Poly(amidoamine) (PAMAM) dendrimers are an archetypal example of water-soluble dendritic polymers. These macromolecules have been considered for applications ranging from gene therapy to chemical sensing, all of which involve their ability to encapsulate small molecules in solution. However, the interactions responsible for these binding events are not yet entirely elucidated. In this study, we prepared simple PAMAM analogues containing the key moieties from those macromolecules, and studied their interactions with carboxylic acid anions, in order to determine how each of these components contributes to the binding properties of the native dendrimer. We examined these interactions using 1H-NMR spectroscopy, through the shifts in signals from both the carboxylates and the analogues in titration experiments, as the fully protonated analogue was titrated into the fully deprotonated carboxylic acid. The resulting peak shift profile was then interpreted, also by comparison with the one corresponding to the simple protonation of the anion (obtained separately). Divergence in the observed behavior from a simple protonation profile can be attributed to a specific binding interaction of the anion with the analogue. The analogue structures under study were chosen to compare the effects of charge and substitution of the amine moiety. K0 contains two basic sites and behaves as a dication when protonated. On the other hand, K1 and K2 lack the tertiary or the primary amine, respectively, thereby allowing us to gauge the impact of those moieties on the binding process by the effects of their absence. Similarly, specific carboxylate anions were chosen to investigate the contribution from charge and substitution (e.g. H-bonding) to the carboxylate’s interaction.

Noncovalent interactions between PAMAM dendrimer analogues and carboxylates

255th National Meeting (2018)

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