Stabilization of Mixed Frenkel-Charge Transfer Excitons Extended Across Both Strands of Guanine-Cytosine DNA Duplexes.
The photoreactive pathways that may lead to DNA damage depend crucially upon the nature of the excited electronic states. The study of alternating guanine-cytosine duplexes by fluorescence spectroscopy and quantum mechanical calculations identifies a novel type of excited states that can be populated following UVB excitation. These states, denoted High-energy Emitting Long-lived Mixed (HELM) states, extend across both strands and arise from mixing between cytosine Frenkel excitons and guanine-to-cytosine charge transfer states. They emit at energies higher than ππ* states localized on single bases, survive for several nanoseconds, are sensitive to the ionic strength of the solution, and are strongly affected by the structural transition from the B form to the Z form. Their impact on the formation of lesions of the genetic code needs to be assessed.
†CNRS, IRAMIS, LIDYL, Laboratoire Francis Perrin, URA 2453, F-91191 Gif-sur-Yvette, France.|§Institut für Physikalische u. Theoretische Chemie, Goethe-Universität, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main, Germany.
Miquel
M
Huix-Rotllant
†CNRS, IRAMIS, LIDYL, Laboratoire Francis Perrin, URA 2453, F-91191 Gif-sur-Yvette, France.
Johanna
J
Brazard
‡Istituto Biostrutture e Bioimmagini- Consiglio Nazionale delle Ricerche, Via Mezzocannone 16, I-80136 Napoli, Italy.
Roberto
R
Improta
§Institut für Physikalische u. Theoretische Chemie, Goethe-Universität, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main, Germany.
Irene
I
Burghardt
†CNRS, IRAMIS, LIDYL, Laboratoire Francis Perrin, URA 2453, F-91191 Gif-sur-Yvette, France.
Dimitra
D
Markovitsi
D003596:Cytosine / Q000737:chemistry*; D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D059371:DNA, B-Form / Q000737:chemistry / Q000378:metabolism; D043542:DNA, Z-Form / Q000737:chemistry / Q000378:metabolism; D006147:Guanine / Q000737:chemistry*; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence; D014466:Ultraviolet Rays
D059371:DNA, B-Form; D043542:DNA, Z-Form; D006147:Guanine; D003596:Cytosine; D004247:DNA
DNA; cytosine; excitons; fluorescence spectroscopy; guanine; quantum chemistry