Peptide hydrogel with self-healing and redox-responsive properties

We have rationally designed a peptide that assembles into a redox-responsive, antimicrobial metallohydrogel. The resulting self-healing material can be rapidly reduced by ascorbate under physiological conditions and demonstrates a remarkable 160-fold change in hydrogel stiffness upon reduction. We provide a computational model of the hydrogel, explaining why position of nitrogen in non-natural amino acid pyridyl-alanine results in drastically different gelation properties of peptides with metal ions. Given its antimicrobial and rheological properties, the newly designed hydrogel can be used for removable wound dressing application, addressing a major unmet need in clinical care.

Polymerization/depolymerization of chiral metallo-supramolecular assembly induced by redox change

We report on the polymerization/depolymerization of chiral metallo-supramolecular assembly by Cu^I /Cu^II redox change. By combining a monotopic enantiopure ligand with a ditopic ligand of opposite configuration, ML₂ -type complexes are generated with chiral self-recognition or self-discrimination depending on the oxidation state of copper. In presence of Cu^I , the formation of heterochiral complexes is favored, thus generating dinuclear species whereas Cu^II advocates for the formation of homochiral species, namely, a mixture of mononuclear species and metallo-supramolecular polymeric species. Thus, cyclic voltammetry was used to study such a chirality-induced stimulus sensitive polymerization/depolymerization process.

Electron-Triggered Metamorphism in Palladium-Driven Self-Assembled Architectures

A metal-induced self-assembly strategy is used to promote the π-dimerization of viologen-based radicals at room temperature and in standard concentration ranges. Discrete box-shaped 2:2 (M:L) macrocycles or coordination polymers are formed in solution by self-assembly of a viologen-based ditopic ligand with cis-[Pd(en)(NO₃)₂], trans-[Pd(CH₃CN)₂(Cl)₂], or [Pd(CH₃CN)₄(BF₄)₂]. Changing the redox state of the bipyridium units involved in the tectons, from their dicationic state to their radical cation state, results in a reversible "inflation/deflation" of the discrete 2:2 (M:L) macrocyclic assemblies associated to a large modification in the size of their inner cavity. Viologen-centered electron transfer is also used to trigger a dissociation of the coordination polymers formed with tetrakis(acetonitrile)Pd(II), the driving force of the disassembling process being the formation of discrete box-shaped 2:2 (M:L) assemblies stabilized by π-dimerization of both viologen cation radicals.

Synthesis of Metallopolymers and Direct Visualization of the Single Polymer Chain

During the past few decades, the study of the single polymer chain has attracted considerable attention with the goal of exploring the structure-property relationship of polymers. It still, however, remains challenging due to the variability and low atomic resolution of the amorphous single polymer chain. Here, we demonstrated a new strategy to visualize the single metallopolymer chain with a hexameric or trimeric supramolecule as a repeat unit, in which Ru(II) with strong coordination and Fe(II) with weak coordination were combined together in a stepwise manner. With the help of ultrahigh-vacuum, low-temperature scanning tunneling microscopy (UHV-LT-STM) and scanning tunneling spectroscopy (STS), we were able to directly visualize both Ru(II) and Fe(II), which act as staining reagents on the repeat units, thus providing detailed structural information for the single polymer chain. As such, the direct visualization of the single random polymer chain is realized to enhance the characterization of polymers at the single-molecule level.

Chiral stimuli-responsive metallo-supramolecular assembly induced by CuII/CuI redox change

We investigated the selective formation of homoleptic and heteroleptic metal complexes controlled by means of the chiral molecular instruction of the ligand and the coordination geometry of the metal.

A dual redox-responsive supramolecular polymer driven by molecular recognition between bisporphyrin and trinitrofluorenone

A dual redox-responsive supramolecular polymer driven by molecular recognition between bisporphyrin (bisPor) and trinitrofluorenone (TNF) has been developed.

Supramolecular Polymer Cross-Linked by Discrete Tris-[2]pseudorotaxane Metallacycles and Its Redox-Responsive Behavior

A new discrete hexagonal metallacycle M containing tris-[2]pseudorotaxane moiety has been successfully designed and synthesized via coordination-driven self-assembly. The newly designed tris-[2]pseudorotaxane metallacycle was well characterized with nuclear magnetic resonance and mass spectra analysis. Such tris-[2]pseudorotaxane metallacycle M and pillar[5]arene dimer (PD) could further form a new family of cross-linked redox-responsive supramolecular polymer M⊃(PD)₃ through a host-guest interaction. Interestingly, the polymer M⊃(PD)₃ displayed redox-responsive behavior and showed tuned weight-average diffusion coefficients D upon redox stimuli, which is attributed to the changed coordination geometries of [Cu(phen)₂]⁺ and [Cu(phen)₂]²⁺ in such system.

Bioinspired Underwater Adhesives by Using the Supramolecular Toolbox

Nature has developed protein-based adhesives whose underwater performance has attracted much research attention over the last few decades. The adhesive proteins are rich in catechols combined with amphiphilic and ionic features. This combination of features constitutes a supramolecular toolbox, to provide stimuli-responsive processing of the adhesive, to secure strong adhesion to a variety of surfaces, and to control the cohesive properties of the material. Here, the versatile interactions used in adhesives secreted by sandcastle worms and mussels are explored. These biological principles are then put in a broader perspective, and synthetic adhesive systems that are based on different types of supramolecular interactions are summarized. The variety and combinations of interactions that can be used in the design of new adhesive systems are highlighted.

Multi-responsive coordination polymers utilising metal-stabilised, dynamic covalent imine bonds

We report how the combination of dynamic covalent imine bonds and coordination bonds in a single polymer material not only imparts enhanced stability to the final polymer, but also allows the material to be sensitive to a range of stimuli, offering more fine-grained control over its properties.

Rubber-elasticity and electrochemical activity of iron(ii) tris(bipyridine) crosslinked poly(dimethylsiloxane) networks

2,2'-Bipyridine-terminated poly(dimethylsiloxane)s (bpyPDMS) with number average molecular weights, M_N, of 3300, 6100, 26 200, and 50 000 g mol^-1 were synthesized. When mixed with Fe(BF₄)₂ at low concentrations, red solutions formed with UV-vis spectra that match those of iron(ii) tris(2,2'-bipyridine) (Fe(bpy)₃²⁺). Upon solvent evaporation, Fe(bpy)₃²⁺ crosslinked PDMS networks (bpyPDMS/Fe(ii)) formed, and were studied using oscillating shear rheometry. The shear storage moduli (0.084 to 2.6 MPa) were found to be inversely proportional to the M_N of the PDMS, though the storage moduli at low molecular weights greatly exceeded the storage moduli of comparable covalently crosslinked PDMS networks. The shear storage moduli exhibited the characteristic rubbery plateau up to ∼135 °C. Films of bpyPDMS/Fe(ii) coated onto electrodes were found to be electrochemically active, especially so when the PDMS M_N is low. The Fe(bpy)₃²⁺ crosslinks can be reversibly oxidized over ∼500 nm away from the electrode surface in the presence of a suitable electrolyte.

Control over the assembly and rheology of supramolecular networks via multi-responsive double hydrophilic copolymers

An orthogonal control over network formation and dynamics is achieved in metallo-supramolecular micellar gels via multi-responsive double hydrophilic copolymers.

Understanding the Structure of Reversible Coordination Polymers Based on Europium in Electrostatic Assemblies Using Time-Resolved Luminescence

In situ characterization of the structure of reversible coordination polymers remains a challenge because of their dynamic and concentration-responsive nature. It is especially difficult to determine these structures in their self-assemblies where their degree of polymerization responds to the local concentration. In this paper, we report on the structure of reversible lanthanide coordination polymers in electrostatic assemblies using time-resolved luminescence (TRL) measurement. The reversible coordinating system is composed of the bifunctional ligand 1,11-bis(2,6-dicarboxypyridin-4-yloxy)-3,6,9-trioxaundecane (L2EO4) and europium ion Eu(3+). Upon mixing with the positively charged diblock copolymer poly(2-vinylpyridine)-b-poly(ethylene oxide) (P2VP41-b-PEO205), electrostatic polyion micelles are formed and the negatively charged L2EO4-Eu coordination complex simultaneously transforms into coordination "polymers" in the micellar core. By virtue of the water-sensitive luminescence of Eu(3+), we are able to obtain the structural information of the L2EO4-Eu coordination polymers before and after the formation of polyion micelles. Upon analyzing the fluorescence decay curves of Eu(3+) before and after micellization, the fraction of Eu(3+) fully coordinated with L2EO4 is found to increase from 32 to 83%, which verifies the occurrence of chain extension of the L2EO4-Eu coordination polymers in the micellar core. Our work provides a qualitative picture for the structure change of reversible coordination polymers, which allows us to look into these "invisible" structures.

Synthesis and characterization of metallo-supramolecular polymers

The incorporation of metal centers into the backbone of polymers has led to the development of a broad range of organometallic and coordination compounds featuring properties that are relevant for potential applications in diverse areas of research, ranging from energy storage/conversion to bioactive or self-healing materials. In this review, the basic concepts and synthetic strategies leading to these types of materials as well as the scope of available characterization techniques will be summarized and discussed.

2,2′:6′,2′′-Terpyridine-functionalized redox-responsive hydrogels as a platform for multi responsive amphiphilic polymer membranes

Amphiphilic polymer co-networks were functionalized with spyropiran and terpyridine yielding multi-responsive membranes with switchable properties and potential applications in drug delivery and medical sensors.

Intermolecular Interactions of CpFePPh3(CO)CO(CH2)5CH3: From a Crystalline Solid to a Supramolecular "Iron-Truss" Polymer

PPh₃CpFe(CO)(CO)(CH₂)₅CH₃ (FpC6) spontaneously forms supramolecular polymers in the solid state. The polymers crystallize slowly over a period of one month and can be recovered by melting the crystals at 65 °C. The rheological profile of FpC6 fits the Maxwell model indicating the presence of chain entanglement. Crystal analysis reveals that FpC6 is able to assemble, via cooperative π-π interactions and weak C-H···O hydrogen bonding, into a duplex chain structure with truss arrangement of iron atoms. Powder X-ray diffraction (PXRD) of the polymers shows a double-peak pattern, characteristic for duplex ladder polymers. FTIR/ATR analysis further supports that carbonyl groups are involved in C-H···O hydrogen bonding responsible for the self-assembly. This discovery opens up new design motifs for organometallic supramolecular polymers.

Dynamic self-assembly of coordination polymers in aqueous solution

The construction of supramolecular polymers has been intensively pursued because the nanostructures formed through weak non-covalent interactions can be triggered by external stimuli leading to smart materials and sensors. Self-assemblies of coordination polymers consisting of metal ions and organic ligands in aqueous solution also provide particular contributions in this area. The main motivation for developing those coordination polymers originates from the value-added combination between metal ions and ligands. This review highlights the recent progress of the dynamic self-assembly of coordination polymers that result from the sophisticated molecular design, towards fabricating stimuli-responsive systems and bio-related materials. Dynamic structural changes and switchable physical properties triggered by various stimuli are summarized. Finally, the outlook for aqueous nanostructures originated from the dynamic self-assembly of coordination polymers is also presented.

CO2-Switchable Supramolecular Block Glycopolypeptide Assemblies

A novel supramolecular block glycopolypeptide, designed to have the viral building blocks and be sensitive to CO₂, a physiological stimulus, was prepared via the orthogonal coupling of two end-functionalized biopolymers, dextran with β-cyclodextrin terminal (Dex-CD) and poly(l-valine) with a benzimidazole tail (BzI-PVal), respectively, driven by the end-to-end host-guest interactions. Due to the CO₂-cleavable CD/BzI connection, both the vesicular and fibrous aggregates of this supramolecular block copolymer self-assembled in aqueous solution can undergo a reversible process of disassembly upon "breathing in" CO₂ and assembly upon "breathing out" CO₂, which mimics, to some extent, the disintegration and construction of viral capsid nanostructures.

Chemical and Electrochemical Manipulation of Mechanical Properties in Stimuli-Responsive Copper-Cross-Linked Hydrogels

Inspiration for the design of new synthetic polymers can be found in the natural world, where materials often exhibit complex properties that change depending on external stimuli. A new synthetic electroplastic elastomer hydrogel (EPEH) that undergoes changes in mechanical properties in response to both chemical and electrochemical stimuli has been prepared based on these precedents. In addition to having the capability to switch between hard and soft states, the presence of both permanent covalent and dynamic copper-based cross links also allows this stimuli-responsive material to exhibit a striking shape memory capability. The density of temporary cross links and the mechanical properties are controlled by reversible switching between the +1 and +2 oxidation states.

Facile Preparation of Supramolecular H-Shaped (Ter)polymers via Multiple Hydrogen Bonding

A well-defined Hamilton wedge (HW) midchain functionalized block copolymer, i.e., polyethylene glycol-b-polystyrene (PEG-HW-PS, M_n,GPC = 5600 Da, PDI = 1.03), was successfully synthesized via a combination of atom transfer radical polymerization (ATRP) and copper-catalyzed azide alkyne cycloaddition (CuAAC). An α,ω-cyanuric acid (CA) difunctional linear homopolymer poly(n-butylacrylate) (CA-PnBA-CA, M_n,GPC = 8100 Da, PDI = 1.09) was concomitantly prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Supramolecular H-shaped macromolecules were-for the first time-prepared through supramolecular self-assembly between HW and CA recognition motifs to generate (PS-b-PEG)·PnBA·(PS-b-PEG) and (PS-b-PS)·PnBA·(PS-b-PS) in CH₂Cl₂ or dichloromethane-d₂ at ambient temperature. The self-assembly process (at a total concentration of the two species of close to 4.5 mM) was evidenced by proton nuclear magnetic resonance (¹H NMR) spectroscopy, diffusion-ordered NMR spectroscopy (DOSY), and dynamic light scattering (DLS) analyses. The results derived via DOSY NMR experiments and DLS combined with a Job plot analysis and in-depth NMR titration experiments indicate that the formation of supramolecular H-shaped macromolecules in 2:1 stoichiometry is efficiently occurring via the employed complementary recognition motifs with high binding constants (between 1.2 and 1.5 × 10⁵ L mol^-1 at ambient temperature).