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THE ABILITY OF THE MM FORCE FIELD FFW TO MODEL COPPER(II) AMINO ACID COMPLEXES IN VACUO, IN CRYSTAL, AND IN SOLUTION

Copper(II) amino acid complexes are a part of the accessible physiological pool of an essential element copper for most tissues. Besides, copper(II) complexes with N-alkylated amino acids are considered to be good model compounds to study the sterical interactions in metal-biomolecule systems. So far, their only experimentally available structures have been those determined by X-ray diffraction. To predict and simulate the properties of anhydrous and aqua copper(II) complexes with amino acids a molecular mechanics model has been proposed and a new force field (named FFW [1]) derived [1, 2]. The modelling included experimental molecular and crystal structures of 13 anhydrous and 10 aqua copper(II) amino acidates [1]. Interactions inside a copper(II) coordination polyhedron are modelled with a Morse potential (between the metal and four amino acid donor atoms), an electrostatic potential (between the four donor atoms), and a torsion-like potential (with minima at 0 and 180 degrees) that should hold the four donor atoms in a coordination plane and allow modelling of both cis- and trans-CuN2O2 coordination modes. The conformational potential energy was minimised for an isolated system (in vacuo or a gas phase approximation), and for a molecule surrounded with other molecules in a crystal lattice (a condensed phase approximation). The empirical parameters of the selected potential energy functions were fitted with respect to the experimental crystalline data of 12 compounds and to the vacuum structures obtained by molecular quantum mechanics for 3 anhydrous [3] and 3 aqua copper(II) amino acidates [1]. The goal has been to develop a reliable vacuum-like force field to predict and simulate the properties of copper(II) complexes with amino acids by explicit calculation of the environmental effects. By now FFW has been applied to study the sterical effects caused by aliphatic-aliphatic interactions in the copper(II) complexes with N, N-dimethylated L-valine, L-leucine [4], and L-isoleucine [5] in relation to their unlike EPR behaviour in the same solvents at different temperatures by means of the conformational analyses of the anhydrous complexes and the complexes surrounded with four water molecules [4, 5]. The conformation analysis was also done for bis(N, N-diethylglycinato)copper(II) to identify the causes that affected the change in the copper(II) coordination sphere upon the complex’ s crystallisation [6]. The FFW’ s reliability in modelling copper(II) amino acidates has been additionally validated by simulating the novel X-ray crystal data of bis(N, N-diethylglycinato)copper(II) [6, 7] and aquabis(N, N-dimethylglycinato)copper(II) [7]. The next step is the force field’ s implementation into a MD program and testing its ability to predict the properties of the copper(II) amino acid complexes in solutions in which the biological reactions take place. 1. J. Sabolović, C. S. Tautermann, T. Loerting, K. R. Liedl, Inorg. Chem. 42 (2003) 2268-2279. 2. B. Kaitner, N. Paulić, G. Pavlović, J. Sabolović, Polyhedron 18 (1999) 2301-2311. 3. J. Sabolović, K. R. Liedl, Inorg. Chem. 38 (1999) 2764-2774. 4. K. Mirosavljević, J. Sabolović, V. Noethig-Laslo, Eur. J. Inorg. Chem. (2004) 3930-3937. 5. J. Sabolović, V. Noethig-Laslo, Cellul. Mol. Biol. Lett. 7 (2002) 151-153. 6. J. Sabolović, B. Kaitner, CrystEngComm Discusssion 2: New Trends in Crystal Engineering: Nottingham, Great Britain 2004, Poster Abstracts, page P.8 7. J. Sabolović, B. Kaitner, 14th Croatian-Slovenian Crystallographic Meeting, Vrsar, Croatia 2005, Book of Abstracts Programme, page 52.

modelling; crystal simulations; parametrisation; metal complexes

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