Measurement of 14N superhyperfine frequencies in stellacyanin by an electron spin echo method

We have measured the 14N superhyperfine frequencies for weakly coupled nitrogen in stellacyanin and in a model compound Cu(II)-diethylenetriamine-imidazole using a 3-pulse spin echo technique. By making computer simulations of the superhyperfine spectrum, we have been able to show that these frequencies result from the interaction of the remote protonated nitrogen of metal-bound imidazole with Cu(II).