Dendrimers higher-order structures

Suehiro, T., Kojima, C., Tsumura, S., Harada, A., and Kono, K. 2010. Higher order structure of short collagen model peptides attached to dendrimers and linear polymers. Biopolymers 93(7), 640-648. 

To investigate this dendritic effect, a dimeric model compound was synthesized which mimics the tethered relationship of two catalytic units within one branch of the PAMAM dendrimer. All dendritic catalysts were more active in the HKR than the parent complex. Furthermore, the dendritic catalysts also displayed significantly higher activity than the dimeric model compound. The authors proposed that this positive dendritic effect arises from restricted conformation imposed by the dendrimer structure, thereby creating a bigger effective molarity of [Co(salen)] units. Alternatively, the multimeric nature of the dendrimer, may lead to higher order in productive cooperative interactions between the catalytic units. 

Figure 11.9 Kratky plots of G1 PS dendrigraft, G3 PS dendrigraft, G4 PAMAM dendrimer and G10 PAMAM dendrimer. Flat high q shows star-like structure, higher order features shows sphere-like structure...

Another important issue is the difference between various branching types such as random hyperbranched [31], dendrigrafts and dendrimers. The complexity of synthesis requirements manifested by the statistical dendritic polymers versus the more structurally controlled dendrimers could make the former orders of magnitude more expensive than hyperbranched. Are the structures as significantly unique and of sufficient value effectiveness to justify the higher costs ... 

When using (rac)-vinylcyclohexane epoxide as a standard substrate (Scheme 4.24), the dendrimer catalysts exhibited significantly higher catalytic activities in the hydrolytic kinetic resolution of terminal epoxides as compared to the monomer or the dimer catalysts. Among the dendrimer catalysts, the first-generation dendrimer catalyst gave the best results and the efficiency of the catalyst on a per-metal basis was in the following order 4-Co(salen)-PAMAM > 8-Co(salen)-PAMAM > 16-Co(salen)-PAMAM. This dendrimer effect was considered to arise from the restricted conformation imposed by the dendrimer structure, which enhanced the... 

In order to clarify the stmctures of dendrimer-Uke star-branched polymers, the representative third-generation (3G) and fifth-generation (5G) polymers are shown in Figure 5.1. As can be seen, these polymers are structurally well defined and similar in branched architecture to dendrimers, but are composed of many polymer chains linked to each other between the junctions in aU generations. Accordingly, they are much higher in molecular weight and much... 

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