Issue 5, 2020

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

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

Supplementary files

Article information

Article type
Paper
Submitted
20 Jul 2019
Accepted
07 Jan 2020
First published
07 Jan 2020

Phys. Chem. Chem. Phys., 2020,22, 2963-2977

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, 22, 2963 DOI: 10.1039/C9CP04065J

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