Density functional theory and topological analysis on the hydrogen bonding interactions in cysteine‐thymine complexes

Hydrogen bonding interactions between amino acids and nucleic acid bases constitute the most important interactions responsible for the specificity of protein binding. In this study, complexes formed by hydrogen bonding interactions between cysteine and thymine have been studied by density functional theory. The relevant geometries, energies, and IR characteristics of hydrogen bonds (H‐bonds) have been systematically investigated. The quantum theory of atoms in molecule and natural bond orbital analysis have also been applied to understand the nature of the hydrogen bonding interactions in complexes. More than 10 kinds of H‐bonds including intra‐ and intermolecular H‐bonds have been found in complexes. Most of intermolecular H‐bonds involve O (or N) atom as H‐acceptor, whereas the H‐bonds involving C or S atom usually are weaker than other ones. Both the strength of H‐bonds and the structural deformation are responsible for the stability of complexes. Because of the serious deformation, the complex involving the strongest H‐bond is not the most stable structures. Relationships between H‐bond length (ΔR_X‐H), frequency shifts (Δv), and the electron density (ρ_b) and its Laplace (?²ρ_b) at bond critical points have also been investigated. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011