Bader's and reactivity descriptors' analysis of DNA base pairs

The characterization of hydrogen bonds (H bonds) present in various canonical and noncanonical base pairs of DNA in terms of the electron density (ρ(rc)), Laplacian of electron density (∇2ρ(rC)), and integrated atomic properties of hydrogen atoms involved in hydrogen bonding has been made. The existence of hydrogen bond critical points (HBCP) and the values of ρ(rC) and ∇2ρ(rC) at HBCP indicate the presence of hydrogen bonding and the closed-shell kind of interactions governing DNA base pairing. It has been observed that the calculated total ρ(rC) at HBCPs of the base pairs varies linearly with their interaction energy. The total ∇2ρ(rC) also exhibits a similar trend with the interaction energy. Integrated atomic properties such as charge, energy, volume, the first moment of the H-bonded hydrogen atoms in the DNA bases and in the H-bonded base pairs, and the change (Δ) in the corresponding properties arising upon pairing have also been calculated and compared. The calculated global chemical hardness of various DNA bases and DNA base pairs has been used to establish a linear relation with interaction energy. The charge transfer involved in the formation of DNA base pairs has also been qualitatively determined using Parr's formula and also from AIM-derived charges