Effect of Dendrigraft Generation on the Interaction between Anionic Polyelectrolytes and Dendrigraft Poly(l-Lysine)

Abstract

In this present work, three generations of dendrigraft poly(l-Lysine) (DGL) were studied regarding their ability to interact with linear poly (acrylamide-co-2-acrylamido-2-methyl-1-propanesulfonate) (PAMAMPS) of different chemical charge densities (30% and 100%). Frontal analysis continuous capillary electrophoresis (FACCE) was successfully applied to determine binding constants and binding stoichiometries. The effect of DGL generation on the interaction was evaluated for the first three generations (G2, G3, and G4) at different ionic strengths, and the effect of ligand topology (linear PLL vs. dendrigraft DGL) on binding parameters was evaluated. An increase of the biding site constants accompanied with a decrease of the DGL-PAMAMPS (n:1) stoichiometry was observed for increasing DGL generation. The logarithm of the global binding constants decreased linearly with the logarithm of the ionic strength. This double logarithmic representation allowed determining the extent of counter-ions released from the association of DGL molecules onto one PAMAMPS chain that was compared to the total entropic reservoir constituted by the total number of condensed counter-ions before the association.

Keywords: binding constants; counter-ion release; dendrimers; frontal analysis continuous capillary electrophoresis; ionic strength dependence; polyelectrolyte complexes.

Figure 1

Example of determination of binding parameters (n and k) by FACCE for the interaction G3-PAMAMPS 30% at 552 mM ionic strength. Electropherograms obtained for different G3-PAMAMPS 30% equilibrated mixtures (A); and the corresponding isotherm of adsorption (B) representing the number of bound G3 entities per PAMAMPS 30% chain according to the free G3 concentration. Experimental conditions: PDADMAC coated capillary 33.5 cm (8.5 cm to the detector) × 50 µm i.d. Background electrolyte: 12 mM Tris, 10 mM HCl, 542 mM NaCl, pH 7.4. Applied voltage + 1 kV with a co-hydrodynamic pressure of +4 mbar. Detection at 200 nm. Samples were prepared in the background electrolyte by 50/50 v/v dilution of the following solutions: PAMAMPS 30% at 2 g/L with G3 at 5, 4, 3, 2.5, 2, 1.6, 1.2, 1, 0.8, 0.6 g/L.

Figure 2

Variation of the ionic strength of recomplexation I_recomp as a function of the molar mass of the purified DGL.

Figure 3

Variation of the interaction stoichiometry n_(Lys/AMPS), expressed as the number of DGL molecules per PAMAMPS chain, as a function of the ionic strength for the interactions between DGL (or PLL50) with PAMAMPS 30% and PAMAMPS 100%.

Figure 4

Variation of the binding site constant k as a function of the ionic strength I for the interactions between DGL (or PLL50) with PAMAMPS 30% and PAMAMPS 100%.

Figure 5

Variation of log β_n as a function of log I for the interactions between DGL (or PLL50) with PAMAMPS 30% and PAMAMPS 100%.

Figure 6

Variation of the number of counter-ions effectively released ($-\frac{\partial <n>\log k}{\partial \log I}$) for the linear PLL50 and for DGL G2, G3 and G4 in interaction with PAMAMPS 30% or PAMAMPS 100%.

Figure 7

Schematic representation of the interaction between one ligand (PLL or DGL molecule) and one binding site –s of a PAMAMPS 30% chain. The DP of one binding site on the PAMAMPS substrate is: 128, 160, 265 and 750 for PLL50, G2, G3 and G4, respectively, as calculated by dividing the DP of PAMAMPS 30% by the stoichiometry n_{(PLL or DGL/PAMAMP)} of the interaction. Red dots represent the negative charge of the sulfonate groups and blue dots represent the positive charge of the ammonium groups.