title: Nonlinearity of cationic aromatic amine sorption to aluminosilicates and soils: role of intermolecular cation-π interactions.
abstract: Through the study of substituted anilines and benzylamines, we demonstrated that cooperative cation-π, π-π, and van der Waals interactions can increase aromatic cationic amine sorption to Na/Ca-montmorillonite well beyond the extent expected by cation exchange alone. Cationic amines exhibiting cooperative interactions displayed nonlinear S-shaped isotherms and increased affinity for the sorbent at low surface coverage; parallel cation exchange and cooperative interactions were noted above a sorption threshold of 0.3-2.3% of exchange sites occupied. Our experiments revealed the predominance of intermolecular cation-π interactions, which occurred between the π system of a compound retained on the surface via cation exchange and the cationic amine group of an adjacent molecule. Compounds with greater amine charge/area and electron-donating substituents that allowed for greater electron density at the center of the aromatic ring showed a greater potential for cation-π interactions on montmorillonite surfaces. However, benzylamine sorption to nine soils, at charge loadings comparable to the experiments with montmorillonite, revealed no significant cooperative interactions. It appears that cation-π interactions may be likely in soils with exceptionally high cation exchange capacities (>0.7 mol charge/kg) and low organic matter contents, abundant in montmorillonite and other expanding clay minerals.
authors.affiliation: Bowdoin College, Department of Chemistry, Brunswick, Maine 04011, United States.
authors.forename: Dharni
authors.initials: D
authors.lastname: Vasudevan
authors.forename: Teresa A
authors.initials: TA
authors.lastname: Arey
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Dickstein
authors.forename: Mark H
authors.initials: MH
authors.lastname: Newman
authors.forename: Tina Y
authors.initials: TY
authors.lastname: Zhang
authors.forename: Heather M
authors.initials: HM
authors.lastname: Kinnear
authors.forename: Mohammad M
authors.initials: MM
authors.lastname: Bader
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates / Q000737:chemistry*; D000588:Amines / Q000737:chemistry*; D001546:Bentonite / Q000737:chemistry; D001596:Benzylamines / Q000032:analysis; D002412:Cations / Q000737:chemistry; D004583:Electrons; D017711:Nonlinear Dynamics; D012987:Soil / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D000588:Amines; D001596:Benzylamines; D002412:Cations; D012987:Soil; D001546:Bentonite; C049037:aluminosilicate; C030796:benzylamine