Synthesis and characterization of polymer-supported cyclodextrin nanoscaffolds for use in future environmental studies

Abstract

The toxicity of transitional and post-transitional metals in natural water systems is well known. Coordination of these metals by selected ligands is a common means of environmental remediation. Macrocyclic coordination complexes impart thermodynamic and kinetic stability beyond their corresponding chelation analogues due to the pre-organized physical constraints of the coordinating ligands. Cyclodextrins are biologically produced and well-studied cyclic glucose macrocycles that possess chemically distinct hydroxyls. Amphiphilic cyclodextrins used as polymer-supported macrocyclic nanoscaffolds that are capable of scavenging trace metal pollutants could offer exciting new avenues of remediation research. Amphiphilic sodium hexakis (2,3-O-dibenzyl-6-O-sulfobutyl) cyclomaltohexaose (DBSBA) and sodium heptakis (2,3-O-dibenzyl-6-O-sulfobutyl) cyclomaltoheptaose (DBSBB) were synthesized in four steps. Aggregation colloids that possess an aromatic pseudophase in an aqueous system could provide new avenues of research for emulsion polymerization studies. The strong [pi]-[pi] interactions between the benzyls on the secondary rim and the polystyrene should anchor cyclodextrin nanoscaffolds to the nanoparticle surface. The aggregation of DBSBA and DBSBB was investigated using diffusion ordered NMR spectroscopy (DOSY), conductivity, and pyrene fluorescence techniques. These amphiphiles were found to possess near spherical symmetry at critical micelle concentrations of approximately 0.1 mM in all techniques used to study the phenomenon. These surfactants contain a high percentage of aromatic moieties in their structures, which affected the thermodynamics of aggregation by decreasing the CMC with increased temperature. Highly charged monodisperse polystyrene latex nanoparticles were produced using DBSBB as a surfactant in emulsion polymerization. The choice of surfactant was selected to examine its effect on polystyrene latex surface properties; amphiphilically modified cyclodextrins have not been used in emulsion polymerization recipes to date. Surface charge densities, up to 27 μS/cm², scaled with increasing amounts of added surfactant with a concomitant decrease in particle size. The addition of increasing amounts of DBSBB into emulsion polymerization recipes resulted in larger percentage coverage of latex particles. ¹H NMR studies found that the primary sulfobutyl substituents possessed fast molecular motions and therefore projected into solution and away from the latex surface. The strong physical adsorption of DBSBB and the presence of solvated primary rim substituents suggests that cyclodextrins can be used as future nanoscaffolds for the alteration of latex surface properties through non-covalent surface modification.