title: Towards a molecular level understanding of the sulfanilamide-soil organic matter-interaction.
abstract: Sorption experiments of sulfanilamide (SAA) on well-characterized samples of soil size-fractions were combined with the modeling of SAA-soil-interaction via quantum chemical calculations. Freundlich unit capacities were determined in batch experiments and it was found that they increase with the soil organic matter (SOM) content according to the order fine silt > medium silt > clay > whole soil > coarse silt > sand. The calculated binding energies for mass-spectrometrically quantified sorption sites followed the order ionic species > peptides > carbohydrates > phenols and lignin monomers > lignin dimers > heterocyclic compounds > fatty acids > sterols > aromatic compounds > lipids, alkanes, and alkenes. SAA forms H-bonds through its polar centers with the polar SOM sorption sites. In contrast dispersion and π-π-interactions predominate the interaction of the SAA aromatic ring with the non-polar moieties of SOM. Moreover, the dipole moment, partial atomic charges, and molecular volume of the SOM sorption sites are the main physical properties controlling the SAA-SOM-interaction. Further, reasonable estimates of the Freundlich unit capacities from the calculated binding energies have been established. Consequently, we suggest using this approach in forthcoming studies to disclose the interactions of a wide range of organic pollutants with SOM.
authors.affiliation: University of Rostock, Institute of Physics, Albert-Einstein-Str. 23-24, D-18059 Rostock, Germany; Steinbeis GmbH & Co. KG für Technologietransfer, 70174 Stuttgart, Germany; University of Cairo, Faculty of Science, Department of Chemistry, 12613 Giza, Egypt. Electronic address: ashour.ahmed@uni-rostock.de.
authors.forename: Ashour A
authors.initials: AA
authors.lastname: Ahmed
authors.affiliation: University of Trier, Soil Science, D-54286 Trier, Germany. Electronic address: thiele@uni-trier.de.
authors.forename: Sören
authors.initials: S
authors.lastname: Thiele-Bruhn
authors.affiliation: Steinbeis GmbH & Co. KG für Technologietransfer, 70174 Stuttgart, Germany; University of Rostock, Soil Science, D-18051 Rostock, Germany. Electronic address: peter.leinweber@uni-rostock.de.
authors.forename: Peter
authors.initials: P
authors.lastname: Leinweber
authors.affiliation: University of Rostock, Institute of Physics, Albert-Einstein-Str. 23-24, D-18059 Rostock, Germany. Electronic address: oliver.kuehn@uni-rostock.de.
authors.forename: Oliver
authors.initials: O
authors.lastname: Kühn
mesh_terms: D000327:Adsorption; D007700:Kinetics; D008956:Models, Chemical; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis / Q000737:chemistry*; D000077145:Sulfanilamide; D013424:Sulfanilamides / Q000032:analysis / Q000737:chemistry*
chemical_list: D012987:Soil; D012989:Soil Pollutants; D013424:Sulfanilamides; D000077145:Sulfanilamide
keywords: Quantitative structure-activity relationship (QSAR); Quantum chemical calculations; Soil organic matter (SOM); Sorption isotherms; Sulfanilamide (SAA)