Dendrimer-Encapsulated Metals and Semiconductors: Synthesis, Characterization, and Applications

Abstract

This chapter describes composite materials composed of dendrimers and metals or semiconductors. Three types of dendrimer/metal-ion composites are discussed: dendrimers containing structural metal ions, nonstructural exterior metal ions, and nonstructural interior metal ions. Nonstructural interior metal ions can be reduced to yield dendrimer-encapsulated metal and semiconductor nanoparticles. These materials are the principal focus of this chapter. Poly(amidoamine) (PAMAM) and poly(propylene imine) dendrimers, which are the two commercially available families of dendrimers, are in many cases monodisperse in size. Accordingly, they have a generation-dependent number of interior tertiary amines. These are able to complex a range of metal ions including Cu 2+ , Pd 2+ , and Pt 2+ . The maximum number of metal ions that can be sorbed within the dendrimer interior depends on the metal ion, the dendrimer type, and the dendrimer generation. For example, a generation six PAMAM dendrimer can contain up to 64 Cu 2+ ions. Nonstructural interior ions can be chemically reduced to yield dendrimer-encapsulated metal nanoparticles. Because each dendrimer contains a specific number of ions, the resulting metal nanoparticles are in many cases of nearly monodisperse size. Nanoparticles within dendrimers are stabilized by the dendrimer framework; that is, the dendrimer first acts as a molecular template to prepare the metal nanoparticles and then as a stabilizer to prevent agglomeration. These composites are useful for a range of catalytic applications including hydrogenations and Heck chemistry. The unique properties of the interior dendrimer microenvironment can result in formation of products not observed in the absence of the dendrimer. Moreover the exterior dendrimer branches act as a selective gate that controls access to the interior nanoparticle, which results in selective catalysis. In addition to single-metal nanoparticles, it is also possible to prepare bimetallic nanoclusters and dendrimer-encapsulated semiconductor nanoparticles, such as CdS, using this same general approach.

Numerical simulations of in vitro nanoparticle toxicity – The case of poly(amido amine) dendrimers

“…14 with those measured by size exclusion chromatography. 51 The values of hydro-dynamic diameter measured by Dynamic Light Scattering in PBS are somewhat larger, as may be expected, but the values still scale systematically with generation and although a slight increase in cell culture medium due to interaction with the medium may be inferred, no significant aggregation/agglomeration of the particles is evident over the dose ranges measured. 16 Thus, a dependence of the rate of endocytosis on N amg 0.25 may represent a dependence on the dendrimer diameter, which varies only slightly with generation number (G4 diameter: 4.5nm, G5 diameter:…”

Dendrimer-Encapsulated Metal Nanoparticles: Synthesis, Characterization, and Applications to Catalysis

“…Spectrophotometric titrations of these materials are consistent with the data for G4-OH, but there is a more complex, pH-dependent equilibrium (a consequence of the terminal primary amines) that is beyond the scope of this discussion. 30 Intradendrimer Complexes between PAMAM Dendrimers and Metal Ions Other than Cu 2+ . In addition to Cu 2+ , many other transition-metal ions, including Pd 2+ , Pt 2+ , Ni 2+ , Fe 3+ , Mn 2+ , Au 3+ , and Ru 3+ , can be extracted into dendrimer interiors.…”

“…29 One final point: both PAMAM and PPI dendrimers contain a statistical distribution of defects, mainly in the form of missing branches and loops. 2,30 Within the resolution of…”

Investigation of silver binding to polyamidoamine (PAMAM) dendrimers by ESI tandem mass spectrometry

“…In addition to numerous applications in fields such as medicine, chemistry, materials science, biology, and physics, there is interest in the use of dendrimers as templates for metal nanoparticle synthesis [3,4]. The ability to synthesize metal nanoparticles with well-defined core sizes has important implications for the study of the sizedependent photochemical, electrochemical, and optical behavior of metal clusters.Polyamidoamine (PAMAM) dendrimers [5,6] (Figure 1 [7][8][9][10][11][12]. Upon chemical reduction of the metal ion/ dendrimer complexes, the PAMAM polymer matrix encapsulates and subsequently stabilizes the metal clusters, thus preventing agglomeration [12].…”