Primary processes underlying the photostability of isolated DNA bases: adenine.
The UV chromophores in DNA are the nucleic bases themselves, and it is their photophysics and photochemistry that govern the intrinsic photostability of DNA. Because stability is related to the conversion of dangerous electronic to less-dangerous vibrational energy, we study ultrafast electronic relaxation processes in the DNA base adenine. We excite adenine, isolated in a molecular beam, to its pipi* state and follow its relaxation dynamics using femtosecond time-resolved photoelectron spectroscopy. To discern which processes are important on which timescales, we compare adenine with 9-methyl adenine. Methylation blocks the site of the much-discussed pisigma* state that had been thought, until now, minor. Time-resolved photoelectron spectroscopy reveals that, although adenine and 9-methyl adenine show almost identical timescales for the processes involved, the decay pathways are quite different. Importantly, we confirm that in adenine at 267-nm excitation, the pisigma* state plays a major role. We discuss these results in the context of recent experimental and theoretical studies on adenine, proposing a model that accounts for all known results, and consider the relationship between these studies and electron-induced damage in DNA.
Satzger
Helmut
H
Steacie Institute for Molecular Sciences, Ottawa, ON, Canada K1A 0R6; and.
Townsend
Dave
D
Steacie Institute for Molecular Sciences, Ottawa, ON, Canada K1A 0R6; and.
Zgierski
Marek Z
MZ
Steacie Institute for Molecular Sciences, Ottawa, ON, Canada K1A 0R6; and.
Patchkovskii
Serguei
S
Steacie Institute for Molecular Sciences, Ottawa, ON, Canada K1A 0R6; and.
Ullrich
Susanne
S
Department of Physics and Astronomy, University of Georgia, Athens, GA 30602-2451.
Stolow
Albert
A
Steacie Institute for Molecular Sciences, Ottawa, ON, Canada K1A 0R6; and albert.stolow@nrc.ca.
D000225:Adenine / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D010777:Photochemistry; D013057:Spectrum Analysis
D004247:DNA; D000225:Adenine