Adenine tautomeric process is not a small perturbation but a significant change of the inner shell configuration. For canonical adenine, ade n9, the inner-shell configuration in the ground electronic states (X1A') is given by 1a'(N(9))2a'(N(10))3a'(N(7))4a'(N(3))5a'(N(1)) 6a'(C(6))7a'(C(8))8a'(C(4))9a'(C(2))10a'(C(5)). Although the five N1s orbitals in the core shell of all adenine amino tautomers are always given as 1a'2a'3a'4a'5a'. The profound tautomer dependent inner-shell electronic reconfiguration has been largely masked by small net differences in their total electronic energies and subtle differences in their valence shell electronic structures. The present quantum mechanical spectral study demonstrates that inner-shell chemical shift of N1s orbitals of adenine amino tautomers is atomic site and tautomer specific: the orbital binding energy shifts of the amino N1s sites (-N-) are smaller than those of the imino N1s sites (-N=) in the same tautomer. The nitrogen N@1s site (an amino site) which connects the mobile hydrogen exhibits the smallest energy shift within a tautomer and therefore, is an indicator of the specific tautomer. The preferential adenine (ade n9) protonation sites are the imino sites in the order of 5a'(N(1)), 4a'(N(3)) and 3a'(N(7)) which agrees with previous observations.
Journal of Physics conference series: proceedings of the 8th Asian International Seminar on Atomic and Molecular Physics, Perth, Western Australia, Australia, 24-28 November 2008,
Vol. 185 (2009), article no. 012040