Molar Amount of PEL Charges. Colloid Titration Results on PEI-25K, PEI-750K, PEI-M-25K, CS

Additional file 1

Molar amount of PEL charges. Colloid titration results on PEI-25K, PEI-750K, PEI-M-25K, CS.

PCD titration was used as an essential method for the determination of the molar amount of charged groups of the used polyelectrolyte (PEL) systems. Thereby, the PEL solution was titrated by defined volumes of a low molecular weight PEL (PDADMAC, PES, respectively) with opposite charge. In the Fig. below the titrated volumes of PEI-M and CS solutions are plotted as a function of concentration. Fig. A shows the titration profile for a rapid titration mode and Fig. B for a slow titration mode. While the rapid titration mode shows linear dependencies only for CS (blue cubes), PEI-25K, PEI-750K and PEI-M-25K (red symbols) show nonlinear dependencies, in which for higher concentrations the titrated volumes were lower than those predicted for a linear dependence. In contrast to the rapid titration mode for the slow titration mode PEI-25K and PEI-M-25K show linear dependencies, while PEI-750K still shows deviation from linearity for higher concentrations (0.075 and 0.1 mg/ml). CS shows linearity in both rapid and slow titration mode. These effects can be interpreted in terms of different accessibilities of charged groups for low molecular PEL of opposite charge. Obviously, the sulphate groups of linear CS are better accessible compared to the primary, secondary and tertiary ammonium groups featuring a composition of 30/40/30% of branched PEI-25K, PEI-750K and PEI-M-25K. This behavior has practical consequences for the preparative complexation of cationic PEI-25K, PEI-750K and PEI-M-25K with anionic CS. At first the titrated volume and thus the number of accessible cationic charges of of these PEI systems have to be determined for exactly the concentration, at which the complexation should be performed. Secondly, the preparative complexation should be performed very slowly.

(A) / (B)
Titrated volumes for PEI-25K, PEI-750K, PEI-M-25K(red, 0.001M PES) and for CS(3) (blue, 0.001M PDADMAC) solutions plotted versus their starting concentrations. (A) Rapid titration mode, (B) Slow titration mode (see Methods).