Theoretical investigation of the intermolecular H-bonding and proton transfer in cytosine assisted by water and methanol

Abstract  

This investigation is devoted to study of the electronic structure of several H-bonded complexes of cytosine tautomers with water and methanol. The stability of these “supersystems” (aggregates) was estimated by calculating the bonding energies ΔE and ΔE _b. The energy barriers of water/methanol-assisted tautomeric conversions were calculated (intermolecular proton transfer), and the electronic structures of the transition states were studied. Each transition state of the proton-transfer reaction was determined as a first-order saddle point on the potential energy surface (full coordinate hyperspace). The crystal structure of the tetramer of cytosine monohydrate was also investigated. It was found that this structure is close to a conical intersection.