Tandem Interplay of the Host-Guest Interaction and Photoresponsive Supramolecular Polymerization to 1D and 2D Functional Peptide Materials

Unravelling denaturation, temperature and cosolvent-driven chiroptical switching in peptide self-assembly with switchable piezoelectric responses

Herein, we explore the intricate pathway complexity, focusing on the dynamic interplay between kinetic and thermodynamic states, during the supramolecular self-assembly of peptides. We uncover a multiresponsive chiroptical switching phenomenon influenced by temperature, denaturation and content of cosolvent in peptide self-assembly through pathway complexity (kinetic vs. thermodynamic state). Particularly noteworthy is the observation of chiroptical switching during the denaturation process, marking an unprecedented phenomenon in the literature. Furthermore, the variation in cosolvent contents produces notable chiroptical switching effects, emphasizing their infrequent incidence. Such chiroptical switching yields switchable piezoresponsive peptide-based nanomaterials, demonstrating the potential for dynamic control over material properties. In essence, our work pioneers the ability to control piezoresponsive behavior by transforming nanostructures from kinetic to thermodynamic states through pathway complexity. This approach provides new insights and opportunities for tailoring material properties in self-assembled systems.

Stimuli-responsive peptide assemblies: Design, self-assembly, modulation, and biomedical applications

Peptide molecules have design flexibility, self-assembly ability, high biocompatibility, good biodegradability, and easy functionalization, which promote their applications as versatile biomaterials for tissue engineering and biomedicine. In addition, the functionalization of self-assembled peptide nanomaterials with other additive components enhances their stimuli-responsive functions, promoting function-specific applications that induced by both internal and external stimulations. In this review, we demonstrate recent advance in the peptide molecular design, self-assembly, functional tailoring, and biomedical applications of peptide-based nanomaterials. The strategies on the design and synthesis of single, dual, and multiple stimuli-responsive peptide-based nanomaterials with various dimensions are analyzed, and the functional regulation of peptide nanomaterials with active components such as metal/metal oxide, DNA/RNA, polysaccharides, photosensitizers, 2D materials, and others are discussed. In addition, the designed peptide-based nanomaterials with temperature-, pH-, ion-, light-, enzyme-, and ROS-responsive abilities for drug delivery, bioimaging, cancer therapy, gene therapy, antibacterial, as well as wound healing and dressing applications are presented and discussed. This comprehensive review provides detailed methodologies and advanced techniques on the synthesis of peptide nanomaterials from molecular biology, materials science, and nanotechnology, which will guide and inspire the molecular level design of peptides with specific and multiple functions for function-specific applications.

Thermoresponsive Injectable Hydrogel To Mimic the Heat- and Strain-Stiffening Behavior of Biopolymers toward Muscle Cell Proliferation

Injectable hydrogels with nonlinear mechanical attributes to emulate natural biopolymers hold paramount significance in tissue engineering, offering the potential to create scaffolds that seamlessly mimic the biomechanical intricacies of living tissues. Herein, we unveil a synthetic design strategy employing Schiff base chemistry to furnish a peptide-polymer hierarchical contractile injectable hydrogel network. This innovative design demonstrates cross-linking of supramolecular peptide nanostructures such as nanofibers, 1NF, and twisted bundles, 1TB, with a thermosensitive aldehyde-functionalized polymer, PCHO. These networks exhibit interesting nonlinear mechanical stiffening responses to temperature and external stress. Furthermore, the hydrogels transform into a gel state at physiological temperature to exhibit injectable behavior and demonstrate compression load-bearing capabilities. Finally, the hydrogel network exhibits excellent biocompatibility and cell proliferation toward fibroblast, L929, and myoblast, C2C12, to validate their use as potential extracellular matrix mimetic injectable scaffolds.

Thermo-Chemical Cues-Mediated Strategy to Control Peptide Self-Assembly and Charge Transfer Complexation

Peptide amphiphiles (PAs) are known for their remarkable ability to undergo molecular self-assembly, a process that is highly responsive to the local microenvironment. Herein, we design a pyrene tethered peptide amphiphile Py-VFFAKK, 1 that exhibits pathway-driven self-assembly from metastable nanoparticles to kinetically controlled nanofibers and thermodynamically stable twisted bundles upon modulations in pH, temperature, and chemical cues. The presence of the pyrene moiety ensures donation of the electron to an electron acceptor, namely, 7,7,8,8-tetracyanoquinodimethane (TCNQ), to form a supramolecular charge transfer complex in aqueous solution that was studied in detail with microscopic and spectroscopic techniques. Excitation of the donor species in its excimer state facilitates electron donation to the acceptor moiety, paving away a long-lived charge-separated state that persists for over a nanosecond, as ascertained through transient absorption spectroscopy. Finally, the self-assembled charge transfer complex is explored toward antimicrobial properties with Escherichia coli while maintaining biocompatibility toward L929 mice fibroblast cells.

Photoresponsive peptide materials: Spatiotemporal control of self-assembly and biological functions

Peptides work as both functional molecules to modulate various biological phenomena and self-assembling artificial materials. The introduction of photoresponsive units to peptides allows the spatiotemporal remote control of their structure and function upon light irradiation. This article overviews the photoresponsive peptide design, interaction with biomolecules, and applications in self-assembling materials over the last 30 years. Peptides modified with photochromic (photoisomerizable) molecules, such as azobenzene and spiropyran, reversibly photo-controlled the binding to biomolecules and nanostructure formation through self-assembly. Photocleavable molecular units irreversibly control the functions of peptides through cleavage of the main chain and deprotection by light. Photocrosslinking between peptides or between peptides and other biomolecules enhances the structural stability of peptide assemblies and complexes. These photoresponsive peptides spatiotemporally controlled the formation and dissociation of peptide assemblies, gene expressions, protein-drug interactions, protein-protein interactions, liposome deformation and motility, cytoskeleton structure and stability, and cell functions by appropriate light irradiation. These molecular systems can be applied to photo-control biological functions, molecular robots, artificial cells, and next-generation smart drug delivery materials.

Stereoselective Plasmonic Interaction in Peptide-tethered Photopolymerizable Diacetylenes Doped with Chiral Gold Nanoparticles

Designing polymeric systems with ultra-high optical activity is instrumental in the pursuit of smart artificial chiroptical materials, including the fundamental understanding of structure/property relations. Herein, we report a diacetylene (DA) moiety flanked by chiral D- and L-FF dipeptide methyl esters that exhibits efficient topochemical photopolymerization in the solid phase to furnish polydiacetylene (PDA) with desired control over the chiroptical properties. The doping of the achiral gold nanoparticles provides plasmonic interaction with the PDAs to render asymmetric shape to the circular dichroism bands. With the judicious design of the chiral amino acid ligand appended to the AuNPs, we demonstrate the first example of selective chiral amplification mediated by stereo-structural matching of the polymer-plasmonic AuNP hybrid pairs. Such ordered self-assembly aided by topochemical polymerization in peptide-tethered PDA provides a smart strategy to produce soft responsive materials for applications in chiral photonics.

Stimuli-Responsive Self-Assembly Disassembly in Peptide Amphiphiles to Endow Block-co-Fibers and Tunable Piezoelectric Response

Supramolecular assemblies with well-defined structural attenuation toward varied functional implications are an emerging area in mimicking natural biomaterials. In that regard, the redox stimuli-responsive ferrocene moiety can reversibly change between a nonpolar ferrocenyl and polar ferrocenium cation that endows interesting modular features to the building blocks with respect to self-assembly/disassembly. We design a series of ferrocene anchored peptide fragment ^NVFFAKK^C using hydrophobic alkyl spacers of different chain lengths. Increasing the spacer length between the redox-responsive and self-assembling motifs increases the propensity to form robust nanofibers, which can be physically cross-linked to form hydrogels. The controlled redox response of the ferrocene moiety tandem with pH control provides access to structural control over the peptide nanostructures and tunable mechanical strengths. Further, such redox-sequestered dormant states hinder the spontaneous nucleation process that we exploit toward seeded supramolecular polymerization to form block cofibers composed of redox-responsive periphery and nonresponsive cores. Finally, such redox sequestration of peptide self-assembly renders an on-off piezoelectric response for potential utilization in peptide bioelectronics.

Anion-responsive self-assembled hydrogels of a phenylalanine-TREN conjugate allow sequential release of propranolol and doxorubicin

Stimuli-responsive self-assembled and supramolecular hydrogels derived from peptide amphiphiles have opened exciting new avenues in biomedicine and drug delivery. Herein, we screened a series of phenylalanine-amphiphiles possessing polyamine and oxyethylene appendages for their self-assembly and anion-responsiveness and found that the tris(aminoethyl)amine (TREN) containing amphiphile NapF-TREN formed injectable hydrogels that could be disrupted upon the addition of stoichiometric amounts of tetrahedral monovalent anions such as H₂PO₄^- and HSO₄^-, while the addition of other anions such as Cl^-, HPO₄^2-, CO₃^2-, HCO₃^- or SO₄^2- did not affect the gel stability. The anion-gelator interaction was investigated by ¹H and ³¹P NMR spectroscopy as well as by Isothermal Titration Calorimetry (ITC). These studies confirmed a 1 : 1 stoichiometry and revealed negative enthalpy and negative entropy for the binding of H₂PO₄^- with NapF-TREN. Microscopic investigations by TEM, AFM, and SAXS revealed that H₂PO₄^- anions induced a nanofiber-to-nanoglobule morphological change in the aqueous self-assemblies of NapF-TREN. However, upon ageing the samples, slow reformation of the nanofibers was also observed, reflecting the reversibility of the anion-gelator interaction. The anion- and pH-responsive nature of the NapF-TREN hydrogels was exploited to program sequential release of entrapped drugs propranolol and doxorubicin.

Hierarchical self-assembly of aromatic peptide conjugates into supramolecular polymers: it takes two to tango

Supramolecular polymers are self-assembled materials displaying adaptive and responsive "life-like" behaviour which are often made of aromatic compounds capable of engaging in π-π interactions to form larger assemblies. Major advances have been made recently in controlling their mode of self-assembly, from thermodynamically-controlled isodesmic to kinetically-controlled living polymerization. Dynamic covalent chemistry has been recently implemented to generate dynamic covalent polymers which can be seen as dynamic analogues of biomacromolecules. On the other hand, peptides are readily-available and structurally-rich building blocks that can lead to secondary structures or specific functions. In this context, the past decade has seen intense research activity in studying the behaviour of aromatic-peptide conjugates through supramolecular and/or dynamic covalent chemistries. Herein, we review those impressive key achievements showcasing how aromatic- and peptide-based self-assemblies can be combined using dynamic covalent and/or supramolecular chemistry, and what it brings in terms of the structure, self-assembly pathways, and function of supramolecular and dynamic covalent polymers.

Dimension switchable auto-fluorescent peptide-based 1D and 2D nano-assemblies and their self-influence on intracellular fate and drug delivery

The production of dynamic, environment-responsive shape-tunable biomaterials marks a significant step forward in the construction of synthetic materials that can easily rival their natural counterparts. Significant progress has been made in the self-assembly of bio-materials. However, the self-assembly of a peptide into morphologically distinct auto-fluorescent nanostructures, without the incorporation of any external moiety is still in its infancy. Hence, in this study, we have developed peptide-based self-assembled auto-fluorescent nanostructures that can shuttle between 1D and 2D morphologies. Different morphological nanostructures are well known to have varied cellular internalization efficiencies. Taking advantage of our morphologically different particles emanating from the same peptide monomer, we further explored the intracellular fate of our nanostructures. We observed that the nanostructures' cellular internalization is a complex process that gets influenced by particle morphology and this might further affect their intracellular drug delivery potential. Overall, this study provides initial cues for the preparation of environment-responsive shape-shifting peptide-nano assemblies. Efforts have also been made to understand their shape driven cellular uptake behaviour, along with establishing them as nanocarriers for the cellular delivery of therapeutic molecules.

Modulation of flexo-rigid balance in photoresponsive thymine grafted copolymers towards designing smart healable coating

Efficacy and durability of the photovoltaic device mandates its protection against hot, humid weather condition, high energy of UV light and unwanted scratches. Such challenges can be mitigated by smart polymeric coating with inherent properties e.g. hydrophobicity to prevent moisture, optimal viscocity for better processibility and crack-healing. The hydrophobic polymers TP1-TP4 containing pendant photo-crosslinkable thymine moieties are designed that undergo [2 + 2] photocycloaddition upon UVB irradiation and can be dynamically reverted back upon irradiation with UVC light. A judicious control of solvent environment, chain length, functionality% and concentration of the polymers regulate the aspects of photodimerization thereby, rendering intra or inter-chain collapse to form diverse nanostructures. Photodimerization of the thymine moieties renders coil to globule transformation in dilute condition whereas irradiation performed at high macromolecular concentration regime exhibits higher order nanostructures. The photoresponsive chain collapse leads to the formation of rigid crosslinked domains within flexible polymer chains akin to the hard-soft phases of thermoplastic elastomers. Such rigidification of the crosslinked segments endows a tool to photomodulate the glass transition temperature (T g) that can dynamically revert back upon decrosslinking. Further, the structural modulation of the polymers is explored towards autonomic and nonautonomic self-healing behaviour at ambient conditions. Moreover, the self-healing efficacy can be tuned with the film thickness and it remains unaltered upon using solar simulator or direct sunlight. Overall, such hydrophobic low T g polymers display photo-regulated self-healing mechanism consisting of both autonomic and non-autonomic self-healing and may find applications in designing smart protective coatings for photovoltaic devices.

Photothermally switchable peptide nanostructures towards modulating catalytic hydrolase activity

Enzymes are the most efficient catalysts in nature that possess an impressive range of catalytic activities, albeit limited by stability in adverse conditions. Functional peptides have emerged as alternative robust biocatalysts to mimic complex enzymes. Here, a rational design of minimalistic amyloid-inspired peptides 1-2 is demonstrated, which leads to pathway-driven self-assembly triggered by heat, light and chemical cues to render 1D and 2D nanostructures by the interplay of hydrogen bonding, host-guest interaction and reversible photodimerization. Such in situ transformable peptide nanostructures by means of external cues are envisaged as a catalytic amyloid for the first time to mimic the hydrolase enzyme activity. Michaelis Menten's enzyme kinetic parameters for the hydrolysis rate correlate the external cue-mediated structure-function augmentation with the twisted bundles, 1_TB being the most efficient biocatalyst among all the dimensionally diverse nanostructures. Unlike the natural enzyme, the peptide nanostructures exhibited the robust nature of the hydrolase activity over a broad range of temperature and pH. Finally, the peptide nanostructures are explored as efficient heterogeneous flow catalysts to improve the turnover number for the hydrolase activity.

Complexation of an Azo Dye by Cyclodextrins: A Potential Strategy for Water Purification

The chemistry of the host-guest complex formation has received much attention as a highly efficient approach for use to develop economical adsorbents for water purification. In the present study, the synthesis of three β-cyclodextrin (β-CD) inclusion complexes with the oil orange SS (OOSS) azo dye as a guest molecule and their potential applications in water purification are described. The complexes were synthesized by the coprecipitation method and characterized by Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). FTIR and thermal analyses confirmed the encapsulation of OOSS dye within the hydrophobic cavity of β-CD. The encapsulation of hydrophobic dye inside the β-CD cavity was mainly due to the hydrophobic-hydrophobic interaction. The results showed that the stability of the OOSS dye had been improved after the complexation. The effect of three different compositions of the host-guest complexes was analyzed. The present study demonstrated that the hydrophobic dye could be removed from aqueous solution via inclusion complex formation. Thus, it can play a significant role in removing the highly toxic OOSS dye from the industrial effluent.

Monolayer nanosheets formed by liquid exfoliation of charge-assisted hydrogen-bonded frameworks

Hydrogen-bonded organic frameworks (HOFs) are a diverse and tunable class of materials, but their potential as free-standing two-dimensional nanomaterials has yet to be explored. Here we report the self-assembly of two layered hydrogen-bonded frameworks based on strong, charge-assisted hydrogen-bonding between carboxylate and amidinium groups. Ultrasound-assisted liquid exfoliation of both materials readily produces monolayer hydrogen-bonded organic nanosheets (HONs) with micron-sized lateral dimensions. The HONs show remarkable stability and maintain their extended crystallinity and monolayer structures even after being suspended in water at 80 °C for three days. These systems also exhibit efficient fluorescence quenching of an organic dye in organic solvents, superior to the quenching ability of the bulk frameworks. We anticipate that this approach will provide a route towards a diverse new family of molecular two-dimensional materials.

Delineating synchronized control of dynamic covalent and non-covalent interactions for polymer chain collapse towards cargo localization and delivery

Synergistic control of photo-responsive dynamic covalent and non-covalent interaction over the chain collapse of single chain thermo-responsive polymers towards cargo localization and augmented release.

Enzyme-responsive chiral self-sorting in amyloid-inspired minimalistic peptide amphiphiles

Self-sorting is a spontaneous phenomenon that ensures the formation of complex yet ordered multicomponent systems and conceptualizes the design of artificial and orthogonally functional compartments. In the present study, we envisage chirality-mediated self-sorting in β-amyloid-inspired minimalistic peptide amphiphile (C₁₀-l/d-VFFAKK)-based nanofibers. The fidelity and stereoselectivity of chiral self-sorting was ascertained by Förster resonance energy transfer (FRET) by the judicious choice of a pyrene (Py)-hydroxy coumarin (HOCou) donor-acceptor pair tethered to the peptide sequences. Seed-promoted elongation of the homochiral peptide amphiphiles investigated by AFM image analyses and Thioflavin-T (ThT) binding study further validated the chiral recognition of the l/d peptide nanofibers. Moreover, direct visualization of the chirality-driven self-sorted nanofibers is reported using super-resolution microscopy that exhibits enantioselective enzymatic degradation for l-peptide fibers. Such enantioselective weakening of the hydrogels may be used for designing stimuli-responsive orthogonal compartments for delivery applications.

Photoresponsive chain collapse in a flexo-rigid functional copolymer to modulate the self-healing behaviour

Synthetic systems mimicking the natural self-folding process are attractive to impart multiple structural control over polymer crosslinking and the subsequent alteration of their macroscopic self-healing properties. In that regard, polymers P1-P5 containing pendant photo-crosslinkable moieties were designed and underwent intra- or interchain collapse to form diverse nanostructures. The shape and dimension of the nanostructures could be efficiently controlled by the concentration, solvent compatibility and characteristics of the polymers. Photodimerization of the coumarin moieties transformed the extended coiled chain of the polymer to uniform sized nanoparticles in a dilute condition, while in the crowded macromolecular concentration regime, the polymer folded into nanostructures with polydisperse topologies that were far from a condensed globule or partially swollen globule conformation. Scaling law exponents for polymer chain compaction suggested an interchain collapse with rigid compact segments connected by flexible polymer chains that draws an analogy with elastomers. Such a hardening of the rigid segment as a consequence of photodimerization rendered a significant increase in the glass transition temperature (Tg), which could be reversibly controlled upon decrosslinking. Lastly, the structural variation of this class of polymers over self-healing was explored and the crosslinked polymers showed phototriggered non-autonomic and intrinsic self-healing behaviour under ambient conditions. This is an interesting approach to access a photomodulated self-healing system with low Tg polymers that shows the coexistence of autonomic and nonautonomic self-healing pathways and that may find application in designing smart coatings for photovoltaic devices.