The Role of Aromaticity, Hybridization, Electrostatics, and Covalency in Resonance-Assisted Hydrogen Bonds of Adenine–Thymine (AT) Base Pairs and Their Mimics

Invited for this issues cover are Dr. Célia Fonseca Guerra from the VU University of Amsterdam and her collaborators at the University of Girona. The cover picture shows H-bonds in the adenine–thymine Watson–Crick base pair. An essential part of these H-bonds is their covalent component arising from donor–acceptor interactions between N or O lone pairs and the N−H antibonding σ* acceptor orbital. This charge-transfer interaction is represented by green figures walking on the pedestrian crossing, connecting the bases. This covalent component is the reason why H-bonds between DNA and/or unsaturated model bases are significantly stronger than those between analogous saturated bases. This contrasts sharply with the classical picture of predominantly electrostatic H-bonds which is not only incomplete in terms of a proper bonding mechanism, but also fails to explain the trend in stability. For more details, see the Full Paper on p. 318 ff.