Photochemical Generation of Ferrocene‐Based Redox‐Polymer Networks

A photochemical approach toward the generation of enzyme‐containing redox polymer networks, which are the key material in enzymatic sensors and biofuel cells, is described. The approach is based on the incorporation of photo‐reactive benzophenone groups into the redox polymers. The obtained polymers are then deposited on the surface of glassy carbon electrodes and cross‐linked by illumination with UV light at 365 nm. If this step is done in the presence of the enzyme glucose oxidase, functional electrodes are obtained that yield electrical power upon addition of glucose. This work specifically addresses the question of electrode stability in buffer and demonstrates how slight variations in the chemistry of the redox polymer have a dramatic effect on the electrochemical performance of the electrodes. Different ferrocene‐containing redox polymer networks are synthesized and their properties in physiological buffer are studied.

     

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A Comparison of Primary and Secondary Hydrogen Abstraction from Organophosphates by Hydroxyl Radical

To compare the effect of primary and secondary C? H bonds on hydrogen?atom abstraction by hydroxyl radical, rate constants for the reactions of OH radicals with trimethyl phosphate [TMPO, (CH₃O)₃P(O)] and triethyl phosphate [TEPO, (CH₃CH₂O)₃P(O)] have been calculated using the semiclassical flux–flux autocorrelation function (SCFFAF) method and compared with experimental measurements over the temperature range 250–350 K. SCFFAF specifies that structures be obtained at the CCSD/6?31++G** level of chemical theory and the height of the activation barrier be determined using an energy extrapolation, here a variant of the G2MP2 method. Dynamics are generated in the SCFFAF method from forces computed with a transfer Hamiltonian, which provides information about the curvature of the potential energy surface in the neighborhood of the transition state (TS), as well as the required internal forces. The temperature?dependent reaction rate constants are calculated for the various possible abstraction pathways, primary hydrogen atom abstraction in the case of TMPO, and primary and secondary in the case of TEPO. Since two energetically favorable parent structures for each system are included in the model, the activation energy is calculated with respect to the conformer that connects to a given TS and the total rate constant at a given temperature is Boltzmann weighted with respect to the parent conformer. The computed temperature?dependent rate curves are consistent with published experimental data in both magnitude and temperature dependence. © 2013 Wiley Periodicals, Inc. Int J Chem Kinet 45: 187–201, 2013     

Chemical etching of zinc oxide for thin-film silicon solar cells

Chemical etching is widely applied to texture the surface of sputter-deposited zinc oxide for light scattering in thin-film silicon solar cells. Based on experimental findings from the literature and our own results we propose a model that explains the etching behavior of ZnO depending on the structural material properties and etching agent. All grain boundaries are prone to be etched to a certain threshold, that is defined by the deposition conditions and etching solution. Additionally, several approaches to modify the etching behavior through special preparation and etching steps are provided.     

Initial stage of pore formation process in anodic aluminum oxide template

The initial stage of pore formation and the growth process in anodic aluminum oxide (AAO) template have been carefully investigated. Detailed features are found concerning the nanostructure configuration formed on the electropolished aluminum foil and the additional fine structures in the first and second anodization resulting from the current limitation effect during the beginning time of about 2 s. It sheds new light onto the mechanism of the pore-organizing process of AAO templates.     

Determination of Arsenic in Drinking Water by Graphite Furnace Atomic Absorption Spectroscopy. An Undergraduate Instrumental Analysis Laboratory

A laboratory exercise, the analysis of arsenic in drinking water by graphite furnace atomic absorption spectroscopy (GFAA), is presented for use in an undergraduate instrumental methods course. The purpose of this GFAA exercise is to expose students to a practical and commonly used application, to provide students with hands-on experience with the instrument, and to reinforce concepts taught in the classroom. Students safely analyze a real-world sample containing an analyte in the parts-per-billion concentration range.     

Gas phase detection of explosives such as 2,4,6-trinitrotoluene by molecularly imprinted polymers

Fast, reliable and inexpensive analytical techniques for trace detection of explosive components are in high demand. Our approach is to develop specific sensor coating materials based on molecularly imprinted polymers (MIPs). Despite the known inhibition of radical polymerisations by nitro groups and the known shrinkage of the polymer lattice during/after drying we were able to synthesize particulate MIPs by suspension polymerisation as well as thin MIP coatings by direct surface polymerisation on quartz crystal microbalances (QCM). The best method to purify the porous beads was Soxhlet extraction followed by supercritical carbon dioxide extraction (SFE with sc-CO₂) at mild conditions (150 bar, 50 °C). At least a removal of >99.7% of the template was achieved. Performance tests of TNT imprinted polymer beads showed that acrylamide (AA) and more pronounced also methacrylic acid (MAA) possessed an enhanced adsorption tendency for gaseous TNT. An adsorption of 2,4-DNT, dinitrotoluene, by these MIPs was not detected. Using 2,4-DNT as template and methacrylamide, MAAM, a positive imprint effect for gaseous 2,4-DNT was achieved with no measurable cross-sensitivity for 2,4,6-TNT.The thin MIP coatings directly synthesized on the QCMs showed thicknesses of 20 to up to 500 nm. Preliminary screening experiments were performed for five different monomers and three different solvents (acetonitrile, chloroform and dimethylformamide). Best adsorption properties for TNT vapour until now showed a PAA-MIP synthesized with chloroform. Direct measurements of the mass attachment, respectively frequency decrease of the coated QCMs during vapour treatment showed a TNT-uptake of about 150 pg per μg MIP per hour. Results look worthy for further studies.     

Theoretical methodology for prediction of tropospheric oxidation of dimethyl phosphonate and dimethyl methylphosphonate

Rate constants for the reactions of OH radicals with dimethyl phosphonate [DMHP, (CH(3)O)(2)P(O)H] and dimethyl methylphosphonate [DMMP, (CH(3)O)(2)P(O)CH(3)] have been calculated by ab initio structural methods and semiclassical dynamics modeling and compared with experimental measurements over the temperature range 250-350 K. The structure and energetics of reactants and transition structures are determined for all hydrogen atom abstraction pathways that initiate the atmospheric oxidation mechanism. Structures are obtained at the CCSD/6-31++G** level of chemical theory, and the height of the activation barrier is determined by a variant of the G2MP2 method. A Transfer Hamiltonian is used to compute the minimum energy path in the neighborhood of the transition state (TS). This calculation provides information about the curvature of the potential energy surface in the neighborhood of the TS, as well as the internal forces that are needed by the semiclassical flux-flux autocorrelation function (SCFFAF) dynamics model used to compute the temperature-dependent reaction rate constants for the various possible abstraction pathways. The computed temperature-dependent rate curves frequently lie within the experimental error bars.