Dendrimer stability

D. X. Liu, J. X. Gao, C. J. Murphy, and C. T. Williams, In situ attenuated total reflection infrared spectroscopy of dendrimer-stabilized platinum nanoparticles adsorbed on alumina, J. Phys. Chem. B 108, 12911-12916(2004). 

Efforts to prepare composites of dendrimers and technologically important QDs [188-191] have so far yielded primarily mferdendrimer composites. Such materials have been shown to be agglomerates in which multiple dendrimers stabilize relatively large CdS QDs. Results from these important studies suggested to us that it might be feasible to prepare mfradendrimer QD nanocomposites equivalent to the dendrimer-encapsulated metals described early in this chapter. 

Dendrimer stabilized Au NP (DSNs) Dendrimer encapsulated Au NP (DENs)... 

Thiol-functionalized dendrimers have also been used as surface stabilizers to obtain dendrimer stabilized Au NPs (DSNs) of very small size (1.5-2.1 nm). The study shows that dendrimer molecules are highly flexible and can undergo a conformational change to accumulate thiol terminal groups on one side of the molecule interacting with the nanoparticle surface [124] (Scheme 3.19). 

Other one-phase preparations of bimetallic nanoparticles include NOct4(BHEt3) (Oct = octyl, Et = ethyl) reduction of platinum and ruthenium chlorides to give Pt/Ru(l/1) nanoparticles by Bonnemann et al. [102-104], sono-chemical reduction of gold and palladium ions to provide Au/Pd nanoparticles by Mizukoshi et al. [105,106], and NaBH4 reduction of PtCl - and PdCl - dendrimer complexes to give dendrimer-stabilized Pd/Pt nanoparticles by Crooks et al. [107]. 

Another possibility, taking advantage of the biphasic environment, is to use fluorous organic solvents as the catalyst phase instead of water [155]. Crooks and coworkers prepared dendrimer-stabilized colloid catalysts soluble in the fluorous phase and used the catalysts in hydrogenation [156] and in a Heck reaction [157]. In both cases the colloidal catalyst in the fluorous phase was recyclable and showed some interesting selectivities and products unique to the nanoenvironment in the dendrimer interior. 

Figure 11.11 (a) Scheme for synthesis of dendrimer-stabilized nanoparticles. (Reproduced... 

The other dendrimer stabilizing strategy carried out by Esumi involves coordination of the NPs by surface amino groups of PAMAM and PPI dendrimers [19c-e], and these catalysts were used for various catalytic reactions including the reduction of 4-nitrophenol. In this case, one may visualize PdNPs surrounded by a number... 

PtNPs and bimetallic dendrimer-stabilized Pd-AuNPs were adsorbed onto a high-surface silica support and thermally activated to remove the dendrimers... 

Employing the same dendrimer-stabilized palladium colloids for Heck reactions in supercritical carbon dioxide, after 24 h reaction time and 55% conversion no further reaction was observed for reasons not clarified. Remarkably, methyl 2-phenylacrylate was formed exclusively instead of the expected methyl cinnamate (Scheme 1) [37]. 

Pittelkow, M., Moth-Poulsen, K.,et al. Poly(amidoamine)-Dendrimer-Stabilized Pd(0) Nanoparticles as a Catalyst for the Suzuki Reaction. Langmuir,l 9(18), 7682-7684 (2003). 

PAMAM dendrimers can also be used as templating agents and nanoparticle stabilizers for the synthesis of bimetallic particles. The unique ability of dendrimers to host various metal precursors enables the simultaneous complexation of multiple metallic species at its various internal functional groups. The three primary methods of bimetallic nanoparticle synthesis through dendrimer stabilization are partial displacement, co-complexation, and sequential complexation. 

D.S. Deutsch, A. Siani, C.T. Williams, and M.D. Amiridis, Synthesis and Characterization of Dendrimer-Stabilized Rhodium Nanoparticles on a Zirconia Support, manuscript in preparatioTL... 

Liu H, et al. Tunable synthesis and acetylation of dendrimer-entrapped or dendrimer-stabilized gold-silver alloy nanoparticles. Colloids Surf B 2012 94 58-67. 

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