Cascade structures, dendritic

Since they were first mentioned in 1978, the concept of cascade or dendritic structures has witnessed a meteoric rise. On the one hand, thanks to their aesthetic beauty, and on the other hand, because of their broad applicability, dendrimers are in considerable demand. As the concept is not limited to one class of substances and, furthermore, allows a simple access on several routes, there is -besides the researchers who started dendrimer chemistry - a growing number of research groups which are dendritically expanding their special areas of interest in different ways and describing new or varying already existing properties. 

Fractals are mathematically defined self-similar structures (Fig. 1.11) [26]. The scaffold of cascade or dendritic molecules is fractal if the atoms are considered to be points and the bonds to be strictly one-dimensional lines. Self-similarity... 

In 1978 we described a synthetic methodology as a repeating-step principle , which led us to the first cascade molecules , today known as dendritic molecules [17]. We recognized then that a synthetic pathway, which allows consecutive repetition, implies the advantage of likewise reactants and reaction conditions and is suited for the building of more or less structure perfect highly branched molecules, particularly of polyamines (Fig. 4). 

The continued interest in dendritic materials as well as the related hyperbranched polymers has sparked the imagination of researchers in many different areas. The incredible increase in annual publications in this topic is best shown in the Figure and thus as the number on new building blocks and core molecules proliferate, the structural composition of precise and controlled design will grow to meet the imagination of molecular architects. This review series was initially conceived to cover the synthesis and supramolecular chemistry of dendritic or cascade supermolecules as well as their less perfect hyperbranched cousins. 

Dendritic molecules (cascade molecules) are repetitively branched compounds. This collective term embraces the various dendrimers. The latter generally exhibit almost perfect structures and display properties characteristic of monodisperse compounds (see also Section 1.3). With regard to their molecular masses, dendrimers range from low-molecular to high-molecular chemistry. 

In conclusion, the potential of soluble, nanosized metallodendrimers as catalysts in homogeneous reactions is well-consolidated. Future applications of these species are foreseen in high-tech nanotechnology applications in the fields of nano- and microreactors, cascade catalysis, and catalytic biomonitoring and biosensing. In this respect, the recent use of noncovalent strategies for the construction of multicomponent catalytic assemblies, and the use of biomacromolecules within dendritic structures is intriguing [60-62,92,93]. 

It should be noted here that, currently, characterization, separation, and purification techniques of the larger cascades or dendrimers (previously discussed in earlier chapters) are straining the limits of present instrumentation. Thus, unequivocal characterization of dendritic networks is currently limited and will necessitate the development of new methods and instrumentation. However, dendritic network structural verification and elucidation should be facilitated by integration of known standard materials science methods, e.g., MS and EM. 

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