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Evidence for an egg-box-like structure in iron(ii)–polygalacturonate hydrogels: a combined EXAFS and molecular dynamics simulation study

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Abstract

The local structure of Fe2+ in Fe2+–polygalacturonic acid (polyGalA) hydrogels has been studied by coupling Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy and molecular dynamics (MD) simulation. The EXAFS fitting results reveal an octahedral coordination geometry of Fe2+ both in aqueous solution and in the hydrogel, with similar Fe–O distances (2.09 ± 0.01 Å in the hydrogel and 2.11 ± 0.01 Å in aqueous solution). The MD simulations evidence that standard empirical force fields are unable to accurately reproduce the EXAFS spectra of Fe2+ in both aqueous solution and hydrogel. Based on the EXAFS distance determinations, we then performed restrained MD simulations of hypothetical octahedral coordination modes of Fe2+ with polyGalA chains. The best agreement between experimental and simulated EXAFS spectra was found when Fe2+ is monodentately coordinated to two carboxylate and two hydroxyl oxygens from a pair of polyGalA chains as well as to two water oxygens in an octahedral coordination geometry compatible with the “egg-box model”.

Graphical abstract: Evidence for an egg-box-like structure in iron(ii)–polygalacturonate hydrogels: a combined EXAFS and molecular dynamics simulation study

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Article information


Submitted
20 Jul 2019
Accepted
07 Jan 2020
First published
07 Jan 2020

Phys. Chem. Chem. Phys., 2020, Advance Article
Article type
Paper

Evidence for an egg-box-like structure in iron(II)–polygalacturonate hydrogels: a combined EXAFS and molecular dynamics simulation study

A. Maire du Poset, A. Zitolo, F. Cousin, A. Assifaoui and A. Lerbret, Phys. Chem. Chem. Phys., 2020, Advance Article , DOI: 10.1039/C9CP04065J

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