Effect of protonation on individual hydrogen bonds in the 8-oxoguanine-cytosine base pair: NMR, NBO and AIM analyses

Abstract

Protonation increases the total binding energy of the 8-oxoguanine-cytosine (8OG:C) base pair by 60-70% at the B3LYP/6-311þþG(d, p) level of theory. It changes the individual H-bond energies, estimated from electron charge densities at bond critical points, by 1.16 to À16.41 kcal mol À1 . The individual H-bond energies and the two bond X-Y spin-spin coupling constants ( 2h J X-Y ) increase with protonation where 8OG behaves as an H-bond donor; the reverse is true for the H-bonds in which the 8OG unit acts as an H-bond acceptor. Similar to 2h J X-Y , the value of 1h J O-H (a one-bond H Á Á Á Y spin-spin coupling constant) is distance dependent and in linear correlation with the O Á Á Á H distance, but the 1h J N-H values are independent of the N-H distance and the PSO term is the predominant portion in it. The 1 J X-H spin-spin coupling constant is dominated by the negative FC term for all hydrogen bonds, although the PSO term is the best to investigate the behaviour of 1 J X-H across the X-H Á Y H-bond.

Conformational, electronic and antioxidant properties of lucidone, linderone and methyllinderone: DFT, QTAIM and NBO studies

“…The results of the investigation on the IHB geometric parameters as well as the BCP data are reported in Table 2. Topological properties at the BCP provide information about H-bonding [62][63][64][65][66][67][68][69]. The magnitude of the electron density (ρ) at the BCP, the sign of its Laplacian (∇ 2 ρ) and the total energy density (H) reveal the characteristics of the interactions.…”