Dendritic Nanoscale Chelating Agents: Synthesis, Characterization, Molecular Modeling and Environmental Applications
|URL:|| http://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/dis... |
|Description:||Dendrimers are monodisperse and highly branched nanostructures with controlled composition and architecture. Poly(amidoamine) (PAMAM) dendrimers possess functional nitrogen and amide groups arranged in regular "branched upon branched" patterns. This high density of nitrogen ligands enclosed within a nanoscale container makes PAMAM dendrimers particularly attractive as high capacity chelating agents for toxic metal ions [Cu(II)], electron transfer mediators [Fe(II)], redox active metal clusters [FeS] and metal clusters with catalytic properties [Pt (II)]. PAMAM dendrimers can also be functionalized with surface groups that make them soluble in appropriate media or bind onto appropriate surfaces. This project explores the fundamental science of metal ion uptake by PAMAM dendrimers in aqueous solutions and assesses the extent to which this fundamental knowledge can be used to develop: 1. high capacity and reusable chelating agents for industrial and environmental separations; and 2. FeS laden nanoparticles with enhanced reactivity, selectivity and longevity for reductive detoxification of PCE in aqueous solutions and subsurface formations.|
- 2002 Progress Report: Dendritic Nanoscale Chelating Agents: Synthesis, Characterization, Molecular Modeling and Environmental Applications
During Year 1 of the project, we focused on the evaluation of PAMAM dendrimers with ethylene diamine (EDA) cores as high capacity and reusable chelating agents for use in environmental and industrial separation processes. To achieve this objective, we structured our research efforts around five tasks: (1) dendrimer synthesis and characterization; (2) measurements of dendrimer protonation in aqueous solutions; (3) measurements of metal ion uptake in aqueous solutions of dendrimers; (4) evaluation of a dendrimer enhanced ultrafiltration (DEUF) system for recovery of toxic metal ions from contaminated water; and (5) molecular dynamics (MD) simulations of proton and metal ion binding to dendrimers in aqueous solutions. The overall results of our experiments and MD simulations illustrate a key feature of dendritic nanoscale chelating agents: i.e., the covalent attachment of nitrogen ligands to conformationally flexible PAMAM chains enclosed within a nanoscale structure results in a substantial increase in binding capacity for metal ions with affinity toward N donors such as Cu[II]. Compared to traditional chelating agents and macrocycles with N donors, which typically bind one Cu(II) ion per molecule, G3, G4 and G5 EDA core PAMAM dendrimers with terminal NH2 groups can bind up to 115, 166, and 292 Cu(II) ions per mole of dendrimer at pH = 9.0, respectively. We also found that dendrimers can effectively be used in membrane-based ultrafiltration (UF) systems to achieve maximum metal ion retention without a significant loss in permeate flux. U.S. Environmental Protection Agency funding is being leveraged to develop and optimize the operation of a continuous bench scale DEUF systemwith a dendrimer recycling unit, for recovering metal ions (e.g., Cu[II], Zn[II] and Ni[II]) from industrial wastewater.
- 2003 Progress Report: Dendritic Nanoscale Chelating Agents: Synthesis, Characterization, Molecular Modeling and Environmental Applications
During Year 2 of the project, we continued our measurements of metal ion binding [Co(II), Ni(II), Ag(I), and Fe(III)] to ethylene diamine core PAMAM dendrimers at Howard University (HU). The Principal Investigator (PI) of this project (Mamadou Diallo) and his group at HU also leveraged U.S. Environmental Protection Agency (EPA) funding to develop Dendrimer Enhanced Ultrafiltration (DEUF) for recovering metal ions from aqueous solutions. DEUF is a patented process that exploits the unique properties of dendritic polymers (e.g., dendrimers, dendrigraft polymers, and hyperbranched polymers) as high capacity and recyclable chelating agents. Co-PI Lajos Balogh and his group at the University of Michigan focused on the synthesis and characterization of FeS dendrimer nanocomposites in solutions, thin films, and mesoporous silica gels. The FeS nanoparticles were prepared using generation four PAMAM dendrimers with amine, hydroxyl, and succinamic acid terminal groups as templates. The ability of the FeS dendrimer nanocomposites (25 ppm of FeS) to reduce PCE (5 ppm) in aqueous solutions was evaluated at HU using gas chromatography with electron capture and flame ionization detectors. We found significant reduction of PCE (40-50% after 3 hours) with no production of tricholoroethylene in all cases.
- Final Report: Dendritic Nanoscale Chelating Agents: Synthesis, Characterization, Molecular Modeling and Environmental Applications
Metal ion complexation is an acid-base reaction that depends on several parameters--including metal ion size, acidity, ligand basicity, and molecular architecture--and solution physical-chemical conditions. Three milestones in coordination chemistry were the discoveries of the Hard and Soft Acids and Bases (HSAB) principle, the chelate effect, and the macrocyclic effect. The invention of dendrimers is another milestone in coordination chemistry. Dendrimers are highly branched nanostructures with controlled composition and architecture. Poly(amido)amine (PAMAM) dendrimers possess functional nitrogen and amide groups arranged in regular "branched upon branched" patterns. This high density of nitrogen ligands enclosed within a nanoscale container makes PAMAM dendrimers particularly attractive as high capacity chelating agents for metal ions. The objectives of this research project were to explore the fundamental science of metal ion uptake by PAMAM dendrimers in aqueous solutions and assess the extent to which this fundamental knowledge could be used to develop high capacity and reusable chelating agents for industrial and environmental separations and to develop FeS-laden nanoparticles with enhanced reactivity, selectivity, and longevity for reductive and detoxification of tetrachloroethylene (PCE) in aqueous solutions.
Below is a list of organizations with individual contacts that are funding this project.
Organizations Receiving Funding
Below is a list of organizations with individual contacts that are receiving funding for this project.
Howard University School of Architecture and Design - Partner
2300 6th Street, NW
Washington, District of Columbia 20059