Chemistry Reference
In-Depth Information
Figure 11.6 Snapshots of calculated structures of dendrimers. For clarity, internal and term-
inal monomers are shaded darker and lighter, respectively, and the size of the core monomer
has been made larger than the other monomers. Reprinted from Giupponi and Buzza
(2005). Copyright 2005 American Institute of Physics.
Experimental Systems.
Experimentally, amphiphilic Fr´chet-type poly(aryl
ether) dendrimers displaying poly(ethylene glycol) (PEG) peripheral arms were
shown to form monomolecular micellar structures exhibiting solvent-sensitive
conformational changes (Fig. 11.7; Gitsov and Frechet 1996).
Similarly, a poly(propylene imine) (PPI) dendrimer fitted with triethyleneoxy
methyl ether and octyl groups at every terminal position was soluble in both
organic and aqueous solvents, indicating sufficient structural flexibility to present
either the hydrophilic or hydrophobic termini toward the solvent (Fig. 11.8; Pan
and Ford 1999, 2000).
Thayumanavan's group reported dendrimers containing polar and apolar groups
at every repeat unit that inverts from a normal to inverted micellar-type conformation
going from aqueous to organic media (Fig. 11.9; Basu et al. 2004; Aathimanikandan
et al. 2005; Klaikherd et al. 2006). This solvent-sensitive conformational behavior
affords a unique capability to solubilize hydrophobic molecules in water and
hydrophillic molecules in lipophilic media.
11.2.3. Polyelectrolyte Dendrimers
The addition of charge to a dendrimer structure could be expected to cause a struc-
tural expansion that minimizes the ensuing coulombic repulsions, similar to the
