Research ArticleBIOCHEMISTRY

Self-folding of supramolecular polymers into bioinspired topology

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Science Advances  07 Sep 2018:
Vol. 4, no. 9, eaat8466
DOI: 10.1126/sciadv.aat8466
  • Fig. 1 Self-assembly of barbiturate-substituted molecule into self-foldable supramolecular polymers.

    (A) Molecular structures of barbiturate-substituted π-conjugated molecules 1 to 3. (B) Schematic representation of the curvature-generating supramolecular polymerization of windmill hexamers (rosettes). (C) Energy landscape of supramolecular polymers of 1 prepared with fast (left side) and slow cooling (right side). Using a fast cooling rate, a kinetically trapped assembly is formed via isodesmic self-assembly mechanism. Upon slow cooling, misfolded supramolecular polymers containing minor amount of helical domains were initially formed following cooperative nucleation-elongation mechanism, and they slowly transformed into fully folded helical supramolecular polymers via different intermediate, partially folded structures. Black arrows indicate the time evolution processes. (D to F) AFM images showing the self-folding process of the supramolecular polymers of 1, which were prepared by cooling a hot MCH solution of 1 (c = 5 × 10−6 M) from 373 to 293 K at a cooling rate of 1.0 K min−1. The samples were spin-coated onto highly oriented pyrolytic graphite (HOPG) substrates after aging at 293 K for 0 min (D), 1 day (E), and 7 days (F). Scale bars, 100 nm. The inset in (F) shows a magnification of the turn segment enclosed by the dashed rectangle.

  • Fig. 2 Dissociation behavior of supramolecular polymers.

    (A) SAXS profiles of the as-prepared solution (green curve) and the 7-day-old solution (orange curve) of 1 (c = 5 × 10−5 M) prepared by cooling from 373 to 293 K at a cooling rate of 1.0 K min−1. The black curve is the profile obtained from subtracting the two data sets. The black dashed curve is a simulation SAXS profile of the as-prepared sample data using a hollow cylinder model. (B) Temperature-dependent ultraviolet-visible (UV-Vis) spectra of an MCH solution of 1 (c = 5 × 10−6 M) upon cooling (1.0 K min−1). The arrows indicate the changes in absorption spectra upon cooling. (C) Cooling and heating curves of 1 (c = 5 × 10−6 M) in MCH obtained by plotting the molar fractions of the aggregated molecules (αagg, calculated from the absorption change at λ = 470 nm) as a function of the temperature during cooling (1.0 K min−1; black dots) and subsequent heating after aging for 0 min (purple dots), 12 hours (blue dots), 1 day (cyan dots), 1.5 days (green dots), 2 days (yellow dots), 3 days (orange dots), 5 days (pink dots), and 7 days (red dots) at 293 K. (D) Heating curves of the 7-day-old MCH solution of 1, prepared using a cooling rate of 1.0 K min−1 at different concentrations (purple dots, c = 5 × 10−6 M; cyan dots, c = 6 × 10−6 M; green dots, c = 7 × 10−6 M; yellow dots, c = 8 × 10−6 M; pink dots, c = 1 × 10−5 M). The black solid curves were obtained from fitting the experimental data to the cooperative model. Inset: van’t Hoff plot obtained from plotting the natural logarithm of cT−1 as a function of Te−1. The red line shows the corresponding linear fit. (E) The proposed mechanism of the thermal dissociation of the as-prepared supramolecular polymer in temperature regimes I and II. (F) AFM images of the as-prepared supramolecular polymer of 1, spin-coated onto HOPG substrate after heating to 343 K for 3 min. Scale bar, 100 nm.

  • Fig. 3 Misfolded supramolecular polymers.

    (A to D) AFM images of fully misfolded supramolecular polymers prepared by cooling a hot solution of 1 (c = 5 × 10−6 M) from 373 to 293 K at a cooling rate of 10 K min−1. The sample was spin-coated onto a HOPG substrate after aging at 293 K for 0 min. Scale bars, 50 nm. (E) Heating curve for fully misfolded supramolecular polymers of 1 prepared at a cooling rate of 10 K min−1 in MCH (red dots, c = 5 × 10−6 M). The black solid curve was obtained from fitting the experimental data to the isodesmic model. Heating curves for as-prepared supramolecular polymers at a cooling rate of 1.0 K min−1 (purple dots; see Fig. 2C) are also shown for comparison.

  • Fig. 4 Mechanically fragmented supramolecular polymers.

    (A) Changes of DLS size distribution of fully folded supramolecular polymers of 1 (c = 5 × 10−6 M) in MCH upon sonication for 0 s (red curve), 30 s (orange curve), 60 s (yellow curve), 120 s (green curve), and 180 s (blue curve) at 293 K. (B) Changes in the heating curves upon sonicating the fully folded supramolecular polymer solution of 1 at 293 K for different time intervals (red dots, 0 s; pink dots, 10 s; orange dots, 30 s; yellow dots, 60 s; green dots, 120 s; cyan dots, 180 s). (C to G) AFM images of twinned helical supramolecular polymers obtained by sonicating the fully folded supramolecular polymers for 30 s. Scale bars, 100 nm. (H to N) AFM images of single helical supramolecular polymers obtained by sonicating the fully folded supramolecular polymers for 180 s. Scale bars, 100 nm. (O) Enthalpy diagram of supramolecular polymers prepared using fast or slow cooling rates and mechanically fragmented supramolecular polymers.

  • Fig. 5 Proposed mechanism for the self-folding of supramolecular polymers.

    (A) Schematic representation of folding of misfolded domains templated by helical domains to give the secondary structure. (B) Schematic representation of the formation of the tertiary structure by folding of helical domains using misfolded segments as “hinge.”

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/9/eaat8466/DC1

    Synthesis and characterization of compounds

    Fig. S1. AFM and TEM images of supramolecular polymers before folding.

    Fig. S2. AFM and TEM images of supramolecular polymers during folding (1-day aged).

    Fig. S3. AFM and TEM images of supramolecular polymers after folding (7-days aged).

    Fig. S4. Morphology analysis of supramolecular polymers.

    Fig. S5. UV-Vis absorption spectra of supramolecular polymers.

    Fig. S6. AFM and TEM images of entirely misfolded supramolecular polymers.

    Fig. S7. UV-Vis heating curves of entirely misfolded supramolecular polymers.

    Fig. S8. Mixing experiment of fully folded and fully misfolded supramolecular polymers.

    Fig. S9. 1H NMR and 13C NMR of 1.

    Table S1. Thermodynamic parameters of supramolecular polymers.

    Reference (35)

  • Supplementary Materials

    This PDF file includes:

    • Synthesis and characterization of compounds
    • Fig. S1. AFM and TEM images of supramolecular polymers before folding.
    • Fig. S2. AFM and TEM images of supramolecular polymers during folding (1-day aged).
    • Fig. S3. AFM and TEM images of supramolecular polymers after folding (7-days aged).
    • Fig. S4. Morphology analysis of supramolecular polymers.
    • Fig. S5. UV-Vis absorption spectra of supramolecular polymers.
    • Fig. S6. AFM and TEM images of entirely misfolded supramolecular polymers.
    • Fig. S7. UV-Vis heating curves of entirely misfolded supramolecular polymers.
    • Fig. S8. Mixing experiment of fully folded and fully misfolded supramolecular polymers.
    • Fig. S9. 1H NMR and 13C NMR of 1.
    • Table S1. Thermodynamic parameters of supramolecular polymers.
    • Reference (35)

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