pH Responsiveness of PAMAM Dendrimer - Structure and Dynamics

Xin Li (Indiana University)

We investigated the structure and dynamics of poly(amidoamine) (PAMAM) dendrimer as a function of molecular protonation in aqueous (D2O) solution. A series of small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) experiments were conducted and our results show a slight consequent increase of the molecular size, which is less clear for low and medium generation (G3 to G6) dendrimers and more noticeable for high generations (G7 and G8). A continuous variation of the intramolecular density profile upon increasing molecular protonation is also revealed. A combined quasi-elastic neutron scattering (QENS) and high-resolution solution NMR spectroscopy study was carried out and exhibits that the local motion of the dendrimer segments becomes more rapid upon the increased charge. Counterion valence has a strong impact on these charge-induced behaviors, and the structured confined water within the dendrimer makes a significant contribution to the scattering functions. The interpretations of the pH responsiveness are discussed based on the comparison between atomistic molecular dynamics (MD) simulation and experimental results.

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