engleski

Modelling Structural Properties of Bis(glycinato)copper(II) in Aqueous Solution

The essential metals, such as iron, copper, zinc, cobalt, and manganese, are present in many biological fluids as free ions or complexed by metalloproteins and low-molecular-weigh complexes with amino acids and peptides. While most spectroscopic and electrochemical methods cannot give complete information on the geometry of the metal-bioligand complexes in solutions (especially if the number of ligand binding sites is larger then 2) and the exact geometries of such complexes are still elusive, the structural properties can be predicted and reproduced with theoretical molecular modelling methods. To reliably predict properties in solution using MD method, it is necessary to use a reliable MM force field. We have developed the MM force field FFW [1] that may reliable reproduce and predict equilibrium molecular geometry of copper(II) complexes with aliphatic amino acid complexes in vacuo and in simulated crystalline environment using the same set of potential energy functions and empirical parameters. Although FFW proved reliable for modelling anhydrous and aqua bis(amino acidato)copper(II) complexes in vacuo and in the crystal [1], FFW's empirical parameters of nonbonded potential energy functions for water oxygen and hydrogen atoms yielded incorrect density and diffusion coefficient of water in MD simulations. Using the empirical parameters of the SPC/E water model, the FFW force field was reparametrised in an exhaustive effort to obtain a set of force-field parameters equally applicable for vacuum, crystal, and aqueous solution. The ability of the new force field to simulate structural properties of copper(II) amino acid complexes in aqueous medium at room temperature has been tested on trans- and cis-isomers of bis(glycinato)copper(II) (surrounded with 2159 water molecules), the system whose structural parameters were obtained experimentally by Xray absorption spectroscopy [2]. The new force field yields the average values of these structural coordinates calculated during 10 ns MD simulation runs within their experimental error values. Although the trans-isomer is predicted more stable that the cis-isomer in the gas phase (by 56.7 kJ mol-1 [3]), the MD simulations prediction is that both isomers have very much similar energy in aqueous solution because of more favourable electrostatic interactions between the cis-isomer and water molecules. [1] Sabolović, J. ; Tautermann, C. S. ; Loerting, T. ; Liedl, K. R. Inorg. Chem. 2003, 42, 2268-2279. [2] D’ Angelo, P. ; Bottari, E. ; Festa, M. R. ; Nolting, H.-F. ; Pavel, N. V. J. Phys. Chem. B 1998, 102, 3114-3122. [3] Tautermann, C. S. ; Sabolović, J. ; Voegele, A. F. ; Liedl, K. R. J. Phys. Chem. B 2004, 108, 2098-2102.

copper; glycine; force field; crystal simulation; MM; MD

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