Optically Active Nucleobase-Functionalized Polynorbornenes Mimicking Double-Helix DNA

Open AccessCCS ChemistryRESEARCH ARTICLE1 Jun 2021Optically Active Nucleobase-Functionalized Polynorbornenes Mimicking Double-Helix DNA Li Wang, Nan Lu, Shuai Huang, Meng Xu-Man Chen and Hong Yang Wang School of Chemistry Chemical Engineering, Jiangsu Province Hi-Tech Key Laboratory for Bio-Medical Research, Institute Advanced Materials, Southeast University, Nanjing 211189 Google Scholar More articles by this author , Lu College Material Science, Shandong Agricultural Taian 271018 Huang *Corresponding author: E-mail Address: [email protected] https://doi.org/10.31635/ccschem.020.202000358 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesTrack Citations ShareFacebookTwitterLinked InEmail The development synthetic polymers that mimic the double-stranded helical structure is a fascinating topic in polymer science. In study, we designed synthesized two chiral norbornene monomers containing adenine thymine, which were mixed form hydrogen-bonding complementary complex, ring-opening metathesis polymerization (ROMP) was performed. High-resolution transmission electron microscopy (HRTEM) undoubtedly showed self-assembly optically active nucleobase-functionalized polynorbornenes into double helix. Computer simulations two-dimensional nuclear Overhauser effect spectroscopy (2D-NOESY) experiment polynorbornene derived from copolymer alternating thymine units. Download figure PowerPoint Introduction Many biological properties functions are attributed superhelical structures self-assembled biomolecules. carrier genetic information, DNA, macromolecule Watson–Crick double-helix formed polynucleotide chains held together interactions between paired nucleobases [adenine–thymine (A–T) guanine–cytosine (G–C)].1–3 unique molecular replication, have motivated intense scientific activity on DNA.4–17 Thus far, has only been found few exquisite polymeric structural motifs based peptide nucleic acids,4–6 metal-ion-coordinated helicates,7,8 aromatic oligoamides,9,10 crescent-shaped m-terphenyl oligomers,11 poly(m-phenylene)s,12 acyclic ethynyl oligomers,13,14 oligopeptide-functionalized poly(diacetylene),15 ladder polymers.16,17 comprises an deoxyribose ring (i.e., five-membered, three-stereocentered heterocyclic ring) rigid, phosphate backbone (Figure 1a). Inspired its macromolecular structure, new with forms superstructure through self-complementary chains. representative class cyclic olefin prepared (ROMP),18,19 living chain-reaction polymerization. However, most known inactive, because commercially available derivatives monomers, though bear carbons, they tend be racemic compounds.20–23 Thus, previously reported usually self-assemble cylindrical20 or spherical21,23 micelles. Although polybisnorbornene-based ferrocene linkers could one-handed helix,16,17 covalently bound dimeric unfortunately, lacked reversible binding-dissociation function, fundamental replication. Therefore, novel active, “all-carbon” backbone. mimicry strategy, as illustrated schematic Figure 1b, consisted using (1S,2S,4S)-cyclopentane replace five-membered internal alkene groups efficiently ROMP.18,19 As laterally attached backbone, consequently possessed recognition capability. 1 | Molecular structures: (a) polydeoxyribose–phosphate constructed polycondensation, (b) Experimental Methods instrumentation, computer simulations, starting materials, detailed procedures, NMR spectra ( Supporting Information Figures S1–S29) compounds 3, 4, 5, 8, 9, 10, 11, monomer 12, 13, complex 13.12, poly(norbornene–adenine) PN-A), poly(norbornene–thymine) PN-T), acid PNNA) provided Information. Typical PNNA synthesis procedure Monomer 12 (48.0 mg, 0.20 mmol), 13 (46.0 anhydrous dichloroethane (30 mL) added Schlenk flask under nitrogen atmosphere stirred at room temperature 3 h hydrogen-bonding-induced 13.12. A Grubbs second-generation catalyst (17.0 0.02 mmol) reaction mixture 40 °C 24 h. One drop ethyl vinyl ether quench reaction. Then methanol centrifuged 10000 r/min 10 minutes. precipitate washed three times dried obtain (89.0 yield: 95.10%) light yellow powder. product characterized proton magnetic resonance (1H NMR), following conditions: 1H (300 MHz, DMSO-d6, δ): 11.171 (s, 1H), 8.107 8.075 (d, 2H), 7.437 7.196, 5.343 4H), 4.075 3.898 C2H4Cl2), 3.461 3.334 H2O), 2.943 2.649 3H), 2.355 2.287 1.880 1.715–1.633 (m, 5H), 1.133 4H). Results Discussion syntheses started enantioselective monomers. binding norbornenes would result amplification level torsional forces centers after ROMP, eventually induce formation nanostructures.24 process these presented Scheme 1a. An esterification acryloyl chloride 1) auxiliary D-pantolactone 2) produced compound further treated freshly redistilled cyclopentadiene TiCl4 carry out highly endoselective asymmetric Diels–Alder prepare key intermediate whose optical rotation values well matched data literature.25 Compound 4 reduced lithium aluminum hydride (LiAlH4) dry tetrahydrofuran (THF) remove yield (−)-(1S,2S)-5-norbornene-2-methanol 5). measured [ α ] D 20 –92o 5 (c = 1.0 g·L−1, 98% ethanol) consistent literature value.26 Two norbornene-functionalized nucleobase norbornene–adenine norbornene–thymine, synthesized, shown N,N-di-Boc-protected 8), N-Boc-protected 9) first according protocols.27,28 weak acidity unprotected imino 8 9 resulted C–N bonds alcohol via Mitsunobu Deprotection Boc corresponding 11 alkaline conditions desired 12) norbornene–thymine 13). rotations –43° CHCl3) –64° CHCl3). (a b) Synthetic routes PN-A, PN-T, PNNA. We applied ROMP 13) synthesize homopolymers, is, PN-A respectively, 1b. carried utilizing 1,2-dichloroethane initial molar ratio norbornene–nucleobase set 20:1. experimental results quantitative PN-T low (∼23.9%). This outcome might poor solubility presence free amino group interfered catalytic catalyst. obtained insoluble chloroform 1,4-dioxane, slightly soluble acetonitrile, dimethylformamide (DMF) dimethyl sulfoxide (DMSO). Gel permeation chromatography (GPC) PNNAs DMF eluent. Table S1, had weights, whereas much higher Mn implied potential aggregates intermolecular hydrogen bonding. To copolymers, one-to-one stable hydrogen-bonded bisnorbornene 13.12 S22 S29), confirmed electrospray ionization mass spectrometry (ESI-MS) [m/z: 512.23752 (monomer + K)+, S23] observation strong (NOE) (Ha–Hg, adenine–thymine) equal amounts (2D) 1H,1H (NOESY) spectrum S24). –55° [c CHCl3).Subsequently, performed (The H-bonds °C, S30.) resulting exhibited single peak GPC profile S40c). weight 3994.287 matrix-assisted laser desorption/ionization-time flight (MALDI-TOF-MS) S43) chains, where degree ∼8–9. also raised 40:1 60:1; however, dramatic decrease DMSO precluded accurate characterization GPC. All subsequent experiments ([M]/[C] 20:1) sample. verified existence adenine–thymine pairs sample performing variable-temperature DMSO-d6 S31). S31a shows chemical shift −NH– 11.152 10.698 ppm during heating 30 60 recovered 11.146 dropping (cooling process). Moreover, S31b shifts −NH2 7.114 °C) 6.887 (60 back 7.113 cooling process, those group. During upfield –NH– indicated gradual opening fully original values, recognized reconnected. PNNA–PNNA process. quantitatively studied stability titration S34 S35) Benesi–Hildebrand model,29–31 whereby, association constant Ka measured. value calculated 24.64 M−1, good agreement regular (∼10–100 CDCl3) base pair literature.24,32–34 used 2D NOESY, investigate structure. NOESY 2 S28 show clear NOE signals (Ha–Hd) protons units units, proving Additionally, significant NOEs appearing c–g, b1–f1, b1–f2 Also, almost all high field. no obvious (Ha–Hb2) Hoogsteen pairs35 S37–S39). According literature, low-populated, short-lived,36 existed transiently.37 mode manuscript. 25 °C. 3a) derive steric hindrance effect. repeating portion not ruled 3b), hypothesized predominant hypothesis quantum calculations density functional theory (DFT) M06-2X38 function Gaussian 03 program.39 stereostructures isomers 3. comparative analysis (see Information) more than above proved polymerized alternately stabilized Stereostructures optimized M06-2X/6-31G* gas phase; red balls represent oxygen atoms, blue gray carbon white atoms. UV–vis absorption their acetonitrile (25 S44, showing appearance peaks 259 nm 268 13), respectively. When 1∶1 ratio, appeared 261 nm. suitable solvent required UV (VT-UV) displayed DMSO, maximum wavelengths pure 270 265 nm, strongly PNNA.24 Besides, attempted use 1,4-dioxane dissolve PNNA; nearly solvent. Fortunately, acetonitrile. VT-UV over 10–75 range rate 0.5 °C·min−1. 4a–4c, 266 272 PNNA), observed trends revealed absorbance decreased gradually along increasing temperatures, matching characteristics thermosensitive polymers.40–42 temperature-sensitive property originated nucleobases.24,43,44 (c) (∼50 mg·L−1) 75 VT-CD (d) (e) (f) 70 It circular dichroism (CD) technique very sensitive solution. Acetonitrile study CD spectra. concentrations solutions 50 mg·L−1 °C). demonstrated S45, negative Cotton wavelengths, accordance regions, chirality method confer monomeric demonstrate this, employed evaluation (VT-CD) temperatures 30, 50, respectively (Figures 4d–4f). 4d, multisignate bands adenine-functionalized 240–300 range. thymine-functionalized 4e) analogous broad ∼248 positive ∼267 zero-crossing point ∼257 implying preferential handed stacking macromolecule.45,46 similar single-stranded systems, poly(deoxyadenylic acid) [poly(dA)] poly(deoxythymidylic [poly(dT)].47,48 Furthermore, 4f) shapes PN-A. ∼268 ∼252 observed. These backbones Similar dependence suggested intensive lower temperatures.45,49,50 Transmission (TEM) conducted behaviors samples dispersed dilute concentration CHCl3. cast copper grids, placed TEM instrument evaporated. 5a–5i, filamentous nanostructures diameters filaments homopolymers ∼6–48 addition, intertwined larger-diameter filaments. For example, 16-nm diameter wound 22-nm filament 5c), 32-nm 20-nm 48-nm 5e), 18-nm 24-nm 5g 5i). large number distinct fibers 5d–5f), blurry samples. images morphologies (a–c) (d–f) (g–i) Eventually, high-resolution observe morphology 6) DMF. dissolved mg·L−1. After casting solution grid evaporation solvents, HRTEM clearly helically arranged nanofiber apparent PNNA, 6a–6d. Especially 6a 6d, helix visible. average pitch lengths ∼2.0 8.3 Here, one ∼27–28 nucleobases, estimated 6e, distance adjacent ∼0.304 DFT program39). general, double-helical 2.0 3.4 nucleobases.1–3 Compared diameter, longer length (8.3 nm), twisting power (unidirectional torsion) weaker (1R,3S,4R) (bidirectional DNA. discovery inspired us adjust nanofilaments modifying R /S configurations monomers.51 6 (a–d) illustration model Conclusion enantiomerically bearing polybisnorbornene acids, followed investigation polymers. copolymers’ TEM. 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