DOUBLE PROTON-TRANSFER - FROM THE FORMAMIDE DIMER TO THE ADENINE THYMINE BASE-PAIR

The cylic formamide dimer was used as a model system for the investigation of proton-transfer phenomena in DNA base pairs. The section of the potential energy surface (PES) in the coordinates of transferring protons was studied using a wide set of computational methods, from semiempirical (PM3,MNDO-M) to the ab initio MP2/DZ+2P level of theory. Three qualitatively different patterns of stationary points were obtained, depending on the computational method used. The MP2/DZ+2P calculation resulted in two minima on the PES, corresponding to the amino-keto and imino-enol tautomeric forms, separated by a low-lying transition state. The amino-keto tautomer was found to be more stable than the imino-enol one by 15.6 kcal/mol.