PAMAM dendrimers reductive amination

Hong et al. (2004) also found that modification of PAMAM dendrimers with a short PEG linker arm could act to reduce nonspecificity caused by the amines on the dendrimer-modified surface. An azido-PEGj-aininc spacer was activated with nitrophenyl carbamate to yield an activated intermediate that could be used to modify the amines on the dendrimer (Figure 7.24). Reaction at high molar ratio resulted in about 61 PEG-azido spacers on the dendrimer. Reduction of the azido group to an amine using triphenylphosphine in THF provided the dendrimer-PEG-amine derivative for surface modification. The added presence of the PEG spacer arm reduced... 

Using an approach similar to that discussed previously, Pd nanoparticles were prepared within amine-terminated PAMAM dendrimers. To prevent coordination of Pd + to the primary amine groups of the dendrimers, the solution pH was adjusted to around 2, which preferentially protonates the exterior amines to a greater extent than the interior tertiary amines. Accordingly, Pd + binds preferentially to the interior tertiary amines and upon reduction Pd particles form only within the dendrimer interior. G4-NH2 dendrimer-encapsulated nanoparticles can then be quantitatively transported from an aqueous phase into toluene by addition of 10-20% of dodecanoic acid to the organic phase (Fig. 21) [19]. This transition is readily visualized by the color change the brown aqueous solution of Pd nanoparticles becomes clear after addition of the acid, while the toluene layer turns brown. Our studies have shown that this is a consequence of... 

More recently. Oh and coworkers" developed PAMAM dendrimers with both primary amines and quaternary ammonium groups at the dendrimer periphery, in an attempt to facilitate templating of Au precursors within the dendrimer. Upon reduction by NaBH4, gold nanoparticles on the order of 1 to 2 nm were formed for DMNs containing between 55 and 300 Au atoms. Utilizing this polycationic dendrimer precursor results in the formation of gold particles with smaller and more controlled particle diameters than those previously reported. - Just as in the case of Pt, however, more work needs to be performed to elucidate the mechanism of Au nanoparticle formation. 

Advincula et al. decorated conventional dendrimers with conjugated dendrons at the periphery [499]. Formylated terthiophene dendron 5.54, which was prepared by Vilsmeyer-Haack formylation of dendron 5.73a (see below), was linked to the periphery of a 64-amine terminated G4-PAMAM dendrimer by reductive amination. The incorporation of Pd or Au nanoparticles in the dendrimer created new hybrid nanomaterials 5.55 (Scheme 1.67). As a consequence of the dendritic architecture, the emission properties... 

The protein analog poly(amidoamine) dendrimer of fourth generation (PAMAM G4) was labeled with ferrocene units by reductive amination with compound 4. 

Fig. 1.7 Strategy pioneered by Crooks for the catalysis by NPs encapsulated in PAMAM or PPI dendrimers complexation of the inner nitrogen atoms of tertiary amines by a metal cation, then reduction to metal(O) by NaBH4 leading to the formation of NPs inside the dendrimer, followed by the catalyzed reaction. The use of PIP dendrimers requires control of the pH before metal ion complexation in order to selectively protonate the terminal...

Polyamidoamine (PAMAM) systems are perhaps the most studied in the area of electrochemistry in the presence of dendrimers. The uptake of by coordination to amine sites followed by reduction to Cu yielded clusters that have potential use for catalysis [38]. The stabiUty of the small clusters suggested that they reside in the cavities of these starburst molecules. Because PAMAM is a nonspecific ligand, the use of this method of preparing clusters is applicable to a wide range of metals. Moreover, the geometry of dendrimers and the variation of size that is available by controlling the generation number allow the prediction that they can be immobilized by a variety of methods at electrode surfaces. 

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