The effect of base-pairing on the shape resonances of nucleobases.

In this work, we have studied the effect of base-pairing on the shape resonances of guanine and cytosine nucleobases. Among the seven π* resonances we identified in the guanine-cytosine (GC) anion radical, three were centered on cytosine, and the remaining were guanine-centered. Relative to the isolated bases, upon base pair formation, the cytosine resonances were redshifted, while the guanine-centered states showed an opposite trend-where their energy was blue shifted. In addition to electronic interactions, geometric distortion and basis-set superposition error also play crucial roles in the resonance positions and widths of the GC radical anion. The electronic interaction from the complementary base seems to have a larger effect on the stabilization of the anionic resonances than the surrounding environment.