Dendrites components

The incorporation of dendritic moieties into amphiphilic structures is attractive as the dendritic component provides a unique opportunity to vary, in a controlled fashion, head group properties such as size and polarity, by simply changing the generation or the nature of its surface groups. Similarly, the length of the linear fragment can easily be modified to adjust properties. 

Stoddart and co-workers have made use of Frechet-type dendrons as dendritic stoppers for self-assembled [n]rotaxanes [65]. The solubility enhancement that results from incorporating dendritic wedges at the termini facilitated the purification of these materials by column chromatography despite the polycationic nature of their bipyridinium backbone. Again, the dendritic wedges did not alter the electrochemical characteristics of the viologen subunits. Flowever, the enhanced solubility resulting from the presence of the dendritic components en-... 

As this brief overview demonstrates, novel copolymers obtained by hybridization of the linear and globular architectural states are readily prepared through a variety of synthetic approaches. In general the dendritic components of the hybrid copolymers are well defined, with unique molecular and structural characteristics. In contrast, all the linear components prepared polymerization are less precisely defined and are polydisperse. Only the very short linear components, themselves prepared by stepwise synthesis just like the dendrons, are monodisperse and can be used to prepare well-defined, monodisperse hybrids. While architectural and structural precision may be of great importance for the determination of ultimate properties, some degree of structural variation is quite acceptable for practical applications in many areas including, for example, surface modification, sensing, or encapsulated delivery. 

This cross-sectional mismatch between the small anchor and the large dendritic component modified the intermolecular packing in the Langmuir-Blodgett mono-layer and film so that sufficient mobUity was present near the azobenzene group. This mobility greatly facihtated efficient molecular reorganization in response to E Z photoisomerization. 

In general, additives have to be highly effective, dosable in small amounts, and readily miscible with other components. Owing their molecular size, bleeding or loss by diffusion of the dendritic components is more difficult than for low-molecular-weight compounds [19]. 

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. 

Novel macromolecular architectures Globular block copolymers containing dendritic components [C. J. Hawker, K. L. Wooley, J. M. J. Frechet, Macromol. Symp. 1994, 77, 11-20],... 

ASSEMBLY OF POLYDISPERSE STRUCTURES CONTAINING DISCRETE DENDRITIC COMPONENTS... 

The synthesis of defined supramolecular dendrimers is an aesthetically appeahng challenge for chemists however, the production of less well-defined supramolecular systems from dendritic components offers equally exciting possibilities. These structures can be produced by assembling precisely synthesized dendrons around a polyvalent receptor. Thus, the polydispersity of the final supramolecular structure is as a consequence of variations in the number of receptor sites available for dendron binding. 

While the majority of the materials based on the dendritic architecture are prepared and used in solution, the amount of dendritic compounds prepared on or postsynthetically conjugated to solid insoluble support is constantly increasing. Although the dendritic components of such composite materials usually constitute only a minor part of the total volume, they can significantly alter the support properties, imparting entirely new features and functions on the solid support. 

Some of these dendrons are cleaved immediately after formation others are used as supported templates for preparation of soluble dendritic conjugates, which are initially constructed on support, but thereafter are cleaved together with the dendritic component. In some comparative studies, this approach showed better results than the preparation of the dendritic conjugate in solution. ... 

Conformal coatings are protective coatings appHed to circuit board assembHes. They protect the interconnect conductors, solder joints, components, and the board itself they reduce permeabiHty to moisture, hostile chemical vapors, and solvents in the coating. Use of conformal coatings eliminates dendritic growth between conductors, conductor bridging from moisture condensation, and reduction in insulation resistance by water absorption. 

Q. Han, J. D. Hunt. Numerical modelling of the growth of a cellular/dendritic array in multi-component alloys. Mater Sci Eng A 255 192, 1997. 

Figure 33. Proposed interface between an electronic component (video camera) and a nerve (optical nerve) that could transduce electronic signals from the equipment to ionic signals that can be understood by dendrites.

The MAPs vary in number and relative abundance in different cell types MAP2 is principally found in dendrites, whereas tau is restricted to axons. This selective distribution of MAP2 molecules is the result of subcellular sorting of its messenger RNA (Lewis et al., 1989). Currently, there is interest in the observation that tau is a component of the neurofibrillary tangles of Alzheimer s disease (Goedert et al., 1989). 

Microtubules, an integral component of the cellular cy-toskeleton, consist of cytoplasmic tubes 25 nm in diameter and often of extreme length. Microtubules are necessary for the formation and function of the mitotic spindle and thus are present in all eukaryotic cells. They are also involved in the intracellular movement of endocytic and exocytic vesicles and form the major structural components of cilia and flagella. Microtubules are a major component of axons and dendrites, in which they maintain structure and participate in the axoplasmic flow of material along these neuronal processes. 

As described earlier, we classify dendritic poiyrotaxanes in which rotaxane building units grow like a dendrimer, as Type III rotaxane dendrimers. Depending on whether ring components are located on the branches or at the branching points. Type III rotaxane dendrimers are further classified as 111-A and 111-B, respectively. 

Dendritic Poiyrotaxanes Incorporating Ring Components on the Branches Type lll-A... 

Dendritic Polyrotaxanes Incorporating Ring Components at Branching Points Type lll-B... 

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