Dendron-containing monomer

In another system, the approach is slightly changed in a way that the porphyrin oligomers (dendrons) contain pyridine units for coordination to ruthenium(II) porphyrin monomer building blocks [30]. The dendrons readily form a mono-coordinated complex with the ruthenium(II) porphyrin. After irradiation, the CO ligand is lost, and a second unit can bind to form the dendritic multiporphyrin array 43 (Fig. 32b), where a total of seven porphyrins are assembled. 

The supramolecular dendrimers and hyperbranched system considered in the previous section are assembled from identical dendrons and monomers that contain complementary noncovalent recognition motifs. In 1997, Zimmerman and coworkers produced a three-component dendrimer (36) whereby two dendrons (37) were brought together around a small dicationic core (38) by complementary electrostatic and hydrogen bonding interactions (Scheme 8). The ditopic core template is also a known pharmaceutical, pentamidine, which is active against Pneumocystis carinii pneumonia —a serious lung infection. Controlled disassembly of the dendrimer in vivo would result in increased... 

In order to investigate dendrimers of a different nature [230], Bradley described the synthesis and transfection efficiency of polyamidourea dendrimers synthesised from isocyanate-containing AB3 monomers [231-234]. The use of this kind of tris-branched building block was addressed to enhance dendrimer synthesis by replacement of the 1,4-addition step typical of PAMAM synthesis and to a rapid increase in terminal functionality. The dendritic structures were synthesised using a divergent, microwave-assisted, solid-phase approach with the dendrimers assembled on polystyrene resin via an acid labile linker (see Fig. 26). In particular, a G3.0 polyamidourea bis-dendron with the peripheral amino groups conjugated to L-lysine residues demonstrated remarkable transfection abilities [234],... 

The DB of branching can be modified by special synthetic approaches, as demonstrated by the NMR quantification of subunits. Copolymerization - for example, the addition of bifunctional monomers AB - resulted in an increase in linear units and, therefore, in a decrease of the DB [109-112]. An enhancement of DB was realized, for example, by employing a slow monomer addition technique [113], the polymerization of prefabricated dendron macromonomers [56, 114], and by a stepwise addition of the monomer mixture for the (A2 + B3) approach [92]. Whereas dendritic and terminal units are essential for a dendritic structure, in the case of hb polymers the content of the linear units can vary greatly. To date, few examples of AB2 hb polymerizations have been reported were the linear unit is a chemically labile structure that either breaks down to the initial educts, or reacts immediately with a further terminal unit to form the stabile dendritic unit. Thus, a hb polymer containing only T and D units is formed, with 100% DB [35,115-119]. 

A dendrimer is composed of a core moiety conneaing branched dendrons, or wedges, based on AB monomers (Figure 5). Each layer of AB repeating units is denoted generation (G). The outer layer contains a multitude of B-groups, which can be further funaionalized. Typically, di-, tri-, and tetrafunaional core moieties are exploited for the construction of dendrimers. When a... 

---