Hybrid dendrimers

Tomalia et al. reported that the surface amines of PAM AM dendrimer can successfully react with methyl esters of other PAMAM dendrimers to afford core-shell tecto-(dendrimer) molecules [65]. Furthermore, they also reported the synthesis of rod-shaped cylindrical dendronized polymers from poly(ethyleneimine) cores without any crosslinking, albeit with the use of excess reagents [58]. These reports lead us to propose a new approach toward hybridized dendrimers and polymers (path C, Figure 15.3). As shown in Scheme 12,... 

Dendritic hybrid architectures of the two dendrimer types - POPAM and PAMAM - designated by Majoros et al. as POMAM dendrimerf [17] are structural rarities. One such dendrimer of this type was assembled with PAMAM branching units starting from a POPAM core unit [18]. Vogtle et al. developed POPAM/PAMAM hybrid dendrimers up to the third generation (Fig. 4.8) [19]. 

J. R. Baker Jr., Synthesis and Characterisation of Novel POPAM-PAMAM (POMAM) Hybrid Dendrimers as a Building Block in Nanotechnology. http //www.forsight.org/conferences/... 

Following up this work, the same group recently published the synthesis of hybrid dendritic ligands containing a combination of dendritic chiral DPEN and Frechet polyether dendrons (Scheme 7) [50]. The solubility of these hybrid dendrimers was found to be controlled by the polyether den-dron. Compared with the simple core-functionalized systems displayed in Fig. 21, the hybrid dendrimers showed similar catalytic activity but reduced recyclability. 

Figure 11.18 Structures of isocyanates AP3-EP3 and synthesis of the solution-phase hybrid dendrimers 11.15-11.17.

In order to facilitate recycling of the multiple TsDPEN-functionalized dendrimer catalysts, the same group recently reported the synthesis of a novel form of hybrid dendrimer ligands by coupling polyether dendrons with peripherally TsDPEN-functionahzed Newkome-type poly(ether-amide) dendrimer (Figure 4.28) [90]. The solubility of these hybrid dendrimers was found to be affected by the generation of the polyether dendron. The ruthenium complexes produced were applied in the asymmetric transfer hydrogenation of ketones, enones, imines and activated... 

Figure 4.28 Chiral hybrid dendrimers bearing TsDPENs located at the periphery.

P. R. L. Malenfant, L. Groenendaal and J. M. J. Fr6chet, Well-defined triblock hybrid dendrimers based on lengthy oligothiophene cores and poly(benzyl ether) dendrons, J. Am. Chem. Soc., 120, 10990-10991 (1998). 

Percec V, Rudick JG, Peterca M, Yurchenko ME, Smidrkal J, Heiney PA (2008) Supramo-lecular structural diversity among first-generation hybrid dendrimers and twin dendrons. ChemEur J 14(ll) 3355-3362. doi 10.1002/chem.200701658... 

Roovers,J., Comanita, B. Dendrimers and Dendrimer-Polymer Hybrids. Vol. 142 pp 179-228,... 

Towards understanding biological electron transfer processes many researchers have reported the synthesis of dendrimers with electroactive cores (e.g., porphyrin). Dendrimers with organic dendrons attached tetrahedrally around an inorganic, electroactive iron-sulfur core were reported by Gorman and coworkers [109]. These are the first examples of dendrimers with a hybrid... 

The latter is an interesting example of self-organizing chiral dendrimers. The construction of the dendrimer is based on the natural property of nucleic acids to recognize and specifically bind to complementary sequences. Pairwise hybridization of two designed DNA strands results in the formation of large monomers which have four single stranded arms and a double stranded waist (24, Fig. 12). 

The surface of each layer has two types of single stranded arms (e.g. one 3 — 5 and one 5 — 3 strand) which can bind to other monomers to render 1st-and 2nd-generation dendrimers 25 and 26. Therefore the molecular scaffold grows exponentially with each sequential layer of hybridization. If an oligonucleotide contains a sequence complementary to those at the surface of these networks it should be hybridized. The remaining free sequences from the other type of arms then bind in a standard nucleic acid blot (after they are bound to... 

Most of the supports so far studied are conventional in the field of catalysis. Some new kinds of support have emerged including mesostructured materials,193 dendrimers, organic-inorganic hybrids, and natural polymers such as polysaccharides or polyaminoacids. Nevertheless, at the moment, supported catalysts still suffer from relatively poor stability when compared to classical heterogeneous catalysts, and from limited activity when compared to homogeneous catalysts. The driving force for this research is thus to make up some of these deficits. 

H. Sashiwa, Y. Shigemasa, and R. Roy, Chemical modification of chitosan. 3. Hyperbranched chitosan-sialic acid dendrimer hybrid with tetraethylene glycol spacer, Macromolecules, 33 (2000) 6913-6915. 

A similar type of biotin-dendritic multimer also was used to boost sensitivity in DNA microarray detection by 100-fold over that obtainable using traditional avidin-biotin reagent systems (Stears, 2000 Striebel et al., 2004). With this system, a polyvalent biotin dendrimer is able to bind many labeled avidin or streptavidin molecules, which may carry enzymes or fluorescent probes for assay detection. In addition, if the biotinylated dendrimer and the streptavidin detection agent is added at the same time, then at the site of a captured analyte, the biotin-dendrimer conjugates can form huge multi-dendrimer complexes wherein avidin or streptavidin detection reagents bridge between more than one dendrimer. Thus, the use of multivalent biotin-dendrimers can become universal enhancers of DNA hybridization assays or immunoassay procedures. 

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