| AVS 61st International Symposium & Exhibition | |
| Biomaterial Interfaces | Tuesday Sessions |
| Session BI+AS-TuA |
| Session: | Characterization of Biointerfaces |
| Presenter: | Richard Rosenberg, Argonne National Laboratory |
| Authors: | R.A. Rosenberg, Argonne National Laboratory J.M. Symonds, Georgia Institute of Technology K. Vijayalakshmi, Argonne National Laboratory D. Mishra, Weizmann Institute of Science, Israel T.M. Orlando, Georgia Institute of Technology R. Naaman, Weizmann Institute of Science, Israel |
| Correspondent: | Click to Email |
High energy ionizing irradiation produces large amounts of low energy (<20 eV) secondary electrons (SEs). These electrons are produced via a cascade process following the ionization of a core (deeply bound) electron. Due to their low energy there is a high probability for the SEs to become trapped in antibonding orbitals, via resonant scattering, forming a temporary negative ion (TNI) resonance. If the lifetime of the TNI state is long enough, then bond rupture can occur by by a process known as dissociative electron attachment (DEA). There is vast literature on the role of TNI states and DEA in DNA related radiation chemistry.[1,2] Due to its high flux density, synchrotron radiation (SR) has often been used to induce and study radiation chemistry in numerous systems,[3] including DNA and related molecules. SR has also been used to probe the electronic structure and bonding of such molecules, primarily by probing the occupied states with X-ray photoelectron spectroscopy (XPS) and the unoccupied states with X-ray absorption (XAS) measurements. Bond overlap and localization can be revealed by XPS while XAS can determine the density of unoccupied states and the orientation of the orbitals. In this presentation we examine X-ray induced reactions of DNA adsorbed on a gold substrate when the DNA is either thiolated (tDNA) or when it is unthiolated (uDNA). By performing polarization-dependent XAS at the N K edge we determined that tDNA protrudes from the surface at ~45 degrees, in agreement with previous studies. We also found that the unthiolated molecules have a similar orientation. However, due to differences in charge transfer between the gold and the DNA in the two systems there is a higher density of unoccupied states in the N-C=N derived π* orbital for tDNA. We also found that the adsorbed tDNA has a significant higher cross section for radiation damage. The reason for this enhancement could arise from the greater probability of forming a TNI state for the tDNA due to the higher density of unoccupied π* states.
1. E. Alizadeh and L. Sanche, Chem. Rev.112, 5578 (2012).
2. R. Naaman and L. Sanche, Chem. Rev.107, 1553 (2007).
3. R. A. Rosenberg and S. P. Frigo, in Chemical Applications of Synchrotron Radiation, Part II: X-ray Applications, edited by T.K. Sham (World Scientific Publishing Co., Singapore, 2002), Vol. 12A, p. 462.