We present a theoretical investigation of the structural and electronic properties of double-electron oxidized adenine-thymine base pair as well as its deprotonated Watson-Crick derivatives. Double-electron oxidation can destabilize the AT unit, leading to a barrier-hindered metastable A'T+ state with a dissociation channel featuring negative dissociation energy. This unusual energetic phenomenon originates from the competition of electrostatic repulsion and attractively hydrogen-bonding interaction co-existing between A*(+) and T*(+). The associated double-proton-transfer process is also explored, suggesting a possible two-step mechanism. Magnetic coupling interactions of various diradical structures are controlled by both intra- and inter-molecular interactions. (C) 2014 Elsevier B.V. All rights reserved.