Hydrogen bonding interactions in noradrenaline-DMSO complexes: DFT and QTAIM studies of structure, properties and topology

The hydrogen bonding interactions between noradrenaline (NA) and DMSO were studied with density functional theory (DFT) regarding their geometries, energies, vibrational frequencies, and topological features of the electron density. The quantum theory of atoms in molecules (QTAIM) and the natural bond orbital (NBO) analyses were employed to elucidate the hydrogen bonding interaction characteristics in noradrenaline-DMSO complexes. The H-bonds involving the hydroxyls hydrogen in NA and the O atom in DMSO are dominant intermolecular H-bonds and are stronger than other H-bonds involving the methyl hydrogen of DMSO as a H-donor. The weak H-bonds also include a pi H-bond which involves the benzene ring as a H-donor or H-acceptor. QTAIM identified the weak H-bonds formed between the methyl hydrogen of DMSO and the N atom in NA in some complexes (AB5, AB6 and AB7), which cannot be further confirmed by NBO and other methods, so there are probably no interactions between hydrogen and nitrogen atoms among these complexes. A good linear relationship between logarithmic electron density (ln rho (b) ) at the bond critical point (BCP) and structural parameter (delta R (H center dot center dot center dot Y)) was found. The formations of new H-bonds in some complexes are helpful to strengthen the original intramolecular H-bond, this is attributed to the cooperativity of H-bonds in complexes and can be learned from the structure results and the NBO and QTAIM analyses. Analysis of various physically meaningful contributions arising from the energy decomposition procedures show that the orbital interactions of H-bond is predominant during the formation of the complex, moreover, both the hydrogen bonding interaction and the structural deformation are responsible for the stability of the complexes.