Nuclear quantum effects on protonated lysine with an asymmetric low barrier hydrogen bond: an ab initio path integral molecular dynamics study

Abstract

The nuclear quantum effect on the short and asymmetric hydrogen bond of protonated lysine (LysH⁺) at room temperature is explored by ab initio path integral molecular dynamics (PIMD) simulation. From static electronic structure calculations, the barrier height of proton transfer in LysH⁺ is 1.1 kcal mol⁻¹, which is much lower than that of typical hydrogen bonds. The hydrogen-bonded proton is delocalized in between two nitrogen atoms in the PIMD simulation including both thermal and nuclear quantum effects, while the proton is localized on a nitrogen atom in a conventional ab initio molecular dynamics simulation including thermal effects alone. We found that the proton transfer barrier found in the static calculation and conventional ab initio simulation is completely washed out in the PIMD simulation. Meanwhile, the proton distribution at the N_ζ atom was larger than that at the N atom, as found in the static calculation and conventional ab initio molecular dynamics simulation. We clarified that an asymmetric low barrier hydrogen bond exists in LysH⁺ at room temperature from our PIMD simulation.