Dendrimer

Dendrimers (from the Greek Dendron - Tree ) are chemical compounds whose structure is based ramification of a branching core like a tree, with one of dendrimers is called when these branches consist of repetitive units, so that they yield a radial symmetry. These must therefore - one starts from a core - include branches, or you will get a chain. There may be a branch to two or more points of attachment. Since dendrimers are monodisperse due to their well-defined structure, they are among the cascade polymer and thus differ from the other polymers. The branches are built up in layers, which are called generations. Viewed in cross section can again draw the analogy of the tree, this time be made with its annual rings. A dendrimer always consists of a core, which are attached to dendrons. Dendrons are regularly branched macromolecules.

Among the pioneers in the development of dendrimer Donald Tomalia heard.

Synthesis strategies

Divergent synthesis

In the divergent synthesis of dendrimers begins with a core of n binding sites are bound to the N units. Thus, the units do not polymerize, they each contain only one active group which forms the new bond. The functional groups, which are intended to serve as a new binding sites in the second synthesis step, therefore, must first be protected or masked, and are activated only after the first step of the synthesis. In summary, the dendrimers grow in the divergent synthesis gradually from the core to the periphery.

Convergent synthesis

In the first convergent synthesis of the dendrons of the peripheral attachment point are synthesized to her and then attached to the core. Here units are required, which have multiple functional groups with the same reactivity and a protected or masked group. This method has the distinct advantage that defective dendrimers can be easily separated from the desired, since a faulty dendrimer in this case differs by a whole dendron from the desired. In the convergent synthesis, it may happen that only one group is absent in the periphery, such a dendrimer is different then neither due to its polarity, size or shape of the desired and therefore can not be removed (by chromatography or similar).

To illustrate an example

, The initiator core, for example three reactive groups, and is obtained by a synthesis sequence branches to two new reactive groups, one obtains six reactive groups in the first step ( 0 generation ). In the next generation, there are already twelve etc.

Therefore observed an exponential growth of the terminal groups. This results in a few synthetic steps to very large, complex molecules. These can not be arbitrarily large because the packing of the terminal groups is more dense. The macroscopic structure thereby approaches to a sphere.

The use of dendrimers based on the one of the multiple functionalization of the surface, on the other hand in the possibility to exploit the different chemical environment of the interior space, resulting in quasi of molecular capsules.