Isomers of adenine

Adenine is one of the four principle bases of nucleic acid, the essential molecule of life and evolution. Apparently, only one configuration of adenine exists in nature giving it unique chemical and biological properties. Using a force field type potential model with parameters fitted to the nucleic acid bases, proteins and other biological molecules (involving the sum of the contributions from bond stretching, bond angle bending, torsional angle twisting, and Coulomb and Lennard–Jones terms) we searched the potential energy surface for other stable isomers of adenine. The search was performed using a genetic algorithm, an efficient and global technique. The most interesting of the lowest energy minima found in the global search were relaxed using quantum-mechanical, semiempirical (PM3), and first principles (Hartree–Fock and density functional theory) methods. These calculations gave similar geometries and energy ordering for the new structures. This work formed part of a larger project to study the binding of nanoclusters of gold to segments of nucleic acid for possible application in the emerging field of nano-electronics. The results could also have implications in mutation and transcription of DNA.