Water-Exchange Mechanism for Zinc(II), Cadmium(II), and Mercury(II) Ions in Water as Studied by Umbrella-Sampling Molecular-Dynamics Simulations
✍ Scribed by Yasuhiro Inada; Ahmed M. Mohammed; Hannes H. Loeffler; Shigenobu Funahashi
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- German
- Weight
- 95 KB
- Volume
- 88
- Category
- Article
- ISSN
- 0018-019X
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
Umbrella‐sampling molecular‐dynamics simulations were performed to investigate the water‐exchange reactions of zinc(II), cadmium(II), and mercury(II) ions in aqueous solution. The dissociation of a coordinating water molecule to the MO distance at 3.34, 3.16, and 3.26 Å for Zn^II^, Cd^II^, and Hg^II^, respectively, leads the system to a transition state. For Zn^II^, the first hydration shell is occupied by five spectator water molecules in the transition state, indicating that the water‐exchange reaction proceeds via a dissociative mode of activation. In contrast, the number of spectator water molecules of 5.85 and 5.95 for Cd^II^ and Hg^II^, respectively, suggests an associative exchange for these larger metal ions. The average MO distance of the spectator molecules is shortened by 0.06 Å for the dissociative exchange of Zn^II^, while it is elongated by 0.04 and 0.03 Å for Cd^II^ and Hg^II^, respectively. The water‐exchange rate constants of 4.1×10^8^, 6.8×10^8^, and 1.8×10^9^ s^−1^ are estimated for Zn^II^, Cd^II^, and Hg^II^, respectively, at 298 K in terms of the transition‐state theory based on the assumption of a transmission coefficient of unity.