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Quantum chemical study of (L-histidinato)(L-asparaginato)copper(II) in the gas phase and aqueous solution

The electrically neutral (L-histidinato)(L-asparaginato)copper(II) [Cu(L-His)(L-Asn)] is part of a small portion of bis(amino acidato)copper(II) complexes in blood plasma supposed to take part in the exchangeable copper pool and in transporting copper [1, 2]. The X-ray crystal and molecular structure of [Cu(L-His)(L-Asn)·H2O]·3H2O and anhydrous Cu(L-His)(L-Asn) were determined [3]. The copper(II) coordination is the same in these complexes, that is, L-His chelates in a histamine-like mode (i.e., via Nam and Nim) with the O atom in the axial position, while L-Asn coordinates in a glycinatomode (i.e., via Nam and O), with two Nam in the cis-position. Their molecular structures differ with respect to the L-Asn side chain conformations. The ESR and absorption spectra measured for Cu(L-His)(L-Asn) in aqueous solution suggested the CuN3O chromophore in the equatorial plane [4]. However, the details of the complex geometry in aqueous solutions are still unknown. To study the effects of intermolecular interactions on the complex properties, conformational analyses are performed in the gas phase and in an implicitly modeled aqueous medium using the density functional theory functional B3LYP. We examine the differences of the energy landscapes in the gas phase relative to aqueous solution, and identified the most stable coordination modes in both environments. ____ [1] P. Z. Neumann, A. Sass-Kortsak, J. Clin. Invest. 1967, 46, 646–658. [2] B. Sarkar, T. P. Kruck, Can. J. Biochem. 1967, 45, 2046–2049. [3] T. Ono, H. Shimanouchi, Y. Sasada, T. Sakurai, O. Yamauchi, A. Nakahara, Bull. Chem. Soc. Jpn. 1979, 52, 2229–2234. [4] P. Cocetta, S. Deiana, L. Erre, G. Micera, P. Piu, J. Coord. Chem. 1983, 12, 213–217.

conformational analysis, copper(II), amino acids, DFT, B3LYP, histidine, asparagine

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