Electron spin resonance studies paramagnetic centres

Electron spin resonance has proved to be one of the most powerful methods for studying paramagnetic centres formed on irradiation. 

Electron paramagnetic resonance (EPR) spectroscopy (also called electron spin resonance (ESR) spectroscopy), is used to study paramagnetic species with one or more unpaired electrons, e.g. free radicals, diradicals, metal complexes containing paramagnetic metal centres, defects in semiconductors and irradiation effects in solids. While diamagnetic materials are EPR silent, paramagnetic species always exhibit an EPR spectrum. This consists of one or more lines, depending on the interactions between the unpaired electron (which acts as a probe ) and the molecular framework in which it is located. Analysis of the shape of the EPR spectrum (the number and positions of EPR lines, their intensities and line widths) provides information... 

Deoxyhemerythrin is paramagnetic, having two high-spin (S = 2) Fe11 centres. The presence of iron(III) centres in oxyhemerythrin is shown by the similarity between the electronic spectra of oxyhemerythrin and the met form. Resonance Raman spectra show a band at 848 cm-1 assigned to (02), as shown by studies with 1802, which is appropriate for a peroxo group. Use of 160—180 shows that the two atoms of the peroxide have different environments,1279 while the iron(III) centres have different environments also, as indicated by the Mossbauer spectra of oxyhemerythrin. These observations are consistent with a structure for oxyhemerythrin in which the peroxide is bound end-on to one iron centre only. 

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