Theoretical investigation of spectral properties and tautomerization mechanism of 2-aminopurine.

In this work the spectral properties and tautomerization mechanism of 2-aminopurine are investigated using quantum chemical calculations. TD-DFT results lead to a conclusion that two tautomers of 2-aminopurine discussed in this work are fluorescent and present the pi-->pi* transition feature of vertical excitation and emission. It is predicted that the tautomerization of 2-aminopurine hardly occurs in a direct isomerization mechanism because of the high barrier. However, the explicit involvement of water molecules into the system reduces the barrier height considerably and hence makes the ground state reaction feasible. An explanation for the almost equal populations of the two tautomers in polar solvent is given through reaction mechanism analysis.