Reactivity and aromaticity of DNA and RNA bases toward an external electric field are analyzed using density functional theory (DFT) and density functional reactivity theory (DFRT). Reactivity of the nucleobases is measured in terms of the DFT-based reactivity descriptor, such as energy of the HOMO, global hardness, electrophilicity, etc. and is observed to be sensitive toward the strength as well as direction of the applied external electric field. In addition, the reactivity pattern follows the maximum hardness and minimum electrophilicity principles. Further, aromaticity of the species is observed to be effected by the presence of an external electric field.

Effect of external electric field on interaction energy as well as stability of the hydrogen-bonding, stacking, and OAHÁ Á Ápbonded systems are analyzed in the light of density functional theory (DFT) and conceptual DFT. Interaction energy and stability measured in terms of global hardness and highest occupied molecular orbital energy of the considered systems are observed to be sensitive toward the strength and direction of the applied external electric field. The curvature of the potential energy surfaces gets changed in presence of an external electric field.

Effect of external perturbation (in terms of external electric field and solvents) on the stability of lysine-aspartic acid salt bridge was analyzed by density functional theory. Because of solvation, interaction energy in the aqueous phase is much lower as compared to gas phase. Interaction energy as well as stability (measured in terms of global hardness, HOMO energy and total electronic energy) are observed to be sensitive towards the strength and direction of the applied electric field. Gap between HOMO energy of the acids and salt bridge also points towards the feasibility of hydrogen bonding.