Metal-Folded Hierarchical Self-Assembly Of Single-Chain Nanoparticles

To access to advanced nanomaterials that mimic the superstructures and functions of biomacromolecules such as protein,single-chain nanotechnology is highly attractive in state-of-the-art research fields.Because parent polymer may be considered analogous to protein' s primary structure and single-chain nanoparticles(SCNPs)analogous to secondary structure,compartmentalization/self-assembly of SCNPs may access to hierarchical tertiary structure.We have recently demonstrated metal-folded single chain nanoparticles(metal-SCNPs)via concurrent deprotonation-coordination of imidazolium motifs of block copolymer,in which ionic repulsion of residual imidazolium motifs and segregation of hydrophilic block played key roles.In this thesis,we describes hierarchical self-assembly of SCNPs,whose hydroxyl-based polymer contains minor statistic imidazole units(9 mol.%),in the presence of Cu(II)in water,driven by Cu(II)-imidazole coordination upon solution neutralization.Histamine methacrylamide(HisMA)and 2-hydroxylpropyl methacrylamide(HPMA)monomers were first synthesized.Well-defined hydrophilic PHisMA60 homopolymer(P-1),PHPMA220-b-PHisMA2i block copolymer(P-2),and P(HPMA202-co-PHisMA20)statistic copolymer(P-3)(subscript:mean degree of polymerization)were synthesized via visible light mediated RAFT polymerization in aqueous solution at 25?.Potentiometric titration and UV-vis spectroscopy demonstrate that the deprotonation of imidazole motifs in the HisMA units leads to Cu(II)-imidazole coordination,in which the monomers distribution exert crucial control over the coordination.Complexation-induced chain-folding was studied using 1H NMR spectroscopy.The results demonstarte that,different from the collapse of block-copolymer analogue,P-3 undergoes a stepwise chain-folding.73%HisMA units fold exclusively without HPMA-collapse up to pH 4.6.Thereafter,PHPMA segments collapsed concurrently.Solution self-assembly was studied by dynamic light scattering(DLS)and NMR diffusion ordered spectroscopy(DOSY).The results unveil that neutralization in pH 3.9-4.6 leads to the self-assembly into metal-SCNPs(NP-1,each contains several 1.2-nm complex nanoclusters).Self-assembly of complex nanoclusters in pH 4.6-5.0 gives rise to concurrent PHPMA-collapse and hence the formation of swollen nanoparticles that shrink into discrete ones in pH 5.0-5.6.As-formed nanoparticle(NP-2)has several sub-5-nm subdomains capable of hierarchical assembly.NP-2 self-assemble into cocoon-like nano-objects in pH 5.6-7.5.Progammable coordination results in exclusive HisMA-folding and subsequently concurrent collapse of PHPMA segments,and hence the controllable bottom-up hierarchical self-assembly.To elucidate hierarchical nanostructures,we studied reduction-responsive behavior of nanoparticles on addition of sodium ascorbate in argon,because reduction of metal centers can release ligands from as-formed complexes.DLS,DOSY and AFM results demonstrate that reduction reaction induces rearrangement into hierarchy to one-order backwoard.NP-2 rearranges into Cu(I)-folded SCNPs with superstructure similar to NP-1.Moreover,NP-3 rearranges to nanoparticles with superstructure analogous to NP-2.The pH-induced self-assembly and reduction-driven rearrangement illustrate compartmentalization into discrete ultrafine(?5 nnm)heterogeneity analogous to protein's tertiray structure through hierarchical assembly of complex nanoclusters within metal-SCNPs.In short,this thesis describes a novel strategy of coordination-driven hierarchical self-assembly of SCNPs.Such pH-induced self-assembly and reduction-driven rearrangement illustrate intrinically dynamic metal-polymer hybridized heterogeneous nanomaterials that are potential in fabrication of biomimetic functional nanomaterials.