Catalysis effect of micro-hydration on the intramolecular proton transfer in cytosine

Structural and thermodynamic properties of nine isomers of cytosine were studied in gas and aqueous phases and in micro-hydrated environment employing B3LYP and MP2 methods. Also, isomerizations of cytosine were studied in gas phase and the activation energies (Ea) and Gibbs free energies (ΔG#) of the internal OH rotations and proton transfer processes were calculated. The calculated OH rotational barriers were smaller than 50 kJ/mol while the activation energies of intramolecular proton transfers were in the range of 110-190 kJ/mol. Effect of mono- and di-hydration of the cytosine isomers on the transition state structures and the energy barriers was investigated. © 2015 Published by Elsevier B.V.