| Abstract
| - The comb-type polycation consisting of apoly[2-(diethylamino)ethyl methacrylate](PDEAEMA)backbone and poly(l-lysine) (PLL) side chains has beenprepared as a novel pH-sensitive DNA carrier.The comb-type copolymer PDEAEMA-graft-PLL was preparedby using the macromonomer method,in which apoly(Nε-carbobenzoxy-l-lysine)macromonomer was radically copolymerized with DEAEMA.The comb-type copolymer exhibited a two-step proton dissociationand a dual ionic character owingto the two cationic segments in the copolymer, as determined byacid−base titration. In addition, thecomb-type copolymer caused no significant turbidity even at pH 10,whereas PDEAEMA homopolymersuddenly precipitated out of the aqueous medium above pH 7.5 owing tothe deprotonation of aminogroups. Furthermore, a 1H NMR study proved thatprotonated PLL segments solubilized the comb-type copolymer with a hydrophobic PDEAEMA core at higher pH.Finally, the pH-dependent behaviorof the DNA complex with the comb-type copolymer was evaluated. Thediscontinuous turbidity changeof the DNA/PDEAEMA-graft-PLL mixture at pH 7.5 suggestedthat the solubility of the complex variedin response to pH. By circular dichroism measurement, we alsofound that the comb-type copolymerwas capable of varying DNA compaction pH-dependently. Inconclusion, we have demonstrated thatthe comb-type copolymer is capable of sensing a pH signal andoutputting the nonlinear change ofthe physicochemical properties of DNA polyelectrolytecomplexes.
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