The dipole moment of cytosine in dilute aqueous solutions was experimentall
y determined through permitivity, refraction index and density measurements
in order to study the solvent effect on the behavior of cytosine under the
action of a low frequency electric field. Buckingham's equation was used,
and mu (exp) = 7.99 D was obtained. A theoretical study was also undertaken
which considered cytosine in isolation and in two association models of th
e solute with four and six molecules of water respectively.
The data for the dipole moment as wen as an estimation of the hydration ene
rgies were obtained from models evaluated at three theoretical levels: Semi
empirical calculations (in particular the AM1 method), ab initio calculatio
ns at the REF/6-31+G* level of theory and density functional theory (B3LYP/
6-31+G*) for the inclusion of electronic correlation. Although the six wate
r molecule model bonded by hydrogen bonds was shown to be the more stable o
ne, the results of mu (exp) confirm that both intermolecular association mo
dels are compatible. (C) 2001 Elsevier Science B.V. All rights reserved.