CONICET | Buscador de Institutos y Recursos Humanos

The aim of this work is the physicochemical characterization of polyamidoamine (PAMAM) dendrimers (D) of generation (G) 4.0 and 4.5, as a function of the pH. PAMAM D are polymers with a branched structure chemically synthesized from a core of ethylenediamine with progressive addition of polyamidoamine groups. These nanoparticles can have complete G (as DG4.0), with a primary amine as terminal groups; or intermediate G (as DG4.5), with carboxylic acid as terminal groups. Both D have interior pockets with amide and tertiary amines. The internal and terminal ionizable groups of the D would change their charge in function of the physicochemical environment. The fluorescence of the PAMAM D is currently a matter of research. It is known that they have two fluorophores. Only one of these fluorophores is identified, while the second is the subject of controversy nowadays. Raman, UV-Vis and fluorescence spectroscopies were used to study the changes that pH causes in the PAMAM D. Acid dissociation constants (pKa) were determined for DG4.0 and DG4.5 by potentiometric titration. Raman spectra showed signals of tertiary amines and carbonyl of the carboxylic acid and amide bond. On the other hand, transitions corresponding to amides and tertiary amines are found on UV-Vis spectrum. Tertiary amines absorb with different intensity according to the pH condition. The detected fluorescence emission reinforces the idea that the main fluorophore in PAMAM D are the inner tertiary amine. However, we found an unusual behavior of the DG4.0 fluorescence with the pH, while the behavior of fluorescence of DG4.5 are shown for the first time. These results could be helpful to understand the structural behavior of PAMAM D according to its environment and to predict its possible interactions with molecules of biomedical interest.