Dendrimer peripheral group

Dendrimer interior functional groups and cavities can retain guest molecules selectively, depending on the nature of the guest and the dendritic endoreceptors, the cavity size, the structure, and the chemical composition of the peripheric groups. Two main methods are known for the synthesis of metal nanoparticles inside dendrimers. The first method consists of the direct reduction of dendrimer-encapsulated metal ions (Scheme 9.4) the second method corresponds to the displacement of less-noble metal clusters with more noble elements [54]. 

Assuming that in the course of the functionalization, each reaction between the reagent and a still free peripheral group occurs without being influenced by the number of already converted moieties,1231 the total yield A of perfectly reacted dendrimer can be calculated by means of the product formula for a stochastically independent event, if the yield of the individual reaction a is known. The yield A is given by a" where n is the number of peripheral functional groups of the dendrimer. 

Another noteworthy difference between core- and periphery-functionalized dendrimers is that much higher costs are involved in the application of core-functionalized dendrimers due to their higher molecular weight per catalytic site. Furthermore, applications may be limited by the solubility of the dendrimer. (To dissolve 1 mmol of catalyst/L, 20 g/L of core-functionalized dendrimer is required (MW 20 000 Da, 1 active site) compared to 1 g/L of periphery-functionalized dendrimer (MW 20 000 Da, 20 active sites). On the other hand, for core-functionalized systems, the solubility of the dendritic catalyst can be optimized by changing the peripheral groups. 

The physical properties of dendrimers such as solubility, arising from their hyperbranched globular shapes and the peripheral groups, can be modified by end-group modification. In core-functionalized dendrimers, the immiscibility of the wedges with a solvent enables precipitation and subsequent separation by filtration. 

Various strategies for the synthesis of peripherally functionalised dendrimers are presented and evaluated in the following sections. The expression peripheral group is used here as a neutral term. It can refer both to a peripheral function-bearing unit and to a peripheral functionality. Terminal groups linked covalently to the periphery can also be - partly - backfolded (see Sections 1.2 and 7.63). 

Introduction of peripheral groups prior to dendrimer growth... 

In the synthesis of functional dendrimers, interest has hitherto been focussed on variation of the functional core unit or peripheral groups and the resulting effects on the properties of the dendrimer. For a long time, the only function ascribed to the dendritic branches and their repeating units was that of a scaffold linking periphery and core. It was overlooked that, in the interior of the dendrimer scaffold, an individual characteristic (nano)environment can arise which is largely dependent upon the chemical characteristics and the polarity of the repeating units used to construct the dendrimer. Moreover, they can facilitate cascade processes and serve as a platform for cooperative effects between dendrimer branches [37]. 

Fig. 3.8 Convergent synthesis of a bifunctionalised dendrimer with two different peripheral groups in separate molecular segments (surface-block dendrimers)...

Surface-block dendrimer with different peripheral groups in separate segments of the molecule. 

Recent studies have shown that RP-HPLC in combination with MALDI-TOF mass spectrometry is suitable for preparative separation and characterisation of PAMAM dendrimers of different generations or with different peripheral groups [8]. Investigations performed so far indicate that the purity of a dendri-... 

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