Excited-state proton transfer in the rare isoguanine-isocytosine base pair in water solution

Context

With the current research, we aim to study the mechanism of the excites state proton transfer (ESPT) between the nucleobases isoguanine (iG) and isocytosine (iC) in their Watson–Crick model. Such research is proposed for the first time and it can partially reveal the question why the nature “has chosen” guanine and cytosine for pairing in the DNA duplex and not their analogs (isoforms). The UV irradiation of the water solution of equimolar mixture of iG and iC implies a tautomeric conversion between the nucleobases. In the research, the mechanism of the ESPT was followed and clarified for the first time. All this reflects to the photostability of the iG-iC base pair in water solution.

Methods

For the purposes of the current research, we chose to use the TD DFT with the hybrid functional B3LYP in combination with the aug-cc-pVDZ basis set. The water surroundings are modeled according to the polarizable continuum model (PCM) modeling the solvation effects on the studying systems. Linear interpolation and intrinsic reaction coordinate approach were applied for the reaction path follow of the ESPT.