Ab initio QM/MM dynamics of H₃O⁺ in water

Abstract

A molecular dynamics (MD) simulation based on a combined ab initio quantum mechanics/molecular mechanics (QM/MM) method has been performed to investigate the solvation structure and dynamics of H3O+ in water. The QM region is a sphere around the central H3O+ ion, and contains about 6-8 water molecules. It is treated at the Hartree-Fock (HF) level, while the rest of the system is described by means of classical pair potentials. The Eigen complex (H9O4+) is found to be the most prevalent species in the aqueous solution, partly due to the selection scheme of the center of the QM region. The QM/MM results show that the Eigen complex frequently converts back and forth into the Zundel (H5O2+) structure. Besides the three nearest-neighbor water molecules directly hydrogen-bonded to H3O+, other neighbor waters, such as a fourth water molecule which interacts preferentially with the oxygen atom of the hydronium ion, are found occasionally near the ion. Analyses of the water exchange processes and the mean residence times of water molecules in the ion's hydration shell indicate that such next-nearest neighbor water molecules participate in the rearrangement of the hydrogen bond network during fluctuative formation of the Zundel ion and, thus, contribute to the Grotthuss transport of the proton.

Effects of metal ion and solute conformation change on hydration of small amino acid

“…[44] that a complete understanding of the water exchange mechanisms requires information on both hydration structures and dynamics, which are closely related to the interactions and momentum transfer between water molecules in the first and second hydration shells. The influence of water molecules in the second hydration shell was also illustrated in our previous work on [NH 4 + ] aq [73] and [H 3 O + ] aq [74]. Especially in the case of [H 3 O + ] aq [74], it was shown that water molecules in the second hydration shell could help promote the proton transfer from H 3 O + to H 2 O, through the formation of the Zundel complex (H 5 O 2 + ).…”

“…The influence of water molecules in the second hydration shell was also illustrated in our previous work on [NH 4 + ] aq [73] and [H 3 O + ] aq [74]. Especially in the case of [H 3 O + ] aq [74], it was shown that water molecules in the second hydration shell could help promote the proton transfer from H 3 O + to H 2 O, through the formation of the Zundel complex (H 5 O 2 + ). The MD trajectory in Fig.…”

Electronic Effects in Organic Chemistry

“…While many investigations are focused on the quality and robustness of the employed theoretical methods [48, 604-606, 609, 614, 616-618, 621], lots of studies on the solvent shell structure around common ions [607-610, 612-617, 619, 624-628] or pure solvents [646] have also been published. Nevertheless, both methods are much better suited to describe experimental results than a description based on pure classical mechanics [608,610,613,622,628]. Both QM methods are known to have severe deficiencies, but the use of more sophisticated methods is, due to their enormous computational demands, limited to small reference systems and benchmark calculations.…”

Explicit proton transfer in classical molecular dynamics simulations

“…Despite these limitations, ab initio simulations have provided important atomistic insights into the transfer mechanism of hydrated protons, which can be used for developing and parameterizing more approximate approaches. In an effort to gain efficiency, while preserving the detailed description of the excess proton, approaches based on semiempirical methods and hybrid quantum/classical protocols have been proposed …”

“…In an effort to gain efficiency, while preserving the detailed description of the excess proton, approaches based on semiempirical methods [3,4] and hybrid quantum/classical protocols have been proposed. [5] More toward a molecular description, but still capable of explicit proton transfer, are empirical valence bond (EVB) [6][7][8][9][10][11] and reactive force field [12][13][14][15][16] approaches. Typically, a classical MD simulation is performed, during which proton transfer is evaluated in an effective potential energy landscape extracted from ab initio calculations of model transfer events.…”