A theoretical study on cytosine tautomers in aqueous media by using continuum models

B3LYP/6-31 + + G** and MP2/6-31 + + G** calculations have been carried out to study six tautomers of the nucleic acid base cytosine in aqueous media. Solvent effects have been analyzed using the self-consistent reaction field theory with two continuum methods. Relative stabilities and optimized geom etries have been calculated for the tautomers and compared with experimenta l data. The present results show the importance of electrostatic solvent ef fects in determining observable properties of the cytosine tautomers. The a mino-oxo form (C1) is the most abundant tautomer in aqueous media while the other amino-oxo form (C4) is the most energetically favored when solvent e ffects are included. These results can be justified by the larger values of the dipole moments for both C1 and C4 tautomers. Theoretical and experimen tal results of the harmonic vibrational frequencies and rotational constant s show good agreement. (C) 2000 Elsevier Science B.V. All rights reserved.