Parole chiave: Cw Epr, Cu(ii) Complexes, Aminoacidate Ligands, Trans Copper Conformers, Electrostatic Interactions, Swv Formal Redox Potentials,
*** IBB - CNR *** Dipartimento di Scienze Chimiche, Università degli Studi di Catania, Viale A. Doria 6, 95125 Catania, Italy CNR, Istituto di Biostrutture e Bioimmagini, Via P. Gaifami 18, 95126 Catania, Italy
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EPR CW measurements at room and low temperature have been carried out on the systems containing<br>63copper(II) nitrate, L-Arg and L-or D-Glu or DL- racemic mixtures of both amino acids in aqueous solution<br>or in mixed solvents. For these copper(II) bis and ternary complexes, RT EPR spectra revealed that mixtures<br>of cis and trans conformers are really present in aqueous solution. In most cases, for these systems,<br>the cis conformer is more abundant at the lowest temperature (275 K). Increasing gradually the temperature<br>from 275 K to 305 K the cis/trans ratio tends towards the trans conformer. This latter is less abundant<br>in the case of [Cu(L-Glu)2], because of the possible interaction of negative side chain carboxylate<br>anions with the water molecules axially bound, and for [Cu(L-Arg)(D-Glu)], probably owing to a possible<br>electrostatic interaction between the two opposite charged side chains which are on the same side of the<br>CuN2O2 coordination plane. Low temperature frozen solution EPR spectra run on these systems show<br>the presence of only one absorbing specie thus giving reason to the stabilization of one conformer over<br>the other, in particular, the cis conformer. There are no evident differences in the anisotropic Spin<br>Hamiltonian parameters derived from the frozen EPR solution spectra of these systems, which are<br>characterized by a tetragonally elongated octahedral stereochemistry. SWV measurements confirmed<br>the EPR spectroscopic data, actually giving rise to the observation of slightly asymmetrical peaks, which<br>revealed two near formal redox potentials assigned to the two conformers.