Binding of Polar rganic ontaminants at Water-Mineral Interfaces: Experimental and omputational Studies Ludmilla Aristilde Assistant Professor ollege of Agricultural and Life Sciences
Binding of Polar rganic ontaminants to Smectite lays (Montmorillonite) xytetracycline Adsorption on Montmorillonite: Influence of ph Microcystin Adsorption on Montmorillonite Surfaces: Influence of Aqueous onditions and organic matter NH 2 H N H + Disrupt several microbial processes involved in nutrient cycling. Has high affinity for clay minerals. Decrease in toxicity in the presence of montmorillonite-rich soils when compared to kaolinitic soils. Aristilde et al. (2010). Environ. Sci. Technol. 44 Aristilde et al. (2013). Langmuir 29 Liver toxins produced by cyanobacteria in algal blooms worldwide. Has high affinity for clay minerals. Previous studies have implicated clay minerals in facilitating the retention of Ms within soil particles in sediments. Pochodylo & Aristilde (2014). In prep
+ + Potential Interaction Mechanisms of Polar ontaminants with Smectite Surfaces H-bonding Interlayer expansion - Al Al Si Mg - - Al Al Si Mg - Surface complexation X- -X M + ation Exchange X + + X + Ternary complexes + - - - -
1. xytetracycline Adsorption on Montmorillonite: Influence of ph Aristilde et al. (2010). Environ. Sci. Technol. 44: 7839-7845 Aristilde et al. (2013). Langmuir 29: 4492-4501 NH 2 H N H + X-ray diffraction and Spectroscopic investigations Monte arlo and Molecular Dynamics Simulations Decreased adsorption as a function of increasing ph
1. xytetracycline Adsorption on Montmorillonite: Influence of ph Aristilde et al. (2010). Environ. Sci. Technol. 44 X-ray diffraction indicates increase in interlayer adsorption with decreasing ph 18.3 Å 12.5 Å Does ph-dependent adsorption a result of ph-dependent interlayer trapping? Increasing interlayer distance
1. xytetracycline Adsorption on Montmorillonite: Influence of ph Aristilde et al. (2010). Environ. Sci. Technol. 44 Solid-state Nuclear Magnetic Resonance (NMR) and Infrared (IR) reveal mechanisms of interactions. a: = stretching band b: N-H bending band c: aromatic = stretching band d: antisymmetric H 3 deformation band T-lay TET-lay T-lay TET-clay cm-1 vs na-clay cm-1 vs otc cm-1 vs ph4 33 cm-1 7 12 6, vs ph8 32 21 cm-1 vs 5 17 15/18 14 ca-otc 16 pure T 31 Transmittance a b c lay TET d 200 175 150 125 100 ppm 75 50 25 0 1710 1620 cm -1 1530 1440
1. xytetracycline Adsorption on Montmorillonite: Influence of ph Aristilde et al. (2010). Environ. Sci. Technol. 44 NH 2 H A B D N H + A D
1. xytetracycline Adsorption on Montmorillonite: Influence of ph Aristilde et al. (2013). Langmuir 29 Model adsorbate structures used to simulate X-ray diffraction patters and determine interlayer stackings following adsorption. Na-MNT T-MNT Experiment (80 mmol T/g clay) model 40% T-layers Random interstratifcation 30% T-layers Segregated interstratifcation 10% T-layers Segregated interstratifcation As ph increases, interlayer adsorption is both decreased and becoming segregated, indicating restricted access of T to some interlayers.
1. xytetracycline Adsorption on Montmorillonite: Influence of ph Aristilde et al. (2010). Environ. Sci. Technol. 44 Aristilde et al. (2013). Langmuir 29 Summary of Findings: Extent of oxytetracycline adsorption to montmorillonite was positively correlated to interlayer adsorption. Both amount adsorbed and interlayer adsorption decreases with increasing ph. ph-dependence of interlayer adsorption implied this adsorption is affected by more than the protonation states of the antibiotic. ph-dependence adsorption implied that interlayer adsorption is affected by more than the protonation states of the antibiotic.
2. Microcystin at water-montmorillonite interfaces: Influence of aqueous conditions and natural organic matter Pochodylo & Aristilde (2014). In prep ation exchange In Nal solution In al 2 solution a-bridging Monte arlo and Molecular Dynamics Simulations Structural re-arrangements of hydrophilic (blue) and hydrophobic (brown) residues in response to different aqueous conditions. pi-pi interactions
2. Microcystin at water-montmorillonite interfaces: Influence of aqueous conditions and natural organic matter Pochodylo & Aristilde (2014). In prep Three scenarios to probe effects of NM. 1. co-adsorption of NM with M 2. M adsorption on NM-coated clay (low NM) 3. M adsorption on NM-coated clay (high NM) Microcystin (M): cyanotoxin variant. ellulodextrin: a 6 glucose polymer derived from cellulose breakdown.
2. Microcystin at water-montmorillonite interfaces: Influence of aqueous conditions and natural organic matter Pochodylo & Aristilde (2014). In prep Summary of Findings: Extent Different aqueous conditions induces changes in the conformations of microcystin molecules. Re-arrangement of hydrophilic and hydrophobic moieties due to metal complexation and intramolecular H-bonding resulted in different M-mineral interactions. Microcystin molecules can compete with sites on mineral surfaces only when co-adsorbed with NM molecules. When adsorbed on clay surfaces pre-coated with the NM molecule, microcystin had no interaction with the clay surface and either remained in solution or trapped within the organic matrix.
Relevance: rganic Molecule Interactions with Mineral Surfaces as Key Regulators of Soil Processes Trapping of polar organic molecules within layered aluminosilicates (clays) requires conditions with favorable ph, exfoliated clay layers. Uneven formation of clay crystallites result in segregation of trapped organics. This may explain the spatial heterogeneity in organomineral matrices. In sediment or wetland soils, the surrounding aqueous conditions of the surface waters may control the mechanisms of interactions of toxins or contaminants. The presence of natural organic matrix at the water-mineral interface is an important, often forgotten, factor that should be addressed in assessing the role of minerals in either trapping or degrading contaminants.
Acknowledgements Fall 2013 --Wonderful group of undergraduate and graduate students and postdocs. --National Science Foundation (Instrument grant from the Division of Earth Sciences). --National Institute for Food and Agriculture (Hatch Grant) Fall 2014
Questions? omments?