Interpolyelectrolyte reactions in solutions of functionalized dextrans with negatively charged groups along the chains

Poly(methacrylate) and functionalized dextrans (obtained by random substitution of soluble dextran with carboxylate, benzylamide, sulfate, and sulfonate groups) were labeled with fluorescent pyrenyl groups. The formation of polyelectrolyte complexes (PEC) of both labeled polyanions with poly(N-ethyl-4-vinylpyridinium) as a quencher, and the competitive reactions in solutions of the PEC were studied by means of the fluorescence quenching technique. A complete excitation of fluorescence was observed when highly sulfated or sulfonated polyanion competitors like heparin and poly(styrenesulfonate) were added to the PEC solutions. We presume that a transfer of the polycation chains from PEC to the polyanion competitors occurs. Modified dextrans are good polyanion competitors due to their content of sulfate and sulfonate groups, even in small amounts. Moreover, the affinity of carboxylate groups containing polyanion competitors to the polycation increases according to the increasing charge density of the chains. Shielding of negative charges of the polyanions by addition of low-molecular weight counterions decreases the efficiency. The data obtained show that both chemical nature of the negatively charged groups and charge density of the polyanion chains are factors that effectively control the equilibrium of competitive interpolyelectrolyte reactions.