PAMAM generation

Zhao et al (70) developed a method for the synthesis of dendrimer-encapsulated metal nanoparticles based on sorbing metal ions into (modified) PAMAM dendrimers followed by a reduction. Dendrimers encapsulating copper, palladium, and platinum nanoparticles have been prepared. Hydroxyl-terminated PAMAM dendrimers were used to prepare encapsulated palladium (PAMAM generations 4, 6, and 8) and platinum (PAMAM generations 4 and 6) nanoparticles. The dendrimer-encapsulated palladium and platinum nanocomposites catalyzed the hydrogenation reaction of allyl alcohol and N-isopropyl acrylamide in water 71). 

Fig. 33. Electrospray ionization mass spectrum of a Starburst PAMAM (generation = 4). Note the last significant peak M = 10632 daltons (degree of polymerization = 93), corresponding to the magic number for ideal structure. The remaining labeled species correspond to M — x(l 14) (defects due to missing monomer units) and the unlabeled species which correspond to M — x(60) (defects due to macrocycle formation)...

Four water-soluble dendritic phosphonated ligands were first synthesized based on poly(amidoamine) (PAMAM) (generation 3 with 32 cascade end groups), with the hydrophilic amine or sulfonic acid groups on the surface of the dendrimer. Their Rh(I) complexes were used as the catalysts in the two-phase hydroformylation of styrene and 1-octene. The results showed that these new water-soluble dendritic catalysts exhibited high catalytic activity [64]. 

Si02-PAMAM-PPh2, [Rh(CO)2Cl]2, CH2CI2, PAMAM generation conversioi(%) ... 

Fig. 3.7-7 Characteristic examples of dendrimers (a) Poly(amidoamine) dendrimer of D.A. Tomalia (PAMAM, generation 2).

PAMAM itself was used as a multivalent macromolecular ligand, probably due to its multiple amino groups, in order to complex and immobilize metal ions, complexes, and nanoparticles with catalytic capabilities. Thus, Kawi and coworkers used PAMAM-on-silica and PAMAM-on-alumina templates to immobilize Rh(l) complexes as hydroformy-lation catalysts. Passivation of the silica OH sites outside the pores of SBA-15 silica resulted in a tighter binding of rhodium complexes inside the pores and led to a series of catalysts that displayed a positive dendritic effect up to the second PAMAM generation." Sreekumar and Krishnan used PAMAM on polystyrene to complex Mn(ll) precursors and catalyze the oxidation of secondary alcohols." " ... 

PAMAM dendrimers are synthesized in a multistep process. Starting from a multifunctional amine (for example ammonia, ethylenediamine, or tris(2-amino-ethyl)amine) repeated Michael addition of methylacrylate and reaction of the product with ethylenediamine leads to dendrimers of different generation numbers [1,9]. Two methylacrylate monomers are added to each bifunctional ethylenediamine generating a branch at each cycle. Unreacted ethylenediamine has to be completely removed at each step to prevent the initiation of additional dendrimers of lower generation number. Excess methylacrylate has also to be removed. Bridging between two branches of the same or of two different dendrimers by ethylenediamine can also be a problem, and has to be avoided by choosing appropriate reaction conditions. 

Fig. 4. Early generation PAMAM dendrimers with amine and ester/acid termini...

Host-guest systems made from dendritic materials have potential in the areas of membrane transport and drug delivery [68, 84, 85]. In a recent report [136] Tomalia and coworkers investigated structural aspects of a series of PAM AM bolaamphiphiles (e.g., 50) with a hydrophobic diamino do decane core unit. Fluorescence emission of added dye (nile red) was significantly enhanced in an aqueous medium in the presence of 50 unlike the cases when 51 and 52 were added (Fig. 23). Addition of anion surfactants to this mixture generated supramolecular assemblies which enhanced their ability (ca.by 10-fold) to accommodate nile red (53). Further increase in emission was noted by decreasing the pH from the normal value of 11 for PAMAM dendrimers to 7. At lower pH values the... 

Okada et al. were the first to synthesize so-called sugar-balls [42]. They functionalized commercially available 3rd- and 4th-generation PAMAM-den-... 

Recently, the Okada group described a new class of polymerization systems [43] oligoglycopeptide-type sugar-balls were obtained by a radial growth polymerization (RGP) of a-amino acid AT-carboxyanhydrides with PAMAM dendrimers of different generations. 

Fig. 9. 3rd-Generation PAMAM-dendrimer functionalized with disaccharide end groups [42]... 

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