Pierre LeBreton
Emeritus Professor
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5417B SES, MC 111
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About
Using photoelectron and fluorescence spectroscopic data, and results from theoretical electronic structure calculations, my group investigates the energetics of DNA damage. We focus principally on events which occur when DNA interacts with ionizing radiation, or with electrophilic alkylating agents. In living cells, these events, which result in DNA lesions, are the first, in a long series that leads ultimately to the formation of cancerous tumors. For decades researchers have characterized the damage which DNA suffers when it is subjected to high energy radiation. However, until recently, an important unanswered question was, "What are the minimum photon energies required for DNA photoionization in an aqueous environment?" We have developed methods, employing gas-phase experimental ionization potentials and results from ab initio quantum mechanical calculations for answering this question. The method and the results are illustrated in the figure which shows gas phase ionization potentials (IPs) of a base model compound. This data permitted us to evaluate aqueous base ionization potentials in a nucleotide as conduction band-edge ionization threshold energies. The valence-electron orbital structure of nucleotides is largely localized on the base, sugar or phosphate groups. This allows us to extend our approach for evaluating nucleotide ionization energies to larger DNA units such as dinucleotides and oligonucleotides, and nucleotides in DNA-protein complexes.
Right: Gas-phase IPs of the nucleotide base model compound, 1,9-dimethyguanine.Left: Aqueous conduction band-edge ionization threshold energies for ionization associated with the more weakly bound base and phosphate electrons in the nucleotide, 2'-deoxyguanosine 5'-phosphate(proc. Natl. Acad. Sci. USA, 1998).
Education
BS, University of Chicago, 1964
PhD, Harvard University, 1970
Postdoctoral Fellow, Freiburg University, Germany, 1970-71
Postdoctoral Fellow, California Institute of Technology and the Jet Propulsion Laboratory, 1971-73
CNRS Fellow, University Louis Pasteur, Strasbourg, France, 1980