Quantitative predictors of charged organic compound sorption to environmental solids has lagged the successful approaches developed for neutral organic compound sorption. Structural modifications of charged organic compounds change both size (solvation) and electron distributions, coupled factors that are well-suited to computational tools. We measured the sorption of organic cations to montmorillonite clays using a suite of compounds chosen to include variations in size and substituent effects on charge per area of the amine group. We examined the applicability of Linear Interaction Energy (LIE) methods to calculate binding energies. LIE methods, translated from the computational biochemistry field, relate the sorption energy to the contributions of van der Waals (vdW) and electronic (el) interaction energies:?Gsorb = a?<EvdW> + �?<Eel> + ?where ? is the difference in <Ei>, the ensemble-averaged interaction energy of type i, between the sorbate in its sorbed state and dissolved in the bulk solvent. Parameters derived for test suite of organic cations on montmorillonite enabled the prediction of sorption coefficients within a factor of three for validation compounds. LIE methods appear to hold promise to account for size and electronic effects on organic cation sorption.

Structure effects of organic cation sorption to clays

248th National Meeting (2014)

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