title: The negative ion states of molecules: adenine and guanine.
abstract: Anions of cytosine and thymine predominate in radiation-damaged DNA. This is in contrast to the experimental order of adiabatic electron affinities: A, 0.95; G, 1.51; >T, 0.79, U, 0.80; C, 0.56 (+/-0.05 eV). Excited negative-ion states of adenine (A) and guanine (G) are identified using semiempirical AM1-MCCI quantum mechanical calculations. A planar G(-) has an excited state adiabatic electron affinity, AEA*, of 0.3 +/- 0.05 eV. This state and the unique Watson-Crick structure are responsible for the preponderance of charge on C(-) in radiation-damaged DNA. By analogy to the value for cytosine, the dipole-bound EA of G is estimated as 0.25 eV. New AEA values from literature reduction potentials for the ribose nucleotides are rC, 0.6; rU, 0.8; and rT, 0.8 (+/-0.1 eV). From literature photoelectron spectroscopy, AEA* vales for U are 0.15, 0.3, 0.5, and 0.6 eV. In GC(-2), stacked [GC:GC](-3), and [GC:GC:GC](-4), the charge moves to G. In [GC:GC:GC](-2 to -4), the charge moves from GC(1) to GC(3) through space without a bridge or bond. This is important to electron conduction, radiation damage and repair, and nanoscale devices.
authors.affiliation: Center for High Performance Software (HiPerSoft), Rice University, MS-41, Houston, Texas 77005, USA. Echen@Rice.edu
authors.forename: E S
authors.initials: ES
authors.lastname: Chen
authors.forename: E C
authors.initials: EC
authors.lastname: Chen
mesh_terms: D000225:Adenine / Q000737:chemistry*; D000838:Anions; D020029:Base Pairing; D004247:DNA / Q000737:chemistry* / Q000528:radiation effects; D004249:DNA Damage; D004563:Electrochemistry; D004583:Electrons; D006147:Guanine / Q000737:chemistry*; D007477:Ions; D008956:Models, Chemical; D008958:Models, Molecular; D008962:Models, Theoretical; D015394:Molecular Structure
chemical_list: D000838:Anions; D007477:Ions; D006147:Guanine; D004247:DNA; D000225:Adenine