The photoelectron spectra of the hydrogen-bonded amino acid side-chain–guanine complexes has been studied at the partial third
order (P3) self-energy approximation of the electron propagator theory. The correlation between the vertical electron detachment energy
and the charge distributions on the guanine moiety reveals that the vertical electron detachment energy (VDE) increases as the positive
charge distribution on the guanine increases. The low VDE values determined for the negatively charged complexes of the guanine–sidechain-
group of Asp/Glu suggest that the influence of the H-bonded anionic groups on the VDE of guanine could be more important than
that of the anionic backbone structure. The even lower vertical electron detachment energy for guanine is thus can be expected in the
H-bonded protein–DNA systems.