Controlling the Chain Folding for the Synthesis of Single-Chain Polymer Nanoparticles Using Thermoresponsive Polymers

Open AccessCCS ChemistryRESEARCH ARTICLE1 Aug 2021Controlling the Chain Folding for Synthesis of Single-Chain Polymer Nanoparticles Using Thermoresponsive Polymers He Zhang, Liang Jichun You, Niboqia Linxiuzi Yu, Huanyu Zhao, Hu-Jun Qian* and Zhong-Yuan Lu Zhang State Key Laboratory Supramolecular Structure Materials, Institute Theoretical Chemistry, Jilin University, Changchun 130012 Google Scholar More articles by this author , College Material, Chemical Engineering, Hangzhou Normal 311121 You Yu Zhao *Corresponding authors: E-mail Address: [email protected] https://doi.org/10.31635/ccschem.020.202000190 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesTrack Citations ShareFacebookTwitterLinked InEmail Synthetic polymer single-chain nanoparticles (SCNPs) are an emerging new class nanomaterials that possess similar folded structures as natural proteins. However, most SCNPs reported so far packed loosely in their interior, resembling those intrinsically disordered proteins (IDPs). Here, we report a facile strategy synthesize with controllable folding aqueous solution. The precursor was mainly composed N-isopropylacrylamide (NIPAM), small percentage hydrophobic photo-cross-linkers, hydrophilic counterparts. Contrary conventional approaches started from extended self-avoiding chain conformations, prefolded conformations thermoresponsive precursors at different temperatures. were synthesized situ triggering reactions between photo-cross-linkers located interior under UV light irradiation. ranging IDP-like fully collapsed globules obtained Our experimental findings also confirmed using molecular dynamics simulations. scaling analysis hydrodynamic radius Rh weight distributions both corresponding showed these high temperatures (>305 K) indeed had globule structure. Besides, wide range, near human body temperature; thus, could be superior candidates future applications drug cargo systems. Download figure PowerPoint Introduction There has been growing interest synthesizing folding/collapsing isolated chains dilution via intrachain cross-linking.1–8 As type macromolecular architecture, have found delivery,9–11 imaging,12,13 nanoreactor,14,15 catalysis.16–19 Beyond applications, society’s goal is produce tightly protein-like accessing true limit Practically, it believed easy efficient way reproduce nature’s biomacromolecules such into defined 3D architectures understand association protein process functions. produced state-of-the-art methods still away well-controlled degree morphology. After summarizing large library available literature, Pomposo et al.20 instead globular adopted open, sparse morphologies (IDPs) locally compact portions peptide connected flexible linkers. Conventional synthesis often good solvent, reactive functional groups (cross-linkers) randomly attached backbone. An cross-linking reaction much higher probability cross-linkers shorter contour distance along backbone condition. This resulted local spheroidization formation structure SCNPs.21,22 It recent computer simulations23,24 decreases rapidly distances. Based on concerns, many efforts devoted improving long-distance subsequent precursor. For instance, orthogonal or multistep schemes proposed enhance SCNPs.23,25,26 At given content cross-linkers, separating linker types can effectively enlarge average same and, therefore, distance. Recent simulation small-angle neutron scattering works27,28 demonstrated that, presence nonreactive acting purely steric crowders concentrated solution, ring crumpled favored fabrication degree. Although all improve extent folding, they limitations. former, short distances due conformation latter, separation solution challenging; especially, there would unavoidable concatenation surrounding nonreaction crowders. Another important issue SCNP avoid interchain collapsing; conventionally achieved doing dilution. works Yang group7,29 aggregation inhibited substantially introducing electrostatic interactions enable intrachain-cross-linking performed solutions. On other hand, experiments ter Huurne al.30,31 indicated delicate balance intra- self-assembly pathways directed carefully tuning polymer’s hydrophilic–hydrophobic supramolecular approach, whereby threefold hydrogen-bonding interactions. They replacing part benzene-1,3,5-tricarboxamide (BTA) grafts (hydrogen-bonding agents) dodecyl, while keeping constant, promote thereby favoring more structured interior. Similarly, Terashima group32,33 amphiphilic random copolymers consisting pendants undergo reversible water intramolecular A detailed discussion role hydrophilic/hydrophobic heterograft review Meijer group,1 who appears indeed. Recently, Gormley group34 studied behavior extensive combinatorial (>450) polymers varying hydrophobicity strength, high-throughput approach. only group (9/457) poly(ethylene glycol) (PEG)-functionalized heteropolymers block exhibited compactness bovine serum albumin (BSA). These results although factor one must aware careful composition might necessary SNCPs In above mentioned systems, single-molecule usually cause-and-effect resulting covalent noncovalent chemistry, where latter not driving force former but fixed configuration situ. strategies, main determining resultant SCNPs. To SCNP, long distances, which hard achieve. study, inverted picture cause effect; namely, triggered after precursors’ precollapse. Such various expected close even, our simulations,24 precollapsed fabricated co-nonsolvency chose poly(N-isopropylacrylamide) (PNIPAM) precursor, widely known its lower critical temperature (LCST) phenomenon coil-to-globular transition ∼32 °C Wu group,35,36 individual PNIPAM change coil coil, then molten globule, eventually thermodynamically stable increased. photo-cross-linking used fix obtaining degrees 4-acryloyloxybenzophenone (ABP) applied agent, reacted efficiently unselectively approaching C−H bonds upon irradiation; ensuring efficiency.37 ABP protected core position, somewhat avoiding intermolecular reaction. tailor-made precursors, methyl ether acrylate (PEGMA) segments ABP’s feature. Furthermore, exhibit approximately temperature. Experimental Section (named PNAE following text) N-Isopropyl acrylamide, ABP, PEGMA addition-fragmentation transfer (RAFT) copolymerization, prepared irradiation Their properties characterized proton nuclear magnetic resonance (1H NMR) spectra, dynamic (DLS), 1H NMR diffusion-ordered spectroscopy (DOSY), size-exclusion chromatography (SEC), Overhauser effect (NOE) differential spectroscopy, transmission electron microscopy (TEM), UV–vis absorption spectra. Further details regarding materials characterizations Supporting Information. Exemplary procedure PNAE-10.5 acrylamide (1.92 g, 17 mmol), (252 mg, 1 (0.96 2 4-cyano-4-[(dodecylsulfanylthiocarbonyl) sulfanyl] pentanoic acid (32 0.08 2,2′-azobis(2-methylpropionitrile) (AIBN) (2.62 mg,0.016 mmol) dissolved anhydrous 1,4-dioxane (7 mL) 10 mL Schlenk tube. mixed degassed five successive freeze–pump cycles tube stirred 24 h 343 K. diluted 5 tetrahydrofuran (THF) purified precipitation n-pentane/ethyl (9/1). PNAE-10 filtration yellow powder (yield 2.73 g). (400 M, CDCl3): 7.40–7.89 ppm (m, 9H), 4.03 (br, 1H), 3.65 (s, 18H), 3.38 3H), 1.14–2.99 1.19 6H). feed ratios monomers. SCNP-10.5-298 (100 mg) ultrapure 500 three-neck round-bottom flask full jacket. lowered 278 K, ultrasonic 30 min, increased 298 irradiated 365 nm 11 evaporation remove water, THF N-pentane/ethyl 96 mg). precursors. Computational simulation, coarse-grained (CGMD) technique. simulated bead-spring model. depicted Information Scheme S1, monomers represented four bead types: (NIPAM) B, respectively. While C D represent side-chain PEGMA, Each length N = NA + NB NC 100, 85, 5, 10. PEG tail modeled nine beads. We use S solvent molecule. | PNIPAM, PEG-PNIPAM, ABP-PNIPAM, PNAE. Finitely extensible nonlinear elastic (FENE) potential describe bonded contour, U FENE ( r ) − k R 0 ln [ ] LJ cut / 6 σ R0=1.5σ, k=30ɛ/σ2. Nonbonded components described Lennard–Jones (LJ) potential, 4 ɛ 12 . Simulations reduced units, energy, length, mass units ɛ, σ, m, respectively; time unit τ m ε ε/kB, kB Boltzmann constant. nonbonded truncated cutoff radius, rcut. supplied Results Discussion Design set copolymers, named PNAE, RAFT copolymerization NIPAM, (Mn 480 g/mol, ∼8.9 oxyethylene average) sulfanyl]pentanoic chain-transfer agent azobis(isobutyronitrile) initiator 1,4-dioxane, shown 1. ∼5 mol %, varied 5.3, 10.5, 12.8 %. labeled PNAE-5.3, PNAE-10.5, PNAE-12.8, weight, polymerization, samples verified SEC NMR, listed Table comparison, bicomponent PNIPAM-PEGMA PNIPAM-ABP homopolymer control polymerization conditions. Detailed data about Overview Composition (Mol %), Number-Averaged Molecular Weight (Mn), Degree Polymerization (DP), Molar Mass Dispersity (Đ) Precursor Compositiona (mol %) Sample NIPAM Mn, SECb (g/mol) ĐSECb DPSECb Mn NMRa DPNMRa 100 18,200 1.28 161 14,100 125 ABP-PNIPAM 95.1 4.9 23,900 1.39 199 21,200 180 PEG-PNIPAM 94.0 6.0 22,500 1.43 167 18,000 134 PNAE-5.3 90.1 4.6 5.3 29,400 1.44 212 153 84.7 4.8 10.5 27,700 1.42 175 21,300 135 PNAE-12.8 82.1 5.1 25,600 1.56 24,500 147 aDetermined spectroscopy. bDetermined THF, calibrated polystyrene standard. Phase first characterize Since LCST-type phase polymers. Techniques DLS, DOSY, NOE difference used. temperature-dependent DLS measurements Figure 1a, (Rh) assembly solutions plotted ([polymer] mg/mL). shows polymers, including PNIAPM, series, aggregated heating temperatures, sudden increase specific Note copolymer insoluble segments’ chain, indicating considerable decrease well below current testing range. Meanwhile, introduction elevated temperature, agreement literature report.38 show typical LCST behavior, easily manipulate incorporating portion constituents. Notably, ∼5%, PNAEs tuned range content. Specifically, ∼290 than PNIPAM. ∼305 ∼312 respectively, (a) Temperature-dependent mg/mL. (b) Hydrodynamic D2O calculated DOSY spectra Stokes–Einstein equation. (c d) (500 MHz) (top) (middle bottom) CDCl3 (c) (d), top left corner assignments signals. speculated state before observed 1a occurred. variation size observe limited accuracy measurements. this, conducted 278–310 Applying equation Equation S1 Information), calculated. 1b. linearly 9.05 6.80 278–305 K; afterward, maintained plateau ∼6.80 306 310 ceased 305 K compared worth noting measured multichain aggregation. importantly, underwent collapsing heating, reached further originated dipole–dipole when space another, distinct J coupling. general, intensity signal depends (r) ∼r−6. carried out reference. Figures 1c 1d deuterated chloroform (CDCl3) (D2O), patterns middle bottom First, noted protons (h) free end patterns) D2O, none signals appeared any protons. contrary, (bottom pattern 1c), adjacent methine (d) (e f) monomer connecting neighboring monomers, note e f chemical monomer; being contact space. very weak since three monomers; numbers pairs NIPAM. o side entire conformation. 1d), irradiated, coupling enhanced 1c). enhancement attributed closer contacts f). (1.0–2.0 ppm, b), strong evidence folding. characterization self-fold promoted heating. Various fine-tuned simply controlling condition presented below. preparation SCNPs, =1 mg/mL) lights (360 nm) series According data, 278–298 278–308 point. SCNP-10.5 SCNP-12.8, ensure systems thermodynamic state, kept irradiation, removed, analyzed SEC, TEM. By comparing spectrum SCNP-12.8 308 significant weaken adsorption 260 complete S6). Therefore, define molar agents 4.6% ∼5.1%, Retention effective 2a, apparent shifts toward longer retention traces (Figure 2a) 2b) underpinning improvement increasing 2c summarize two sets increased, Mw decreased, SCNP. low disappeared (>290 K), dominated, took With consistent 1b). investigated 2d TEM images 288 cast carbon coat grids stained OsO4. clearly black dotted particles (<10 without aggregates >20 nm, offered direct (THF, RI) (a), (b), Weight-averaged PS calibration. image uniform (1 Reaction Temperature, Weight, Precursors Corresponding Determined Calibration Temperature Đ 39,400 31,400 23,100 35,400 1.54 19,100 28,700 1.50 283 20,900 33,600 1.61 16,200 24,400 1.51 19,200 23,000 1.57 15,100 293 18,100 26,600 1.47 303 14,700 1.45 16,400 24,700 13,900 20,300 1.46 21,800 1.34 14,800 1.38 sizes. schematic view synthetic route 2. right 2, share property is, expansion cooling shrinkage