Supercharged pyridinium polycations and polyelectrolyte complexes

Supercharged polycations bearing pH-insensitive double-charged units were synthesized by alkylation of poly(4-vinylpyridine) with bromo-alkyl-trimethylammonium bromides (alkyl = propyl and pentyl) yielding polymers with 3 and 5 methylene groups in spacer between charges, respectively. Virtually all charged groups of the exhaustively alkylated polycations were accessible for polyanions. The ion pairing with pyrenyl-tagged poly(methacrylate) anion which was monitored by fluorescence quenching techniques revealed pronounced binding of both polycations and relatively high water-salt stability of the complexes, in particular formed by polycation with shorter spacer. For partially quaternized (co)polymers, a decrease in alkylation degree weakened the binding in slightly alkaline solutions but markedly enhanced the interaction at pH <= 7.0 due to strengthening the systems by both H-bonds and additional ion pairing induced by protonation of the pyridine groups. The disclosed tune pH-control over the stability in neutral media could form a platform for practical implementation of the supercharging, specifically in biotechnology. (C) 2015 Elsevier Ltd. All rights reserved.