Interaction energies between metal ions (Zn2+ and Cd2+) and biologically relevant ligands
Article first published online: 23 JUL 2013
Copyright © 2013 Wiley Periodicals, Inc.
International Journal of Quantum Chemistry
Volume 113, Issue 23, pages 2554–2562, 5 December 2013
How to Cite
How to cite this article: Int. J. Quantum Chem. 2013, 113, 2554–2562. DOI: 10.1002/qua.24506, , , .
- Issue published online: 22 OCT 2013
- Article first published online: 23 JUL 2013
- Manuscript Accepted: 14 JUN 2013
- Manuscript Revised: 6 JUN 2013
- Manuscript Received: 7 MAR 2013
- Linnæus University Centre for biomaterials chemistry, Linnæus University, Sweden [Metal ions in life]
- eSSENCE National Strategic Research Program in e-science
- dissociation energy curve;
- localized molecular orbital energy decomposition analysis;
- density functional theory;
Interactions between the group XII metals Zn2+ and Cd2+ 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 Zn2+ or Cd2+ 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 Zn2+ and Cd2+, in particular at ion–ligand separations that are longer than the equilibrium distances. © 2013 Wiley Periodicals, Inc.