Red Light-Initiated Cross-Linking of NIR Probes to Cytoplasmic RNA: An Innovative Strategy for Prolonged Imaging and Unexpected Tumor Suppression

Improving the enrichment of drugs or theranostic agents within tumors is very vital to achieve effective cancer diagnosis and therapy while greatly reducing the dosage and damage to normal tissues. Herein, as a proof of concept, we for the first time report a red light-initiated probe-RNA cross-linking (RLIPRC) strategy that can not only robustly promote the accumulation and retention of the probe in the tumor for prolonged imaging but also significantly inhibits the tumor growth. A near-infrared (NIR) fluorescent probe f-CR consisting of a NIR dye (Cyanine 7) as a signal reporter, a cyclic-(arginine-glycine-aspartic acid) (cRGD) peptide for tumor targeting, and a singlet oxygen (¹O₂)-sensitive furan moiety for RNA cross-linking was rationally designed and synthesized. This probe possessed both passive and active tumor targeting abilities and emitted intense NIR/photoacoustic (PA) signals, allowing for specific and sensitive dual-modality imaging of tumors in vivo. Notably, probe f-CR could be specifically and covalently cross-linked to cytoplasmic RNAs via the cycloaddition reaction between furan and adenine, cytosine, or guanine under the oxidation of ¹O₂ generated in situ by irradiation of methylene blue (MB) with 660 nm laser light, which effectively blocks the exocytosis of the probes resulting in enhanced tumor accumulation and retention. More excitingly, for the first time, we revealed that the covalent cross-linking of probe f-CR to cytoplasmic RNAs could induce severe apoptosis of cancer cells leading to remarkable tumor suppression. This study thus represents the first red light-initiated RNA cross-linking system with high potential to improve the diagnostic and therapeutic outcomes of tumors in vivo.

Bioimaging and Biodistribution of the Metal-Ion-Controlled Self-Assembly of PYY3-36 Studied by SPECT/CT

The controlled self-assembly of peptide- and protein-based pharmaceuticals is of central importance for their mode of action and tuning of their properties. Peptide YY_3-36 (PYY_3-36 ) is a 36-residue peptide hormone that reduces food intake when peripherally administered. Herein, we describe the synthesis of a PYY_3-36 analogue functionalized with a metal-ion-binding 2,2'-bipyridine ligand that enables self-assembly through metal complexation. Upon addition of Cu^II , the bipyridine-modified PYY_3-36 peptide binds stoichiometric quantities of metal ions in solution and contributes to the organization of higher-order assemblies. In this study, we aimed to explore the size effect of the self-assembly in vivo by using non-invasive quantitative single-photon emission computed tomography/computed tomography (SPECT/CT) imaging. For this purpose, bipyridine-modified PYY_3-36 was radiolabeled with a chelator holding ¹¹¹ In^III , followed by the addition of Cu^II to the bipyridine ligand. SPECT/CT imaging and biodistribution studies showed fast renal clearance and accumulation in the kidney cortex. The radiolabeled bipyridyl-PYY_3-36 conjugates with and without Cu^II presented a slightly slower excretion 1 h post injection compared to the unmodified-PYY_3-36 , thus demonstrating that higher self-assemblies of the peptide might have an effect on the pharmacokinetics.

Chemistry and Biofunctional Significance of Bioactive Peptide Interactions with Food and Gut Components

Food-derived bioactive peptides (BAPs) have gained significant interest as functional agents for developing food products with health benefits. To elucidate the underlying bioactivity mechanisms, current research investigates mostly the structure-activity relationship of native peptides. However, peptide structures are highly susceptible to chemical modifications, which can subsequently influence their physiological behaviors and bioactivities. This paper highlights the peptide structure modifications occurring with major food components during processing and the digestive environment of the gut as well as associated changes in peptide properties and biofunctions. Given the modification propensity of peptides, focus should be shifted toward characterizing the nature, biofunctions, gut activity, bioavailability, and safety of the modified peptides toward achieving pragmatic food applications of BAPs.

Recent advances in the fabrication, functionalization, and bioapplications of peptide hydrogels

Self-assembled peptide-based nanomaterials have exhibited wide application potential in the fields of materials science, nanodevices, biomedicine, tissue engineering, biosensors, energy storage, environmental science, and others. Due to their porous structure, strong mechanical stability, high biocompatibility, and easy functionalization, three-dimensional self-assembled peptide hydrogels revealed promising potential in bio-related applications. To present the advances in this interesting topic, we present a review on the synthesis and functionalization of peptide hydrogels, as well as their applications in drug delivery, antibacterial materials, cell culture, biomineralization, bone tissue engineering, and biosensors. Specifically, we focus on the fabrication methods of peptide hydrogels through physical, chemical, and biological stimulations. In addition, the functional design of peptide hydrogels by incorporation with polymers, DNA, protein, nanoparticles, and carbon materials is introduced and discussed in detail. It is expected that this work will be helpful not only for the design and synthesis of various peptide-based nanostructures and nanomaterials, but also for the structural and functional tailoring of peptide-based nanomaterials to meet specific demands.

Ordered Nanofibers Fabricated from Hierarchical Self-Assembling Processes of Designed α-Helical Peptides

Peptide self-assembly is fast evolving into a powerful method for the development of bio-inspired nanomaterials with great potential for many applications, but it remains challenging to control the self-assembling processes and nanostrucutres because of the intricate interplay of various non-covalent interactions. A group of 28-residue α-helical peptides is designed including NN, NK, and HH that display distinct hierarchical events. The key of the design lies in the incorporation of two asparagine (Asn) or histidine (His) residues at the a positions of the second and fourth heptads, which allow one sequence to pack into homodimers with sticky ends through specific interhelical Asn-Asn or metal complexation interactions, followed by their longitudinal association into ordered nanofibers. This is in contrast to classical self-assembling helical peptide systems consisting of two complementary peptides. The collaborative roles played by the four main non-covalent interactions, including hydrogen-bonding, hydrophobic interactions, electrostatic interactions, and metal ion coordination, are well demonstrated during the hierarchical self-assembling processes of these peptides. Different nanostructures, for example, long and short nanofibers, thin and thick fibers, uniform metal ion-entrapped nanofibers, and polydisperse globular stacks, can be prepared by harnessing these interactions at different levels of hierarchy.

Synthetic peptide hydrogels as 3D scaffolds for tissue engineering

The regeneration of tissues and organs poses an immense challenge due to the extreme complexity in the research work involved. Despite the tissue engineering approach being considered as a promising strategy for more than two decades, a key issue impeding its progress is the lack of ideal scaffold materials. Nature-inspired synthetic peptide hydrogels are inherently biocompatible, and its high resemblance to extracellular matrix makes peptide hydrogels suitable 3D scaffold materials. This review covers the important aspects of peptide hydrogels as 3D scaffolds, including mechanical properties, biodegradability and bioactivity, and the current approaches in creating matrices with optimized features. Many of these scaffolds contain peptide sequences that are widely reported for tissue repair and regeneration and these peptide sequences will also be discussed. Furthermore, 3D biofabrication strategies of synthetic peptide hydrogels and the recent advances of peptide hydrogels in tissue engineering will also be described to reflect the current trend in the field. In the final section, we will present the future outlook in the design and development of peptide-based hydrogels for translational tissue engineering applications.

pH- and concentration-dependent supramolecular self-assembly of a naturally occurring octapeptide

Peptide-based biopolymers represent highly promising biocompatible materials with multiple applications, such as tailored drug delivery, tissue engineering and regeneration, and as stimuli-responsive materials. Herein, we report the pH- and concentration-dependent self-assembly and conformational transformation of the newly synthesized octapeptide PEP-1. At pH 7.4, PEP-1 forms β-sheet-rich secondary structures into fractal-like morphologies, as verified by circular dichroism (CD), Fourier-transform infrared (FTIR) spectroscopy, thioflavin T (ThT) fluorescence spectroscopy assay, and atomic force microscopy (AFM). Upon changing the pH value (using pH 5.5 and 13.0), PEP-1 forms different types of secondary structures and resulting morphologies due to electrostatic repulsion between charged amino acids. PEP-1 can also form helical or random-coil secondary structures at a relatively low concentration. The obtained pH-sensitive self-assembly behavior of the target octapeptide is expected to contribute to the development of novel drug nanocarrier assemblies.

A rationally designed peptoid for the selective chelation of Zn2+ over Cu2

The selective removal of Zn²⁺ from proteins by using a synthetic chelator is a promising therapeutic approach for the treatment of various diseases including cancer. Although the chelation of Zn²⁺ is well known, its removal from a protein in the presence of potential competing biologically relevant ions such as Cu²⁺ is hardly explored. Herein we present a peptoid - N-substituted glycine trimer - incorporating a picolyl group at the N-terminus, a non-coordinating but structurally directing benzyl group at the C-terminus and a 2,2':6',2''-terpyridine group in the second position, that selectively binds Zn²⁺ ions in the presence of excess Cu²⁺ ions in water. We further demonstrate that this chelator can selectively bind Zn²⁺ from a pool of excess biologically relevant and competitive ions (Cu²⁺, Fe³⁺, Ca²⁺, Mg²⁺, Na⁺, and K⁺) in a simulated body fluid (SBF), and also its ability to remove Zn²⁺ from a natural zinc protein domain (PYKCPECGKSFSQKSDLVKHQRTHTG) in a SBF.

Controlling the properties and self-assembly of helical nanofibrils by engineering zinc-binding β-hairpin peptides

This work illustrates a series of novel peptides that have the capability to bind Zn2+ ions and to produce fibrillar structures. The location and the type of the residues along the peptide sequence can determine the nature of the fibril. This work presents a proof-of-concept milestone for designing peptides with different properties to produce diverse materials.

An ssDNA aptamer specific for detection and purification of hexahistidine-tagged proteins

Aptamers are small-sized RNA or ssDNA ligands with a unique structure, which have high specificity and affinity to their cognate targets. Thus, in addition to the extensive values in various bio-medical fields, aptamers can also be alternatively used as affinity ligands in the bioprocess, such as for protein purification. In the present study, a hexahistidine specific aptamer named AptHis-C, was developed through the SELEX methodology, which has high affinity to hexahistidine, and its dissociation constant was as low as 20.8 nM. The structural prediction revealed that AptHis-C contains two connected stem-loop conformations. AptHis-C can only specifically recognize recombinant proteins with the hexahistidine-tag in simple or complex situations, and not to those with other tags. When immobilized on magnetic beads, AptHis-C can be used as a tool for hexahistidine-tagged recombinant protein purification. Its effectiveness is as good as traditional Ni-based beads. Besides, due to the intrinsic characteristics of nucleic acids, such as high thermal/chemical stability, immobilized aptamer-magnetic beads can be reused many times without an obvious decrease of purification effectiveness. This aptamer may represent a novel method for the detection and purification of hexahistidine-tagged recombinant proteins.

Tumor microenvironment-oriented adaptive nanodrugs based on peptide self-assembly

The aberrant metabolism of tumor cells creates an inimitable microenvironment featuring acidic pH, high glutathione (GSH) levels, and overexpression of certain enzymes, which benefits the overwhelming progress of a tumor. Peptide self-assembly, emerging as a biofriendly and versatile fabrication strategy, harnesses multiple noncovalent interactions to obtain a variety of nanostructures tailored on demand. Orchestrating the reversible nature of noncovalent interactions and abnormal physiological parameters in the tumor microenvironment enables peptide-based nanodrugs to be targetable or switchable, thereby improving the drugs' bioavailability and optimizing the treatment outcome. This review will focus on peptide-modulated self-assembly of photosensitizers, chemotherapeutic drugs, immunoactive agents for tumor microenvironment-oriented adaptive phototherapy, chemotherapy, immunotherapy and combinatorial therapy. We will emphasize the building block design, the intermolecular interaction principle, adaptive structural transformation in the tumor microenvironment and corresponding therapeutic efficacy, and aim to elucidate the critical role of peptide-modulated, tumor microenvironment-oriented adaptive assemblies in improving the therapeutic index. Challenges and opportunities will be covered as well to advance the development and clinical application of tumor therapies based on peptide self-assembly materials and techniques.

Glycosyltransferase-Induced Morphology Transition of Glycopeptide Self-Assemblies with Proteoglycan Residues

We previously proposed the deprotection-induced block copolymer self-assembly (DISA), that is, the deprotection of hydroxyl groups of saccharides resulted in self-assembly of glycopolymers (Qi et al. J. Am. Chem. Soc. 2018, 140 (28), 8851-8857 and Su et al. ACS Macro Lett. 2014, 3 (6), 534-539). In this study, we further combined glycochemistry and self-assembly strategy by introducing glycosyltransferase as the trigger, which constructs another glycosidic bonds and another carbohydrate building blocks in situ. Herein, we propose to utilize glycosyltransferase to induce the morphology transition of glycopeptide assemblies in the process of glycosidic bonds construction, which has never been reported in literature. This strategy provides us an alternative tool to construct proteoglycan-mimicking polymeric materials and deepens our understanding on the natural process of proteoglycan construction better in the future.

Ultrashort Peptide Self-Assembly: Front-Runners to Transport Drug and Gene Cargos

The translational therapies to promote interaction between cell and signal come with stringent eligibility criteria. The chemically defined, hierarchically organized, and simpler yet blessed with robust intermolecular association, the peptides, are privileged to make the cut-off for sensing the cell-signal for biologics delivery and tissue engineering. The signature service and insoluble network formation of the peptide self-assemblies as hydrogels have drawn a spell of research activity among the scientists all around the globe in the past decades. The therapeutic peptide market players are anticipating promising growth opportunities due to the ample technological advancements in this field. The presence of the other organic moieties, enzyme substrates and well-established protecting groups like Fmoc and Boc etc., bring the best of both worlds. Since the large sequences of peptides severely limit the purification and their isolation, this article reviews the account of last 5 years' efforts on novel approaches for formulation and development of single molecule amino acids, ultra-short peptide self-assemblies (di- and tri- peptides only) and their derivatives as drug/gene carriers and tissue-engineering systems.

Nine-Residue Peptide Self-Assembles in the Presence of Silver to Produce a Self-Healing, Cytocompatible, Antimicrobial Hydrogel

Silver compounds have been used extensively for wound healing because of their antimicrobial properties, but high concentrations of silver are toxic to mammalian cells. We designed a peptide that binds silver and releases only small amounts of this ion over time, therefore overcoming the problem of silver toxicity. Silver binding was achieved through incorporation of an unnatural amino acid, 3'-pyridyl alanine (3'-PyA), into the peptide sequence. Upon the addition of silver ions, the peptide adopts a beta-sheet secondary structure and self-assembles into a strong hydrogel as characterized by rheology, circular dichroism, and transmission electron microscopy. We show that the resulting hydrogel kills Escherichia coli and Staphylococcus aureus but is not toxic to fibroblasts and could be used for wound healing. The amount of Ag(I) released by hydrogels into the solution is less than 4% and this low amount of Ag(I) does not change in the pH range 6-8. These studies provide an initial indication for use of the designed hydrogel as injectable, antimicrobial wound dressing.

Strategies for conjugating iridium(III) anticancer complexes to targeting peptides via copper-free click chemistry

We report the synthesis and characterization of novel pentamethylcyclopentadienyl (Cp*) iridium(III) complexes [(Cp*)Ir(4-methyl-4'-carboxy-2,2'-bipyridine)Cl]PF6 (Ir-I), the product (Ir-II) from amide coupling of Ir-I to dibenzocyclooctyne-amine, and its conjugate (Ir-CP) with the cyclic nona-peptide c(CRWYDENAC). The familiar three-legged 'piano-stool' configuration for complex Ir-I was confirmed by its single crystal X-ray structure. Significantly, copper-free click strategy has been developed for site-specific conjugation of the parent complex Ir-I to the tumour targeting nona-cyclic peptide. The approach consisted of two steps: (i) the carboxylic acid group of the bipyridine ligand in complex Ir-I was first attached to an amine functionalized dibenzocyclooctyne group via amide formation to generate complex Ir-II; and (ii) the alkyne bond of dibenzocyclooctyne in complex Ir-II underwent a subsequent strain-promoted copper-free cycloaddition with the azide group of the modified peptide. Interestingly, while complex Ir-I was inactive towards A2780 human ovarian cancer cells, complex Ir-II exhibited moderate cytotoxic activity. Targeted complexes such as Ir-CP offer scope for enhanced activity and selectivity of this class of anticancer complexes.

High-Efficiency Fluorescence through Bioinspired Supramolecular Self-Assembly

Peptide self-assembly has attracted extensive interest in the field of eco-friendly optoelectronics and bioimaging due to its inherent biocompatibility, intrinsic fluorescence, and flexible modulation. However, the practical application of such materials was hindered by the relatively low quantum yield of such assemblies. Here, inspired by the molecular structure of BFPms1, we explored the "self-assembly locking strategy" to design and manipulate the assembly of metal-stabilized cyclic(l-histidine-d-histidine) into peptide material with the high-fluorescence efficiency. We used this bioorganic material as an emissive layer in photo- and electroluminescent prototypes, demonstrating the feasibility of utilizing self-assembling peptides to fabricate a biointegrated microchip that incorporates eco-friendly and tailored optoelectronic properties. We further employed a "self-encapsulation" strategy for constructing an advanced nanocarrier with integrated in situ monitoring. The strategy of the supramolecular capture of functional components exemplifies the use of bioinspired organic chemistry to provide frontiers of smart materials, potentially allowing a better interface between sustainable optoelectronics and biomedical applications.

Prebiotic Peptides: Molecular Hubs in the Origin of Life

The fundamental roles that peptides and proteins play in today's biology makes it almost indisputable that peptides were key players in the origin of life. Insofar as it is appropriate to extrapolate back from extant biology to the prebiotic world, one must acknowledge the critical importance that interconnected molecular networks, likely with peptides as key components, would have played in life's origin. In this review, we summarize chemical processes involving peptides that could have contributed to early chemical evolution, with an emphasis on molecular interactions between peptides and other classes of organic molecules. We first summarize mechanisms by which amino acids and similar building blocks could have been produced and elaborated into proto-peptides. Next, non-covalent interactions of peptides with other peptides as well as with nucleic acids, lipids, carbohydrates, metal ions, and aromatic molecules are discussed in relation to the possible roles of such interactions in chemical evolution of structure and function. Finally, we describe research involving structural alternatives to peptides and covalent adducts between amino acids/peptides and other classes of molecules. We propose that ample future breakthroughs in origin-of-life chemistry will stem from investigations of interconnected chemical systems in which synergistic interactions between different classes of molecules emerge.

Light-triggered syneresis of a water insoluble peptide-hydrogel effectively removes small molecule waste contaminants

A short peptide based hydrogel exhibits aqueous insolubility, thixotropy and efficient light induced syneresis. Upon irradiation with UV light, the hydrogel shrinks and expells ∼50% of the solvent. Syneresis is caused by light-triggered trans-cis isomerisation of an azobenzene moiety in the peptide derivative. This expulsion of solvent can be effectively exploited in the removal of low molecular weight contaminants in water.

Synthesis and Self-Assembly Behavior of Chlorophyll Derivatives for Ratiometric Photoacoustic Signal Optimization

Self-assembly provides researchers powerful tools for creating ordered functional structures and complex architectures. Investigation of in vivo self-assembly reveals the assembly/aggregation-induced retention (AIR) effect and enhanced targeting effect, which can be applied to promising biomedical applications by enhancing molecular accumulation in the target region. These unique bioeffects inspire the interest of researchers in construction of self-assembled nanomaterials in biological systems. Although many efforts have been achieved, the in-depth analysis of the relationship between assemblies and functions is rarely reported. Here, we focus on the relationship of chlorophyll-derivative assemblies and their photoacoustic signals and attempt to establish a method for monitoring the aggregation efficiency in vivo based on photoacoustic signals. Three arginine-rich peptide-purpurin molecules were designed and synthesized. The assembled capabilities and assembly processes of these molecules were characterized and monitored by UV, fluorescence, and CD spectra images of gradually changing polarities in mixed solvents, and the morphologies of the assemblies were observed by TEM. Furthermore, the relationship between the aggregation ratios of the molecules and the ratiometric photoacoustic signals was systemically studied. We prospect that the fundamental research in revealing objective laws will be useful for future guidance in optimizing photoacoustic detection windows and assembled molecule design.

Self-assembly of a Sequence-shuffled Short Peptide Amphiphile Triggered by Metal Ions into Terraced Nanodome-like Structures

We highlight the structural diversity of strategically designed two short peptide amphiphiles (sPAs) and describe their structure-function relationship studies. The shuffling of two key amino acids, that is, tyrosine and phenylalanine, in a designed sPA lead to a pair of constitutional isomers. Such small and strategic alteration can bring a substantial change in the self-assembling pattern. Inspired from the naturally occurring metallopeptides, bioactive transition-metal ions were used for constructing the unusual nanostructures. Use of appropriate metal ions created bigger differences between the properties of these isomers and hence the self-assembly. Coordination of appropriate transition metal ions modifies the internal nanoscale structures of sPA, thus leading to the formation of vertically stacked terraced layers with decreasing size, which possess a high degree of dimensional regularity. We propose that such metal-induced terraced nanodome-like hierarchical self-assembly may have relevance for specific biotechnology applications.

Effect of Transition-Metal Ions on the Conformation of Encephalin Investigated by Hydrogen/Deuterium Exchange and Theoretical Calculations

We have studied the effects of different 3d orbitals in divalent transition-metal ions [G²⁺ = Mn²⁺ (d⁵), Fe²⁺ (d⁶), Co²⁺ (d⁷), Ni²⁺ (d⁸), Cu²⁺ (d⁹), or Zn²⁺ (d¹⁰)] on the conformations of leucine encephalin (LE) and methionine encephalin (ME) in the gas phase using hydrogen/deuterium exchange mass spectrometry (HDX-MS) and theoretical calculations at the molecular level. The HDX-MS reveals a 1:1 stoichiometric monovalent complex of [LE/ME + G - H]⁺ and observed that the different HDX reactivities follow the trend Fe²⁺ < Co²⁺ < Ni²⁺ < Mn²⁺ < Cu²⁺ ≈ Zn²⁺ and that [ME + Mn/Cu/Zn - H]⁺ > [LE + Mn/Cu/Zn - H]⁺, while [LE + Fe/Co/Ni - H]⁺ > [ME + Fe/Co/Ni - H]⁺. We cross-correlated the collision-induced dissociation energies of the complexes with the HDX results and found that the more stable the complex, the harder it is for it to undergo HDX. Furthermore, we used theoretical calculations to optimize the favorable conformations of the complexes and found the same interaction structure of G²⁺ coordination with the five carbonyl oxygens of LE/ME that have different bond lengths. Finally, we calculated the proton affinity (PA) values of the optimized complexes in order to interpret the HDX observations that the higher the PA values, the more difficult it is for the complex to undergo HDX. Overall, both the experiments and the theoretical calculations show that the six metal ions have different effects on the LE/ME conformation, with the low-energy stability of the G²⁺ 3d orbitals corresponding to more dramatic effects on the LE/ME conformation. In addition, the hardness of the ionic acid corresponding to the fully filled Mn²⁺ and half-filled Zn²⁺ orbitals also contributes strongly to the coordination effect; the conformation effect of Fe²⁺/Co²⁺/Ni²⁺ on LE is greater than that on ME, whereas the conformation effect of Mn²⁺/Cu²⁺/Zn²⁺ on ME is greater than that on LE.

Transition metal ions induced secondary structural transformation in a hydrophobized short peptide amphiphile

Transition metal ions mediate the secondary structural transformation of hydrophobized sPA and can be applied to the design and development of stimuli-responsive nanomaterials.

Metal self-assembly mimosine peptides with enhanced antimicrobial activity: towards a new generation of multitasking chelating agents

Mimosine is a non-protein amino acid that can be used as a building block in peptides with metal coordination ability.

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.

Metal Ion Binding to the Amyloid β Monomer Studied by Native Top-Down FTICR Mass Spectrometry

Native top-down mass spectrometry is a fast, robust biophysical technique that can provide molecular-scale information on the interaction between proteins or peptides and ligands, including metal cations. Here we have analyzed complexes of the full-length amyloid β (1-42) monomer with a range of (patho)physiologically relevant metal cations using native Fourier transform ion cyclotron resonance mass spectrometry and three different fragmentation methods-collision-induced dissociation, electron capture dissociation, and infrared multiphoton dissociation-all yielding consistent results. Amyloid β is of particular interest as its oligomerization and aggregation are major events in the etiology of Alzheimer's disease, and it is known that interactions between the peptide and bioavailable metal cations have the potential to significantly damage neurons. Those metals which exhibited the strongest binding to the peptide (Cu²⁺, Co²⁺, Ni²⁺) all shared a very similar binding region containing two of the histidine residues near the N-terminus (His6, His13). Notably, Fe³⁺ bound to the peptide only when stabilized toward hydrolysis, aggregation, and precipitation by a chelating ligand, binding in the region between Ser8 and Gly25. We also identified two additional binding regions near the flexible, hydrophobic C-terminus, where other metals (Mg²⁺, Ca²⁺, Mn²⁺, Na⁺, and K⁺) bound more weakly-one centered on Leu34, and one on Gly38. Unexpectedly, collisional activation of the complex formed between the peptide and [Co^III(NH₃)₆]³⁺ induced gas-phase reduction of the metal to Co^II, allowing the peptide to fragment via radical-based dissociation pathways. This work demonstrates how native mass spectrometry can provide new insights into the interactions between amyloid β and metal cations.

One- and two-photon responsive injectable nano-bundle biomaterials from co-assembled lipopeptides for controlling molecular diffusion

An injectable biomaterial has been prepared through co-assembly of lipopeptides C₄-Bhc-Glu-Glu-NH₂ and C₁₄-Phe-Lys-Lys-NH₂. This biomaterial contained a large number of nanofibre bundles (nano-bundles, NBs) of lipopeptide co-assemblies and performed like hydrogels. The morphologies of the NBs were observed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The rheological properties were investigated with a rheometer. Excitingly, the NB biomaterials exhibited shear thinning and self-healing properties, and could be used as injectable biomaterials. The coumarin group in the lipopeptides endowed the NB biomaterials with both ultraviolet (UV, a one photon process) and near-infrared (NIR) light (a two photon process) responsiveness. A small molecule (Doxorubicin, DOX) and a large molecule (bovine serum albumin, BSA) were used as model drugs, and both of them could be encapsulated in the NB biomaterials and could also be released sustainably or explosively under different conditions (with or without one- and two-photon irradiation). DOX and BSA have different release behaviors because of the NBs. Cell assays showed that the co-assembled NB biomaterials exhibited low cytotoxicity to normal cells. However, when DOX was loaded, the NB biomaterials could kill HeLa cells sustainably. Under UV and NIR irradiation, HeLa cells could be killed rapidly because of the burst release of DOX. The co-assembled supramolecular NB biomaterials with dual-responsiveness, tunable rheological properties and multi-drug encapsulating ability might have potential in biomedical engineering.

Sn-Triggered Two-Dimensional Fast Protein Assembly with Emergent Functions

The discovery of a general strategy for organizing functional proteins into stable nanostructures with the desired dimension, shape, and function is an important focus in developing protein-based self-assembled materials, but the scalable synthesis of such materials and transfer to other substrates remain great challenges. We herein tackle this issue by creating a two-dimensional metal-protein hybrid nanofilm that is flexible and cost-effective with reliable self-recovery, stability, and multifunctionality. As it differs from traditional metal ions, we discover the capability of Sn²⁺ to initiate fast amyloid-like protein assembly (occurring in seconds) by effectively reducing the disulfide bonds of native globular proteins. The Sn²⁺-initiated lysozyme aggregation at the air/water interface leads to droplet flattening, a result never before reported in a protein system, which finally affords a multifunctional 2D Sn-doped hybrid lysozyme nanofilm with an ultralarge area (e.g., 0.2 m²) within a few minutes. The hybrid film is distinctive in its ease of coating on versatile material surfaces with endurable chemical and mechanical stability, optical transparency, and diverse end uses in antimicrobial and photo-/electrocatalytic scaffolds. Our approach provides not only insights into the effect of tin ions on macroscopic self-assembly of proteins but also a controllable and scalable synthesis of a potential biomimic framework for biomedical and biocatalytic applications.

Peptide Tectonics: Encoded Structural Complementarity Dictates Programmable Self-Assembly

Programmable self-assembly of peptides into well-defined nanostructures represents one promising approach for bioinspired and biomimetic synthesis of artificial complex systems and functional materials. Despite the progress made over the past two decades in the development of strategies for precise manipulation of the self-assembly of peptides, there is a remarkable gap between current peptide assemblies and biological systems in terms of structural complexity and functions. Here, the concept of peptide tectonics for the creation of well-defined nanostructures predominately driven by the complementary association at the interacting interfaces of tectons is introduced. Peptide tectons are defined as peptide building blocks exhibiting structural complementarity at the interacting interfaces of commensurate domains and undergoing programmable self-assembly into defined supramolecular structures promoted by complementary interactions. Peptide tectons are categorized based on their conformational entropy and the underlying mechanism for the programmable self-assembly of peptide tectons is highlighted focusing on the approaches for incorporating the structural complementarity within tectons. Peptide tectonics not only provides an alternative perspective to understand the self-assembly of peptides, but also allows for precise manipulation of peptide interactions, thus leading to artificial systems with advanced complexity and functions and paves the way toward peptide-related functional materials resembling natural systems.

Inversion of Circularly Polarized Luminescence of Nanofibrous Hydrogels through Co-assembly with Achiral Coumarin Derivatives

Control over the handedness of circularly polarized luminescence (CPL) in supramolecular gels is of special significance in biology and optoelectronics; however, it still remains a great challenge to precisely and efficiently regulate the chirality of CPL. Herein, a chiral phenylalanine-derived hydrogelator and achiral coumarin derivatives can co-assemble into nanofibrous hydrogels with controllable chirality, and the handedness of CPL of these hydrogels can be efficiently inverted by coumarin derivatives through noncovalent interactions, which can be further tuned at will by incorporating metal ions into the co-assembly. The hydrogen bonds, coordination interactions, and steric hindrance are proved to be the crucial factors for the CPL inversion. This study provides feasible strategies to efficiently regulate the handedness of CPL through co-assembly, and these CPL materials may have potential applications in the fields of photoelectric devices, smart chiroptical materials, and biological systems.

In situ hydrogelation of forky peptides in prostate tissue for drug delivery

Herein, we have designed and synthesized a novel forky peptide D3F3 that transforms into a hydrogel through crosslinking induced by ZIs stimuli. We have employed D3F3 as a suitable drug carrier that is conjugated with DOX. Since the concentration of zinc ions necessary for triggering gelation falls into the physiological range present in prostate tissue, while other cationic ions fail to trigger at physiological concentrations, the peptide-based drug delivery system (DDS) is injectable and would achieve prostate tissue-specific self-assembly in situ. The D3F3 hydrogels exhibited an optimal gelation time, satisfactory mechanical strength (can be enhanced after incorporation of DOX) as well as excellent thixotropic properties. The DDS reserved some DOX in the prostate 24 h after the injection, making local sustained release possible. In addition, the peptide materials demonstrated no cytotoxicity against normal fibroblast cells and no damage was observed to the prostate tissue of rats. The drug release followed a non-Fickian diffusion model, with no burst release observed. Importantly, the DOX-hydrogel system exhibited good anti-cancer efficacy when incubated with prostate cancer cells DU-145. Therefore, this study lays the groundwork for the future design of tissue-specific DDSs that are triggered by cationic ions (e.g. zinc ions), and the platform could be further developed to incorporate other potent drugs utilized in the field of prostate cancer therapy, thereby increasing their potency and reducing their side effects.

Cation-Directed Self-Assembly of Macrocyclic Diacetylene for Developing Chromogenic Polydiacetylene

The cation-directed self-assembly process has emerged as a fascinating approach for constructing supramolecular architectures and manifested a diverse range of assembly related applications. Herein, we synthesized a macrocyclic structure containing bis-amidopyridine and photopolymerizable diacetylene template, PyMCDA. Owing to the metal coordination affinity of bis-amidopyridine and the π-π stacking characteristic of diacetylene template and complementary to the cyclic molecular framework, Cs⁺-directed organic nanotubes are generated via unidirectional self-assembly of PyMCDA. The monomeric PyMCDA nanotubes are transformed into the covalently cross-linked chromogenic polydiacetylene nanotubes (PyMCPDA-Cs⁺) by UV-promoted topochemical polymerization. The result of a metal-ligand coordination characteristic, geometric parameters in solid-state assemblies, and topochemical polymerization behavior reveals a generation of Cs⁺ ion inserted nanotubes. Interestingly, PyMCDA-Cs⁺ nanotubes display thermochromic property with a brilliant blue-to-red color transition.

Design of self-assembly dipeptide hydrogels and machine learning via their chemical features

Hydrogels that are self-assembled by peptides have attracted great interest for biomedical applications. However, the link between chemical structures of peptides and their corresponding hydrogel properties is still unclear. Here, we showed a combinational approach to generate a structurally diverse hydrogel library with more than 2,000 peptides and evaluated their corresponding properties. We used a quantitative structure-property relationship to calculate their chemical features reflecting the topological and physicochemical properties, and applied machine learning to predict the self-assembly behavior. We observed that the stiffness of hydrogels is correlated with the diameter and cross-linking degree of the nanofiber. Importantly, we demonstrated that the hydrogels support cell proliferation in culture, suggesting the biocompatibility of the hydrogel. The combinatorial hydrogel library and the machine learning approach we developed linked the chemical structures with their self-assembly behavior and can accelerate the design of novel peptide structures for biomedical use.

Peptide-modulated self-assembly as a versatile strategy for tumor supramolecular nanotheranostics

Advances in supramolecular self-assembly have promoted the development of theranostics, the combination of both therapeutic and diagnostic functions in a single nanoplatform, which is closely associated with antitumor applications and has shown promising potential in personalized medicine. Peptide-modulated self-assembly serves as a versatile strategy for tumor supramolecular nanotheranostics possessing controllability, programmability, functionality and biosafety, thus promoting the translation of nanotheranostics from bench to bedside. In this review, we will focus on the self-assembly of peptide-photosensitizers and peptide-drugs as well as multicomponent cooperative self-assembly for the fabrication of nanotheranostics that integrate diagnosis and therapeutics for antitumor applications. Emphasis will be placed on building block design, interaction strategies and the potential relationships between their structures and properties, aiming to increase understanding of the critical role of peptide-modulated self-assembly in advancing antitumor supramolecular nanotheranostics.

Polar-π Interactions Promote Self-assembly of Dipeptides into Laminated Nanofibers

Precise incorporation of functional residues into sequences allows for tailoring the noncovalent interactions between peptides to guide their self-assembly into well-defined nanostructures, thus facilitating creation of artificial functional materials resembling natural systems. Here, we report on the self-assembly of dipeptides consisting of one fluorinated phenylalanine unit (Z residue) and one natural aromatic residue into laminated nanofibers predominately driven by polar-π interactions. On the basis of characterizations using transmission electron microscopy, scanning electron microscopy, atomic force microscopy, circular dichroism, Fourier transform infrared spectroscopy, and thioflavin T binding assay, we found that the face-centered stacking pattern of the dipeptides FZ, ZF, and ZY stabilized by the polar-π interactions and antiparallel β-sheet H-bonding interactions led to lamination of nanofibers and formation of ribbonlike nanostructures. Our findings demonstrate that incorporation of fluorinated aromatic units into short peptides not only promotes of polar-π interactions as alternative self-assembling driving forces but also governs the organizing pattern of peptides, thus benefiting creation of well-defined peptide nanostructures.

Peptide Self-Assembly into Hydrogels for Biomedical Applications Related to Hydroxyapatite

Amphiphilic peptides can be self-assembled by establishing physical cross-links involving hydrogen bonds and electrostatic interactions with divalent ions. The derived hydrogels have promising properties due to their biocompatibility, reversibility, trigger capability, and tunability. Peptide hydrogels can mimic the extracellular matrix and favor the growth of hydroxyapatite (HAp) as well as its encapsulation. Newly designed materials offer great perspectives for applications in the regeneration of hard tissues such as bones, teeth, and cartilage. Furthermore, development of drug delivery systems based on HAp and peptide self-assembly is attracting attention.

Residue-Specific Solvation-Directed Thermodynamic and Kinetic Control over Peptide Self-Assembly with 1D/2D Structure Selection

Understanding the self-organization and structural transformations of molecular ensembles is important to explore the complexity of biological systems. Here, we illustrate the crucial role of cosolvents and solvation effects in thermodynamic and kinetic control over peptide association into ultrathin Janus nanosheets, elongated nanobelts, and amyloid-like fibrils. We gained further insight into the solvation-directed self-assembly (SDSA) by investigating residue-specific peptide solvation using molecular dynamics modeling. We proposed the preferential solvation of the aromatic and alkyl domains on the peptide backbone and protofibril surface, which results in volume exclusion effects and restricts the peptide association between hydrophobic walls. We explored the SDSA phenomenon in a library of cosolvents (protic and aprotic), where less polar cosolvents were found to exert a stronger influence on the energetic balance at play during peptide propagation. By tailoring cosolvent polarity, we were able to achieve precise control of the peptide nanostructures with 1D/2D shape selection. We also illustrated the complexity of the SDSA system with pathway-dependent peptide aggregation, where two self-assembly states ( i.e., thermodynamic equilibrium state and kinetically trapped state) from different sample preparation methods were obtained.