Density functional study of the 5-methylcytosine tautomers

B3LYP/6-31++G** calculations to study seven tautomers of 5-methylcytosine i n aqueous media have been carried out. Optimized geometries and relative st abilities for the different tautomers have been calculated in the gas phase , including interaction with two discrete water molecules and taking into a ccount the solvent effects by using the self-consistent reaction field theo ry. The role of specific and bulk contributions of solvent effect on the ob servable properties of the 5-methylcytosine is clarified. The amino-oxo for m is the most abundant tautomer in aqueous media. A reaction pathway connec ting amino-oxo and amino-hydroxy forms along the corresponding transition s tructures has been characterized. Good agreement between theoretical and av ailable experimental results of harmonic vibration frequencies is found. (C ) 2001 Elsevier Science B.V. All rights reserved.