Dendrimer array

Since the properties of the modular components are known and different modules can be located in the desired positions of the dendrimer array, synthetic control of the various properties can be obtained. It is therefore possible, as schematically shown in Figure 2, to construct arrays where the electronic energy migration pattern can be predetermined, so as to channel the energy created by light absorption on the various components towards a selected module (antenna effect). 

Considerable attention has been given to the synthesis of compounds in which a single mono- or multinuclear coordination unit is at the center of a dendrimer array. These systems have been prepared by the construction of ligands with pendant dendritic wedges with subsequent convergent assembly upon coordination of a metal ion at the center or by covalent synthesis of an appropriate dendrimer-functionalized macrocyclic core. The primary interest for the study of such compounds lies in the very unusual, usually hydrophobic, environment in which the metal(s) at the center find themselves. This environment has been likened to that at the active site of a metalloenzyme and numerous studies have dealt with the catalytic and biomimetic activity of such conjugates. A general introduction to the area and the concept of chemistry within dendrimers is available. " The term dendrizyme has been used to describe these systems. 

Other supramolecular structures such as dendrimers have also been synthesized with zinc-containing porphyrins. Sixteen free base and sixteen zinc porphyrin units were added at the fifth generation of dendritic poly(L-lysine) and intramolecular fluorescence energy transfer was observed.823 Assembly of supramolecular arrays in the solid state has been achieved with the incorporation of an amide group for hydrogen bonding. Zinc meso-tetra(4-amidophenyl)porphyrin... 

Fig. 2. A supramolecular array (9 a) obtained enclosing the eight ferrocene units of dendrimer 9 into (3-CD molecules... 

In the pentaporphyrin array 46, light absorption by the four peripheral Zn-por-phyrins is followed by efficient energy transfer to the central free base porphyrin [68], as it happens in the polypyridine dendrimers discussed above [53b]. 

Assemblage of the dendritic molecules by chemical crosslinking into an array, which is more or less organized. The specific functions of dendrimers can be possibly amplified when they are assembled into superstructures [65]. 

Figure 11.16 is a cryo-TEM image of G10 PAMAM dendrimers in water. The cryo technique involves flash freezing of the dendrimer solution as a thin film on a grid and is described elsewhere [20]. Individual dendrimers appear to be organized into an array of single dendrimer thickness. While there are complicating factors due to the sample preparation, the picture is consistent with... 

Long-range electron transfer reactions have attracted attention relative to the initial stages of photosynthesis, and special interest has been focused on the design of noncovalently assembled donor-acceptor arrays. Dendrimers with spatially isolated porphyrin cores are potential motifs for investigating such long-range electron transfer reactions [12],... 

One particular dendrimer system was reported to have increased the loading capacity 10-fold over direct coupling of the oligonucleotide to the surface. Unfortunately, the presumed improvement in hybridization efficiency was not discussed in quantitative terms. Reusability of the array was a primary objective of the work. Again, quantitative information was not provided. As the authors note, the array withstood >7 actual hybridization stripping cycles and 30 simulated (lacking target) cycles. 

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