Pyridine, a substructure in numerous drugs, herbicides, and insecticides, is often positively charged at environmentally relevant pH values. Cationic pyridines can sorb to soil minerals via cation exchange. Our goal is to develop a predictive model for the equilibrium sorption constant (Kd) for pyridines. This allows us to anticipate environmental fate of chemicals with pyridine moieties. Our study investigates how substituent identity and position on the aromatic ring influences the Kd values for pyridine cation exchange to Ca-montmorillonite. We find that Kd values for methyl-pyridines is greater than pyridine and increases by location as follows: ortho < meta < para. This trend is consistent with compound hydrophobicity (logKow) and to a smaller extent with amine charge. Substituent effects will be quantified by evaluating the difference between Kd values for unsubstituted pyridine and substituted pyridines. Structure-activity relationships will then be developed following the Hammett constant approach using a range of substituents.

Structure based prediction of substituted pyridine cation exchange to Ca-montmorillonite

245th National Meeting (2013)

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