Research ArticleSUPRAMOLECULAR CHEMISTRY

Spontaneous structural transition and crystal formation in minimal supramolecular polymer model

See allHide authors and affiliations

Science Advances  12 Feb 2016:
Vol. 2, no. 2, e1500827
DOI: 10.1126/sciadv.1500827
  • Fig. 1 Macroscopic view and imaging of Fmoc-DOPA assembly process.

    (A) Chemical structure of Fmoc-DOPA. (B) Three macroscopically observable changes of Fmoc-DOPA preparation over time: turbidity change, gaining gel-like viscoelastic characteristics as indicated by a simple qualitative vial inversion assay, and spontaneous formation of crystals in the gel (from left to right). (C) Transmission electron microscopy (TEM) micrographs of Fmoc-DOPA samples taken immediately upon the initiation of assembly (time 0) and 42 hours after the initiation of the assembly at the semitransparent gel-like state.

  • Fig. 2 Cryo-TEM analysis of Fmoc-DOPA assembly.

    Samples of Fmoc-DOPA (1 mg/ml) were imaged using cryo-TEM at different time points after the initiation of assembly. Micrographs of time 0 are from samples of a turbid solution. Micrographs of 4 hours and 9 days are from semitransparent gel-like samples. Micrographs of 1.5 months are from a gel containing macroscopically observable crystals. Black arrows point to spheres that adhere to the carbon-coated grid, forming menisci at the point of adhesion. Red arrows point to fibers. Orange arrows point to twisted ribbons. Green arrows point to helical ribbons. Blue arrows point to tubes.

  • Fig. 3 Spectroscopic investigation of Fmoc-DOPA assembly.

    (A) Near-UV time-dependent CD spectra of Fmoc-DOPA (1 mg/ml) and a corresponding macroscopic vial inversion assay. The inset shows a magnification of the CD spectra collected between 295 and 315 nm during the first hours of assembly. (B) Temperature-dependent CD spectra of Fmoc-DOPA (1 mg/ml). (C) Fourier transform infrared (FTIR) spectra of the amide I’ region for Fmoc-DOPA samples (1 mg/ml) taken at different time points. FTIR spectra were normalized and vertically offset for clarity.

  • Fig. 4 NMR structural analysis of Fmoc-DOPA assemblies.

    (A) 1D 1H NMR spectra of Fmoc-DOPA assembly by solution NMR at different time points. (B) 2D 1H radio frequency–driven recoupling (RFDR) data of lyophilized Fmoc-DOPA samples prepared immediately (time 0), 2 hours, 5 hours, and 1 month after the assembly was initiated.

  • Fig. 5 X-ray structure of Fmoc-DOPA single crystals.

    (A) View of the asymmetric unit, showing a single Fmoc-DOPA molecule with thermal ellipsoids at 50% probability level. (B) Crystal packing of 16 molecules along the crystallographic b axis. The interlocking hydrogen bonding network is shown in teal. (C) Extended crystal packing along the crystallographic a axis. (D) Extended crystal packing along the crystallographic c axis.

  • Fig. 6 Suggested model for the Fmoc-DOPA structural transition process.

    (A) Schematic diagram showing a sol-gel-crystal transition that occurs at the macroscopic level, with an underlying morphological transition at the microscopic level. This process includes a morphological transition from spheres into fibers and twisted ribbons, and finally into helical ribbons and tubes. (B) Energy landscape of the Fmoc-DOPA transition process. This process involves the transition of metastable spheres into thermodynamically favorable crystalline ultrastructure.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/2/e1500827/DC1

    Fig. S1. Turbidity assay to monitor Fmoc-DOPA optical transition over time.

    Fig. S2. Sealed capillary assay to monitor Fmoc-DOPA assembly.

    Fig. S3. Cryo-TEM of Fmoc-DOPA assemblies at additional time points.

    Fig. S4. Additional NMR analysis of Fmoc-DOPA assembly.

    Fig. S5. The influence of lyophilization on the assemblies.

    Fig. S6. Exploring Fmoc-DOPA phase transition.

    Table S1. Hydrogen bonding parameters from Fmoc-DOPA crystal structure.

    Table S2. Crystal data and structure refinement for the Fmoc-DOPA crystal.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Turbidity assay to monitor Fmoc-DOPA optical transition over time.
    • Fig. S2. Sealed capillary assay to monitor Fmoc-DOPA assembly.
    • Fig. S3. Cryo-TEM of Fmoc-DOPA assemblies at additional time points.
    • Fig. S4. Additional NMR analysis of Fmoc-DOPA assembly.
    • Fig. S5. The influence of lyophilization on the assemblies.
    • Fig. S6. Exploring Fmoc-DOPA phase transition.
    • Table S1. Hydrogen bonding parameters from Fmoc-DOPA crystal structure.
    • Table S2. Crystal data and structure refinement for the Fmoc-DOPA crystal.

    Download PDF

    Files in this Data Supplement:

Stay Connected to Science Advances

Navigate This Article