Abstract
Base pairs involving protonated nucleobases play important roles in the DNA republication. Xanthine is an oxidative product of guanine. In this work, we employ density functional theory to investigate the protonation properties of xanthine (X), adenine (A), cytosine (C), guanine (G), and thymine (T). With regard to the proton affinity, we study the protonated base pairs between X and A, C, G, T. The quantum theory of atoms in molecule and the natural bond orbital analysis are employed to elucidate the interaction characteristics. The interaction energy and structural parameters show the relative stability of the protonated base pairs: X:AH+ > X:CH+ > X:GH+ > XH+:T. The occurrence of X(syn):AH+(anti) structure may lead to a G:C → T:A transition.
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