Infrared signatures of proton transfer in guanine.cytosine and adenine.thyrnine base pairs:: DFT study

The structures of all stable tautomers of guanine. cytosine and adenine-thymine Watson-Crick base pairs produced by single and double proton transfers from the most stable structures are optimized using density functional theory (DFT) at the B3LYP/6-31G(d,p) level. The zwitterionic tautomer of guanine cyosine is stable in a high-dielectric medium (water), but not in the gas phase. Normal mode calculations show that the infrared peak positions and intensities of the carbonyl, N-H, and O-H stretching modes are sensitive to the tautomer geometries.