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

- Keto form of cytosine is the most stable isomer in aqueous and hydrated forms.
- In gas phase, the stability of enol and keto isomers is the same, approximately.
- Activation energies of the keto → enol tautomerisms are 150-190 kJ/mol.
- Water molecules decrease the activation energies and catalyze the tautomerisms.