A QM/QTAIM microstructural analysis of the tautomerisation via the DPT of the hypoxanthine center dot adenine nucleobase pair

作者：Brovarets Ol'ha O; Zhurakivsky Roman O; Hovorun Dmytro M^*

来源：Molecular Physics, 2014, 112(15): 2005-2016.

DOI：10.1080/00268976.2013.877170

• keto and enol tautomers of the hypoxanthine
• amino and imino tautomers of the adenine
• hypoxanthine center dot adenine base pair
• sweeps of the energetic, electron-topological, geometric, polar and NBO parameters along the IRC
• the double proton transfer
• cooperativity of the H-bonds
• B3LYP and MP2 levels of QM theory
• QTAIM analysis

We provide a pathway for the tautomerisation of the biologically important hypoxanthine adenine (Hyp center dot Ade) nucleobase pair (C-s) formed by the keto tautomer of the Hyp and the amino tautomer of the Ade into the Hyp*center dot Ade* base pair (Cs) formed by the enol tautomer of the Hyp and the imino tautomer of the Ade by applying quantum-mechanical calculations and Bader's Quantum Theory of Atoms in Molecules analysis. It was found out that the dipole active Hyp center dot Ade <-> Hyp*center dot Ade* tautomerisation occurs via the asynchronous concerted double proton transfer (DPT) through the TSHyp center dot Ade <-> Hyp*center dot Ade* (Cs). Based on the sweeps of the energies of the intermolecular H-bonds along the intrinsic reaction coordinate, it was established that the N6H center dot center dot center dot O6 H-bond (5.40) is cooperative with the N1H center dot center dot center dot N1 H-bond (6.99) in the Hyp Ade base pair, as well as the O6H center dot center dot center dot N6 H-bond (11.50) is cooperative with the N1H center dot center dot center dot N1 H-bond (7.28 kcal mol(-1)) in the Hyp*center dot Ade* base pair, mutually strengthening each other. The Hyp*center dot Ade* base pair possesses an extremely short lifetime 2.68.10(-14) s, which is predetermined by the negative value of the Gibbs free energy of the reverse barrier of its tautomerisation, and all of the six low-frequency intermolecular vibrations cannot develop during this period of time. Consequently, the Hyp center dot Ade -> Hyp*center dot Ade* DPT tautomerisation cannot serve as a source of the rare tautomers of the bases.

• 出版日期2014