Poly(amidoamine) Dendrimers: A New Class of High Capacity Chelating Agents for Cu(II) Ions

Abstract

This communication describes preliminary results of an experimental investigation of the binding of Cu(II) ions to poly(amidoamine) (PAMAM) dendrimers in aqueous solutions. Dendrimers are highly branched polymers with controlled composition and architecture consisting of three structural components:  a core, interior branch cells, and terminal branch cells. PAMAM dendrimers possess functional nitrogen and amide groups arranged in regular “branched upon branched” patterns which are displayed in geometrically progressive numbers as a function of generation level. Terminal groups of PAMAM dendrimers may be any organic substituent such as primary amines, carboxylic groups, etc. In aqueous solutions, PAMAM dendrimers can serve as high capacity nanoscale containers for toxic metal ions such as Cu(II). Compared to traditional chelating agents (e.g., triethylene tetramine) and macrocyles (e.g., cyclams) with nitrogen donors, which can typically bind only one Cu(II) ion per molecule, a generation eight (G8) PAMAM dendrimer can bind up 153 ± 20 Cu(II) ions per molecule. This clearly illustrates a distinct advantage of dendrimers over traditional chelating agents and macrocycles; that is the covalent attachment of nitrogen ligands to conformationally flexible PAMAM chains enclosed within a nanoscopic structure results in a substantial increase in binding capacity