Dendrimer functional groups

By manipulating the chemical properties of dendrimer functional groups, hydrophilic guest molecules can be dissolved in nonpolar solvents and hydro-phobic molecules can be dissolved in polar solution. This is possible because, independent of an encapsulated guest, dendrimers terminated in hydropho-... 

Dendrimer micelles of this type have been formulated as drug delivery vehicles. Dendrimers with a hydrophobic interior have been used to entrap a hydrophobic drug such as indomethacin. This is retained because of the hydrophilic periphery containing ethylene glycol functional groups, and is released slowly because of the collapsed configuration of the interior, through which molecular diffusion is obstructed. 

Both energy and electron transfer quenchers have been employed to show that the quenching rates of the fullerene triplet state are decreased as a function of the size of the dendrimer shell [36]. These results further demonstrate that fullerene is an excellent functional group to probe the accessibility of a dendrimer core by external molecules. 

Because of their proximity, the various functional groups of a dendrimer may easily interact with one another. Interaction can also occur between dendrimer units and molecules hosted in the dendritic cavities or associated to the dendrimer surface. 

One of the main applications of dendrimers is in catalysis allowing easy recycling of the homogeneous catalyst by means of nanofiltration. Carbosilane dendrimers functionalized with diphenylphosphine groups at the periphery have been synthesized and characterized. Palladium complexes of these dendrimers have been used as catalysts in the allylic alkylation reaction. These dendrimeric catalysts can be used in a continuous process using a membrane reactor.509... 

Fig. 19. Anthraquinonoid dendrimers with internal modifiable functional groups...

Organometallic dendrimers have been constructed to act as potential electro-or photo-active materials, the synthesis of which will be discussed in the following section. Apart from the examples discussed above, surface modification of dendrimers with a variety of functional groups has afforded novel redox active materials [110-116]. 

Due to their well defined geometrical sizes, globular shapes, and uniform multiple surface functional groups, dendrimers are promising candidates for the construction of mono- or multi-layer films. 

At present, improved methods of dendrimer construction have made possible the commercial availability of these macromolecules with a variety of molecular weight ranges and surface functional groups. Instead of testing the limits... 

Application of the Horner-Wadsworth-Emmons reaction to the functionalization of dendrimers allows one to prepare amino acid terminated macromolecules. Such a reaction conducted with dendrimers 10-[G ], 10-[G 3], lO-fG ] and phosphonates unsubstituted at the carbon a to the phosphoryl group affords in moderate yield dendrimers bearing various a, / unsaturated functional groups on the surface [18]. (Schemes 17 and 18). 

This work demonstrates that functionalization of the internal cavities of various dendrimers can be done via a post modification of the skeleton. Various functional groups can be selectively introduced aminophosphite, aldehyde, hydrazone, dichlorophosphane sulfide. Therefore all the chemistry reported on the surface of dendrimers can be now envisaged to be done into the cavities and it is demonstrated for the first time that a macromolecular chemistry can be performed into the internal voids of a dendrimer. 

P(X)Cl2 (X=S,0) terminated units allow the grafting of various other functional groups and the preparation of multiplurifunctionalized dendrimers, i.e. dendrimers possessing a large number of sets of two, three or four different functionalities on the surface. 

Phosphorus also permits the postmodification of the backbone of dendrimers. Indeed charges, and also various functional groups, can be selectively introduced into the internal voids. Such a transformation can be performed where and when required. 

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

Fig. 15. Optical activities of poly(propylene imine) dendrimers, functionalized at the periphery with protected phenylalanine or f-butoxy methoxy benzyl acetate groups, depend on the number of end groups [2]...

Practically all dendrimers [ 1 ] known today have cores with a few, typically three to six functional groups to which the corresponding number of dendrons (dendritic wedges) are attached. The fact that these dendrons are connected to one another by a small, almost dot-like molecule results in considerable steric congestion in the space around the core. This congestion is a unique structural feature and has one led to view dendrimers, specifically those of high genera-... 

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