Enhanced interlayer trapping of a tetracycline antibiotic within montmorillonite layers in the presence of Ca and Mg.

Authors:
Dr. Ludmilla Aristilde, PhD
Dr. Ludmilla Aristilde, PhD
Cornell University
Associate Professor
Environmental Chemistry; Environmental Biochemistry; Environmental Engineering.
Ithaca, NY | United States
Bruno Lanson
Bruno Lanson
University of Grenoble Alpes
Claire Marichal
Claire Marichal
Université de Strasbourg (UdS)
Strasbourg | France
Laurent Charlet
Laurent Charlet
Université Grenoble Alpes
France

J Colloid Interface Sci 2016 Feb 14;464:153-9. Epub 2015 Nov 14.

Institut des Sciences de la Terre, ISTerre, Univ. Grenoble-Alpes, CNRS, F-38041 Grenoble, France.

The formation of a ternary antibiotic-metal-clay complex is hypothesized as the primary adsorption mechanism responsible for the increased adsorption of tetracycline antibiotics on smectites in the presence of divalent metal cations under circumneutral and higher pH conditions. To evaluate this hypothesis, we conducted a spectroscopic investigation of oxytetracycline (OTC) interacting with Na-montmorillonite in the presence and absence of Ca or Mg salts at pH 6 and pH 8. Despite a two-fold increase in OTC adsorbed in the presence of Ca or Mg, both solid-state nuclear magnetic resonance and infrared signatures of the OTC functional groups involved in metal complexation implied that the formation of an inner-sphere ternary complexation was not significant in stabilizing the adsorbate structures. The spectroscopic data further indicated that the positively-charged amino group mediated the OTC adsorption both in the absence and presence of the divalent metal cations. Focusing on the experiments with Mg, X-ray diffraction analysis revealed that the metal-promoted adsorption was coupled with an increased intercalation of OTC within the montmorillonite layers. The resulting interstratified clay layers were characterized by simulating X-ray diffraction of theoretical stacking compositions using molecular dynamics-optimized montmorillonite layers with and without OTC. The simulations uncovered the evolution of segregated interstratification patterns that demonstrated how increased access to smectite interlayers in the presence of the divalent metal cations enhanced adsorption of OTC. Our findings suggest that specific aqueous structures of the clay crystallites in response to the co-presence of Mg and OTC in solution served as precursors to the interlayer trapping of the antibiotic species. Elucidation of these structures is needed for further insights on how aqueous chemistry influences the role of smectite clay minerals in trapping organic molecules in natural and engineered soil particles.

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http://dx.doi.org/10.1016/j.jcis.2015.11.027DOI Listing
February 2016
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