Electron paramagnetic resonance study of weak exchange interactions between metal Ions in a model system: CuIIGly-Trp

Abstract

The structure of the copper compound with the peptide Gly-Trp belongs to the space group P212121, with Z = 4. The four chemically identical but magnetically nonequivalent Cu(II) molecules in the unit cell are weakly connected by a network of biologically relevant pathways involving hydrogen bonds and cation- interactions. The magnitudes of the exchange interactions between copper ions (J) transmitted along these paths were evaluated from the angular variation of the line width and the collapse of the EPR lines observed at 9.5 and 35 GHz with the magnetic field in the three crystalline planes of oriented single-crystal samples. Values J/kB = 3 ± 1 and 12 ± 3 mK were obtained for the couplings transmitted through bridges containing H-bonds, and J/kB = 5 ± 2 mK for the interaction transmitted through bridges containing a cation- contact. These magnitudes are analyzed in terms of the structural information about the intervening long chemical paths.