Unnatural Covalent DNA Base Pairing: Quantum Chemical Study

The present work is aimed to perform a high-level ab initio computational study of the unnatural covalent bond base pairs, recently designed by Gao and Orgel (Proc. Natl. Acad. Sci. U.S.A. 1999, 96, 14837) and Kishi et al. ( Angew. Chem., Int. Ed. Engl. 1999, 38, 928; Angew. Chem., Int. Ed. Engl. 2001, 40, 1471), for a better understanding of the underlying structural and energetic features of their base pair formations and for a demonstrating of how they actually accommodate the DNA double helix architecture. In addition, three new tautomeric forms of the Gao−Orgel covalent pair are found and their shape complementarity is analyzed.