Dendrimer characteristics

With these emerging applications, there is a critical need for analytical techniques that will provide insights to fundamental questions concerning dendrimer characteristics and properties (e.g. their dimensions, uniformity of size, shape and degree of rigidity, etc.) [8-10], atomic force microscopy (AFM) offers this... 

Aryl platinum(II) dendrimers, characteristics, 12, 491-492 Aryl porphyrin complexes, with iron, 6, 107 Arylpyridines, arylations, 10, 229 2-Arylpyridines, intramolecular C-H functionalizations,... 

Dendrimers have distinctive properties, such as the ability to entrap small molecules in their core region and very low intrinsic viscosities in solution. Such properties require molecules to have achieved a particular size, and not all molecules with branches radiating from a core are large enough to develop the characteristic properties of true dendrimers. Branched molecules below this critical size are called dendrons and are the equivalent in dendrimer chemistry of oligomers in polymer chemistry. 

It is possible to take advantage of the differing characteristics of the periphery and the interior to promote chemical reactions. For example, a dendrimer having a non-polar aliphatic periphery with highly polar inner branches can be used to catalyse unimolecular elimination reactions in tertiary alkyl halides in a non-polar aliphatic solvent. This works because the alkyl halide has some polarity, so become relatively concentrated within the polar branches of the dendrimer. This polar medium favours the formation of polar transition states and intermediates, and allows some free alkene to be formed. This, being nonpolar, is expelled from the polar region, and moves out of the dendrimer and into the non-polar solvent. This is a highly efficient process, and the elimination reaction can be driven to completion with only 0.01 % by mass of a dendrimer in the reaction mixture in the presence of an auxiliary base such as potassium carbonate. 

The properties of these rotaxane dendrimers are quite different from those of the individual rotaxanes or dendrimers and often a blend of both. In view of the versatile characteristics that a dendron or dendrimer can manifest, several new properties can be imparted to the rotaxanes. For example, the solubility of rotaxanes in organic solvents as well as in water can be significantly improved when large dendrimer units are appended enhancing the prospects of their use as molecular machines. The dendritic units can also influence the photo/electro-chemical properties of the rotaxanes. Employing photo-receptive dendron units, photo chemically driven molecular machines may be developed, where the dendrons act as antenna for photo-harvesting [62]. 

That dendrimers are unique when compared with other architectures is confirmed by an investigation on porphyrin core dendrimers and their isomeric linear analogues [63]. The isomers displayed dramatically different hydrodynamic properties, crystallinity, and solubility characteristics when compared to those of their dendritic analogues, and photophysical studies showed that energy transfer from the poly(benzylether) backbone to the core was more efficient in the dendrimer because of the shorter distance between the donor units and the acceptor core. 

PAMAM dendrimers have the following characteristics which are important for their use as transfection reagents. They bind and form complexes with nucleic acids, allow transfer of the DNA-dendrimer complex into the cytoplasm of the... 

Fant K, Esbjomer EK, Lincoln P, Norden B (2008) DNA condensation by PAMAM dendrimers self-assembly characteristics and effect on transcription. Biochemistry 47 1732-1740... 

Each step in dendrimer synthesis occurs independent of the other steps therefore, a dendrimer can take on the characteristics defined by the chemical properties of the monomers used to construct it. Dendrimers thus can have almost limitless properties depending on the methods and materials used for their synthesis. Characteristics can include hydrophilic or hydrophobic regions, the presence of functional groups or reactive groups, metal chelating properties, core/shell dissimilarity, electrical conductivity, hemispherical divergence, biospecific affinity, photoactivity, or the dendrimers can be selectively cleavable at particular points within their structure. 

Figure 7.8 The pendent groups available on the surface of dendrimer molecules are highly varied. Some groups provide functional or reactive groups for bioconjugation, while other groups create unique solubility characteristics for the dendrimer.

After a variety of very different dendrimers had become available up to high generations, many groups directed their attention more and more to designing and synthesizing functionalized dendrimers, i.e., dendrimers adorned with functionalities that are intended to give them characteristic properties favourable for application purposes.14,141... 

Will these emerging megameric structures of poly(dendrimers) represent a new class of macromolecular architecture with unique properties and characteristics ... 

Dendrimers with a carbon-silicon core were prepared by a divergent hy-drosilylation - vinylation method followed by methoxylation [72], Hydrolysis and condensation resulted in gels only in the case of generation two dendrimers, while the sol-gel reaction products of generation one were still soluble, apparently due to strong cyclization characteristics of the sol-gel reactions. 

Dendrimer synthesis involves a repetitive building of generations through alternating chemistry steps which approximately double the mass and surface functionality with every generation as discussed earlier [1-4, 18], Random (statistical) hyperbranched polymer synthesis involves the self-condensation of multifunctional monomers, usually in a one-pot single series of covalent formation events [31], Random hyperbranched polymers and dendrimers of comparable molecular mass have the same number of branch points and terminal units, and any application requiring only these two characteristics could be satisfied by either architectural type. Since dendrimer synthesis requires many defined synthetic and process purification steps while hyperbranched synthesis may involve a one-pot synthetic step with no purification, the dendrimers will necessarily be a much more expensive material to produce. 

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