Proton transfer reactions of nucleic acid bases: A semiempirical molecular orbital study

摘要

The possibilities open for tautomerism, for protonation and for de-protonation in the five nucleic acid bases are examined theoretically using the semiempirical AMI SCF-MO methodology. The tautomers predicted to be the most stable, other than the usual forms, all involve proton shifts to adjacent sites. The sites predicted to be the most favourable for protonation are the N~7-G, N~3-A, N~3-C, O~4-T and O~4-U positions of guanine, adenine, cytosine, thymine and uracil respectively. The protons predicted to be the most acidic for each base are the N~l-G, N~9-A, N~1-C, N~3-T and N~3-U protons. These predictions accord well with the conclusions drawn from experimental work so far as assignments of acidic protons and basic sites for the particular basesare concerned. However, the relative feasibility of these reactions for the different bases is not well predicted by these gas-phase calculations.