In:
Zeitschrift für Physikalische Chemie, Walter de Gruyter GmbH, Vol. 232, No. 5-6 ( 2018-5-24), p. 819-844
Abstract:
For the application of iron oxide nanoparticles from thermal decomposition approaches as contrast agents in magnetic resonance imaging (MRI), their initial hydrophobic ligands have to be replaced by hydrophilic ones. This exchange can influence the surface oxidation state and the magnetic properties of the particles. Here, the effect of the anchor group of three organic ligands, citric acid and two catechols, dihydrocaffeic acid and its nitrated derivative nitro dihydrocaffeic acid on iron oxide nanoparticles is evaluated. The oleate ligands of Fe 3 O 4 /γ-Fe 2 O 3 nanoparticles prepared by the thermal decomposition of iron oleate were exchanged against the hydrophilic ligands. X-ray absorption spectroscopy, especially X-ray magnetic circular dichroism (XMCD) measurements in the total electron yield (TEY) mode was used to investigate local magnetic and electronic properties of the particles’ surface region before and after the ligand exchange. XMCD was combined with charge transfer multiplet calculations which provide information on the contributions of Fe 2+ and Fe 3+ at different lattice sites, i.e. either in tetrahedral or octahedral environment. The obtained data demonstrate that nitro hydrocaffeic acid leads to least reduction of the magnetizability of the surface region of the iron oxide nanoparticles compared to the two other ligands. For all hydrophilic samples, the proportion of Fe 3+ ions in octahedral sites increases at the expense of the Fe 2+ in octahedral sites whereas the percentage of Fe 3+ in tetrahedral sites hardly changes. These observations suggest that an oxidation process took place, but a selective decrease of the Fe 2+ ions in octahedral sites ions due to surface dissolution processes is unlikely. The citrate ligand has the least oxidative effect, whereas the degree of oxidation was similar for both catechol ligands regardless of the nitro group. Twenty-four hours of incubation in isotonic saline has nearly no influences on the magnetic properties of the nanoparticles, the least on those with the nitrated hydrocaffeic acid ligand.
Type of Medium:
Online Resource
ISSN:
2196-7156
,
0942-9352
DOI:
10.1515/zpch-2017-1084
Language:
English
Publisher:
Walter de Gruyter GmbH
Publication Date:
2018
detail.hit.zdb_id:
201103-7
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