Cleavage of duplex DNA using two-photon excitation of N-(alkoxy)pyridine thiones

Abstract

DNA photocleaving reagents are a unique class of molecules that display the ability to cleave DNA, causing strand breaks, upon exposure to an irradiation source. In terms of biological applications, achieving excitation through a two-photon absorption event provides for unique benefits that can be useful in such applications as photodynamic therapy and cell viability studies. Thus, this thesis pertains to the study of a class of photocleaving reagents that have been shown to become excited through a twophoton process during irradiation with a pulsed femtosecond laser at 775 nm. N-(Alkoxy)pyridinethiones were selected as possible oxygen-based radical generators upon irradiation at two-photon wavelengths. Experiments were carried out with pBR 322 plasmid DNA to determine if these N-(alkoxy)pyridinethiones could cause strand cleavage and if so how efficient they are in doing so. Several compounds were found to be effective DNA strand cleavers when irradiated at two-photon wavelengths, displaying the utility of two-photon excitation in biological studies. Rationale is suggested for the observed variation in cleaving efficiency based on inherent properties of the generated radicals. A second study was done to measure the two-photon cross section of the compound N-(anthracenoyloxy)pyridinethione. The two-photon cross section was found by measuring the fraction of substrate remaining after specific periods of femtosecond laser irradiation at 775 nm, and the two-photon cross section was found to be 0.051 GM.