CONJUGATED DUAL HYDROGEN-BONDS MEDIATING 2-PYRIDONE 2-HYDROXYPYRIDINETAUTOMERISM/

Tautomeric equilibria of 2-pyridone (PD) and 2-hydroxypyridine (HP) di meric forms as well as PD/HP complexes mediated by the conjugated dual hydrogen-bonding (CDHB) formation have been studied by ab initio mole cular orbital calculations up to the 6-31+G* basis set at the Moller- Plesset level. The result in combination with the semiempirical solvat ion free-energy calculation reasonably predicts the relative free ener gy and consequently the tautomeric equilibria between PD, HP, their co rresponding dimers and PD/HP complex in the gas phase as well as in so lution. The results also indicate that the strength of dual hydrogen b onding resonantly affects the PD and HP electronic structures upon CDH B formation, resulting in an additional stabilization energy. Further calculation shows that the tautomeric equilibria can be fine-tuned by the formation of a hydrogen-bonded complex with guest molecules posses sing bifunctional hydrogen bonds. The results lead to a possible mecha nism suggesting that the tautomerization of a specific DNA base may be induced by forming a complex with an intruder, i.e., a specific molec ule with multiple hydrogen-bonding capability, which triggers the muta tion process.