Premium
Theoretical Study of the Intramolecular Proton Transfer in the Tautomers of Cytosine Assisted by Water
Author(s) -
Zheng Haitao,
Zhao Dongxia,
Yang Zhongzhi
Publication year - 2011
Publication title -
chinese journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.28
H-Index - 41
eISSN - 1614-7065
pISSN - 1001-604X
DOI - 10.1002/cjoc.201180387
Subject(s) - tautomer , chemistry , intramolecular force , cytosine , isomerization , molecule , computational chemistry , hydrogen bond , proton , transition state theory , reaction coordinate , solvent , enol , potential energy surface , photochemistry , stereochemistry , kinetics , organic chemistry , dna , reaction rate constant , catalysis , biochemistry , physics , quantum mechanics
Ab initio MP2 and DFT studies on the tautomers of cytosine and the related hydrated tautomers have been carried out. The ground‐state structures of four tautomers of cytosine and related transition states were fully optimized. The vibrational frequency analysis was performed on all the optimized structures. Detailed intrinsic reaction coordinate (IRC) calculations were carried out to guarantee the optimized transition‐state structures being connected to the related tautomers. We obtained the relative stability order for the tautomers of cytosine and the related hydrated tautomers. In the isolated and hydrated condition, the bond types of C(2)O(7) and C(4)N(8) greatly affect the stability of the cytosine tautomers. Moreover, we have explored the influence of the water molecules on the intramolecular proton transfer between the keto and enol forms of the cytosine tautomers. The first water molecule obviously decreases the isomerization activation energy for the monohydrated cytosine tautomers. It is shown that the isomerization energy barrier changes only a little when the second and third water molecules are added in the reaction loop. The solvent effects have an obvious influence on the proton‐transfer barrier of the isolated cytosine. However, the solvent effects seem to be insignificant for the isomerization energy barriers of the monohydrated, dihydrated and trihydrated cytosine. The water molecule in these complexes can be looked on as the explicit water. Therefore, the explicit water model may be more credible to explore the intramolecular proton transfer, in comparison with the PCM which is the implicit water model.