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Interaction energies between metal ions (Zn 2+ and Cd 2+ ) and biologically relevant ligands
Author(s) -
Ahlstrand Emma,
Spångberg Daniel,
Hermansson Kersti,
Friedman Ran
Publication year - 2013
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.24506
Subject(s) - chemistry , solvation , ion , interaction energy , density functional theory , binding energy , computational chemistry , atomic physics , molecule , physics , organic chemistry
Interactions between the group XII metals Zn 2+ and Cd 2+ and amino acid residues play an important role in biology due to the prevalence of the first and the toxicity of the second. Estimates of the interaction energies between the ions and relevant residues in proteins are however difficult to obtain. This study reports on calculated interaction energy curves for small complexes of Zn 2+ or Cd 2+ and amino acid mimics (acetate, methanethiolate, and imidazole) or water. Given that many applications and models (e.g., force fields, solvation models, etc.) begin with and rely on an accurate description of gas‐phase interaction energies, this is where our focus lies in this study. Four density functional theory (DFT)‐functionals and MP2 were used to calculate the interaction energies not only at the respective equilibrium distances but also at a relevant range of ion–ligand separation distances. The calculated values were compared with those obtained by CCSD(T). All DFT‐methods are found to overestimate the magnitude of the interaction energy compared to the CCSD(T) reference values. The deviation was analyzed in terms of energy components from localized molecular orbital energy decomposition analysis scheme and is mostly attributed to overestimation of the polarization energy. MP2 shows good agreement with CCSD(T) [root mean square error (RMSE) = 1.2 kcal/mol] for the eight studied complexes at equilibrium distance. Dispersion energy differences at longer separation give rise to increased deviations between MP2 and CCSD(T) (RMSE = 6.4 kcal/mol at 3.0 Å). Overall, the results call for caution in applying DFT methods to metalloprotein model complexes even with closed‐shell metal ions such as Zn 2+ and Cd 2+ , in particular at ion–ligand separations that are longer than the equilibrium distances. © 2013 Wiley Periodicals, Inc.