Ab initio path integral molecular dynamics (PIMD) simulation was performed to understand the nuclear quantum effect on the out-of-plane @entity85 of @entity15912 anion and investigate the existence of a stable structure with @entity85 , which was suggested in experimental observation (Fillaux et al., Chem. Phys. 1999, 120, 387-403). The isotope effect and the temperature effect are studied as well. We first investigated the nuclear quantum effect on the proton transfer. In static calculation and classical ab initio molecular dynamics simulations, the proton in the @entity3884 bond is localized to either @entity26 atom. On the other hand, the proton is located at the center of two @entity26 atoms in quantum ab initio PIMD simulations. The nuclear quantum effect washes out the barrier of proton transfer. We next examined the nuclear quantum effect on the motion of @entity15912 anion. Principal component analysis revealed that the out-of-plane ring bending modes have dominant contribution to the entire molecular motion. In quantum ab initio PIMD simulations, structures with @entity85 were the global minimum for the deuterated isotope at 300 K. We analyzed the out-of-plane ring bending mode further and found that there are three minima along a ring distortion mode. We successfully found a stable structure with @entity85 of @entity15912 for the first time, to our knowledge, using theoretical calculation. The structures with @entity85 found in quantum simulation of the deuterated isotope allowed the proton transfer to occur more frequently than the planar structure. Static ab initio electronic structure calculation found that the structures with @entity85 have very small proton transfer barrier compared to the planar structure. We suggest that the "proton transfer driven" mechanism is the origin of stabilization for the structure with out-of-plane @entity85 .

Ab Initio Path Integral Molecular Dynamics Study of the Nuclear Quantum Effect on Out-of-Plane Ring Deformation of XXXX Anion.

@entity85 :: ('MESH:D009140', 'Disease') :: ['ring deformation'] @entity26 :: ('MESH:D010100', 'Chemical') :: ['oxygen'] @entity3884 :: ('MESH:D006859', 'Chemical') :: ['hydrogen'] @entity15912 :: ('MESH:C030272', 'Chemical') :: ['hydrogen maleate']
@entity15912 :: (MESH:C030272,Chemical) :: ['Hydrogen Maleate']
