Dendrimer modification

Indeed, recent results from our laboratory indicate that dendrimer-encapsulated CdS QDs can be prepared by either of two methods [192]. The first approach is analogous to the methodology described earlier for preparing dendrimer-encapsulated metal particles. First, Cd and S salts are added to an aqueous or methanolic PAMAM dendrimer solution. This yields a mixture of intradendrimer (templated) and interdendrimer particles. The smaller, dendrimer-encapsulated nanoparticles may then be separated via size-selective photo etching [193], dendrimer modification and extraction into a nonpolar phase [19], or by washing with solvent in which the dendrimer-encapsulated particles are preferentially soluble. An alternative, higher-yield method relies on sequential addition of very small aliquots of Cd + and S " to alcoholic dendrimer solutions. 

Elemental analyses were conducted to confirm successful synthesis of the G3-PAMAM MNP and to monitor the increasing nitrogen content of the G0-G3 dendrimer (Table 8.2). Some sulfur contamination is apparent (presumably from the ferrous sulfate used in the MNP synthesis) which is, however, washed out during the repeated sonication/washing processes during subsequent PAMAM dendrimer modification. 

Monomers of die type Aa B. are used in step-growth polymerization to produce a variety of polymer architectures, including stars, dendrimers, and hyperbranched polymers.26 28 The unique architecture imparts properties distinctly different from linear polymers of similar compositions. These materials are finding applications in areas such as resin modification, micelles and encapsulation, liquid crystals, pharmaceuticals, catalysis, electroluminescent devices, and analytical chemistry. 

Figure 19 explains what in principle happens the cluster monolayer on the dendrimer film is mobilized by means of CH2CI2 vapour (a b). The phosphines are then removed by the SH functions (b->c). The bare AU55 nanoclusters move between the dendrimer molecules to form crystals (Auss) which finally appear on the surface (c d). The formation of crystalline superlattices of naked AU55 particles proves their stability which is founded in their perfect cuboctahedral shape. The (Auss) species is a novel modification of the element gold. 

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]. 

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. 

The molar ellipticity of these dendrimers was found to increase proportional to the number of chiral end groups. This is to be expected, in the absence of interactions between the terminal tryptophane moieties. No higher-generation dendrimers of this type have been reported. Other amino-acid-containing chiral dendrimers have been described by Meijer et al. who attached various amino acid derivatives to the periphery of poly(propylene imine) dendrimers (see Sect. 3) and more recently by Liskamp et al. (modification of polyamide dendra) [22] and Ritter et al. (synthesis of grafted polymerizable dendrimers containing L-aspartic acid components) [23]. 

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. 

Other than the epoxy groups available on one Priostar dendrimer type and a methyl ester available on a PAMAM dendrimer, the commercial suppliers generally don t offer a selection of spontaneously reactive dendrimers for bioconjugation purposes. For this reason, most of the applications published for coupling biomolecules to dendrimers have used various modification or activation steps to create the appropriate reactive groups for conjugation (e.g., Leon etal., 1996). 

Modification of Amine-Dendrimers with Suifo-NHS-LC-SPDP... 

A common choice of crosslinker for this type of reaction is sulfo-SMCC, which has been used extensively for antibody conjugation (Chapter 20, Section 1.1). A better option for dendrimer conjugation is to use a similar crosslinker design, but one that contains a hydrophilic PEG spacer arm to promote dendrimer hydrophilicity after modification. Derivatization of an amine-dendrimer with a NHS-PEG-maleimide can create an intermediate that is coated with water-soluble PEG spacers. This modification helps to mask any potential for nonspecific interactions that the PAMAM surface may have, while providing terminal thiol-reactive maleimides for coupling ligands (Figure 7.10). 

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