AB-INITIO MOLECULAR-ORBITAL CALCULATIONS OF RADICALS FORMED BY H-CENTER-DOT AND CENTER-DOT-OH ADDITION TO THE DNA BASES - ELECTRON-AFFINITIES AND IONIZATION-POTENTIALS
Ao. Colson et Md. Sevilla, AB-INITIO MOLECULAR-ORBITAL CALCULATIONS OF RADICALS FORMED BY H-CENTER-DOT AND CENTER-DOT-OH ADDITION TO THE DNA BASES - ELECTRON-AFFINITIES AND IONIZATION-POTENTIALS, Journal of physical chemistry, 99(34), 1995, pp. 13033-13037
Ab initio molecular orbital calculations of the ionization potentials
(IP's) and electron affinities (EA's) of DNA base radicals formed by a
ddition of H-. or OH. to DNA bases are presented in this work. IP's an
d EA's are obtained by calculating the energies of the LUMO and HOMO (
Koopmans' values) of the cationic and anionic states, respectively. Sc
aling of the theoretical values to experimentally known ionization pot
entials and electron affinities of other small radical compounds leads
to predicted trends in IP's and EA's of the DNA base adducts. These t
rends are shown to be in good agreement with experimental redox trends
and aid our understanding of possible electron transfer processes. Th
e present results indicate the OH. and H-. adducts of the pyrimidines
at C6 are most oxidizing, while the H-. adduct of cytosine at N3 is mo
st reducing. The calculated trend in electron affinities in conjunctio
n with experimental observations results in the prediction that only a
fraction of the base adducts will be reduced via electron transfer pr
ocesses from thiols. All five sugar radicals have nearly equal electro
n affinities; however, their ionization potentials substantially diffe
r. Delocalization effects which result in less electron repulsion in t
he anionic state are shown to account for differences in EA and IP sca
les. Conformational distortion of the purine bases upon adduct formati
on at the C4 and C5 sites is shown to be significant.