrogen gas electrode, is developed according to a scheme described earlier. The hydrogen ion sensitivity and the sodium ion error of a glass electrode can be determined with three different aqueous solutions of amine buffers and their hydrochlorides; two of these have different pH values and one also contains a sodium salt (at the higher pH value). A cell without a liquid/liquid junction, containing silver/silver chloride reference electrodes, is used at 37° C. The accuracy of both determinations is ±0.2 mV (±0.003 pH). The results for some commercial glass electrodes tested with this method are presented.     

Effect of a cationic guest on the characteristics of the molecular capsule of resorcinarene: a diffusion NMR study

[reaction: see text] NMR diffusion measurements were used to probe the differences in the characteristics of the hexameric capsule of [c]-undecane resorcin[4]arene (1b) in a CDCl(3) solution in the absence and presence of tetrahexylammonium bromide (THABr). It was found that the nonencapsulated THABr forms a 1:1 complex with 1b, which is in fast exchange with its constituents. We found that water molecules seem not to participate in the construction of the THABr hexameric capsule of 1b in a CDCl(3) solution, in contrast to the finding in the absence of THABr, where the major species in CDCl(3) seems to be [(1b)(6)(H(2)O)(8)].     

Activation catalytique des réactifs de grignard par des complexes du nickel en série organosiliciée : I. Réactions de substitution avec les réactifs de grignard non réducteurs

A new method of Si-C bond formation is described which involves coupling reactions between non-reducting Grignard reagents and Si-H bonds catalyzed by Ni^II complexes. The steric environment of the silicon atom has little effect on the reaction.Cobalt complexes are moderate catalysts, and those of iron, copper, zirconium and titanium are inactive.The reactions proceed with retention of configuration at the silicon atom. This use of Grignard reagents avoids the awkward preparations of unsaturated lithium or sodium analogues (allyl, crotyl, benzyl, vinyl).     

Light-dependent Oxygen Consumption in Bacteriochlorophyll-Serine-treated Melanoma Tumors: On-line Determination Using a Tissue-inserted Oxygen Microsensor

Successful application of anticancer therapy, and especially photodynamic therapy (PDT) mediated by type II (PDTII) processes, depends on the oxygen content within the tumor before, during and after treatment. The high consumption of oxygen during type II PDT imposes constraints on therapy strategies. Although rates of oxygen consumption and repletion during PDTII were suggested by theoretical studies, direct measurements have not been reported. Application of a novel oxygen sensor allowed continuous and direct in situ measurements (up to a depth of 8–9 mm from the tumor surface and for several hours) of temporal variations in the oxygen partial pressure (pO₂) during PDT. Highly pigmented M2R mouse melanoma tumors implanted in CD1 nude mice were treated with bacteriochlorophyll-serine (Bchl-Ser; a new photodynamic reagent) and were subjected to fractionated illumination (700 < λ. < 900 nm) at a fluence rate of 12 mW cm^-2. This illumination led to total oxygen depletion with an average consumption rate of 7.2 uAf(O₂) s^-1. Spontaneous reoxygenation (at an average rate of 2.5 µM(O₂)/s) was observed during the following dark period. These rates are in good agreement with theoretical considerations (Foster et al., Radiat. Res. 126, 296,1991 and Henning et al, Radiat. Res. 142, 221, 1995). The observed patterns of oxygen consumption and recovery during prolonged periods of light/dark cycles were interpreted in terms of vasculature damage and sensitizer clearance. The presented data support the previously suggested advantages of fractionated illumination for type II photodynamic processes.