APPLICATIONS OF COSY TO PARAMAGNETIC HEME-CONTAINING SYSTEMS

1H TOCSY experiments and a series of different COSY experiments have been performed at 600 MHz on the monocyano, monoimidazoleferric protohemin complex, a model compound for the heme-containing proteins, with the aim of evaluating the best practical approach for the obtainment of scalar connectivities in paramagnetic systems at high field. TOCSY experiments work best for signals close to the transmitter, but suffer most from the difficulty of homogeneously irradiating the whole spectral region, especially for the smallest J Δν ratios. Magnitude COSY and ISECR COSY give the best overall results. Even if the magnitude COSY is superior to the ISECR COSY in terms of absolute signal-to-noise ratios, the latter allows the detection of cross peaks with smaller J Δν ratios and resolves much better cross peaks close to the diagonal. © 1991.