The effect of pH and solvent on the photophysics of thymine

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" The effect of pH and solvent on the photophysics of thymine "
A. M. Abdallah

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1112817
Doc. No	:	TLpq304303126
Main Entry	:	A. M. Abdallah
Title & Author	:	The effect of pH and solvent on the photophysics of thymine\ A. M. Abdallah
College	:	King Fahd University of Petroleum and Minerals (Saudi Arabia)
Date	:	1996
student score	:	1996
Degree	:	M.S.
Page No	:	95
Abstract	:	The effect of pH and various alcohol-water mixtures on the electronic spectra and excited state dynamics of thymine, one of the DNA constituents, have been investigated. A mode-locked Nd:YAG laser in combination with a cavity-dumped synchronously-pumped dye laser is used as a source of excitation. Fluorescence decay and time-resolved spectra were recorded with picosecond photon counting spectrometer. Steady-state fluorescence spectra as well as ultraviolet absorption spectra were also recorded. Fluorescence spectra of thymine in aqueous solutions where thymine exists in the neutral form have been found to vary in shape as the excitation wavelength is increased. This change in shape is explained by the presence of another tautomer beside the predominant diketo tautomer of thymine. This minor tautomer is believed to be 5-methyl-2-hydoxy-4(3H)-pyrimidinone or the keto-enol tautomer. Lifetime analysis of fluorescence decays support this explanation where a biexponential decay with lifetimes of around 0.7 and 4 ns is observed for the neutral form of thymine. Time-resolved spectra are in accordance with this explanation. Fluorescence lifetimes of thymine do not vary in methanol-water and ethanol-water mixtures. While the lifetime of the keto-enol tautomer is found to vary with viscosities of the 1-propanol-water mixtures. This is explained by solvent-solvent and solute-solvent interaction. According to the steady-state and time-resolved fluorescence spectra in the various alcohol-water mixtures, thymine does nor undergo a pKa shift in the excited state.
Subject	:	Biochemistry
	:	Chemistry
	:	Pure sciences