Dendrimer construction

At present, improved methods of dendrimer construction have made possible the commercial availability of these macromolecules with a variety of molecular weight ranges and surface functional groups. Instead of testing the limits... 

I. Baussanne, J. M. Benito, C. Ortiz Mellet, J. M. Garcia Fernandez, and J. Defaye, Synthesis and comparative lectin-binding affinity of mannosyl-coated /i-cyclo-dextrin-dendrimer constructs, Chem. Commun. (2000) 1489-1490. 

The polyvalent nature of dendrimers has been investigated as vehicles for carrying multiple chelator groups to enhance signals in various imaging applications (Barthand Soloway, 1994 Yoo et al., 1999 Kobayashi et al., 2000, 2001 Sato et al., 2001). In addition, in certain chelate-dendrimer constructs, excess amines on the dendrimer surface can aid in the cellular uptake process through charge-mediated endocytosis. 

Other chelate-dendrimer constructs may be prepared using alternative bifunctional chelating agents according to Chapter 10. 

The broad emission band displayed by these silver/dendrimer constructs actually was found to consist of 5 overlapping fluorescent peaks caused by individual silver/dendrimer complexes. Each of these complexes evidently contained a uniquely sized silver nanocluster, which resulted in an individual emission peak. Therefore, all the silver/dendrimer complexes together in solution presented a combined average of these 5 discrete emission peaks, and thus displayed the broad emission band covering nearly 200 nm in width across the spectrum. 

Figure 1.13 Overview of synthetic strategies for (a) branch cell construction, (b) dendron construction and (c) dendrimer construction annotated with discovery scientists...

Overall, each of these dendrimer construction strategies offers advantage and disadvantages. Some of these issues, together with experimental laboratory procedures, are viewed in more detail in several of the following chapters. 

While the convergent strategy, as described above, has been exceptionally successful, a considerable amount of effort has been devoted to improving its speed and synthetic efficiency. The remainder of this chapter reviews the major methodological developments and improvements in the accelerated, covalent, convergent synthesis of dendrimers. Dendrimers constructed via self-assembly and noncovalent interactions, as well as inorganic dendrimers [25], are beyond the scope of this brief chapter. 

Fig. 6. Use of ruthenium-containing building blocks for dendrimer construction, 31...

II. Oi anometallic Dendrimers Constructed From Oiganosilicon Dendritic Cores. .154... 

II. ORGANOMETALLIC DENDRIMERS CONSTRUCTED FROM ORGANOSILICON DENDRITIC CORES... 

The local chirality of a core unit is not necessarily manifested in a macroscopic chirality of the dendrimer. This is clearly apparent from the example of the dendrimers constructed by Meijer et al. from a glycerol unit as chiral core unit and four Frechet-type dendrons of different generations (Fig. 4.66). No optical activity could be measured with available instrumentation for the two enantiomeric forms (S)-l and (i )-l [2 a]. 

Fig. 6.7 Convergent covalent attachment of - inert or functional - dendrons during dendrimer construction.

Scheme 11.2 Dendrimer construction via the complexes-as-metals/complexes-as-ligands strategy -dendrimer generation increases ascending the diagram but growth is terminated by the horizontal processes.

There is a growing interest in polymers with architectures that differ from the classical linear polymers, since new polymer architectures may exhibit unusual behavior. For example, the combination of dendrimers and linears polymers in hybrid materials has evolved from a curiosity into an important trend in current chemistry. Therefore, various dendrimer construction strategies have been developed on the basis of classical organic and inorganic chemistry [65,66],... 

In their quest for large molecular cavities capable of binding molecules or ionic guests, Vogtle and coworkers 1 synthesized non-cyclic polyaza compounds via a repetitive stepwise process (one-directional case Scheme 4.2). The use of two-directional cores (Scheme 4.5), e.g., ethylenediamine, 2,6-di(aminomethyl)pyridine (8) or l,3-di(amino-methyl)benzene, with acrylonitrile afforded the tetranitrile 9, which was reduced with Co(n)-catalyzed borohydride to produce hexaamine 10. This terminal tetraamine was subsequently treated with excess acrylonitrile to generate the octanitrile 11 although the process was terminated at this stage, a foundation of dendrimer construction was established. 

Scheme 4.22. Alkyl silane dendrimer construction by Pt-mediated silane alkenylation and vinylation.

Repetitive Diels-Alder reactions utilizing bis-ort/io-quinodimethane units have been employed[14bl for the construction of polymeric and oligomeric [60]-fullerenes with molecular weights up to 80,000 amu. The potential of using this method for dendrimer construction was suggested. 

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