Changes in the hydration structure of imidazole upon protonation: Neutron scattering and molecular simulations

Elise Duboué-Dijon (1) , Philip E Mason (1) , Henry Fischer (2) , Pavel Jungwirth (1)

1 IOCB / CAS - Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences
2 ILL

The imidazole motif is widely encountered in biomolecules, and its biological role, for instance as a proton relay, is often linked to its ability to form hydrogen bonds with water molecules. Detailed characterization of the hydration pattern of imidazole and its changes upon protonation is thus of high interest. Here, we combine neutron scattering experiments with force field simulations to provide an unprecedented characterization of the neutral and protonated imidazole solvation at the atomistic level. We show that neutron diffraction data can be used to assess the quality of the imidazole force field in molecular simulations. Simulations using the CHARMM general force field for imidazole are in excellent agreement with the experimental neutron scattering data and we use them to provide an atomic scale interpretation of the neutron scattering patterns. Upon protonation, we clearly identify the signature of the reorganization in the hydration pattern caused by the change from one H-bond donor and one H-bond acceptor group for imidazole to two H-bond donor groups for imidazolium. We also point the limits of the experiment, which is rather insensitive to details of the H-bond geometry at the deprotonated nitrogen of imidazole and further complement the description of the hydration structure with ab initio molecular dynamics simulations.

Domaines: Chimie théorique et/ou physique

Elise Duboué-Dijon, Philip E Mason, Henry Fischer, Pavel Jungwirth. Changes in the hydration structure of imidazole upon protonation: Neutron scattering and molecular simulations. Journal of Chemical Physics, 2017, 146 (18), pp.185102. ⟨10.1063/1.4982937⟩. ⟨hal-02104534⟩