Electron Spin Echo Envelope Modulation (ESEEM) Study of Hyperfine Coupling Between Cu(II) and Distal 14N in a Macrocyclic System
The magnitude of the hyperfine coupling constant for the interaction between the unpaired electron and the distal nitrogens in CuZnL was determined to be roughly 0.5 MHz. this is in contrast to apara = 490 MHz for Cu(II) and apara = 30-40 MHz for the proximal 14N's. Absence of the zinc atom results in a greatly reduced hyperfine coupling interaction. The ability of EPR to detect such miniscule spin density (delocalized over such a great intra-molecular distance) illustrates the useful nature of this tool in studying metalloproteins and electron tansfer complexes.