engleski

Role of apically bound water molecule on aliphatic-aliphatic side-chain interactions in bis[N,N-dimethyl-L-alpha-isoleucinato]copper(II) complex by EPR spectroscopy

Hydrophobic interactions in the metal ion complexes with aliphatic amino-acids were extensively studied (1). Sigel and coworkers (2) studied the influence of organic solvents on these interactions by potentiometric pH-titrations. The interactions between aliphatic-aliphatic amino-acid side-chains can be formed only when 2N/2O atoms in the metal-ion ligand field of the complex are arranged in the trans-fashion. In this arrangement the amino-acid side-chains are located on the same side of the metal-ion coordination sphere. This was shown by EPR spectroscopy in a number of copper(II) complexes with aliphatic amino-acids (3,4). Sigel (2) supposed that water molecule coordinated to the copper(II) in the complex might favor the amino-acid side-chain interactions. On the other hand, the crystal structures of the two modifications of bis[N,N-dimethyl-isoleucinato]copper(II) complex suggested just the opposite (5). In this work we studied a role of the water molecule coordinated to copper(II) on the motional properties of bis[N,N-dimethyl-isoleucinato]copper(II) complex dissolved in several organic solvents. Temperature dependence of EPR spectra of bis[N,N-dimethyl-isoleucinato]copper(II) and bis[N,N-dimethyl-alaninato]copper(II) complexes will be compared. In the alaninato complex amino-acid side chains are too short (-CH3) to form intra-molecular van der Waals contacts (6). Thus, if the aliphatic-aliphatic side-chain interactions are formed in bis[N,N-dimethyl-isoleucinato]copper(II) complex, this has to be reflected in changes of the solute-solvent interactions and in the temperature dependence of EPR spectra. 1. B. E: Fisher and H. Sigel, (1980) J. Am. Chem. Soc. 102, 2998. 2. G. Liand, R. Tribolet and H. Sigel, (1989) Inorg. Chim. Acta 155, 273. 3. V. Noethig-Laslo and N. Paulić, (1992) J. Chem. Soc. Dalton Trans. 2045. 4. V. Noethig-Laslo and N. Paulić, (1995) Z. anorg. Allg. Chem. 621, 84. 5. B. Kaitner, N. Paulić and N. Raos (1991) J. Coord. Chem. 22, 269. 6. V. Noethig-Laslo and N. Paulić, (1999) Polyhedron 18, 1609.

bis[N;N-dimethyl-isoleucinato]copper(II); aliphatic-aliphatic interaction; EPR

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