free nucleobases and nucleobases in single strand (sDNA), double strand DNA (dsDNA)
and in solid state. Our first principles investigation was carried out using the Gaussian 2009
set of programs to implement the Hartree-Fock procedure combined with many-body effects
included using many-body perturbation theory. The positions of the atoms were taken from
structural data for DNA systems , for solid nucleobases from x-ray data [2-5] and by
geometry optimization based on the total energy for the free nucleobases. As expected for
NQI in general, many-body effects are found to be small. Results will be presented for the
nuclear quadrupole coupling constants (e2qQ) and asymmetry parameters (η) for the
nucleobases in the various systems, and trends in e2qQ and η in the different systems will be
discussed. Our results show that there are substantial changes in the NQI parameters e2qQ and
η, at the positions of the nuclei, on going from free nucleobases to the nucleobases attached to
single strand DNA (sDNA), between the latter and the nucleobases in double strand DNA
(dsDNA) and between free nucleobases and solid nucleobases. Our results for the 17O NQI
parameters in the solid nucleobases agree well with experimental results  obtained by the
magic angle spinning nuclear magnetic resonance technique. Comparison with the results of
an earlier theoretical investigation  on the solid nucleobases with our theoretical results
will be presented and discussed.
It is hoped that the results of experimental measurements of NQI parameters for 17O
nuclei in these nucleobases for single strand and double strand DNA and for other nuclei (14N
and 2H) will be available in the future to compare with our theoretical predictions.
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