Dimethylacetamide (DMA) solvent is oxidized catalytically to CH₃CON(CH₃)CH₂OOH and CH₃CON(CH₃)CHO under H₂/0₂ mixtures at 50°C in the presence of the dimethylsulfoxide complex RhCl₃(DMSO)₃ (I) at a rate which is much faster than peroxide-initiated autoxidation of DMA under O₂ alone. The hydroperoxide is thought to be the initial product, and the N-formyl derivative its decomposition product. An accompanying metal-catalyzed hydrogenolysis of 0₂ leads to H₂0₂ and H₂0. Hydrogen peroxide and CH₃CON(CH₃)CH₂OOH are the only products formed in the early stages of the catalytic reaction. The maximum rate of gas uptake in this initial region is independent of the partial pressure of 0₂, but shows linear dependences on Rh and H₂. Stoichiometry, rate and spectral data are consistent with an initiation reaction between complex I and H₂, and then 0₂ to give a catalytically active RhIII (0₂=) (DMA) species (II) (eq. 1) [formula omitted] The autoxidation of DMA and the hydrogenolysis of 0₂ are postulated to occur via independent pathways involving II (eqs. 2 and 3). [formula omitted] In the absence of H2, II degenerates to catalytically inactive species. The role of H₂ in the DMA autoxidation is thought to be the regeneration of Rh I species and hence II, from deactivated forms of II. Eventual slow, irreversible deactivation of the catalyst and the probable participation of the H₂0₂ product in peroxide initiated free-radical autoxidations complicate the interpretation of later stages of reaction. Diphenylsulfide (DPS) is catalytically oxidized to the sulfoxide by complex I under H₂/O₂ in DMA at 50°C, but accompanying oxidation of the solvent persists even in the presence of a 100-fold excess of DPS over Rh. Oxidation of the sulfide is thought to involve H₂0₂ liberated in the catalytic hydrogenolysis of 0₂. Complex I in CH₂C1₂ or C₂H₄CL₂ reacts with CO to give the dimethylsulfide complex RhCL₃(DMS)₃ via a facile reduction of DMSO ligands. Dimethylsulfoxide is reduced also by RhI species in CH₂CL₂ in the presence of two equivalents of acid to yield DMS, RhIII and H₂0. However, Rh I /2H⁺/DMS0 systems are relatively stable in DMA, because of the proton affinity of the solvent. Complex I reacts also with the strongly basic tertiary amine NEt₃ via a redox process in which the RhIII is reduced to Rh I with an accompanying dehydrogenation of the amine (eq. 4). RhCl₃ + 3NEt₃ → RhCl + 2NEt₃ HCl + CH₂=CHNEt₂ (4) The resulting ethenamine then reacts with I to give the ƞ¹-ylidic complex, RhCl₃(DMS̠O)₂(⁻CH₂CH=⁺NEt₂). Data from an earlier thesis, on a reaction between complex I and 1,8-bis(dimethylamino)naphthalene (or Proton Sponge), are reinterpreted in terms of a similar redox reaction that gives an N-carbene fragment (eq. 5),which is stabilized within the RhIII complex, RhCl₃(DMS̠O)₂(=CH-N(Me)-C₁₀H₆NMe₂•HCl). [formula omitted] / Science, Faculty of / Chemistry, Department of / Graduate

Dissertation (Ph.D.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Ph.D. / The aim of this study was the development of a new technology for the manufacturing of amorphous silicon (a-Si:H) solar cells on flexible substrates. Kapton R , a commercially available polymer, was used as a substrate to this end. The use of such a polymer, as opposed to glass, results in dramatic savings and also affords the possibility for technological innovation. From the start the project was planned to develop and commission a medium-scale pilot plant manufacturing process. The project thus consisted of two sections: the design, fabrication and implementation of a large-area deposition system, as well as research and development of the materials and cells. A pilot plant was developed and successfully implemented. The optimization of the reactor resulted in very homogeneous materials with good electrical- and optical characteristics. The individual materials were optimized and incorporated into the standard cell configuration (on glass). This process was then transferred to kapton and the configuration was optimized. The use of kapton, as opposed to glass, implies the growth of silicon on a metal film on the kapton. This process leads to a number of phenomena occurring in cells on kapton which do not occur in standard cells on glass. The phenomena include the crystallization of a-Si:H at low temperatures, degradation of the material properties and unwanted microstructure. The origin of these phenomena can be linked to the high occurence of metal/Si-interdiffusion. It was found that this inter-diffusion can be decreased by the insert i on of a thin ZnO buffer layer between the back metal contact and the a-Si:H. The flexible cells were successfully developed and optimized for large areas. An operational manufacturing process was thus developed and the product of this study can now be applied successfully in practical applications.

Thesis (Ph.D. (Biochemistry, Microbiology & Biotechnology)) - Rhodes University, 2008.

The ultimate objective of this work was to develop a real-time method for detecting and monitoring β-D-galactosidase as a suitable indicator of the potential presence of total coliform bacteria in water environments. Preliminary comparison of the chromogenic substrate, chlorophenol red β-D-galactopyranoside and the fluorogenic substrate, MuGAL, revealed unreliable results with the fluorogenic technique due to interference from compounds commonly found in environmental water samples. Thus, the chromogenic assay was further explored. Hydrolysis of the chromogenic substrate chlorophenol red β-D-galactopyranoside by β-D-galactosidase to yield chlorophenol red was the basis of this assay. Fundamental studies with chlorophenol red β-Dgalactopyranoside showed that β-D-galactosidase occurs extracellularly and in low concentrations in the polluted water environment. A direct correlation between enzyme activity and an increase in environmental water sample volume, as well as enzyme activity with total coliform colony forming unit counts were observed. Spectrophotometric detection was achieved within a maximum period of 24 h with a limit of detection level of 1 colony forming unit 100 ml[superscript -1]. This enzyme also exhibited physical and kinetic properties different from those of the pure commercially available β-D-galactosidase. Cell permeabilisation was not required for releasing enzymes into the extracellular environment. PEG 20 000 offered the best option for concentrating β-D-galactosidase. The source of β-D-galactosidase in the polluted environmental water samples was confirmed as Escherichia coli through SDS-PAGE, tryptic mapping and MALDI-TOF, thus justifying the further use of this method for detecting and/or monitoring total coliforms. Several compounds and metal ions commonly found in environmental water samples (as well as those used in water treatment processes) did have an effect on β-D-galactosidase. All the divalent cations except Mg [superscript 2+], at the concentrations studied, inhibited the relative activity of β-D-galactosidase in both commercial β-D-galactosidase and environmental samples. Immobilisation of chlorophenol red β-D-galactopyranoside onto a solid support material for the development of a strip bioprobe was unsuccessful, even though the nylon support material yielded some positive results. A monthly (seasonal) variation in β-Dgalactosidase activity from the environmental water samples was observed, with the highest activity coinciding with the highest monthly temperatures. Electro-oxidative detection and/or monitoring of chlorophenol red was possible. Chlorophenol red detection was linear over a wide range of concentrations (0.001-0.01 μg ml[superscript -1]). Interference by chlorophenol red β-D-galactopyranoside in the reduction window affected analysis. A range of phthalocyanine metal complexes were studied in an attempt to reduce fouling and/or increase the sensitivity of the biosensor. The selected phthalocyanine metal complexes were generally sensitive to changes in pH with a reduction in sensitivity from acidic pH to alkaline pH. The tetrasulphonated phthalocyanine metal complex of copper was, however, more stable with a minimum change of sensitivity. The phthalocyanine metal complexes were generally stable to changes in temperature. While only two consecutive scans were possible with the unmodified glassy carbon electrode, 77 consecutive scans were performed successfully with the CuPc-modified glassy carbon electrode. Among the phthalocyanine metal complexes studied, the CuPc-modified glassy carbon electrode therefore provided excellent results for the development of a biosensor. The CuPc modified-glassy carbon electrode detected 1 colony forming unit 100 ml[superscript -1] in 15 minutes, while the plain unmodified glassy carbon electrode required 6 hours to detect the equivalent number of colony forming units. CoPc, ZnPc and CuTSPc required 2, 2.25 and 1.75 h, respectively, to detect the same numbers of colony forming units. The CuPcmodified glassy carbon electrode detected 40 colony forming units 100 ml[superscript -1] instantly. In general, a direct correlation between colony forming units and current generated in the sensor was observed (R2=0.92). A higher correlation coefficient of 0.99 for 0-30 coliform colony forming units 100 ml[superscript -1] was determined. Current was detected in some water samples which did not show any colony forming units on the media, probably due to the phenomenon of viable but non-culturable bacteria, which is the major disadvantage encountered in the use of media for detecting indicator microorganisms. This novel biosensor therefore presents a very robust and sensitive technique for the detection and/or monitoring of coliform bacterial activity in water.