Collaborative Research: RUI: Novel Computational Tools to Predict Anionic Pesticide and Pharmaceutical Sorption to Soil Oxides

点击翻译按钮获取中文摘要

1604305 / 1603755 / 1604165MacKay / Vasudevan / JohnstonThe last decade has witnessed a radical shift in the prioritization of environmental contaminants. No longer is our primary concern non-polar compounds that persist and bioaccumulate, but the inventory of organic contaminants has expanded greatly to include many polar and ionic compounds with potential adverse ecotoxicological effects. This study offers an innovative approach to adapt computational chemical tools to the prediction of organic ligand sorption to metal oxides.The proposed approach represents a transformative advance in the quantitative a priori prediction of sorption coefficients for polar and ionic compounds in the environment. The integration of molecular dynamics calculations to obtain quantum mechanics measures of van der Waals, electrostatic energies and solvation effects overcomes the challenge of deconvoluting coupled structure effects from experimental measures of sorption energies alone, is at the current state of the science. Furthermore, other related sorption problems provide opportunity to expand Linear Interaction Energy approximation techniques because environmental sorbent characteristics are more generalizable than protein binding site characteristics. The overarching hypothesis of the project is: that changes in organic ligand structure by the addition/removal of non-ligand group substituents impart regular changes in sorption free energy as a result of coupled hydrophobic, electronic and proximity (i.e., steric and chelation) effects that are in turn mediated by solvent effects. The ultimate goal is to quantitatively describe organic ligand sorption to oxides as a function of specific sorbate structure criteria. A novel approach is used to identify structural criteria by bridging well-established experimental techniques with innovations in computationally relevant environmental surface chemistry, and by using the representative soil oxide, goethite. Task 1: The goethite force field will be fine-tuned using density functional theory to determine accurate compound conformations for a library of test sorbates. The chosen library includes sorbates with incremental changes in structure that allow us to identify the influence of specific ligand and non-ligand structural moieties. Computational efforts will be validated by infrared spectra to delineate binding mechanisms and transmission electron microscopy to identify relevant crystal faces. Quantum mechanics calculations will be used to calculate free energies of the inner sphere complexation reaction. Task 2: Experimental measures of sorption energies, infrared spectra and goethite measures will be obtained for test sorbates sorbed to high purity goethite. Task 3: The Linear Interaction Energy approximation will be used with molecular dynamics simulations and Task 1 force fields and inner sphere binding energies to calculate van der Waals and electrostatic contributions to overall sorption free energies. Linear Interaction Energy offers significant reductions in computational cost because molecular dynamics simulations are conducted only for the bound and unbound states. van der Waals and electrostatic energies will be regressed against experimental measures of sorption free energies to generate a predictive model for sorption coefficients. Findings from Tasks 1-3 will be integrated to identify how specific structural features can be linked to regular changes in van der Waals and electrostatic energies, thereby indicating structure-sorption relationships relevant to quantitative models. The PIs will mentor graduate and undergraduate researchers through the processes of experimental design, manuscript preparation and national professional society presentations. They will also work closely with high school students and teachers to introduce sorption concepts into public education with hands-on demonstration modules of everyday applications: home drinking water treatment and pesticide application. The PIs will continue their committed record of engaging student researchers from groups underrepresented in the sciences and engineering.