## LSU Historical Dissertations and Theses

1994

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

Chemistry

Mary D. Barkley

#### Abstract

The relationship between ground-state structure and fluorescence lifetime of tomaymycin was studied using steady-state and time-resolved fluorescence, absorption, NMR, and photochemical techniques. Excited-state proton transfer and intersystem crossing were identified as the major nonradiative processes. Solvent isotope effect was found in aqueous solution, which did not involved C8OH. Photochemical H-D exchange on aromatic C6H and C9H were observed with similar rate. At 77 K, the total luminescence quantum yield was determined as 0.99. The quantum yield ratio of phosphorescence to fluorescence was 1.2. The limiting anisotropy was ${\sim}0.34$ for fluorescence and $-$0.1 for phosphorescence. The number and type of tomaymycin-DNA adducts present on natural DNA were identified using time-resolved fluorescence spectroscopy. At low bonding density, only two species were observed with lifetimes of 4.3 and 7.1 ns and amplitude ratio of 0.4:0.6, presumably representing $R5\sp\prime$ and $S3\sp\prime$ binding modes at preferred bonding site 5$\sp\prime$AGA. These species were present over a range of solution conditions. The two species have the same emission spectra, but slightly shifted absorption spectra. The fluorescence lifetimes were weakly temperature dependent with $E\sb{\rm a}$ = 21 kJ $\cdot$ mol$\sp{-1}$. The kinetics of adduct formation was also studied. At saturating bonding density, the fluorescence decay showed a bimodal lifetime distribution whether analyzed by least squares assuming a Gaussian distribution model or by the maximum entropy method. The bimodal distributions were centered around 2-3 and 6-6.6 ns, reflecting multiple species on different bonding sequences. Flexibility of calf thymus DNA and poly(dAdG) $\cdot$ poly(dCdT) (1000 $\pm$ 50 bp) were measured in $\le$41 ns range using time-resolved fluorescence emission anisotropy. A global data analysis program was developed from the predicted non-exponential anisotropy decay model for twisting and bending motions of a semi-flexible rod. The program provides options of linking or fixing decay parameters and associating lifetimes with anisotropies. Initial anisotropy of ${\sim}0.36$ and orientation of the emission transition dipole of the drug toward the DNA helix axis of ${\sim}35\sp\circ$ were obtained for both DNA samples. The torsional rigidities were 2.4 and $2.2\times10\sp{-19}$ erg $\cdot$ cm$\sp{-1}$, and the persistence lengths were 470 and 140 A, respectively.

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