Nanoscale Solution Structure and Transfer Capacity of Amphiphilic Poly(amidoamine) Dendrimers Having Water and Polar Guest Molecules Inside

Poly(amidoamine) (PAMAM) dendrimers of third and fourth generation (G3 and G4) are peripherally modified with hydrophobic stearyl acrylate via the Michael addition reaction. The hydrophobically modified dendrimers (P3 and P4) are investigated to mimic the conventional inverse micelles in toluene medium by encapsulating organic polar dye Acid Red 1 (AR-1) and copper(II) salt from water phase to afford red and blue toluene phase, respectively. The efficacies of micelle-assisted transfer of AR-1 from aqueous solution into toluene phase are investigated, and the maximum numbers of dye loading per dendritic core are determined to be approximately 8 for P3 and 24 for P4. The unimolecular natures as well as the structural characterizations of these dendritic inverse micelles in toluene before and after encapsulation of polar guest molecules such as water, AR-1, and copper(II) salt are studied by small-angle X-ray scattering (SAXS) experiments at 25 °C. The initial amphiphilic dendrimers of P3 and P4 have a globular structure in toluene and show scattering patterns similar to oblate ellipsoid of revolution with 17.7 and 25.9 Å in radius of gyration (R g), respectively. Encapsulation of the polar guests such as water and AR-1 into the amphiphiles expands their chain conformation in toluene, and copper(II) salt increases the R g value up to 34.5 Å for P3 and 43.2 Å for P4. The scattering profiles of the expanded dendrimers are well described by those calculated from the sphere with a constant density.