Dendrimers trifunctional

Fig. 4.6 Third-generation (G3) PAMAM dendrimer with trifunctional core unit (nitrilotripropionamide) and AB2 branching...

Figure 5-5.The first threegenerations of a hypothetical dendrimer built up from a trifunctional core.

Trifunctional cross-linkers are commonly employed to create dendrimers or dendritic layers on a surface [10,43,44]. The higher amount of receptor-molecules on the surface leads to a higher coupling density of capture probes [45]. An attractive application for trifunctional and multifunctional cross-linkers is the coupling of more specific biochemical species in one spot (Fig. 16). 

Hypothetical structure of a dendrimer synthesised from three distearyl-amines or -amides and a trifunctional isocyanate X(N=C=0)3. 

Measurements of molecular density and intrinsic viscosity of PAMAM dendrimers indicate an unusual variation with dendrimer generation. Minimum density and maximum intrinsic viscosity were observed at around G4, which suggests that the fully developed dendrimers have a high accessible internal surface area in a solvent-filled intramolecular free volume that may consist of internal cavities and channels. Similar findings were reported by Mourey et al. for PBE monodendrons (based on dihydroxybenzyl alcohol) and tridendrons produced by coupling these dendrons to a trifunctional core, l,l,l-tris(4 -hydro-xyphenyl)ethane prepared by the convergent method. A maximum intrinsic viscosity occurred at G3 for tridendrons and G5 for monodendrons, consistent with the model developed by Lescanec and Muthukumar... 

For the purpose of this article, a traditional covalently bound core will be defined as a low molecular weight molecule with one or more functionalities capable of covalently coupling to the focal point of a dendron. This distinction is made to differentiate these cores from polymeric or self-assembled cores. The first dendrimer cores reported were simple di-or trifunctional molecules capable of coupling with dendrons utilizing identical chemistry as that repeated during dendron growth. For example, the earliest dendrimer cores (Scheme 2) include the trisphenolic core, 13, reported by Hawker and Fre-chet,10 and the 1,3,5-triiodobenzene core reported by Moore and co-workers.231... 

Fig. 8.1 Schematic representation of a trifunctional fifth generation self-similar starburst dendrimer following Boris and Rubinstein [80],... 

FIGURE 5.1 Schematic representation of a fourth-generation dendrimer with a trifunctional... 

Figure 33.10 Increase in functionality with generation of different heteromultifunctional dendrimers. Calculations are made considering a trifunctional core for the dendrimers, and a difunctional core for the didendron.

In the case of the PBisMPA-based family of dendrimers, the effect of the core has been investigated. It was fotmd that for 2-ethyl-2-(hydroxymethyl)-l,3-propanediol (TMP), a rather small trifunctional core, the shape transition occurs at generation 4, while the use of a tetrafunctional core, 2,2 -oxybis (methylene)bis(2-ethyl-1,3-propanediol) (di-TMP), shifts the transition to generation 3. A similar trend is observed when TPh is used as a core. ... 

Two recent papers on furan-containing dendrimers have been added to the original work based on the DA reaction discussed in Section 6.8.2. The first describes the formation of star polymers induced by the cyclotrimerization of furan derivatives bearing aliphatic aldehyde functions attached at the 2 and 5 ring positions [76]. This hyper-branched structure was therefore generated by the formation of trifunctional acetal moieties, as shown in 42, and should therefore be readily hydrolyzed making the whole process reversible, although this latter aspect was not pointed out by the authors. 

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