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Dehydrogenation of nucleobases upon electron attachment to isolated nucleotides

Dehydrogenation of nucleobases upon electron attachment to isolated nucleotides Steen Brøndsted Nielsen Department of Physics and Astronomy University of Aarhus. June 24-27, 2004, Lyon-France  . DNA DAMAGE. HOW DOES UV RADIATION CAUSE GENETIC DAMAGE ?.

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Dehydrogenation of nucleobases upon electron attachment to isolated nucleotides

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  1. Dehydrogenation of nucleobases upon electron attachment to isolated nucleotides Steen Brøndsted Nielsen Department of Physics and Astronomy University of Aarhus June 24-27, 2004, Lyon-France 

  2. DNA DAMAGE

  3. HOW DOES UV RADIATION CAUSE GENETIC DAMAGE ? Modification of nucleobases may lead to loss of base-pairing specificity • Direct absorption of light by the nucleobases followed by physical and chemical reactions • and / or • 2) Ionisation of water (H2O  H2O+ + e-) followed by electron attachment to nucleobases

  4. OUR APPROACH Elucidate the processes at the single-molecule level. Isolated damage to nucleotides, the basic building blocks of DNA and RNA, upon electron attachment.

  5. TOOLBOX ELECTROSPRAY IONISATION MASS SPECTROMETRY: ACCELERATOR INSTRUMENT ION STORAGE RING ELISA LASERS QUANTUM CHEMICAL CALCULATIONS

  6. ELECTROSPRAY IONISATION droplets BARE IONS

  7. ELECTROSPRAY ION SOURCE Tube lens Octapole Skimmer Lenses Acceleration tube ESI needle 4kV 10-6 mbar 10-3 mbar 10-5 mbar 1 mbar Heated capillary 22-pole ion trap

  8. R GAS-PHASE EXPERIMENTS ON NUCLEOTIDE ANIONS PROBLEM: Attachment of an electron to a negative ion is unlikely because of the repulsion between the two negative charges. SOLUTION: High-energy collisions with sodium: electron transfer from Na to the ion. Compare: the violent reaction of sodium with water ! Nielsen et al., J. Am. Chem. Soc. 125, 9592-9593 (2003). Liu et al., Chem. Phys. Chem.4, 1341-1344 (2003).

  9. + ACCELERATOR INSTRUMENT Na collision cell R = 2 m B = 1.4 T T=500 K Magnet Electrostatic analyser 0 V Channeltron detector 50 kV ESI source

  10. COLLISION INTERACTION TIME: FEW FEMTOSECONDS Nucleotide anion - 105 m/s 1 nm Na The electron transfer process is nearly vertical.

  11. Electron attachment to AMP anions Ne Na m/q 346 Liu et al., Chem. Phys. Chem.4, 1341-1344 (2003).

  12. High-energy collisions between dAMP anions and Na and Ne dAMP2- dAMP- fragment ions m/q 330

  13. Spectrum obtained after collisions between AMP-(H2O)13 andNa AMP-(H2O)13 AMP2- AMP2-(H2O)9 AMP-

  14. Electron transfer from Na to dinucleotide anions dianion dG2 nucleobase dT2 sugar - phosphate nucleobase dC2 sugar dA2

  15. IS THE NUCLEOTIDE DIANION INTACT ? H loss is observed upon electron attachment to nucleobases in vacuo. C. Desfrancois, H. Abdoul-Carime, and J. P. Schermann, J. Chem. Phys. 104, 7792 (1996). S. Gohlke, H. Abdoul-Carime, and E. Illenberger, Chem. Phys. Lett.380, 595 (2003). G. Hanel, B. Gstir, S. Denifl, P. Scheier, M. Probst, B. Farizon, M. Farizon, E. Illenberger, and T. D. Märk, Phys. Rev. Lett.90, 188104 (2003). H. Abdoul-Carime, S. Gohlke, and E. Illenberger, Phys. Rev. Lett.92, 168103 (2004). H loss is observed upon electron attachment to deoxyribose in vacuo. S. Ptasińska, S. Denifl, P. Scheier, and T. D. Märk, J. Chem. Phys.18, 8505 (2004).

  16. AMP dissolved in CD3OD: Selection of deuterium-labelled ions for collision experiments Intact dianion - H - D # of D in AMP- 0 1 2 3 Exchangeable hydrogens Liu et al., J. Chem. Phys., issued for Sept. 1 (2004).

  17. WHAT IS THE ORIGIN OF THE HYDROGEN ? -POH phosphoric acid group -OH sugar -NH2 nucleobase -CH sugar or nucleobase

  18. Electron attachment to nucleotides: dehydrogenation at nitrogen sites Thymine Uracil Adenine Cytosine Guanine 1 2 3

  19. Cross section for formation of dehydrogenated dianion

  20. Dissociative electron attachment to deuterated thymine • H-loss from N • No D-loss from C H. Abdoul-Carime, S. Gohlke, and E. Illenberger, Phys. Rev. Lett.92, 168103 (2004).

  21. THE DNA DOUBLE HELIX

  22. Watson-Crick base pairs Base mispairing Biological relevance?

  23. WHAT IS THE LIFETIME OF THE DIANION ?

  24. ELectrostatic Ion Storage Ring Aarhus (ELISA) Channeltron Ion bunch Magnet Sodium Injection Micro-channel plate detector 1 m Accelerator with electrospray ion source S.P. Møller, NIM A394, 281 (1997). J.U. Andersen, J.S. Forster, P. Hvelplund, T.J.D. Jørgensen, S.P Møller, S. Brøndsted Nielsen, U.V. Pedersen, S. Tomita, and H. Wahlgreen, Rev. Sci. Instrum.73, 1284-1287 (2002).

  25. Electron autodetachment from the AMP dianion Liu et al., J. Chem. Phys., issued for Sept. 1 (2004).

  26. Long-lived component ? Dump of a remaining beam in the micro-channel platedetector after 34 ms of storage time. Channeltron Ion bunch Magnet Sodium Injection Micro-channel plate detector 1 m Accelerator with electrospray ion source

  27. Dump of beam in the detector after 34 ms of storage time AMP2- (m/q 172.5) 13C-AMP2- (m/q 173)

  28. CONCLUSIONS • Electron transfer to nucleotide anions occurs in • collisions with sodium vapour. • Electron attachment leads to dehydrogenation of • the nucleobase nitrogens. • The dehydrogenated dianion is longlived. Other fragmentation channels than H-loss upon electron attachment ?

  29. ACKNOWLEDGEMENTS University of Aarhus: Preben Hvelplund Jens Ulrik Andersen Shigeo Tomita Bo Liu Jimmy Rangama Leopold-Franzens Universität Innsbruck: Paul Scheier Gabriel Hasan FUNDING The Danish Natural Science Research Council Aarhus Center for Atomic Physics (ACAP)

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