title: Surface complexation modeling of the sorption of 2-, 3-, and 4-aminopyridine by montmorillonite.
abstract: The sorption of 2-, 3-, and 4-aminopyridine on K-saturated Wyoming (SWy-K) and Texas (STx-K) and Ca-enriched Texas (STx-Ca) montmorillonite was measured at 25 degrees C with 10 mM KNO(3) or 3.3 mM Ca(NO(3))(2) as the background electrolyte. The aminopyridines adsorbed to montmorillonite at low pH, but not at high pH. Extended constant capacitance surface complexation models (ECCMs) and attenuated total reflectance-FTIR data indicate that aminopyridines sorb to the silica-like faces by cation exchange, forming outer-sphere complexes between aminopyridinium ions and permanent negatively charged surface sites (X(-)). X-ray diffraction data and sorption kinetics suggest that sorption occurs not only at external X(-) sites but also at those in the interlayer spaces. Differences in the sorption behaviors of 2-, 3-, and 4-aminopyridine result from differences in their pK(a)s. The extent of sorption of aminopyridines by the montmorillonite samples (SWy-K>STx-K>STx-Ca) results from the higher cation-exchange capacity of SWy-K, and from the fact that Ca(2+) is much more effective than K(+) in competing with protonated aminopyridines for the X(-) sites.
authors.affiliation: Colloid and Environmental Chemistry Laboratory, La Trobe University, P.O. Box 199, Bendigo, Victoria 3552, Australia.
authors.forename: Jaslin
authors.initials: J
authors.lastname: Ikhsan
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Angove
authors.forename: John D
authors.initials: JD
authors.lastname: Wells
authors.forename: Bruce B
authors.initials: BB
authors.lastname: Johnson
mesh_terms: D015761:4-Aminopyridine / Q000737:chemistry*; D000327:Adsorption; D000631:Aminopyridines / Q000737:chemistry*; D001546:Bentonite / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry; D007616:Kaolin / Q000737:chemistry; D007700:Kinetics; D046911:Macromolecular Substances / Q000737:chemistry; D008956:Models, Chemical; D026902:Potassium Channel Blockers / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties
chemical_list: D000631:Aminopyridines; D005456:Fluorescent Dyes; D046911:Macromolecular Substances; D026902:Potassium Channel Blockers; D001546:Bentonite; D007616:Kaolin; C031283:3-aminopyridine; D015761:4-Aminopyridine; C032439:alpha-aminopyridine