Double thermoresponsive polybetaine-based ABA triblock copolymers with capability to condense DNA

ABA type MPDSAHy-b-PMEO2MAx-b-MPDSAHy (A = N-(3-(methacryloylamino)propyl)-N,N-dimethyl-N-(3-sulfopropyl) ammonium hydroxide (MPDSAH), B = 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA)) triblock copolymers with narrow polydispersity index were prepared by atomic transfer radical polymerization (ATRP) in the mixture of water/methanol with addition of sodium chloride. The copolymer solution was shown to exhibit UCST and LCST behaviors. The dual temperature sensitiveness was investigated via turbidity measurement and steady-state fluorescence spectroscopy. The UCST was found to be dependent upon the solution concentration, and UCST shifted towards LCST with the increment in the block length of MPDSAH block. In the selected low temperature region, the micropolarity of pyrene slightly increased due to the weak positive–negative interaction in diluted solution; while above LCST, pyrene experienced more hydrophobic milieu owing to the noticeable dehydration of PMEO2MA. The analysis of ethidium bromide displacement suggested the strong capability of MPDSAH homopolymer to bind DNA; MEO2MA moieties in copolymers weakened the binding ability of PMPDSAH to DNA, but 54–60% EB was still replaced by copolymers at complexing ratio of 10/1. AFM confirmed that PMPDSAH and copolymers were capable of condensing DNA to nanoparticles at an appropriate complexing ratio. Complexing with DNA, UCST of solution vanished, but LCST was slightly increased due to the enhanced hydrophilicity caused by liberation of negative charges.