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

Abstract

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 / N a , where a 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.

Diffusion NMR Study of Generation-Five PAMAM Dendrimer Materials

“…23 Spectra were obtained on a Varian VNMRS 700 apparatus employing DOSY_for_VnmrJ_3.x software. The temperature was set to 30 °C, and samples were allowed to equilibrate for no fewer than 15 min.…”

Local hydrodynamics of solvent near diffusing dendrimers: A test of the new Stokes–Einstein relation

“…It has been reported that the size of dendrimers is influenced by different pH values . We ignore this in the simple model of dendrimers without atom details, and so did the cited experimental size data of dendrimers which closely match the simulation data.…”

“…ϵ is the interaction force parameter. (b) Hydrodynamic radii ( ) of the dendrimers G1–1, G2–1, G3–1, and G4–1 with fixed branch length from simulations in comparison with dendrimers (PA MAM) in methanol from published experiments in green solid squares fitted by the green solid line, in comparison with PAMAM in aqueous solution from published experiments in green circles fitted by dotted line and green stars fitted by dashed line, and in comparison with those from published simulations 2 in purple and pink. Note here the and R g from literatures were scaled for clear comparisons.…”

“…We ignore this in the simple model of dendrimers without atom details, and so did the cited experimental size data of dendrimers which closely match the simulation data. We now plot the size data from the simulations in literature to test the possible effects of pH on the modified Stokes–Einstein. As shown in Figure (b), the size data of PAMAM under high pH appropriately match the simulations in this study.…”

Drug release kinetics of pH‐responsive microgels of different glass‐transition temperatures

“…The time correlation function of the scattered intensity, G 2 (t) was analyzed using the inverse Laplace transformation technique (regularized positive exponential sum in our case) to produce the distribution function of decay times. With this, the apparent hydrodynamic radius, R h , can be determined from the decay rate using the Stokes–Einstein equation: where k is the Boltzmann constant, T is the absolute temperature, η is the solvent viscosity, Γ is the decay rate, and q is the scattering vector (, where θ is the scattering angle, n is the refractive index of the solution, and λ is the wavelength of the incident laser light in vacuum).…”