PAMAM second generation

According to cascadane nomenclature, the second-generation PAMAM dendri-mer shown in Fig. 1.25 has the name ... 

In the present context, solid-phase synthesis has been used primarily for the preparation of peptide and glycopeptide dendrimers [23]. For example, a second-generation dendrimer could be prepared by successive addition of branched polyproline building blocks to a solid phase [24]. The divergent synthesis of polyamide dendrimers on polystyrenes was accomplished [25] by Frechet el al. 1991 (cf. Fig. 2.8) [26]. PAMAM dendrons could be grown up to the fourth-... 

Less has so far been published about carbohydrate core units [54] than about dendrimers with carbohydrate terminal groups. The first PAMAM dendrimer with a carbohydrate core unit was prepared from the a-D-glycoside 1 as core unit precursor. Up to second-generation PAMAM dendrimers with a D-glucose core could be prepared by iteration Fig. 4.30 shows the first generation [55]. 

Note that this behavior is in marked contrast to that of the zeroth to the second generation of related PAMAM and PPI dendrimers (Nc = 3, Mb = 2) with 4 -cyanobiphenyl hydrogen glutarate that did not produce any mesomorphic behavior, except a lyotropic nematic phase in 80 wt % N,N -dimethylformamide (DMF) solutions containing lithium bromide [204,205]. 

Later, Bai and coworkers used both, dendrons built from chiral monomers and achiral dendritic backbone decorated with chiral selectors, to prepare CSPs. First, they tested the polyamido dendrons prepared from benzenetricarbonyl trichloride and enantiopure stilbene diamine capped with phenylurea function (see Section 15.2.2.4 and Scheme 15.10). " The separation ability decreased with the generation, possibly as a result of imperfect dendron architecture. Subsequently, the authors decorated silica-bound PAMAM with chiral selectors A-tosyl-L-phenylalanine and a chiral unit derived from 2-amino-1,2-diphenylethanol (Scheme 15.48). CSPs derived from third- and second-generation dendrons showed the highest separating ability. The second selector was inferior to the first, in spite of possessing an additional chiral center. 

Jacobsen et al. reported enhanced catalytic activity by cooperative effects in the asymmetric ring opening (ARO) of epoxides.[38] Chiral Co-salen complexes (Figure 4.27) were used, which were bound to different generations of commercial PAMAM dendrimers. As a direct consequence of the second-order kinetic dependence on the [Co(salen)] complex concentration of the hydrolytic kinetic resolution (HKR), reduction of the catalyst loading using monomeric catalyst leads to a sharp decrease in overall reaction rate. 

In fact, it has been previously observed that measured diameters of dendrimer molecules by AFM are much larger than the theoretical values, which indicates that the dendrimers spread out and flatten on the surface [25, 26], Three major factors could account for this deformation. First, the unique architecture and chemical structure of PAMAM dendrimers result in macromolecules that are not solid balls, but instead are relatively open and hence soft materials. It is expected that the rigidity will increase substantially with increasing generation number [9]. Therefore, when deposited on solid substrates, they tend to deform to different degrees as a result of the interplay between their inherent rigidity and surface energetics from the interaction between the dendrimer molecules and the mica surface. Secondly, amine-terminated PAMAM dendrimers possess a... 

These palladium-functionalized dendrimers show selectivity for the linear reaction product. A drop in activity was found when the catalysts were reused (1-decene as substrate/G(4)Pd(PPh3)2 dendrimer as catalyst 92, 75, 73, and 45% yield for the first, second, third, and fourth, respectively). The (dba)Pd-PPh2-PAMAM-Si02 dendrimers of generations 0—4 showed activity for the oxidation of terminal alkenes under mild conditions. The catalytic activity was found to be dependent on... 

Figure 7.6. L Reaction scheme of the syntheses of the first 313a. second 313b and third 313c generations of the PAMAM dendrimer.

Table 4.2 I ncrease of PAMAM parameters with the number of generations (dendrimer type, see Fig. 4.6) [3]. The second column lists the number of terminal groups of 1 ->3-branched aliphatic Newkome type dendrimers (see Figs. 1-5 and 4.60 for typical formulae)...

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." " ... 

The first dendrimeric structures peripherally functionalized with a polyhedral borane were reported by Barth et al. in 1994. For that purpose, zero, first, second, and third generation of amino-terminated PAMAM startbust dendrimers were boronated by their reaction with Na(CH3)3NB,oH8NCO. After that, the boronated dendrimers reacted with the monoclonal antibody MoAb IB16-6, previously derivatized with A-succinimidyl 3-(2-pyridyldithio)propionate, to obtain stable immunoconjugates. 

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