Quantum mechanical studies on the existence of AC mismatches through Prototopic tautomerization pathway in Adenine and Cytosine recognition.

The gas phase studies on the electronic stabilities and thermochemical properties of metastable AC mismatches have been performed and the results are analyzed to explain the features of experimentally available AC mismatches. The hydrogen bonding patterns observed in these mismatches are relevant to the formation of stable AC mismatches. In these AC pairs, the H migration mechanism to generate other tautomeric forms is not observed, which shows the compatibility of H bonding capacity of the sites involved in H bonds. The presence of hydrogen bond type -N center dot center dot center dot H-N-may contribute to better AC pairing, hence cisA1-1cisC2, transA2-cisC1 and transA1-1cisC2 are found to be more favorable pairs compared to other AC pairs.