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Water‐Exchange Mechanism for Zinc(II), Cadmium(II), and Mercury(II) Ions in Water as Studied by Umbrella‐Sampling Molecular‐Dynamics Simulations
Author(s) -
Inada Yasuhiro,
Mohammed Ahmed M.,
Loeffler Hannes H.,
Funahashi Shigenobu
Publication year - 2005
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200590030
Subject(s) - chemistry , dissociation (chemistry) , aqueous solution , zinc , molecular dynamics , cadmium , molecule , transition metal , inorganic chemistry , ion , metal ions in aqueous solution , ion exchange , umbrella sampling , metal , analytical chemistry (journal) , mercury (programming language) , computational chemistry , catalysis , chromatography , organic chemistry , computer science , programming language
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.