Dendrimer surface modifications

Dendrimers have attracted considerable attention in the polymer field over the past two decades as they have been recognized as the most important macromolecules possessing tunable internal packing density, void volumes, solvent-dependent size, branching dimensions, and surface functionalities. Since the first report of a dendrimer-like molecule in 1978 [33], significant progress has been made in the dendrimer chemistry. A large number of dendrimer compositions (families) and dendrimer surface modifications have been reported. A plethora of applications related to controlled release of pharmaceuticals have been reported. Currently, there are two widely studied dendrimer families, namely the Tomalia-type polyamidoamine (PAMAM) dendrimers and the Frdchet-type polyether dendrimers. PAMAM dendrimers are the first complete dendrimer family to have been synthesized. 

Dendrons and dendrimers are the most intensely investigated subset of dendritic polymers. In the past decade, over 6,000 literature references have appeared dealing with this xmique class of structure-controlled polymers. The word dendrimer is derived from the Greek words dendri- (tree branch-like) and meros (part of), and was coined by Tomalia et al. about 20 years ago in the first full paper on poly (amidoamine) (PAMAM) dendrimers [47,72]. Since this early disclosure, over 100 dendrimer compositions (families) and 1,000 dendrimer surface modifications have been reported. The two most widely studied dendrimer families are the Frechet-type polyether compositions and the Tomalia-type PAMAM dendrimers. PAMAM dendil-mers constitute the first dendrimer family to be commercialized, and represent the most extensively characterized and best-understood series at this time [46]. 

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]. 

Hong et al. (2004) also found that modification of PAMAM dendrimers with a short PEG linker arm could act to reduce nonspecificity caused by the amines on the dendrimer-modified surface. An azido-PEGj-aininc spacer was activated with nitrophenyl carbamate to yield an activated intermediate that could be used to modify the amines on the dendrimer (Figure 7.24). Reaction at high molar ratio resulted in about 61 PEG-azido spacers on the dendrimer. Reduction of the azido group to an amine using triphenylphosphine in THF provided the dendrimer-PEG-amine derivative for surface modification. The added presence of the PEG spacer arm reduced... 

Testing of G-l, G-2, and G-3 dendrimers in this application provided insight into the density of surface modification needed to passivate completely the particles and prevent aggregation. The G-l dendron was insufficient in this regard, but both the G-2 and G-3 dendron were big enough to create a surface barrier, which resulted in excellent colloidal stability of the particles in solution. 

Figure 7.26 Dendrimers made with a disulfide-containing core can be reduced to produce dendrons having free thiol groups for surface modification. Dative binding of these thiol-dendrons to gold or metallic surfaces can provide a high density of amine groups for coupling proteins or other molecules.

TRIDENDRON DENDRIMER AND GENERAL PROCEDURE FOR SURFACE MODIFICATION OF THE HYDROXYL TERMINATED DENDRIMERS... 

Keywords Dendrimer Hyperbranched grafts Nanocomposite Polyvalency Surface modification... 

Choi JS, Nam K, Park JY et al (2004) Enhanced transfection efficiency of PAMAM dendrimer by surface modification with L-arginine. J Control Release 99 445 156... 

While the previous sections have largely addressed variation of the dendrimer periphery by covalent transfunctionalisation, an alternative concept is based on modification of the dendrimer surface by non-covalent interactions [18]. Selective interactions of guest molecules with dendritic hosts depend upon the nature of both the dendrimer core and the dendrimer shell. 

On account of their controllable size, geometry, and functionality, dendrimers command interest for surface modification and for enlargement of (active) surfaces. 

PAMAM]. The final step of this functionalization relied on activation and cross-linking of attached dendrimers with a homobifunctional spacer (DSG or PDITC). Alternatively, after attachment of dendrimers to the surface, glutaric anhydride activated with V-h ydrox vsucc i n i m i de can be used. This surface modification yields a thin, chemically reactive polymer film, which is covalently attached to the glass support and can be directly used for the covalent attachment of amino-modified components, such as DNA or peptides (Fig. 14.2b). 

Meijer et al.123 constructed a series of novel dendritic boxes by surface modification of divergently prepared, amine-terminated poly(propyleneimine) dendrimers 24 (e.g., 30 Scheme 7.7) by attachment of A-protected chiral amino acid caps (see Section 4.3.1). 

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