Background: The study of the effect of External Electric Field (EEF) on the
structure of several biologically important compounds is now extended to pyrimidine and
Objectives: The present study involves computations of changes in energy and dipole
moments, the charge density of pyrimidine bases (cytosine, thymine and uracil) and purine
bases (adenosine and guanine) in the external electric field of 0.00, 5.14, 25.70 and 51.40
Method: The computations were performed applying HyperChem 8.0 software together
with the PM3 method for optimization of the conformation of the molecules.
Results: The rise in the EEF strength to 5.14 MV/cm has a subtle effect on the molecular
energy of the bases under consideration. A slight tendency in decreasing that energy can,
however, be observed. On elevating the strength up to 25.70 MV/cm the decrease in
molecular energy was more significant. EEF has a tremendous effect on the reorientation
of the molecules in the Cartesian system. It influences tautomeric equilibria.
Conclusion: Observed changes evoked by the EEF were specific for particular molecules.
They resulted mainly from the polarization of the bonds and from steric deformations of