Scaling trend in diffusion coefficients of low generation G0-G3 PAMAM dendrimers in aqueous solution at high and neutral pH

Aqueous solution diffusion coefficients for G0-G3 PAMAM dendrimers were determined from DOSY-NMR spectroscopy at high and neutral pH. The study was performed in a dilute regime and diffusion coefficients at infinite dilution (D-0) were estimated from the variation of diffusion coefficients with dendrimer concentration. Hydrodynamic radii (R-h) for each dendrimer were estimated from D-0 using the Stoke-Einstein relationship at both pH. According to D-0 and R-h values, the structure of G0-G1 PAMAM dendrimers is almost insensitive to pH variations, whereas G2-G3 PAMAM dendrimers undergo swelling at neutral pH, due to surface amino groups protonation. Experimental diffusion coefficients show a scaling trend with the number of dendrimer atoms (N), with scaling laws of the type D-0 proportional to N-alpha, where alpha takes values of -0.39 and -0.50 at pH 12 and 7, respectively. For the first time, experimental data accounts for the scaling behavior of aqueous diffusion coefficients for low generation PAMAM dendrimers, as previously reported from molecular dynamics simulations.