Construction And Self-Assembly Of Cu(Ⅱ)-Bonded Single-Chain Polymer Nanoparticles Via Electrostatic Repulsion And Coordination Association

Metalloproteins are importamt in functions of living biological tissues. Simultaneous coordination-association and electrostatic-repulsion interactions play critical roles in the construction and stabilization of enzymatic function metal-centers in water. These interactions can induce construction and self-assembly of single-chain nanoparticles(SCNPs) of artificial polymers in water. Herein, we report the construction and assembly of dative-bonded aqueous SCNPs via simultaneous coordination-association and electrostatic-repulsion interactions within single-chains of imidazole-based block copolymer.For this purpose, 2-4-imidazolylethyl acrylamide(IEAM) and 2-hydroxypropyl methacrylamiade(HPMA) were selected as hydrophilic monomers. Water-soluble poly(2-hydroxypropylmethacrylamiade)-block-poly(2-4-imidazolylethylacrylamide)(PHPMA-b-PIEAM) copolymer was synthesized via reversible addition-fragmenta- tion chain transfer(RAFT) polymerization in aqueous solution under visible light irradiation at 25 oC. This block copolymer is well-defined with narrow molar mass distribution. The copolymer has remarkable pH-responsible phase transition behavior, which is highly soluble in acidic water, and can assemble into micelle at pH 9.5.Ionic imidazolium-motifs in acidic water provide electrostatic repulsion, and are weakened by alkalized into nonionic imidazole-motifs. Meanwhile, the in situ Cu(II)-coordination induces single-chain collapsing into SCNPs in acidic water. SCNPs are stabilized by the electrostatic repulsion of dative-bonded block and steric shielding of nonionic water-soluble block, and have huge specific surface area of the metal-centers accessible to substrates in acidic water.Moreover, coordination interaction can be intensified and electrostatic interaction weakened upon adjusted from pH 5.6 to pH 7.5. The simultaneous variations of coordination-association/electrostatic-repulsion interactions leads to the self-assembly of initially-assembled SCNPs. SCNPs assemble into micelle over pH 5.6~6.6, and network nanostructures around p H 6.8. These networks have been ruptured and further assembled into large-particle on adjusted to pH 7.1 and pH 7.5. This programmable pH-responsive self-assembly of SCNPs from micelle, network to large-particle endows SCNPs with media-sensitive phase transformation behavior. Therefore, this new strategy provided a general and versatile platform for construction of enzyme-inspired aqueous catalysts.In short, the construction and self-assembly of Cu(II)-bonded aqueous single-chain nanoparticles(SCNPs) can be achieved via simultaneous coordination-association and electrostatic-repulsion interactions in the imidazole-based block of double-hydrophilic block copolymer. Moreover, the SCNPs can self-assemble into micelles, networks and large-particles in a programmable manner in response to solution pH. The mediasensitive phase transformation behaviors hold amazing potentials for the construction of enzyme-inspired smart aqueous catalysts.