Hydrogen bonds in quinoline <Emphasis Type="Italic">N</Emphasis>-oxide derivatives: first-principle molecular dynamics and metadynamics ground state study

Car–Parrinello molecular dynamics simulations were carried out for 8-hydroxyquinoline N-oxide (1) and 2-carboxyquinoline N-oxide (2) in vacuo and in the solid state. The first-principle approach was employed to intramolecular hydrogen bond features present in the studied quinoline N-oxides. Grimme’s dispersion correction was employed throughout the study. Special attention was devoted to the solid-state computations knowing that in the molecular crystals, strong and weak interactions are responsible for spatial organization and molecular properties of molecules. On the basis of Car–Parrinello molecular dynamics, it was possible to reproduce the hydrogen bond dynamics as well as to investigate the vibrational features on the basis of Fourier transform of the atomic velocity autocorrelation function. The free energy surfaces for proton motion were reproduced by unconstrained CPMD runs as well as by metadynamics. Larger flexibility of the bridge proton in 2 was noticed. The computations are verified by experimental X-ray and IR data available.