Conformational Analysis of Bis( L ‐ N , N ‐dimethylvalinato)copper( II ) and Bis( L ‐ N , N ‐dimethylleucinato)copper( II ) in Different Solvents by EPR Spectroscopy and a Molecular Mechanics Study

An EPR study on the Brownian motion of bis( L ‐ N , N ‐dimethylvalinato)copper( II ), Cu( L ‐Me 2 Val) 2 and bis( L ‐ N , N ‐dimethylleucinato)copper( II ), Cu( L ‐Me 2 Leu) 2 , dissolved in different solvents (CD 3 OD, CH 3 CH 2 OH, CDCl 3 ) as a function of temperature is presented. The theoretical fits of the EPR spectra revealed different EPR behaviour for the two copper( II ) complexes in hydrogen bond making solvents. In order to examine whether the different behaviour could be explained on conformational (steric) grounds, a conformational analysis of the copper( II ) complexes with L ‐ N , N ‐dimethylated amino acids was performed with a molecular mechanics force field. The ability of the most stable conformations to bind a water molecule in the copper( II ) first coordination sphere was also examined using the force field. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)