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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".
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https://hal-univ-bourgogne.archives-ouvertes.fr/hal-02513922
Contributeur : Pam - Université de Bourgogne <>
Soumis le : samedi 21 mars 2020 - 10:29:35
Dernière modification le : lundi 19 octobre 2020 - 14:26:01

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Aline Maire Du Poset, Andrea Zitolo, Fabrice Cousin, Ali Assifaoui, Adrien Lerbret. Evidence for an egg-box-like structure in iron( ii )–polygalacturonate hydrogels: a combined EXAFS and molecular dynamics simulation study. Physical Chemistry Chemical Physics, Royal Society of Chemistry, 2020, 22 (5), pp.2963-2977. ⟨10.1039/c9cp04065j⟩. ⟨hal-02513922⟩

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