Dendrimers architectural components

Fig. 3. Dendrimer architectural components as a function of molecular genealogy associated with CMDPs that contribute to endo- and exo-receptor properties...

In contrast to traditional polymers, dendrimers are unique core-shell structures possessing three basic architectural components namely, (I) a core, (II) an interior of shells (,generation) consisting of repetitive branch cell units and (III) terminal functional groups (i.e. the outer shell or periphery) as illustrated in Figures 1.13 and 1.14. 

Figure 1.14 Three-dimensional projection of dendrimer core-shell architecture for G = 4.5 poly(amidomine) (PAMAM) dendrimer with principal architectural components (I) core, (II) interior and (III) surface...

The unique topology and architectural components of dendrimers suggest many important applications that may be possible. We have identified at least five important factors that pose questions concerning these technological applications. Table 11.1 lists these factors along with the applicability of SANS, SAXS and TEM to address the questions. 

Starburst dendrimers, such as above, possess three major architectural components. 

Fig. 49. Empirical structure for a Comb-burst dendrimer series (Generation = 0 — i), wherein the key architectural components (a) initiator core chain, (b) interior and (c) terminal chains are designated...

STRUCnjRE Dendrimers are three-dimensional macromolecules consisting of three major architectural components a core, branch cells, and terminal groups. These products are constructed from repeat units called branch cells [e.g.,... 

STRUCTURE Dendrimers are three-dimensional macromolecules consisting of three major architectural components a core, branch cells, and terminal groups. These products are constructed from repeat units called branch cells [e.g., —CH2—CH2—CH2—N(CH2—CH2—012)2] iri concentric generations (G) surrounding various cores according to dendritic rules and principles, where = multiplicity of core N, = multiplicity of branch cell and Z = terminal groups (i.e., -CN or —CH2-NH2). 

Dendrimers may be viewed as unique, information processing, nanoscale devices. Each architectural component (core, interior, and surface) manifests a specific function, while at the same time defining properties for these nanostructures as they are grown generation by generation. For example, the core may be thought of as the molecular information center from which size, shape, directionality, and multiplicity are expressed via the covalent connectivity to the outer shells. Within the interior, one finds the branch cell amplification region, which defines the type... 

Pis. 27 Core-shell architecture of the PAMAM corerfullerene shell [S-l (H-5)3o] type of nanocompound. Z mdieates terminal -NH2 or -NH- groups on the PAMAM dendrimer core component of the core-shell nanocompound [177]... 

This concept was refined by the research group of Li, who employed the thiol-yne reaction instead of the olefin cross-metathesis reaction as key step [60]. In this case, the carboxylic acid component served as anchor, whereby terminal alkynes were introduced by the remaining components (5-hexyn-l-al and propargyl isocyanoacetamide). Interestingly, thiol-yne addition of 3-mercaptopropionic acid to the pendant alkynes enabled not only the incorporation of further carboxylic acids, but also resulted in additional branching. Therefore, the second generation dendrimer, synthesized in three steps, exhibited 16 peripheral triple bonds. Moreover, this concept offers the opportunity to introduce structural diversity into the dendrimer architecture because the use of only one alkyne-functionalized compound in the Passerini-3CR still results in branching due to the thiol-yne reaction. Here, a structural sequence of employed phenylacetaldehyde and 2-nitrobenzaldehyde was demonstrated. 

Advances in synthesis and characterization methodologies have permitted the synthesis of relatively high-MW dendrimers with a variety of functional moieties. Dendrimers consist of three different architectural components an initiator core which can be a single atom or a group of atoms, an exterior (surface groups) which can have several functional groups. In between the core and the surface group is the interior part of the... 

Figure 59 Dendritic structure (left) showing the three architectural components of a dendrimer core (C) interior branching units (M, N, and 0), and periphery or surface groups (P) and hyperbranched polymer (right).

Construction of organic nanotubes starting from porphyrin dendrimers with core/shell architecture is also feasible. Figure 8.29 also shows how covalent nanotubes can be produced by removal of the dendritic component of the molecule. A coordination polymer is first synthesised from a dendritic metallopor-phyrin with alkene end groups. This is subjected to intramolecular and intermo-lecular crosslinking by ring-closing metathesis at the periphery. 

This topic was partially covered in CHEC-II(1996) <1996CHEC-II(9)809> under the subentry Catenanes and Rotaxanes . In this section, emphasis is given to the design and construction (and to some extent, the properties) of supramolecular architectures derived from or incorporating crown ethers rather than to the synthesis of the crown ether component present in them. The crown ether rings described herein are either covalently linked (dendrimers), mechanically interlocked (rotaxanes, catenanes), or just bound by noncovalent interactions (pseudorotaxanes) to the rest of the supermolecule to which they belong. 

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