Molecular environment of iodine in naturally iodinated humic substances: Insight from X-ray absorption spectroscopy

Michel L. Schlegel 1 Pascal E. Reiller 2 Florence Mercier-Bion 1 Nicole Barré 1 Valérie Moulin 3
1 LRSI - Laboratoire de Réactivité des Surfaces et des Interfaces
DPC - Département de Physico-Chimie : DEN/DPC
2 LSRM - Laboratoire de Spéciation des Radionucléides et des Molécules
DPC - Département de Physico-Chimie : DEN/DPC
3 LAMBE - UMR 8587 - Laboratoire Analyse et Modélisation pour la Biologie et l'Environnement
Abstract : The molecular environment of iodine in reference inorganic and organic compounds, and in dry humic and fulvic acids (HAs and FAs) extracted from subsurface and deep aquifers was probed by iodine L 3-edge X-ray absorption spectroscopy. The X-ray absorption near-edge structure (XANES) of iodine spectra from HAs and FAs resembled those of organic references and displayed structural features consistent with iodine forming covalent bonds with organic molecules. Simulation of XANES spectra by linear combination of reference spectra suggested the predominance of iodine forming covalent bonds to aromatic rings (aromatic-bound iodine). Comparison of extended X-ray absorption fine structure (EXAFS) spectra of reference and samples further showed that iodine was surrounded by carbon shells at distances comparables to those for references containing aromatic-bound iodine. Quantitative analysis of EXAFS spectra indicated that iodine was bound to about one carbon at a distance d (I–C) of 2.01(4)–2.04(9) A ˚ , which was comparable to the distances observed for aromatic-bound iodine in references (1.99(1)–2.07(6) A ˚), and significantly shorter than that observed for aliphatic-bound iodine (2.15(2)–2.16(2) A ˚). These results are in agreement with previous conclusions from X-ray photoelectron spectros-copy and from electrospray ionization mass spectrometry. These results collectively suggest that the aromatic-bound iodine is stable in the various aquifers of this study.
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Michel L. Schlegel, Pascal E. Reiller, Florence Mercier-Bion, Nicole Barré, Valérie Moulin. Molecular environment of iodine in naturally iodinated humic substances: Insight from X-ray absorption spectroscopy. Geochimica et Cosmochimica Acta Supplement, Pergamon, 2006, 70 (22), pp.5536­5551. ⟨10.1016/j.gca.2006.08.026⟩. ⟨cea-01270133⟩

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