A dendrimer is a molecule with a form like the branches of a tree. The name comes from the Greek dendra, meaning "tree." In 1979, the first dendrimer was synthesized by D.A. Tomalia and other researchers at the Dow Chemical Company, and dendrimers have been studied all over the world because their form is unique (Fig. 1).
Figure 1. Dendrimers
Synthesis
In the synthesis of dendrimers, monomers lead to a monodisperse polymer , tree-like, or generational structure (Fig. 2). There are two defined methods of dendrimer synthesis, divergent synthesis and convergent synthesis. The former assembles the molecule from the core to the periphery and the latter from the outside to termination at the core.
However, because a repeated reaction which consists of many steps is needed to protect the active site, it is difficult to synthesize dendrimers even if both methods are used. This is why there are obstacles to the synthesis of large quantities of dendrimers.
Figure 2. Synthesis of dendrimer
Properties and applications
Drug delivery systems
The properties of dendrimers are dominated by the functional groups on the molecular surface. For example, a dendrimer for which the end group is a hydrophilic group like a carboxyl group is water soluble; it is possible to design a water-soluble dendrimer with internal hydrophobicity. A dendrimer like this can keep a hydrophobic drug inside.
Another property is that the volume of a dendrimer increases when the dendrimer has a positive charge. If we apply this property, we can use the dendrimer for drug delivery systems (DDS) that can give medication to the affected part inside a patient's body directly.
Photonic excited molecules
The inside of a dendrimer has a unique environment chemically because of its high density. From this property, it has been discovered that azobenzene is photoisomerized by very weak infrared rays when dendrimer covers the azobenzene [1]. Through the discovery of a function that catches light and conveys this energy using excitation of the molecule, attempts have recently been made to synthesize dendrimers that insert porphyrin, absorb light, and photosynthesize artificially. In addition, the development of organic electroluminescent devices and their applications has been undertaken by researchers all over the world.
Reference
[1] Dong-Lin Jiang, Takuzou Aida, Nature 388, 454-456 (1997)