Interaction of Astramol poly(propyleneimine) dendrimers with linear polyanions

Interaction between Astramol poly(propylene imine) dendrimers of five gener ations, DAB-dendr-(NH2)(x) (where x is equal to 4, 8, 16, 32, or 64) and li near poly(sodium acrylate), poly(acrylic) acid, poly(sodium styrenesulfonat e), or native DNA was studied in salt-free solutions by means of potentiome tric, argentometric, and turbidimetric titrations. In addition to x outer p rimary amine groups the dendrimer molecule contains x - 2 inner tertiary am ine groups, It is found that the pH-controlled interpolyelectrolyte couplin g reaction resulting in formation of the corresponding interpolyelectrolyte complexes occurs on mixing of the dendrimer and the polyanion solutions. A peculiar finding was that all dendrimer amine groups being protonated can form ion pairs with carboxylate or sulfonate groups of the polyanions. In o ther words DAB-dendr-(NH2)(x) molecules are fully penetrable for rather fle xible oppositely charged polyelectrolyte chains. However, this is not the c ase for rigid negatively charged DNA double helixes which apparently bind o nly to the dendrimer shell. The complexes of dendrimers, with polyanions co ntaining equal amounts of cationic and anionic groups mostly ion-paired (st oichiometric complexes), are insoluble in water. At the same time water sol uble nonstoichiometric interpolyelectrolyte complexes can be obtained if th e dendrimer is a deficient component of the complex species. This behavior is similar to that of complexes formed by oppositely charged linear polyion s.