Base-Dependent Electron Photodetachment from Negatively Charged DNA Strands upon 260-nm Laser Irradiation

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• 作者：Val&eacute ; rie Gabelica ; Fr&eacute ; d&eacute ; ric Rosu ; Thibault Tabarin ; Catherine Kinet ; Rodolphe Antoine ; Michel Broyer ; Edwin De Pauw ; Philippe Dugourd
• 刊名：Journal of the American Chemical Society
• 出版年：2007
• 出版时间：April 18, 2007
• 年：2007
• 卷：129
• 期：15
• 页码：4706 - 4713
• 全文大小：307K
• 年卷期：v.129,no.15(April 18, 2007)
• ISSN：1520-5126

文摘

DNA multiply charged anions stored in a quadrupole ion trap undergo one-photon electron ejection(oxidation) when subjected to laser irradiation at 260 nm (4.77 eV). Electron photodetachment is likely afast process, given that photodetachment is able to compete with internal conversion or radiative relaxationto the ground state. The DNA [6-mer]^3- ions studied here show a marked sequence dependence of electronphotodetachment yield. Remarkably, the photodetachment yield (dG₆ > dA₆ > dC₆ > dT₆) is inverselycorrelated with the base ionization potentials (G < A < C < T). Sequences with guanine runs show increasedphotodetachment yield as the number of guanine increases, in line with the fact that positive holes are themost stable in guanine runs. This correlation between photodetachment yield and the stability of the baseradical may be explained by tunneling of the electron through the repulsive Coulomb barrier. Theoreticalcalculations on dinucleotide monophosphates show that the HOMO and HOMO-1 orbitals are localized onthe bases. The wavelength dependence of electron detachment yield was studied for dG₆^3-. Maximumelectron photodetachment is observed in the wavelength range corresponding to base absorption (260-270 nm). This demonstrates the feasibility of gas-phase UV spectroscopy on large DNA anions. Thecalculations and the wavelength dependence suggest that the electron photodetachment is initiated at thebases and not at the phosphates. This also indicates that, although direct photodetachment could alsooccur, autodetachment from excited states, presumably corresponding to base excitation, is the dominantprocess at 260 nm. Excited-state dynamics of large DNA strands still remains largely unexplored, andphoto-oxidation studies on trapped DNA multiply charged anions can help in bridging the gap betweengas-phase studies on isolated bases or base pairs and solution-phase studies on full DNA strands.