Dendrimers encapsulation

Cornils B (1999) Modern Solvent Systems in Industrial Homogeneous Catalysis.206 133-152 Crooks RM, Lemon III BI, Yeung LK, Zhao M (2001) Dendrimer-Encapsulated Metals and Semiconductors Synthesis, Characterization, and Applications. 212 81 -135 Croteau R, see Davis EM (2000) 209 53 - 95 CurranDP, see Maul JJ (1999) 206 79-105... 

Activation of Dendrimer Encapsulated Pt Nanoparticles for Heterogeneous Catalysts... 

Dendrimer encapsulated Pt nanoparticles (DENs) were prepared via literature methods (1, 11). PtCl42 and dendrimer solutions (20 1 Pt2+ dendrimer molar ratio) were mixed and stirred under N2 at room temperature for 3 days. After reduction with 30 equivalents of BH4 overnight, dialysis of the resulted light brown solution (2 days) yielded Pt2o nanoparticle stock solution. The stock solution was filtered through a fine frit and Pt concentration was determined with Atomic Absorption Spectroscopy (11). Details on catalyst characterization and activity measurements have been published previously (11). 

Zheng, J., and Dickson, R.M. (2002) Individual water-soluble dendrimer-encapsulated silver nanodot fluorescence./. Am. Chem. Soc. 124, 13982-13983. 

Dendrimer interior functional groups and cavities can retain guest molecules selectively, depending on the nature of the guest and the dendritic endoreceptors, the cavity size, the structure, and the chemical composition of the peripheric groups. Two main methods are known for the synthesis of metal nanoparticles inside dendrimers. The first method consists of the direct reduction of dendrimer-encapsulated metal ions (Scheme 9.4) the second method corresponds to the displacement of less-noble metal clusters with more noble elements [54]. 

The team of Crooks is involved in the synthesis and the use of dendrimers and, more particularly, poly(amidoamine) dendrimers (PAMAM), for the preparation of dendrimer-encapsulated mono- or bimetallic nanoparticles of various metals (Pt, Pd, Cu, Au, Ag, Ni, etc.) [55, 56]. The dendrimers were used as nanocatalysts for the hydrogenation of allyl alcohol and N-isopropylacrylamide or other alkenes under different reaction conditions (water, organic solvents, biphasic fluorous/or-ganic solvents or supercritical COz). The hydrogenation reaction rate is dependent on dendrimer generation, as higher-generation dendrimers are more sterically... 

Table 9.3 Hydrogenation of alkenes using dendrimer-encapsulated Pd nanoparticles.a) (Reprinted with permission of the American Chemical Society [59])...

Rhee and coworkers published the synthesis of bimetallic Pt-Pd nanoparticles [57] or Pd-Rh nanoparticles [58] within dendrimers as nanoreactors. These nanocatalysts showed a promising catalytic activity in the partial hydrogenation of 1,3-cyclooctadiene. The reaction was carried out in an ethanol/water mixture at 20 °C under dihydrogen at atmospheric pressure. The dendrimer-encapsulated nanoclusters could be reused, without significant loss of activity. 

Crooks, M. et al., Dendrimer-encapsulated metal nanoparticles synthesis, characterization, and applications to catalysis, Acc. Chem. Res., 34, 181, 2001. 

Figure 21.1 A-Structure of the host PAPAM dendrimer. B-Fabrication procedure for metal-dendrimer nanocomposites. C- Pd and Pt dendrimer encapsulated nanoparticles prepared by displacement reactions [66]. D, E -External and internal dendrimer nanocomposite topologies, respectively [70,77],...

The emission of the metal particles may thus originate from a band-to-band transition in the metal particle, which occurs at about 516 nm for gold [60, 119]. As stated above, the nature of the interaction of the dendrimer (PAMAM) host is still uncertain, there could be very strong electrostatic interactions that may play a part in the enhancement of the metal particles quantum efficiency for emission. However, one would expect that this enhancement would result in slightly distorted emission spectra, different from what was observed for the gold dendrimer nanocomposite. Further work is necessary to completely characterize the manner in which the dendrimer encapsulation enhances the emission of the metal nanoparticles. With further synthetic work in preparation of different size nanoparticles (in other words elongated and nonspherical shape particles, including nanorods) it may be possible to develop the accurate description of a... 

Crooks RM, Lemon III BI, Yeung LK, Zhao M (2001) Dendrimer-Encapsulated Metals and Semiconductors Synthesis, Characterization, and Applications. 212 81-135... 

The possibility of using electrostatic charge attraction has been exploited in the preparation of gold dendrimer encapsulated nanoparticles (DENs), which under appropriate conditions can be fully distributed along the surface of monodispersed MWCNTs (Fig. 3.21) [103]. 

Y. M. Chung and H. K. Rhee, Partial hydrogenation of 1,3-cyclooctadiene using dendrimer-encapsulated Pd-Rh bimetallic nanoparticles, J. Mol. Catal. A—Chem. 206, 291-298 (2003). 

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