Interactions between oppositely charged dendrimers
The interactions between cationic (G3, G4, and G5) and anionic (G4.5) poly(amidoamine) (PAMAM) dendrimers were investigated by isothermal titration calorimetry (ITC), photometric titration, nuclear magnetic resonance (NMR), and dynamic light scattering (DLS) studies. The results suggest that the formation of anionic-cationic dendrimer aggregates is an enthalpy-driven process. Ionic interactions occur between the cationic and anionic dendrimers, followed by the formation of supramolecular aggregates and precipitates. The phase separation of the resulting aggregate depends on dendrimer generation, surface charge density, anionic-cationic dendrimer molar ratio, and solution pH values. G5, with a relatively rigid structure, displayed a different binding behavior with G4.5 as compared to the G3 and G4 dendrimers with more flexible scaffolds. G4.5 and G5 with a molar ratio of 0.5 : 1 form the largest aggregates among the investigated G4.5-G5 molar ratios. G4.5 and G5 form aggregates in a size range of 300-3000 nm depending on the G4.5-G5 molar ratio. The G4.5-G5 supramolecular aggregates are not stable and will disassemble after several days of incubation. The results help us to understand the interactions between globular polyelectrodes as well as oppositely charged biomacromolecules.