Neutral coatings for the study of polycation/multicharged anion interactions by capillary electrophoresis: application to dendrigraft poly-L-lysines with negatively multicharged molecules.

The study of interactions between oppositely multicharged (macro)molecules remains a challenging issue. In frontal analysis capillary electrophoresis (FACE), it is difficult to avoid the adsorption of one of the interacting partners onto the capillary wall. In this work, we demonstrate the possibility to use FACE and affinity capillary electrophoresis (ACE) on a neutrally coated capillary for the study of interactions between a polycationic dendrigraft (or linear) poly-l-lysines, on one hand, and a multicharged anionic biomolecule (adenosine monophosphate, AMP, or adenosine triphosphate, ATP), on the other hand. A systematic comparison of four different neutral coatings (hydroxypropyl cellulose, polydimethylacrylamide, polyacrylamide, polyethylene glycol) has been performed based on the repeatability of the electrophoretic migration of the dendrigraft poly-l-lysines at pH close to neutrality. Both FACE and ACE methodogies were then used to study the interactions and to get the association constants and the stoichiometry of the complex. Multisite interactions, with two classes of independent sites, were determined. The specificity of the dendritic polylysine structure compared with linear polylysine in the interaction with ATP or AMP is also emphasized.