EPR investigations of the iron domain in neuromelanin

Abstract

The interactions between iron and neuromelanin (NM) have been studied by means of EPR spectroscopy. The variable temperature EPR spectral features of a specimen of NM extracted from normal human midbrains clearly indicate that iron is present as polynuclear oxy-hydroxy ferric aggregates as well as isolated Fe(III) centres. Ferric oxy-hydroxy phases are typical of the iron storage proteins ferritin and hemosiderin, but the comparison of the variable temperature EPR spectra of ferritin and NM highlights significant differences between the two iron(III)oxy-hydroxy domains. Moreover, further investigations on melanin models synthesised in the presence of either ferritin or a ferric salt as iron sources suggest that the same pathway of formation and inclusion of the polynuclear iron oxide is operating in NM and in the model systems, whatever is the source of iron.

Ferromagnetic Resonance of Horse Spleen Ferritin: Core Blocking and Surface Ordering Temperatures

“…The EPR signal of horse spleen ferritin core disappears for temperatures lower than 14 ± 5 K, indicating zero magnet moment and suggesting this temperature as the T ord . Although this effect was not observed before for a freeze-dried sample with low iron content (10), no resonance were observed at 4.2 K for a ferritin wet paste (6). This temperature is much lower than the ordering temperature estimated by Mössbauer spectroscopy, but it can be understood under the view of the new structure proposed for the ferritin core.…”

“…The iron centers in ferritin have been extensively studied with a wide range of techniques such as extended X-ray absorption fine structure (EXAFS) (3,4), Mössbauer spectroscopy (5-7), and magnetic measurements (8). However, EPR (electron paramagnetic resonance) measurements on mammalian holoferritin have been rather limited (6,(9)(10)(11)(12).…”

Diluted Fe 3+ in silicate glasses: Structural effects of Fe-redox state and matrix composition. An optical absorption and X-band/Q-band EPR study

“…[17] Different scenarios have been proposed: (i) a signal due to exchange-coupled pairs or clusters of more than two atoms [18] involving edge-or face-sharing Fe 3+ sites [16,19,20]. These clusters could be trimers [21] up to nano-clusters as in ferritine [22], nanoparticles [23] or obsidian wt.% glasses [7,24]; (ii) a paramagnetic signal due to Fe 3+ in axially distorted sites (E/D ~ 0) [19], this signal being enhanced by dipole-dipole interactions. [25] The proportion of these two overlapping contributions depends on glass composition and Fe-redox state.…”

“…Low-temperature EPR measurements have shown the presence of paramagnetic clusters in Fe-doped borate glasses, because small clusters exhibit an antiferromagnetic behavior, whereas the EPR signal of diluted Fe 3+ exhibits a paramagnetic behavior. [28] Thus, the disappearance of the g = 2 signal when temperature decreases is used as evidence of the presence of Fe 3+ containing clusters, as observed in ferritin [22] or nanoparticles [23]. …”

Electrocatalytic and Magnetic Properties of Ultrathin Nanostructured Iron–Melanin Films on Au(111)

“…[6] Little is known about the state of aggregation of iron in melanins. [7] X-ray absorption fine-structure and infrared spectroscopic studies suggested that iron in neuromelanin is bonded to oxygen from phenolic groups in an octahedral configuration. [7] It has been reported that the melanin-redox-active-metal systems have peroxidase activity, which promotes the formation of reactive oxygen species.…”