Title

Catalysis using porous nanocrystalline electrodes of titanium dioxide and electrochemical analysis of DNA damage

Date of Completion

January 1999

Keywords

Biology, Molecular|Health Sciences, Toxicology|Chemistry, Analytical

Degree

Ph.D.

Abstract

The general goals of this thesis were to develop catalytic reactions at thin nanocrystalline films of titanium dioxide (TiO2). and to explore electrochemical assay methods for DNA damage by organic molecules. ^ A novel electrochemical cell was developed in which pollutants are decomposed at nanocrystalline TiO2 anodes, and hydrogen gas produced simultaneously at platinum black cathodes. Visible light was the only external energy source. 4-chlorophenol and 2,4,5-trichlorophenol were decomposed completely and quantitatively to carbon dioxide, water and chloride ions. 4,4-dicholorobiphenyl adsorbed to soil was also decomposed. Hydrogen gas was produced simultaneously from the photodecomposition of water. The cell is a battery as well. Efficiency for production of hydrogen and electricity was about 2% of light absorbed. ^ Chemisorbing vitamin B12 hexacarboxylate onto nanocrystalline TiO2 electrodes greatly enhanced catalytic efficiency of mediated electrosyntheses of organic compounds in microemulsions. This is the first example of a catalytic electrode for organic synthesis in microemulsions. Turnover numbers were much higher than for the same catalyst in solution. ^ Evidence is presented of the electrochemically driven formation of ferrylmyoglobins in hydrogel films of the polyester sulfonic acid ionomer, Eastman AQ. An ionomer is an ionic polymer in which only a fraction of the groups per monomer unit can ionize. The application of these films to catalyze oxidation of styrene is described. Catalytic turnover using myoglobin in the films was 5 fold higher compared to myoglobin in solution. ^ Finally, an electrochemical biosensor to detect damage of DNA by pollutant molecules using derivative Osteryoung square wave voltammetry (OSWV) was developed. Film electrodes were prepared by casting films of DNA and the polyester sulfonic acid ionomer Eastman AQ 38 onto pyrolitic graphite (PG) and by covalently binding DNA via amide linkages on activated PG. Derivative square wave voltammetry was used to detect oxidation peaks from damaged DNA. Four types of DNA gave oxidation peaks at 0.6 V, 0.8 V and 0.9 V vs SCE, which increased with time of incubation with damage agent styrene oxide. Because of lower backgrounds, films of DNA-AQ gave better performance for assaying DNA damage than films in which DNA was covalently bound to electrodes. ^