title: Energy Thresholds of DNA Damage Induced by UV Radiation: An XPS Study.
abstract: This work stresses on damage at the molecular level caused by ultraviolet radiation (UV) in the range from 3.5 to 8 eV, deoxyribonucleic acid (DNA) films observed by X-ray photoelectron spectroscopy (XPS). Detailed quantitative XPS analysis, in which all the amounts are relative to sodium-assumed not to be released from the samples, of the carbon, oxygen, and particularly, nitrogen components, reveals that irradiation leads to sugar degradation with CO-based compounds release for energies above 6.9 eV and decrease of nitrogen groups which are not involved in hydrogen bonding at energies above 4.2 eV. Also the phosphate groups are seen to decrease to energies above 4.2 eV. Analysis of XPS spectra allowed to conclude that the damage on bases peripheral nitrogen atoms are following the damage on phosphates. It suggests that very low kinetic energy photoelectrons are ejected from the DNA bases, as a result of UV light induced breaking of the phosphate ester groups which forms a transient anion with resonance formation and whereby most of the nitrogen DNA peripheral groups are removed. The degree of ionization of DNA was observed to increase with radiation energy, indicating that the ionized phosphate groups are kept unchanged. This result was interpreted by the shielding of phosphate groups caused by water molecules hydration near sodium atoms.
authors.affiliation: †CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
authors.forename: P J
authors.initials: PJ
authors.lastname: Gomes
authors.affiliation: ‡Centro de Química-Física Molecular and IN, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal.
authors.forename: A M
authors.initials: AM
authors.lastname: Ferraria
authors.affiliation: ‡Centro de Química-Física Molecular and IN, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal.
authors.forename: A M
authors.initials: AM
authors.lastname: Botelho do Rego
authors.affiliation: §ISA, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, Building 1520, DK-8000 Aarhus C, Denmark.
authors.forename: S V
authors.initials: SV
authors.lastname: Hoffmann
authors.affiliation: †CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
authors.forename: P A
authors.initials: PA
authors.lastname: Ribeiro
authors.affiliation: †CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
authors.forename: M
authors.initials: M
authors.lastname: Raposo
mesh_terms: D004247:DNA / Q000737:chemistry* / Q000235:genetics*; D004249:DNA Damage; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D056951:Photoelectron Spectroscopy; D013816:Thermodynamics; D014466:Ultraviolet Rays / Q000009:adverse effects*
chemical_list: D004247:DNA