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/6-311++G(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 −16.41 kcal mol⁻¹. The individual H-bond energies and the two bond X–Y spin–spin coupling constants (^2hJ_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 ^2hJ_X–Y, the value of ^1hJ_O–H (a one-bond H ··· Y spin–spin coupling constant) is distance dependent and in linear correlation with the O ··· H distance, but the ^1hJ_N–H values are independent of the N–H distance and the PSO term is the predominant portion in it. The ¹J_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 ¹J_X–H across the X–H · Y H-bond.

Keywords:

• hydrogen bond
• DNA damage
• coupling constant
• chemical shift
• 8OG:C base pair