| Atomic oxygen O(3P), a potent oxidant has received a lot of investigation in the gas phase. In water, however it suffers from lack of facile and efficient source. The recent discovering of dibenzothiophene-S-oxide (DBTO) as a photochemical precursor has made the investigation of atomic oxygen O(3P) in condensed phase feasible. However, the use of DBTO asO(3P) precursor in aqueous medium is faced with two problems: low quantum yield and lack of solubility in water. This dissertation presents work on new derivatives of DBTO synthesized to generate O(3P) in water. The solubility of these derivatives was measured by the octanol-water coefficient and found to be about 100-fold more soluble in water compared to DBTO. Photolysis of 4,6-dihydroxlmethyldibenzothiophene-S-oxide and 2,8- dihydroxlmethyldibenzothiophene-S-oxide in water resulted in deoxygenation at significantly higher quantum yield than in organic medium. The deoxygenation reaction is accompanied by internal oxidation of the hydroxyl substituent depending on the experimental conditions. The DBTOs mechanism was proposed to depend on the pH of the aqueous solution.;To investigate the photo-induce DNA cleavage by O(3P), three aqueous soluble derivatives of DBTO were investigated for their ability to photochemically cleave DNA. The photoirradition of the DBTO derivatives in water was performed in the presence of pUC19 plasmid DNA and the conversion of circular DNA to nicked DNA was monitored by gel electrophoresis. To determine if O(3P) was involved in the DNA cleavage, the experiment was performed in the presence of glutathione. All the sulfoxides employed showed effective photo-induce DNA cleavage ability. Thiols are known to be oxidized by atomic oxygen. Therefore the inhibition of DNA cleavage by glutathione indicates O(3P) was involve in the DNA cleavage.;This dissertation also presents the theoretical prediction of the bond dissociation enthalpy of sulfoxide. The S-O BDEs were predicted by B3LYP, CCSD, CCSD(T), M05-2X, M06-2X, and MP2 combined with aug-cc-pV(n+d)Z, aug-cc-pVnZ, and Pople-style basis sets. The accuracy of these predictions was determined by comparing the computationally predicted values to the experimentally determined S-O BDE. Values within experimental error were obtained for dialkyl sulfoxides when the S-O BDEs were estimated using an isodesmic oxygen transfer reaction at the M06-2X/aug-cc-pV(T+d)Z level of theory. However, the S-O BDE of divinyl sulfoxide was overestimated by this method. |
