Magnetic resonance spectroscopy is an outstanding tool to learn about the electronic structure of paramagnetic heme proteins. Hyperfine NMR shifts due to the coupling between unpaired electrons and nuclei have been investigated for decades. Present-day methodologies and technologies allow researchers to detect, through NMR spectroscopy, the nuclei of heme even under fast nuclear relaxation conditions.
Magnetic susceptibility anisotropy is routinely achieved and is related to the geometric and donor strength properties of the axial ligands [1]. This is particularly true for S = 1/2 (iron(III)) and S = 2 (iron(II)). The unpaired electron delocalization on heme has been successfully studied by NMR and MO calculations, and this is another issue which has been settled [2,3].
Nowadays it is very fashionable to study proteins in oriented systems or where they are self-oriented in high magnetic fields. A new body of information on the coupling between unpaired electrons and nuclei is being obtained under conditions of the occurrence of residual dipolar couplings [4]. Reports related to the above issues will be discussed at the conference during the present symposium, and we hope that new breakthroughs in the understanding of the electronic structure of heme and the interaction of unpaired electrons with nuclei will be presented and discussed.