Dendrimers shape changes

Dendrimer Shape Change A Nanoscale Molecular Morphogenesis. 344... 

Fig. 30 Congestion-induced dendrimer shape changes (/, //, III) with development of nanocontainer properties for a family of [core l,2-diaininoethane] (4 2) dendn-poly (amidoamine)-(NH2)z (G = 0-10) PAMAM dendiimers with core multiplicity = 4 and branch cell multiplicity A/b = 2. Distances between Z surface groups are shown as a fimction of generation [138]...

A similar approach was taken by Moore [27], utilizing poly(phenyl acetylene) dendrimers with a dimethylbenzene moiety attached at the core of the dendrimer. An anomalous shift (41 nm) in the fluorescence spectra of the probe in various nonpolar hydrocarbon solvents was observed for G5 and G6, but not for G1 to G4. This observation confirmed significant in the size and shape changes for these dendrimers between G4 and G5. 

For all three types of dendrimers described above, a flattened, disk-like conformation was observed for the higher generations. However, the molecular shape at the air-water interface is also intimately associated with the polarity, and hence the type of dendrimer used. In case of the polypropylene imine) and PAMAM dendrimers the hydrophilic cores interact with the sub-phase and hence these dendrimers assume an oblate shape for all generations. The poly(benzyl ether) dendrimers, on the other hand, are hydrophobic and want to minimize contact with the water surface. This property results in a conformational shape change from ellipsoidal, for the lower generations, to oblate for the higher generations [46]. 

Figure 3 A dendrimer series with core multiplicity (N = 3) and branch cell multiplicity (Nc = 2) illustrating molecular shape changes, surface branch cells, surface Z-groups, and molecular weights as a function of generation.

However, for the dendrimer nanocomposite metallic systems this change in shape was not observed. Again, due to the high stability to intense laser pulses, the anisotropy value of the gold dendrimer nanocomposite, which can be viewed as a measure of the symmetry of the particle, did not change after several repeated cycles of measurements. It is possible that the initial optical pumping of the electron-phonon modes of the metal particles is partially absorbed by the encapsulating PAMAM dendrimer. 

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