Size Invariance of Polyelectrolyte Dendrimers

Abstract

To quantify the swelling response of polyelectrolyte dendrimers in aqueous solutions as affected by changes in solution conditions, we have studied eighth generation, G8, poly(amidoamine) (PAMAM) dendrimers in D 2O using small-angle neutron scattering. The charge density is manipulated by varying the pH of the solution in order to protonate and deprotonate the primary and tertiary amines. The coherent scattered intensity at high q values yields size information from the form factor of individual dendrimers. The distance distribution functions of the dendrimers in a variety of experimental situations were determined by indirect Fourier transform. For all the conditions studied, we find that the size of G8 dendrimers is essentially insensitive to variations of the pH (4.7 < pH < 10.1) and of ionic strength (up to 3 M of NaCl). In all cases, the scattering curves yield density profiles that correspond well to a uniform sphere with a radius of gyration R G ) 4.0 ( 0.15 nm. We conclude that the dendrimer size is essentially independent of the charge density or ionic strength of the solvent, contrary to the predictions of current models and simulations.

Hydrodynamic Behavior of Dendrigraft Polylysines in Water and Dimethylformamide

“…For well known dendrimers such as diaminobutane dendrimer (DAB) or PAMAM, there was no detected significant change of the molecular hydrodynamic size with pH or in different solvents. For instance, the invariance of PAMAM dendrimers under variable pH conditions was asserted from small angle neutron scattering data [20,21]. Furthermore, the PAMAM dendrimer dimension was found to vary in the range of 5 to 10%, depending on the solvent quality [22].…”

The Structure of Dendrimers with Charged Terminal Groups: Monte Carlo Simulations

“…For instance, it is still rather unclear if the dendrimer size is sensitive to the charge density or ionic strength of the solvent. On one hand, simulations indicate such a dependence, whereas small-angle neutron scattering does not [5].…”

“…Some examples of their use include lithographic materials, nanoscale catalysts, drug delivery systems, rheology modifiers, bioadhesives, and magnetic resonance imaging (MRI) contrast agents [3]. Though experimental studies [4][5][6][7][8][9], theory and simulations [10][11][12][13][14] have already brought about some insight into the way charged dendrimers react to various conditions, the research on them is far from being completed. For instance, the number of simulation papers is still very limited and some predictions reported in them contrast with experimental results.…”

Conformations of Highly Charged Dendronized Polymers in Aqueous Solutions of Varying Ionic Strength

“…[1] Size invariance and the density profiles of such dendrimers in solutions have been predicted by molecular modeling [2] and experimentally proven using small-angle neutron scattering. [3,4] Experimental efforts have also been focused on the complexation of charged dendrimers with oppositely charged polyelectrolytes. [5][6][7][8] All these investigations focus on spherical dendrimers carrying ionogenic terminal groups, e.g., polyamidoamine and polypropyleneimine.…”