Co-binding of pharmaceutical compounds at mineral surfaces: Molecular investigations of dimer formation at goethite/water interfaces

Jing Xu (1, 2) , Remi Marsac (1) , Dominique Costa (3) , Wei Cheng (4) , Feng Wu (2) , Jean-François Boily (5) , Khalil Hanna (4)

1 ISCR - Institut des Sciences Chimiques de Rennes
2 State Key Laboratory of Water Resources and Hydropower Engineering Science
3 IRCP - Institut de Recherche de Chimie Paris
4 ENSCR - Ecole Nationale Supérieure de Chimie de Rennes
5 Umeå University

The emergence of antibiotic and anti-inflammatory agents in aquatic and terrestrial systems is becoming a serious threat to human and animal health worldwide. Because pharmaceutical compounds rarely exist individually in nature, interactions between various compounds can have unforeseen effects on their binding to mineral surfaces. This work demonstrates this important possibility for the case of two typical antibiotic and anti-inflammatory agents (nalidixic acid (NA) and niflumic acid (NFA)) bound at goethite (α-FeOOH) used as a model mineral surface. Our multidisciplinary study, which makes use of batch sorption experiments, vibration spectroscopy and periodic density functional theory calculations, reveals enhanced binding of the otherwise weakly bound NFA caused by unforeseen intermolecular interactions with mineral-bound NA. This enhancement is ascribed to the formation of a NFA-NA dimer whose energetically favoured formation (-0.5 eV compared to free molecules) is predominantly driven by van der Waals interactions. A parallel set of efforts also showed that no co-binding occurred with sulfamethoxazole (SMX) because of the lack of molecular interactions with co-existing contaminants. As such, this article raises the importance of recognising drug co-binding, and lack of co-binding, for predicting and developing policies on the fate of complex mixtures of antibiotics and anti-inflammatory agents in nature.

Domaines: Géochimie; Hydrologie; Chimie théorique et/ou physique; Sciences de l'environnement

Jing Xu, Remi Marsac, Dominique Costa, Wei Cheng, Feng Wu, et al.. Co-binding of pharmaceutical compounds at mineral surfaces: Molecular investigations of dimer formation at goethite/water interfaces. Environmental Science and Technology, 2017, 51 (15), pp.8343-8349. ⟨10.1021/acs.est.7b02835⟩. ⟨insu-01557413⟩