Analysis of dielectric properties of cytosine in aqueous solution

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.