Tham khảo tài liệu 'dendrimers iii episode 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Dendrimer-Encapsulated Metals and Semiconductors Synthesis Characterization and Applications Richard M. Crooks Buford I. Lemon III Li Sun Lee K. Yeung Mingqi Zhao Texas A M University Department of Chemistry . Box 30012 College Station TX 77842-3012 USA E-mail crooks@ 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 Cu2 Pd2 and Pt2 . 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 Cu2 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 .
