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

1604305 / 1603755 /1604165 MacKay/ Vasudevan /Johnston过去十年，环境污染物的优先次序发生了根本性的变化。我们主要关注的不再是持久存在和生物累积的非极性化合物，但有机污染物的清单已大大扩大，包括许多具有潜在不利生态毒理学影响的极性和离子化合物。本研究提供了一种创新的方法，以适应计算化学工具来预测有机配体吸附到金属氧化物，所提出的方法代表了一个变革性的进步，在定量的先验预测吸附系数的极性和离子化合物在环境中。整合分子动力学计算以获得货车德瓦耳斯、静电能和溶剂化效应的量子力学测量克服了仅从吸附能的实验测量解卷积耦合结构效应的挑战，这是目前的科学状态。此外，其他相关的吸附问题提供了机会，以扩大线性相互作用能近似技术，因为环境吸附剂的特点是更概括比蛋白质结合位点的特点。该项目的首要假设是：通过添加/去除非配体基团取代基而引起的有机配体结构的变化由于耦合的疏水性、电子性和邻近性（即，空间和螯合）作用，其又由溶剂作用介导。最终的目标是定量描述有机配体吸附氧化物作为一个功能的特定的山梨酸盐结构标准。一种新的方法是用来确定结构的标准，通过桥接完善的实验技术与创新的计算相关的环境表面化学，并通过使用代表性的土壤氧化物，针铁矿。任务一：针铁矿力场将使用密度泛函理论进行微调，以确定测试山梨酸酯库的准确化合物构象。所选的库包括山梨酸酯与结构的增量变化，使我们能够确定特定的配体和非配体结构部分的影响。计算的努力将通过红外光谱来验证，以描绘结合机制和透射电子显微镜，以确定相关的晶面。量子力学计算将被用来计算内球络合反应的自由能。任务二：对吸附在高纯针铁矿上的吸附物进行了吸附能、红外光谱和针铁矿测量。任务三：线性相互作用能近似将与分子动力学模拟和任务1力场和内球结合能一起使用，以计算货车德瓦尔斯和静电对总吸附自由能的贡献。线性相互作用能提供了显着降低计算成本，因为分子动力学模拟只进行了绑定和未绑定状态。将货车德瓦尔斯能和静电能与吸附自由能的实验测量值进行回归，以生成吸附系数的预测模型。任务1-3的结果将被整合，以确定具体的结构特征如何与货车范德华力和静电能的规律性变化联系起来，从而表明与定量模型相关的结构-吸附关系。PI将通过实验设计，手稿准备和国家专业学会演示文稿的过程指导研究生和本科生研究人员。他们还将与高中学生和教师密切合作，通过日常应用的实践演示模块将吸附概念引入公共教育：家庭饮用水处理和农药应用。PI将继续致力于吸引来自科学和工程领域代表性不足的群体的学生研究人员。

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.