Fluorescent Labeling of a Bisurea-Based Supramolecular Polymer

Bisurea-Based Supramolecular Polymers for Tunable Biomaterials

Water-soluble supramolecular polymers show great potential to develop dynamic biomaterials with tailored properties. Here, we elucidate the morphology, stability and dynamicity of supramolecular polymers derived from bisurea-based monomers. An accessible synthetic approach from 2,4-toluene diisocyanate (TDI) as the starting material is developed. TDI has two isocyanates that differ in intrinsic reactivity, which allows to obtain functional, desymmetrized monomers in a one-step procedure. We explore how the hydrophobic/hydrophilic ratio affects the properties of the formed supramolecular polymers by increasing the number of methylene units from 10 to 12 keeping the hydrophilic hexa(ethylene glycol) constant. All bisurea-based monomers form long, fibrous structures with 3-5 monomers in the cross-section in water, indicating a proper hydrophobic\hydrophilic balance. The stability of the supramolecular polymers increases with an increasing amount of methylene units, whereas the dynamic nature of the monomers decreases. The introduction of one Cy3 dye affords modified supramolecular monomers, which co-assemble with the unmodified monomers into fibrous structures. All systems show excellent water-compatibility and no toxicity for different cell-lines. Importantly, in cell culture media, the fibrous structures remain present, highlighting the stability of these supramolecular polymers in physiological conditions. The results obtained here motivate further investigation of these bisurea-based building blocks as dynamic biomaterial.

Fluorescent Supramolecular Polymeric Materials

Fluorescent supramolecular polymeric materials are rising stars in the field of fluorescent materials not only because of the inherent optoelectronic properties originating from their chromophores, but also due to the fascinating stimuli-responsiveness and reversibility coming from their noncovalent connections. Especially, these noncovalent connections influence the fluorescence properties of the chromophores because their state of aggregation and energy transfer can be regulated by the assembly-disassembly process. Considering these unique properties, fluorescent supramolecular polymeric materials have facilitated the evolution of new materials useful for applications in fluorescent sensors, probes, as imaging agents in biological systems, light-emitting diodes, and organic electronic devices. In this Review, fluorescent supramolecular polymeric materials are classified depending on the types of main driving forces for supramolecular polymerization, including multiple hydrogen bonding, electrostatic interactions, π-π stacking interactions, metal-coordination, van der Waals interactions and host-guest interactions. Through the summary of the studies about fluorescent supramolecular polymeric materials, the status quo of this research field is assessed. Based on existing challenges, directions for the future development of this field are furnished.

Evaporation-induced self-structuring of organised silica nanohybrid films through cooperative physical and chemical interactions

In this work, we develop the concept of evaporation-induced self-structuring as a novel approach for producing organised films by exploiting cooperative physical and chemical interactions under far-from-equilibrium conditions (spin-coating), using sol-gel precursors with multiple functional groups. Thin films of self-structured silsesquioxane nanohybrids have been deposited by spin coating through the sol-gel hydrolysis and condensation of a bridged organosilane bearing self-assembling urea groups. The resulting nanostructure, investigated by FTIR, AFM and SEM, is shown to be highly dependent on the catalyst used (nucleophilic or acidic), and can be further modulated by varying the spinning rate. FTIR studies revealed the presence of highly organised structures under acidic catalysis due to strong hydrogen bonding between urea groups and hydrophobic interactions between long alkylene chains. The preferential orientation of the urea cross-links parallel to the substrate is shown using polarized FTIR experiments.

Hydrogen-Bonded Multifunctional Supramolecular Copolymers in Water

We have investigated the self-assembly in water of molecules having a single hydrophobic bis-urea domain linked to different hydrophilic functional side chains, i.e., bioactive peptidic residues and fluorescent cyanine dyes. By using a combination of spectroscopy, scattering, and microscopy techniques, we show that each one of these molecules can individually produce well-defined nanostructures such as twisted ribbons, two-dimensional plates, or branched fibers. Interestingly, when these monomers of different functionalities are mixed in an equimolar ratio, supramolecular copolymers are preferred to narcissistic segregation. Radiation scattering and imaging techniques demonstrate that one of the molecular units dictates the formation of a preferential nanostructure, and optical spectroscopies reveal the alternated nature of the copolymerization process. This work illustrates how social self-sorting in H-bond supramolecular polymers can give straightforward access to multifunctional supramolecular copolymers.