Electrophoretic mobility and molecular distribution studies of poly(amidoamine) dendrimers of defined charges

Abstract

Generation 5 ethylenediamine (EDA)-cored poly(amidoamine) (PAMAM) dendrimers (E5, E denotes the EDA core and 5 the generation number) with different degrees of acetylation and carboxylation were synthesized and used as a model system to investigate the effect of charge and the influence of dendrimer surface modifications on electrophoretic mobility (EM) and molecular distribution. The surface-modified dendrimers were characterized by size-exclusion chromatography, 1H NMR, MALDI-TOF-MS, PAGE, and CE. The focus of our study was to determine how EM changes as a function of particle charge and molecular mass, and how the molecular distribution changes due to surface modifications. We demonstrate that partially modified dendrimers have much broader migration peaks than those of fully surface functionalized or unmodified E5 dendrimers due to variations in the substitution of individual dendrimer surfaces. EM decreased nonlinearly with increases in surface acetylation for both PAMAM acetamides and PAMAM succinamic acids, indicating a complex migration activity in CE separations that is not solely due to charge/mass ratio changes. These studies provide new insights into dendrimer properties under an electric field, as well as into the characterization of dendrimer-based materials being developed for medical applications.

CE of poly(amidoamine) succinamic acid dendrimers using a poly(vinyl alcohol)‐coated capillary

“…The counterion binding effect, in certain circumstances, could play an important role in the separation of dendrimers. For instance, using a bare silica capillary and a positive polarity condition, the EM of a G5 PAMAM dendrimer with different carboxylation degrees does not display a linear relationship as a function of the charge/mass ratio [26]. Dubin and co-workers [32] studied the effects of pH and ionic strength on the mobility of Newkome's carboxyl-terminated dendrimers using CE.…”

“…Consequently, the apparent EM of PAMAM-SAHs increases with the number of dendrimer generations (Table 1). Carboxyl-terminated dendrimers often experience a counterion binding effect when subjected to separation under an electric field [26,32,33]. The counterion binding effect, in certain circumstances, could play an important role in the separation of dendrimers.…”

“…As opposed to polycationic dendrimers, negatively charged PAMAM-SAH dendrimers do not adsorb onto the bare silica capillary surface, and thus the migration of these dendrimers is largely dependent on the EOF and the charge/ mass ratio [23,26]. Due to the relatively similar charge/mass ratio for PAMAM-SAH dendrimers of different generations, separation of a mixed dendrimer sample with different generations was not possible [23].…”

“…It was previously reported that separation of polycationic PAMAM dendrimers using a bare fused-silica capillary lacks reproducibility because of the strong interaction between the dendrimers and the capillary surface [30,34]. In order to improve the separation reproducibility, the surface of the capillary was modified through silanization [26][27][28][29], dynamic polymer coating [35], or permanent polymer coating [31] to decrease the interaction of the polycationic dendrimers with the capillary surface. A recent report shows that separation of polycationic PAMAM dendrimers using a poly(vinyl alcohol) (PVA)-coated capillary can achieve excellent reproducibility [31].…”

“…CE is one such powerful bioanalytical technique and has been successfully applied to characterize biomolecules like DNA [24] and proteins [25]. Due to its high efficiency, high sensitivity, automation, and fairly short run times, CE is being routinely used as a quality control tool in the characterization of dendrimers [14,15,23,[26][27][28][29][30][31][32][33][34][35][36]. The separation principle is mainly based on the difference in the charge/ mass ratios.…”