Dendritic network

As new synthetic methods are pursued in future to synthesize dendrimers more efficiently and cheaply on an industrial scale, one of the most promising areas for these macromolecules is seen in the construction of higher order assemblies or dendritic networks [213]. 

Scheme 9 Dendronized TADDOL ligands which are cross-linked to form a dendritic network [58]...

Scheme 8.6. Core modification has to include metal coordinating sites has allowed entrance into specifically constructed dendritic networks (see Chapter 9). a KOH, DMSO b DCC/l-HBT c = d = f HCQ2H.

As defined, dendritic networks are considered to result from the one-, two-, and three-dimensional orientation of dendrimers thus ordering can be geometrically likened to rods surfaces or sheets and cubes, tetrahedrons, or spheres, respectively. Due to the broad scope and breadth of potential macromolecular architectures that can be obtained by application of different modes of connectivity, we will herein concentrate on networks constructed from the simplest dendritic structures, namely those that are pseudospheri-cal or globular. The principles that are presented here pertaining to network formation should be easily adaptable to non-spheroidal dendritic structures as well as macromolecular assemblies possessing only limited dendritic character. 

It should be noted here that, currently, characterization, separation, and purification techniques of the larger cascades or dendrimers (previously discussed in earlier chapters) are straining the limits of present instrumentation. Thus, unequivocal characterization of dendritic networks is currently limited and will necessitate the development of new methods and instrumentation. However, dendritic network structural verification and elucidation should be facilitated by integration of known standard materials science methods, e.g., MS and EM. 

Figure 9.2. Dendritic network classification via dendrimer connectivity.

All ordered and random dendritic networks that are constructed via covalent or non-covalent means result from positioning of one dendrimer relative to another. Thus, macroassembly positioning can be effected via at least one of three different methods of connectivity. These methods are geometrically rooted in dendritic chemistry. 

Figure 9.5. An idealized representation of an ordered dendritic network constructed by the procedure of Watanabe and Regen. 81 ...

The potential for amplification of airway responses is intriguing. Mast cell products released by specific antigen-IgE interactions could stimulate C-fibers to release tachykinins, and these tachykinins could then stimulate the mast cells that fell within the dendritic network of the particular nerve involved. Therefore, local antigen-induced stimulation of mast cells could spread far beyond the diffusion distance for the antigen in question. The specific relevance of this proposed amplification mechanism to human disease has not been evaluated. 

Geckos use a sophisticated assembly of submicroscopic foot hairs to walk along a ceiling upside down [1], Such a dendritic network of hairs takes advantage of multiple adhesive forces, resulting in an efficient multivalency effect. 

There are a number of studies on pyrene labelled or doped polymer materials. Dendritic size and electrostatic forces in poly(amido) dendrimers with pyrene residues have been determined through the use of a variety of quenchers. As the dendritic size increases so the Stern-Volmer quenching constant decreases, owing to blocking of the pyrene chromophore by the growing dendritic network. The photophysical properties of poly(acrylic acids) tagged with pyrene has been measured in micellar media at various pHs." The ratio of monomer to excimer gave valuable information on the micropolarity sensed by the pyrene label, as well as the influence of external stimuli. The surfactant... 

Newkome and coworkers also examined a dendritic system in which bipyridine molecules, incorporated into the branches, were subsequently complexed to yield dendrimers containing ruthenium tris-bipyridyl moieties dangling from the dendritic arms. In the electrochemistry of these compounds, the metal centers, surrounded by a dendritic network, exhibited irreversible kinetic behavior, as is commonly found in such systems. On the other hand, there are three separately identifiable ligand-based reductions, each of the... 

Self-assembled, three-dimensional dendritic network structures possessing critical jr-type surface groups have been reported to exhibit unique electrical conducting properties. Miller/Tomalia and coworkers [270] observed unusually high conductivities (i.e., 18 sec/cm at 90% humidity) for... 

Vignjevic, D., D. Yarar, M.D. Welch, J. Peloquin, T. Svitkina, and G.G. Borisy, Formation of fllopodia-fike bundles in vitro from a dendritic network. J. Cell Biol, 2003,160 951-962. 

As a unique method of controlled/living radical polymerization, ATRP has had a tremendous impact on the synthesis of macromolecules with well-defined compositions, architectures, and functionalities, including star- and comb-like polymers as well as branched, hyperbranched, dendritic, network, cyclic type structures and so forth. 

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