Zinc-Triggered Hydrogelation of a Self-Assembling β-Hairpin Peptide

Anion Tuned Structural Modulation and Nonlinear Optical Effects of Metal-Ion Directed 310 -Helix Networks

Metals play an important role in the structure and functions of various proteins. The combination of metal ions and peptides have been emerging as an attractive field to create advanced structures and biomaterials. Here, we are reporting the anion-influenced, silver ion coordinated diverse networks of designed short tripeptide 310 -helices with terminal pyridyl groups. The short peptides adopted classical right-handed, left-handed and 310 EL -helical conformations in the presence of different silver salts. The peptides have displayed conformational flexibility to accommodate different sizes and interactions of anions to yield a variety of metal-coordinated networks. The complexes of metal ions and peptides have shown different porous networks, right- and left-handed helical polymers, transformation of helix into superhelix and 2 : 2 metal-peptide macrocycles. Further, the metal-peptide crystals with inherent dipoles of helical peptides gave striking second harmonic generation response. The optical energy upconversion from NIR to red and green light is demonstrated. Overall, we have shown the utilization of short 310 -helices for the construction of diverse metal-coordinated helical networks and notable non-linear optical effects.

Enzyme-Instructed Self-Assembly (EISA) and Hydrogelation of Peptides

Self-assembly is a powerful tool for constructing supramolecular materials for many applications, ranging from energy harvesting to biomedicine. Among the methods to prepare supramolecular materials for biomedical applications, enzyme-instructed self-assembly (EISA) has several advantages. Herein, the unique properties and advantages of EISA in preparing biofunctional supramolecular nanomaterials and hydrogels from peptides are highlighted. EISA can trigger molecular self-assembly in situ. Therefore, using overexpression enzymes in disease sites, supramolecular materials can be formed in situ to improve the selectivity and efficacy of the treatment. The precursor may be involved during the EISA process, and it is actually a two-component self-assembly process. The precursor can help to stabilize the assembled nanostructures of hydrophobic peptides formed by EISA. More importantly, the precursor may determine the outcome of molecular self-assembly. Recently, it was also observed that EISA can kinetically control the peptide folding and morphology and cellular uptake behavior of supramolecular nanomaterials. With the combination of other methods to trigger molecular self-assembly, researchers can form supramolecular nanomaterials in a more precise mode and sometimes under spatiotemporal control. EISA is a powerful and unique methodology to prepare supramolecular biofunctional materials that cannot be generated from other common methods.

Rational Approach Towards Designing Metallogels From a Urea-Functionalized Pyridyl Dicarboxylate: Anti-inflammatory, Anticancer, and Drug Delivery

A structural rationale was adopted to design a series of metallogels from a newly synthesized urea-functionalized dicarboxylate ligand, namely, 5-[3-(pyridin-3-yl)ureido]isophthalic acid (PUIA), that produces metallogels upon reaction with various metal salts (Cu^II , Zn^II , Co^II , Cd^II , and Ni^II salts) at room temperature. The gels were characterized by dynamic rheology and transmission electron microscopy (TEM). The existence of a coordination bond in the gel state was probed by FTIR and ¹ H NMR spectroscopy in a Zn^II metallogel (i.e., MG2). Single crystals isolated from the reaction mixture of PUIA and Co^II or Cd^II salts characterized by X-ray diffraction revealed lattice inclusion of solvent molecules, which was in agreement with the hypothesis based on which the metallogels were designed. MG2 displayed anti-inflammatory response (prostaglandin E₂ assay) in the macrophage cell line (RAW 264.7) and anticancer properties (cell migration assay) on a highly aggressive human breast cancer cell line (MDA-MB-231). The MG2 metallogel matrix could also be used to load and release (pH responsive) the anticancer drug doxorubicin. Fluorescence imaging of MDA-MB-231 cells treated with MG2 revealed that it was successfully internalized.

Quantum confined peptide assemblies with tunable visible to near-infrared spectral range

Quantum confined materials have been extensively studied for photoluminescent applications. Due to intrinsic limitations of low biocompatibility and challenging modulation, the utilization of conventional inorganic quantum confined photoluminescent materials in bio-imaging and bio-machine interface faces critical restrictions. Here, we present aromatic cyclo-dipeptides that dimerize into quantum dots, which serve as building blocks to further self-assemble into quantum confined supramolecular structures with diverse morphologies and photoluminescence properties. Especially, the emission can be tuned from the visible region to the near-infrared region (420 nm to 820 nm) by modulating the self-assembly process. Moreover, no obvious cytotoxic effect is observed for these nanostructures, and their utilization for in vivo imaging and as phosphors for light-emitting diodes is demonstrated. The data reveal that the morphologies and optical properties of the aromatic cyclo-dipeptide self-assemblies can be tuned, making them potential candidates for supramolecular quantum confined materials providing biocompatible alternatives for broad biomedical and opto-electric applications.

Injectable self-healing carboxymethyl chitosan-zinc supramolecular hydrogels and their antibacterial activity

Injectable and self-healing hydrogels have found numerous applications in drug delivery, tissue engineering and 3D cell culture. Herein, we report an injectable self-healing carboxymethyl chitosan (CMCh) supramolecular hydrogels cross-linked by zinc ions (Zn²⁺). Supramolecular hydrogels were obtained by simple addition of metal ions solution to CMCh solution at an appropriate pH value. The mechanical properties of these hydrogels were adjustable by the concentration of Zn²⁺. For example, the hydrogel with the highest concentration of Zn²⁺ (CMCh-Zn4) showed strongest mechanical properties (storage modulus~11,000Pa) while hydrogel with the lowest concentration of Zn²⁺ (CMCh-Zn1) showed weakest mechanical properties (storage modulus~220Pa). As observed visually and confirmed rheologically, the CMCh-Zn1 hydrogel with the lowest Zn²⁺ concentration showed thixotropic property. CMCh-Zn1 hydrogel also presented injectable property. Moreover, the antibacterial properties of the prepared supramolecular hydrogels were studied against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) by agar well diffusion method. The results revealed Zn²⁺ dependent antibacterial properties against both kinds of strains. The inhibition zones were ranging from ~11-24mm and ~10-22mm against S. aureus and E. coli, respectively. We believe that the prepared supramolecular hydrogels could be used as a potential candidate in biomedical fields.

Instant Hydrogelation Inspired by Inflammasomes

Based on the recent near-atomic structures of the PYRIN domain of ASC in the protein filament of inflammasomes and the observation that the active form of vitamin B6 (pyridoxal phosphate, P5P) modulates the self-assembly of ASC, we rationally designed an N-terminal capped nonapeptide (Nap-FFKKFKLKL, 1) to form supramolecular nanofibers consisting of α-helix. The addition of P5P to the solution of 1 results in a hydrogel almost instantly (about 4 seconds). Several other endogenous small molecules (for example, pyridoxal, folinic acid, ATP, and AMP) also convert the solution of 1 into a hydrogel. As the demonstration of correlating assemblies of peptides and the relevant protein epitopes, this work illustrates a bioinspired approach to develop supramolecular structures modulated by endogenous small molecules.

A novel H2O2responsive supramolecular hydrogel for controllable drug release

We reported a peptide-based supramolecular hydrogel possessing a gel–sol phase transition triggered by H₂O₂.

Designing hydrogels for controlled drug delivery

Hydrogel delivery systems can leverage therapeutically beneficial outcomes of drug delivery and have found clinical use. Hydrogels can provide spatial and temporal control over the release of various therapeutic agents, including small-molecule drugs, macromolecular drugs and cells. Owing to their tunable physical properties, controllable degradability and capability to protect labile drugs from degradation, hydrogels serve as a platform in which various physiochemical interactions with the encapsulated drugs control their release. In this Review, we cover multiscale mechanisms underlying the design of hydrogel drug delivery systems, focusing on physical and chemical properties of the hydrogel network and the hydrogel-drug interactions across the network, mesh, and molecular (or atomistic) scales. We discuss how different mechanisms interact and can be integrated to exert fine control in time and space over the drug presentation. We also collect experimental release data from the literature, review clinical translation to date of these systems, and present quantitative comparisons between different systems to provide guidelines for the rational design of hydrogel delivery systems.

Supramolecular nanofibers of self-assembling peptides and DDP to inhibit cancer cell growth

The addition of cis-dichlorodiamineplatinum(ii) to a taxol-peptide amphiphile results in hydrogelations.

Enzymatic Dissolution of Biocomposite Solids Consisting of Phosphopeptides to Form Supramolecular Hydrogels

Enzyme-catalyzed dephosphorylation is essential for biomineralization and bone metabolism. Here we report the exploration of using enzymatic reaction to transform biocomposites of phosphopeptides and calcium (or strontium) ions to supramolecular hydrogels as a mimic of enzymatic dissolution of biominerals. (31) P NMR shows that strong affinity between the phosphopeptides and alkaline metal ions (e.g., Ca(2+) or Sr(2+) ) induces the formation of biocomposites as precipitates. Electron microscopy reveals that the enzymatic reaction regulates the morphological transition from particles to nanofibers. Rheology confirms the formation of a rigid hydrogel. As the first example of enzyme-instructed dissolution of a solid to form supramolecular nanofibers/hydrogels, this work provides an approach to generate soft materials with desired properties, expands the application of supramolecular hydrogelators, and offers insights to control the demineralization of calcified soft tissues.

Supramolecular Assemblies Responsive to Biomolecules toward Biological Applications

Stimuli-responsive supramolecular assemblies consisting of small molecules are attractive functional materials for biological applications such as drug delivery, medical diagnosis, enzyme immobilization, and tissue engineering. By use of their dynamic and reversible properties, many supramolecular assemblies responsive to a variety of biomolecules have been designed and synthesized. This review focuses on promising strategies for the construction of such dynamic supramolecular assemblies and their functions. While studies of biomolecule-responsive supramolecular assemblies have mainly been performed in vitro, it has recently been demonstrated that some of them can work in live cells. Supramolecular assemblies now open up new avenues in chemical biology and biofunctional materials.

Peptide self-assembly triggered by metal ions

This review summarizes the recent development of structures, functions, as well as strategies of a peptide self-assembly induced by metal ions.

Histidine-iridium(III) coordination-based peptide luminogenic cyclization and cyclo-RGD peptides for cancer-cell targeting

In the field of peptide drug discovery, structural constraining and fluorescent labeling are two sought-after techniques important for both basic research and pharmaceutical development. In this work, we describe an easy-to-use approach for simultaneous peptide cyclization and luminescent labeling based on iridium(III)-histidine coordination (Ir-HH cyclization). Using a series of model peptides with histidine flanking each terminus, the binding activity and reaction kinetics of Ir-HH cyclization of different ring sizes were characterized. In the series, Ir-HAnH (n = 2, 3) with moderate ring sizes provides appropriate flexibility and proper distance between histidines for cyclic formation, which leads to the best binding affinity and structural stability in physiological conditions, as compared to other Ir-HH-cyclized peptides with smaller (n = 0, 1) or larger (n = 4, 5) ring sizes. Ir-HRGDH, an Ir-HH-cyclized peptide containing integrin targeting motif Arg-Gly-Asp (RGD), showed better targeting affinity than its linear form and enhanced membrane permeability in comparison with fluorescein-labeled cyclic RGDyK peptide. Cell death inducing peptide KLA-linked Ir-HRGDH (Ir-HRGDH-KLA) showed dramatically enhanced cytotoxicity and high selectivity for cancer cells versus noncancer cells. These data demonstrate that the method conveniently combines structural constraining of peptides with luminescent imaging capabilities, which facilitates functional and intracellular characterization of potential peptide-based drug leads, thus introducing a new tool to meet emerging needs in medicinal research.

Peptide-Nanofiber-Supported Palladium Nanoparticles as an Efficient Catalyst for the Removal of N-Terminus Protecting Groups

Sonication-induced tryptophan- and tyrosine-based peptide bolaamphiphile nanofibers have been used to synthesize and stabilize Pd nanoparticles under physiological conditions. The peptide bolaamphiphile self-assembly process has been thoroughly studied by using several spectroscopic and microscopic techniques. The stiffness of the soft hydrogel matrix was measured by an oscillatory rheological experiment. FTIR and circular dichroism (CD) experiments revealed a hydrogen-bonded β-sheet conformation of peptide bolaamphiphile molecules in a gel-phase medium. The π-π stacking interactions also played a crucial role in the self-assembly process, which was confirmed by fluorescence spectroscopy. Electron (SEM and TEM) and atomic force microscopy (AFM) studies showed that the peptide bolaamphiphile molecules self-assemble into nanofibrillar structures. Pd nanoparticles were synthesized in the hydrogel matrix in which redox-active tryptophan and tyrosine residues reduce the metal ions to metal nanoparticles. The size of the Pd nanoparticles are in the range of 3-9 nm, and are stabilized by peptide nanofibers. The peptide-nanofiber-supported Pd nanoparticles have shown effective catalytic activity for the removal of N-terminus protecting groups of amino acids and peptides.

Multi-stimuli responsive self-healing metallo-hydrogels: tuning of the gel recovery property

A series of amphiphilic tyrosine based self-healable, multi-stimuli responsive metallo-hydrogels have been discovered. Formation of these hydrogels is highly selective to Ni(2+) ions. The self-healing property and the stiffness of these metallo-hydrogels can be tuned by varying the chain length of the corresponding gelator amphiphile.

Interfacial metal coordination in engineered protein and peptide assemblies

Metal ions are frequently found in natural protein-protein interfaces, where they stabilize quaternary or supramolecular protein structures, mediate transient protein-protein interactions, and serve as catalytic centers. Paralleling these natural roles, coordination chemistry of metal ions is being increasingly utilized in creative ways toward engineering and controlling the assembly of functional supramolecular peptide and protein architectures. Here we provide a brief overview of this emerging branch of metalloprotein/peptide engineering and highlight a few select examples from the recent literature that best capture the diversity and future potential of approaches that are being developed.

Self-Assembly for the Synthesis of Functional Biomaterials

The use of self-assembly for the construction of functional biomaterials is a highly promising and exciting area of research, with great potential for the treatment of injury or disease. By using multiple noncovalent interactions, coded into the molecular design of the constituent components, self-assembly allows for the construction of complex, adaptable, and highly tunable materials with potent biological effects. This review describes some of the seminal advances in the use of self-assembly to make novel systems for regenerative medicine and biology. Materials based on peptides, proteins, DNA, or hybrids thereof have found application in the treatment of a wide range of injuries and diseases, and this review outlines the design principles and practical applications of these systems. Most of the examples covered focus on the synthesis of hydrogels for the scaffolding or transplantation of cells, with an emphasis on the biological, mechanical, and structural properties of the resulting materials. In addition, we will discuss the distinct advantages conferred by self-assembly (compared with traditional covalent materials), and present some of the challenges and opportunities for the next generation of self-assembled biomaterials.