IR Vibrational spectra of H-bonded complexes of adenine, 2-aminopurine and 2-aminopurine+ with cytosine and thymine: Quantum-chemical study

Using theoretical study on the B3LYP/6-311++G(d,p) level of theory, we have compared vibrational spectra of 2-aminopurine (as neutral or protonated at N1 atom species) with adenine and H-bonded complexes of 2-aminopurine (as neutral or protoned at N1 atom species) center dot cytosine or 2-aminopurine center dot thymine with adenine center dot cytosine and adenine center dot thymine base pairs. The nature of the base pairing between adenine, 2-aminopurine, 2-aminopurine(+) and cytosine or thymine have been investigated by means of quantum-mechanical calculations. We have investigated the effect of the hydrogen bond formation on the vibrational spectra of the investigated base pairs. The main differences in the vibrational spectra as for bases so for base pairs have been observed in the high-frequency region.