Microscopic protonation equilibria of poly(amidoamine) dendrimers from macroscopic titrations

Poly(amidoamine) (PAMAM) dendrimers of generations G0, G1, G2, G3, G4, and G6 are investigated by potentiometric (acid-base) titrations. The data are interpreted with a site binding model, which offers the possibility to model the titration curves for all generations of the dendrimers and to describe all dendrimers within a common parameter set. These parameters involve the microscopic ionization constants for each group in the fully deprotonated state and nearest-neighbor pair interaction parameters. From this model we can further obtain all microscopic ionization constants as well as conditional microstate probabilities. The protonation. of PAMAM dendrimers first involves protonation of primary amine groups at the outer rim of the dendrimer at high pH, while the tertiary amine groups in the dendrimer core protonate at lower pH. The last group to protonate at low pH is a central tertiary amine.