Multifunctional, biocompatible supramolecular hydrogelators consist only of nucleobase, amino acid, and glycoside

Understanding the gelation properties of the fluorophenyl glycosides of arabinoside gelators: experimental and theoretical studies

In supramolecular gelation, fluorinated gelators are important due to the unique properties displayed by these compounds that arise out of the presence of fluorine atoms. Generally, incorporation of fluorine leads to higher mechanical strength of the gels compared to their non-fluorinated counterparts and this property is enhanced with increasing the number of fluorine atoms. Herein, we show that the incorporation of fluorine into the phenyl ring of phenyl arabinoside allows the molecule to act as a gelator, unlike the non-fluorinated compound. We also show that the mechanical strength and stiffness of the gels is not only dependent on the positions of the fluorine atoms but also guided by their number. Detailed experimental studies, supported by computational studies, allowed us to rationalize the observed supramolecular interactions and propose reasons based on the conformational preferences of these compounds that allow additional hydrogen bonds and π-π interactions which guide the self-assembly, in addition to the primary H-bonding interactions. This, in turn, affects the mechanical behavior of these gels.

Tryptophan-PNA gc Conjugates Self-Assemble to Form Fibers

Peptide nucleic acids and their conjugates to peptides can self-assemble and generate complex architectures. In this work, we explored the self-assembly of PNA dimers conjugated to the dipeptide WW. Our studies suggest that the indole ring of tryptophan promotes aggregation of the conjugates. The onset of fluorescence is observed upon self-assembly. The structure of self-assembled WWgc is concentration-dependent, being spherical at low concentrations and fibrous at high concentrations. As suggested by molecular modeling studies, fibers are stabilized by stacking interactions between tryptophans and Watson-Crick hydrogen bonds between nucleobases.

Glycopeptide-Based Supramolecular Hydrogels Induce Differentiation of Adipose Stem Cells into Neural Lineages

We applied a bottom-up approach to develop biofunctional supramolecular hydrogels from an aromatic glycodipeptide. The self-assembly of the glycopeptide was induced by either temperature manipulation (heating-cooling cycle) or solvent (DMSO to water) switch. The sol-gel transition was salt-triggered in cell culture media and resulted in gels with the same chemical compositions but different mechanical properties. Human adipose derived stem cells (hASCs) cultured on these gels under basal conditions (i.e., without differentiation factors) overexpressed neural markers, such as GFAP, Nestin, MAP2, and βIII-tubulin, confirming the differentiation into neural lineages. The mechanical properties of the gels influenced the number and distribution of the adhered cells. A comparison with gels obtained from the nonglycosylated peptide showed that glycosylation is crucial for the biofunctionality of the hydrogels by capturing and preserving essential growth factors, e.g., FGF-2.

Hepatic Spheroid Formation on Carbohydrate-Functionalized Supramolecular Hydrogels

Two synthetic supramolecular hydrogels, formed from bis-urea amphiphiles containing lactobionic acid (LBA) and maltobionic acid (MBA) bioactive ligands, are applied as cell culture matrices in vitro. Their fibrillary and dynamic nature mimics essential features of the extracellular matrix (ECM). The carbohydrate amphiphiles self-assemble into long supramolecular fibers in water, and hydrogels are formed by physical entanglement of fibers through bundling. Gels of both amphiphiles exhibit good self-healing behavior, but remarkably different stiffnesses. They display excellent bioactive properties in hepatic cell cultures. Both carbohydrate ligands used are proposed to bind to asialoglycoprotein receptors (ASGPRs) in hepatic cells, thus inducing spheroid formation when seeding hepatic HepG2 cells on both supramolecular hydrogels. Ligand nature, ligand density, and hydrogel stiffness influence cell migration and spheroid size and number. The results illustrate the potential of self-assembled, carbohydrate-functionalized hydrogels as matrices for liver tissue engineering.

Self-assembling NBD-tripeptide as a dual-mode colorimetric platform for naked eye and smartphone joint detection of micro to nanomolar Copper(II) ions

Compared to conventionally synthesized organic compounds, peptides with amphiphiles have unique advantages, especially in self-assembly. Herein, we reported a peptide-based molecule rationally designed for the visual detection of copper ions (Cu²⁺) in multiple modes. The peptide exhibited excellent stability, high luminescence efficiency, and environmentally responsive molecular self-assembly in water. In the presence of Cu²⁺, the peptide undergoes an ionic coordination interaction and a coordination-driven self-assembly process that leads to the quenching of fluorescence and the formation of aggregates. Therefore, the concentration of Cu²⁺ can be determined by the residual fluorescence intensity and the color difference between peptide and competing chromogenic agents before and after Cu²⁺ incorporation. More importantly, this variation in fluorescence and color can be presented visually, thus allowing qualitative and quantitative analysis of Cu²⁺ based on the naked eye and smartphones. Overall, our study not only extends the application of self-assembling peptides but also provides a universal method for dual-mode visual detection of Cu²⁺, which would significantly promote point-of-care testing (POCT) of metal ions in pharmaceuticals, food, and drinking water.

Diversity of Bioinspired Hydrogels: From Structure to Applications

Hydrogels are three-dimensional networks with a variety of structures and functions that have a remarkable ability to absorb huge amounts of water or biological fluids. They can incorporate active compounds and release them in a controlled manner. Hydrogels can also be designed to be sensitive to external stimuli: temperature, pH, ionic strength, electrical or magnetic stimuli, specific molecules, etc. Alternative methods for the development of various hydrogels have been outlined in the literature over time. Some hydrogels are toxic and therefore are avoided when obtaining biomaterials, pharmaceuticals, or therapeutic products. Nature is a permanent source of inspiration for new structures and new functionalities of more and more competitive materials. Natural compounds present a series of physico-chemical and biological characteristics suitable for biomaterials, such as biocompatibility, antimicrobial properties, biodegradability, and nontoxicity. Thus, they can generate microenvironments comparable to the intracellular or extracellular matrices in the human body. This paper discusses the main advantages of the presence of biomolecules (polysaccharides, proteins, and polypeptides) in hydrogels. Structural aspects induced by natural compounds and their specific properties are emphasized. The most suitable applications will be highlighted, including drug delivery, self-healing materials for regenerative medicine, cell culture, wound dressings, 3D bioprinting, foods, etc.

Designer, Programmable DNA-peptide hybrid materials with emergent properties to probe and modulate biological systems

The chemistry of DNA endows it with certain functional properties that facilitate the generation of self-assembled nanostructures, offering precise control over their geometry and morphology, that can be exploited for advanced biological applications. Despite the structural promise of these materials, their applications are limited owing to lack of functional capability to interact favourably with biological systems, which has been achieved by functional proteins or peptides. Herein, we outline a strategy for functionalizing DNA structures with short-peptides, leading to the formation of DNA-peptide hybrid materials. This proposition offers the opportunity to leverage the unique advantages of each of these bio-molecules, that have far reaching emergent properties in terms of better cellular interactions and uptake, better stability in biological media, an acceptable and programmable immune response and high bioactive molecule loading capacities. We discuss the synthetic strategies for the formation of these materials, namely, solid-phase functionalization and solution-coupling functionalization. We then proceed to highlight selected biological applications of these materials in the domains of cell instruction & molecular recognition, gene delivery, drug delivery and bone & tissue regeneration. We conclude with discussions shedding light on the challenges that these materials pose and offer our insights on future directions of peptide-DNA research for targeted biomedical applications.

Synthesis and Investigation of Backbone Modified Squaramide Dipeptide Self-Assembly

Dipeptides are minimalistic peptide building blocks that form well ordered structures through molecular self-assembly. The driving forces involved are cooperative noncovalent interactions such as π-π stacking, hydrogen bonding, and ionic as well as hydrophobic interactions. One of the most intriguing self-assembled motifs that has been extensively explored as a low molecular weight hydrogel for drug delivery, tissue engineering, imaging and techtonics, etc. is Phe-Phe (FF). The backbone of the dipeptide is very crucial for extending secondary structures in self-assembly, and any subtle change in the backbone drastically affect the molecular recognitions. The squaramide (SQ) motif has the unique advantage of hydrogen bonding which can promote the self-assembly process. In this work we have integrated the SQ unit into the dipeptide FF backbone to achieve molecular self-assembly. The resulting carbamate protected backbone modified dipeptide (BocFSAF-OH, 10) has exhibited molecular self-assembly with a fibrilar network. It formed a stable hydrogel (with CAC of 0.024 ± 0.0098 wt %) via the solvent switch method and was found to possess excellent enzymatic stability. The dipeptide and the resulting hydrogel were found to be cytocompatible. When integrated with a polysaccharide based biopolymer, e.g. sodium alginate, the resulting matrix exhibited strong hydrogel character. Therefore, the dipeptide hydrogel of 10 may find its applications in a variety of fields including drug delivery and tissue engineering.

Self-Assembly, Bioactivity, and Nanomaterials Applications of Peptide Conjugates with Bulky Aromatic Terminal Groups

The self-assembly and structural and functional properties of peptide conjugates containing bulky terminal aromatic substituents are reviewed with a particular focus on bioactivity. Terminal moieties include Fmoc [fluorenylmethyloxycarbonyl], naphthalene, pyrene, naproxen, diimides of naphthalene or pyrene, and others. These provide a driving force for self-assembly due to π-stacking and hydrophobic interactions, in addition to the hydrogen bonding, electrostatic, and other forces between short peptides. The balance of these interactions leads to a propensity to self-assembly, even for conjugates to single amino acids. The hybrid molecules often form hydrogels built from a network of β-sheet fibrils. The properties of these as biomaterials to support cell culture, or in the development of molecules that can assemble in cells (in response to cellular enzymes, or otherwise) with a range of fascinating bioactivities such as anticancer or antimicrobial activity, are highlighted. In addition, applications of hydrogels as slow-release drug delivery systems and in catalysis and other applications are discussed. The aromatic nature of the substituents also provides a diversity of interesting optoelectronic properties that have been demonstrated in the literature, and an overview of this is also provided. Also discussed are coassembly and enzyme-instructed self-assembly which enable precise tuning and (stimulus-responsive) functionalization of peptide nanostructures.

Emerging low-molecular weight nucleopeptide-based hydrogels: state of the art, applications, challenges and perspectives

Over the last twenty years, low-molecular weight gelators and, in particular, peptide-based hydrogels, have drawn great attention from scientists thanks to both their inherent advantages in terms of properties and their high modularity (e.g., number and nature of the amino acids). These supramolecular hydrogels originate from specific peptide self-assembly processes that can be driven, modulated and optimized via specific chemical modifications brought to the peptide sequence. Among them, the incorporation of nucleobases, another class of biomolecules well-known for their abilities to self-assemble, has recently appeared as a new promising and burgeoning approach to finely design supramolecular hydrogels. In this minireview, we would like to highlight the interest, high potential, applications and perspectives of these innovative and emerging low-molecular weight nucleopeptide-based hydrogels.

Structure-Based Programming of Supramolecular Assemblies in Living Cells for Selective Cancer Cell Inhibition

Here we report on the design, synthesis, and assembly of an enzymatic programmable peptide system inspired by endocytic processes to induce molecular assemblies formation spatiotemporally in living cancer cells, resulting in glioblastoma cell death mainly in necroptosis. Our results indicate the stability and glycosylation of molecules play an essential role in determining the final bioactivity. Detailed mechanistic studies by CLSM, Flow cytometry, western blot, and Bio-EM suggest the site-specific formation of assemblies, which could induce the LMP and activate the downstream cell death pathway. Moreover, we also demonstrate that our strategy can boost the activity of commercial chemotherapy drug by escaping lysosome sequestration. We expected this work would be expanded towards artificial intelligent biomaterials for cancer therapy and imaging precisely.

From Prebiotic Chemistry to Supramolecular Biomedical Materials: Exploring the Properties of Self-Assembling Nucleobase-Containing Peptides

Peptides and their synthetic analogs are a class of molecules with enormous relevance as therapeutics for their ability to interact with biomacromolecules like nucleic acids and proteins, potentially interfering with biological pathways often involved in the onset and progression of pathologies of high social impact. Nucleobase-bearing peptides (nucleopeptides) and pseudopeptides (PNAs) offer further interesting possibilities related to their nucleobase-decorated nature for diagnostic and therapeutic applications, thanks to their reported ability to target complementary DNA and RNA strands. In addition, these chimeric compounds are endowed with intriguing self-assembling properties, which are at the heart of their investigation as self-replicating materials in prebiotic chemistry, as well as their application as constituents of innovative drug delivery systems and, more generally, as novel nanomaterials to be employed in biomedicine. Herein we describe the properties of nucleopeptides, PNAs and related supramolecular systems, and summarize some of the most relevant applications of these systems.

Supramolecular Hydrogels for Protein Delivery in Tissue Engineering

Therapeutic proteins, such as growth factors (GFs), have been used in tissue engineering (TE) approaches for their ability to provide signals to cells and orchestrate the formation of functional tissue. However, to be effective and minimize off-target effects, GFs should be delivered at the target site with temporal control. In addition, protein drugs are typically sensitive water soluble macromolecules with delicate structure. As such, hydrogels, containing large amounts of water, provide a compatible environment for the direct incorporation of proteins within the hydrogel network, while their release rate can be tuned by engineering the network chemistry and density. Being formed by transient crosslinks, afforded by non-covalent interactions, supramolecular hydrogels offer important advantages for protein delivery applications. This review describes various types of supramolecular hydrogels using a repertoire of diverse building blocks, their use for protein delivery and their further application in TE contexts. By reviewing the recent literature on this topic, the merits of supramolecular hydrogels are highlighted as well as their limitations, with high expectations for new advances they will provide for TE in the near future.

Impact of C-Terminal Chemistry on Self-Assembled Morphology of Guanosine Containing Nucleopeptides

Herein, we report the design and characterization of guanosine-containing self-assembling nucleopeptides that form nanosheets and nanofibers. Through spectroscopy and microscopy analysis, we propose that the peptide component of the nucleopeptide drives the assembly into β-sheet structures with hydrogen-bonded guanosine forming additional secondary structures cooperatively within the peptide framework. Interestingly, the distinct supramolecular morphologies are driven not by metal cation responsiveness common to guanine-based materials, but by the C-terminal peptide chemistry. This work highlights the structural diversity of self-assembling nucleopeptides and will help advance the development of applications for these supramolecular guanosine-containing nucleopeptides.

Fibrillar Network Dynamics during Oscillatory Rheology of Supramolecular Gels

Supramolecular gels are three-dimensional network structures formed by the hierarchical self-assembly of small molecules through weak noncovalent interactions. On the basis of the various interactions contributed by specific functional groups/moieties, gels with different architectures can be constructed that are smart to the external stimuli such as pH, type of solvent, stress, temperature, etc. In the present work, we explore the oscillatory shear response of supramolecular self-assembled systems formed by the low-molecular-weight (LMW) gelator based on difunctionalized amino acid, florenylmethoxycarbonyl (Fmoc)-lysine(Fmoc), Fm-K(Fm) in aqueous buffer solution, at two different pH (6 and 7.4). Small amplitude oscillatory shear (SAOS) reported weak frequency dependence of moduli indicating a gel-like network structure. Large amplitude oscillatory shear (LAOS) indicated flow regimes dictated by yielding and subsequent network dynamics analogous to cagelike soft glassy events reported for colloidal systems. The three interval thixotropy test (3iTT) indicated recovery of moduli due to regelation contributed by the reversible interactions. A generalized network model framework is utilized to investigate the transient network characteristics of the Fm-K(Fm) gels. The "network creation" and "network loss" rates were chosen as exponential functions of scaled shear stress (= |τ12(t)G|) to effectively describe the complex response. On the basis of the insights, possible mechanisms to explain the differences/similarities in the response at different pH are speculated. It is further illustrated that the modeling strategy can be extended to supramolecular gels of different classes because of the commonality/universality of their response features under oscillatory shear.

Enzymatic Noncovalent Synthesis

Enzymatic reactions and noncovalent (i.e., supramolecular) interactions are two fundamental nongenetic attributes of life. Enzymatic noncovalent synthesis (ENS) refers to a process where enzymatic reactions control intermolecular noncovalent interactions for spatial organization of higher-order molecular assemblies that exhibit emergent properties and functions. Like enzymatic covalent synthesis (ECS), in which an enzyme catalyzes the formation of covalent bonds to generate individual molecules, ENS is a unifying theme for understanding the functions, morphologies, and locations of molecular ensembles in cellular environments. This review intends to provide a summary of the works of ENS within the past decade and emphasize ENS for functions. After comparing ECS and ENS, we describe a few representative examples where nature uses ENS, as a rule of life, to create the ensembles of biomacromolecules for emergent properties/functions in a myriad of cellular processes. Then, we focus on ENS of man-made (synthetic) molecules in cell-free conditions, classified by the types of enzymes. After that, we introduce the exploration of ENS of man-made molecules in the context of cells by discussing intercellular, peri/intracellular, and subcellular ENS for cell morphogenesis, molecular imaging, cancer therapy, and other applications. Finally, we provide a perspective on the promises of ENS for developing molecular assemblies/processes for functions. This review aims to be an updated introduction for researchers who are interested in exploring noncovalent synthesis for developing molecular science and technologies to address societal needs.

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.

A thermo-responsive supramolecular hydrogel that senses cholera toxin via color-changing response

A Pyrene-based hydrogel with terminal lactose residue has been developed for the detection of cholera toxin via color changing response, accompanied by gel to sol transition.

Cementum protein 1-derived peptide (CEMP 1-p1) modulates hydroxyapatite crystal formation in vitro

A cementum protein 1-derived peptide (CEMP1-p1) consisting of 20 amino acids from the CEMP1's N-terminus region: MGTSSTDSQQAGHRRCSTSN, and its role on the mineralization process in a cell-free system, was characterized. CEMP1-p1's physicochemical properties, crystal formation, and hydroxyapatite (HA) nucleation assays were performed. Crystals induced by CEMP1-p1 were analyzed by scanning electron microscopy, Fourier-transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and atomic force microscopy. The results indicate that CEMP1-p1 lacks secondary structure, forms nanospheres that organize into three-dimensional structures, possesses affinity to HA, and induces its nucleation. CEMP1-p1 promotes the formation of spherical structures composed by densely packed prism-like crystals, which revealed a Ca/P ratio of 1.56, corresponding to HA. FTIR-ATR showed predominant spectrum peaks that correspond and are characteristic of HA and octacalcium phosphate (OCP). Analysis by XRD indicates that the crystals show planes with a preferential crystalline orientation for HA and for OCP. HRTEM showed interplanar distances that correspond to crystalline planes of HA and OCP. Crystals are composed by superimposed lamellae, which exhibit epitaxial growth, and each layer of the crystals is structured by nanocrystals. This study reveals that CEMP1-p1 regulates HA crystal formation, somehow mimicking the in vivo process of mineralized tissues bioformation.

Self-Assembly of Diphenylalanine-Peptide Nucleic Acid Conjugates

The synthesis and self-assembled nanostructures of a series of nucleopeptides (NPs) derived from the dipeptide Phe-Phe and the peptide nucleic acid unit which are covalently attached through an amide or a triazole linker are described. Depending on the variables such as protecting groups, linkers, and nucleobases, spherical nanoparticles were observed through scanning electron microscopy and high-resolution transmission electron microscopy images, and the porous nature of representative NPs was corroborated by carboxyfluorescein entrapment. Hydrophobic substituents on different sites of NPs and solvents employed for peptide self-assembly played a crucial role for corresponding morphologies. The stability of nanoparticles was also probed under external stimuli such as pH, temperature, and enzymatic hydrolysis using proteolytic enzymes. The semiconducting nature of the NP-modified carbon electrodes suggested their potential use as a new capacitor material.

Self-assemblies of nucleolipid supramolecular synthons show unique self-sorting and cooperative assembling process

The inherent control of the self-sorting and co-assembling process that has evolved in multi-component biological systems is not easy to emulate in vitro using synthetic supramolecular synthons. Here, using the basic component of nucleic acids and lipids, we describe a simple platform to build hierarchical assemblies of two component systems, which show an interesting self-sorting and co-assembling behavior. The assembling systems are made of a combination of amphiphilic purine and pyrimidine ribonucleoside-fatty acid conjugates (nucleolipids), which were prepared by coupling fatty acid acyl chains of different lengths at the 2'-O- and 3'-O-positions of the ribose sugar. Individually, the purine and pyrimidine nucleolipids adopt a distinct morphology, which either supports or does not support the gelation process. Interestingly, due to the subtle difference in the order of formation and stability of individual assemblies, different mixtures of supramolecular synthons and complementary ribonucleosides exhibit a cooperative and disruptive self-sorting and co-assembling behavior. A systematic morphological analysis combined with single crystal X-ray crystallography, powder X-ray diffraction (PXRD), NMR, CD, rheological and 3D X-ray microtomography studies provided insights into the mechanism of the self-sorting and co-assembling process. Taken together, this approach has enabled the construction of assemblies with unique higher ordered architectures and gels with remarkably enhanced mechanical strength that cannot be derived from the respective single component systems.

Supramolecular Assemblies of Peptides or Nucleopeptides for Gene Delivery

Using non-covalent interactions between nucleic acids (DNA, siRNA, miRNA, and mRNA) with peptides or nucleopeptides is a promising strategy to construct supramolecular assemblies for gene delivery and therapy. Comparing to conventional strategies for gene delivery, the assemblies of peptides or nucleopeptides provide several unique advantages: i) reversible interactions between the assemblies and the nucleic acids; ii) minimal immunogenicity; iii) biocompatibility. This field has advanced considerably in recent years so that it is worth summarizing the recent progresses and future challenges. In this review, we introduce the development of assemblies of peptides or nucleopeptides for applications in gene delivery and related fields. After introducing the promises of gene therapy and the current strategies for the delivery, we discuss the unique advantage of using peptide assemblies for gene delivery. Then we describe several representative strategies for gene delivery by the assemblies of peptides or nucleopeptides. Finally, we discuss the key factors for designing such assemblies for gene delivery, and speculate future directions and challenges in the field, particularly the rational design and the spatiotemporally controlled release in live cells.

Formation of Polymeric Particles by Direct Polymerization on the Surface of a Supramolecular Template

Formation of polymeric materials on the surface of supramolecular assemblies is rather challenging because of the often weak noncovalent interactions between the self-assembled template and the monomers before polymerization. We herein show that the introduction of a supramolecular anion recognition motif, the guanidiniocarbonyl pyrrole cation (GCP), into a short Fmoc-dipeptide 1 leads to self-assembled spherical nanoparticles in aqueous solution. Negatively charged diacetylene monomers can be attached onto the surface of these nanoparticles, which, after UV polymerization, leads to the formation of a polymer shell around the self-assembled template. The hybrid supramolecular and polymeric nanoparticles demonstrate intriguing thermal hysteresis phenomena. The template nanoparticles could be disassembled upon treatment with organic base, which cleaved the Fmoc moiety on 1. This strategy thus showed that a supramolecular anion recognition motif allows the post-assembly formation of polymeric nanomaterials from anionic monomers around a cationic self-assembled template.

Glucosamine-Based Supramolecular Nanotubes for Human Mesenchymal Cell Therapy

Herein, we demonstrate an example of glucosamine-based supramolecular hydrogels that can be used for human mesenchymal cell therapy. We designed and synthesized a series of amino acid derivatives based on a strategy of capping d-glucosamine moiety at the C-terminus and fluorinated benzyl group at the N-terminus. From a systematic study on chemical structures, we discovered that the glucosamine-based supramolecular hydrogel [pentafluorobenzyl (PFB)-F-Glu] self-assembled with one-dimensional nanotubular structures at physiological pH. The self-assembly of a newly discovered PFB-F-Glu motif is attributed to the synergistic effect of π-π stacking and extensive intermolecular hydrogen bonding network in aqueous medium. Notably, PFB-F-Glu nanotubes are proven to be nontoxic to human mesenchymal stem cells (hMSCs) and have been shown to enhance hMSC proliferation while maintaining their pluripotency. Retaining of pluripotency capabilities provides potentially unlimited source of undifferentiated cells for the treatment of future cell therapies. Furthermore, hMSCs cultured on PFB-F-Glu are able to secrete paracrine factors that downregulate profibrotic gene expression in lipopolysaccharide-treated human skin fibroblasts, which demonstrates that PFB-F-Glu nanotubes have the potential to be used for wound healing applications. Overall, this article addresses the importance of chemical design to generate supramolecular biomaterials for stem cell therapy.

Nucleopeptide Assemblies Selectively Sequester ATP in Cancer Cells to Increase the Efficacy of Doxorubicin

Herein, we report that assemblies of nucleopeptides selectively sequester ATP in complex conditions (for example, serum and cytosol). We developed assemblies of nucleopeptides that selectively sequester ATP over ADP. Counteracting enzymes interconvert ATP and ADP to modulate the nanostructures formed by the nucleopeptides and the nucleotides. The nucleopeptides, sequestering ATP effectively in cells, slow down efflux pumps in multidrug-resistant cancer cells, thus boosting the efficacy of doxorubicin, an anticancer drug. Investigation of 11 nucleopeptides (including d- and l-enantiomers) yields five more nucleopeptides that differentiate ATP and ADP through either precipitation or gelation. As the first example of assemblies of nucleopeptides that interact with ATP and disrupt intracellular ATP dynamics, this work illustrates the use of supramolecular assemblies to interact with small and essential biological molecules for controlling cell behavior.

The effect of carbohydrate structures on the hydrogelation ability and morphology of self-assembled structures of peptide-carbohydrate conjugates in water

We describe the construction of peptide-carbohydrate conjugates, namely glycopeptides, capable of self-assembling in water. We found that disaccharide structures (epimer or glycosidic-bond geometry) appended to the glycopeptides have a noticeable effect on the hydrogel formation ability as well as the morphology of the self-assembled structures. The soft materials consisting of self-assembled structures with carbohydrates on their surface and various types of morphologies might be useful as matrices to investigate the function of carbohydrates in biological events.

Fmoc-phenylalanine displays antibacterial activity against Gram-positive bacteria in gel and solution phases

In the quest for new antimicrobial materials, hydrogels of Fmoc-protected peptides and amino acids have gained momentum due to their ease of synthesis and cost effectiveness; however, their repertoire is currently limited, and the mechanistic details of their function are not well understood. Herein, we report the antibacterial activity of the hydrogel and solution phases of Fmoc-phenylalanine (Fmoc-F) against a variety of Gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA). Fmoc-F, a small molecule hydrogelator, reduces the bacterial load both in vitro and in the skin wound infections of mice. The antibacterial activity of Fmoc-F is predominantly due to its release from the hydrogel. Fmoc-F shows surfactant-like properties with critical micelle concentration nearly equivalent to its minimum bactericidal concentration. Similar to Fmoc-F, some Fmoc-conjugated amino acids (Fmoc-AA) have also shown antibacterial effects that are linearly correlated with their surfactant properties. At low concentrations, where Fmoc-F does not form micelles, it inhibits bacterial growth by entering the cell and reducing the glutathione levels. However, at higher concentrations, Fmoc-F triggers oxidative and osmotic stress and, alters the membrane permeabilization and integrity, which kills Gram-positive bacteria. Herein, we proposed the use of the Fmoc-F hydrogel and its solution for several biomedical applications. This study will open up new avenues to enhance the repertoire of Fmoc-AA to act as antimicrobial agents and improve their structure-activity relationship.

A photo-degradable supramolecular hydrogel for selective delivery of microRNA into 3D-cultured cells

Multi-functional supramolecular hydrogels have emerged as smart biomaterials for diverse biomedical applications. Here we report a multi-functional supramolecular hydrogel formed by the conjugate of the bioactive GRGDS peptide with biaryltetrazole that is the substrate of photo-click reaction. The hydrogel was used as a biocompatible matrix to encapsulate live cells for 3D culture. The presence of the RGD epitope in the hydrogelator enhanced the interaction of the nanofiber with integrin over-expressing cells, which resulted in the selective enhancement in the miRNA delivery into the encapsulated U87 cells. The intramolecular photo-click reaction of the biaryltetrazole moiety in the hydrogelator leads to a sensitive photo-response of the hydrogel, which allowed photo-degradation of the hydrogel for release of the encapsulated live cells for further bio-assay of the intracellular species.

A shear-induced network of aligned wormlike micelles in a sugar-based molecular gel. From gelation to biocompatibility assays

A new low molecular weight hydrogelator with a saccharide (lactobionic) polar head linked by azide-alkyne click chemistry was prepared in three steps. It was obtained in high purity without chromatography, by phase separation and ultrafiltration of the aqueous gel. Gelation was not obtained reproducibly by conventional heating-cooling cycles and instead was obtained by shearing the aqueous solutions, from 2 wt% to 0.25 wt%. This method of preparation favored the formation of a quite unusual network of interconnected large but thin 2D-sheets (7nm-thick) formed by the association side-by-side of long and aligned 7nm diameter wormlike micelles. It was responsible for the reproducible gelation at the macroscopic scale. A second network made of helical fibres with a 10-13nm diameter, more or less intertwined was also formed but was scarcely able to sustain a macroscopic gel on its own. The gels were analysed by TEM (Transmission Electronic Microscopy), cryo-TEM and SAXS (Small Angle X-ray Scattering). Molecular modelling was also used to highlight the possible conformations the hydrogelator can take. The gels displayed a weak and reversible transition near 20°C, close to room temperature, ascribed to the wormlike micelles 2D-sheets network. Heating over 30°C led to the loss of the gel macroscopic integrity, but gel fragments were still observed in suspension. A second transition near 50°C, ascribed to the network of helical fibres, finally dissolved completely these fragments. The gels showed thixotropic behaviour, recovering slowly their initial elastic modulus, in few hours, after injection through a needle. Stable gels were tested as scaffold for neural cell line culture, showing a reduced biocompatibility. This new gelator is a clear illustration of how controlling the pathway was critical for gel formation and how a new kind of self-assembly was obtained by shearing.

Supramolecular biofunctional materials

This review discusses supramolecular biofunctional materials, a novel class of biomaterials formed by small molecules that are held together via noncovalent interactions. The complexity of biology and relevant biomedical problems not only inspire, but also demand effective molecular design for functional materials. Supramolecular biofunctional materials offer (almost) unlimited possibilities and opportunities to address challenging biomedical problems. Rational molecular design of supramolecular biofunctional materials exploit powerful and versatile noncovalent interactions, which offer many advantages, such as responsiveness, reversibility, tunability, biomimicry, modularity, predictability, and, most importantly, adaptiveness. In this review, besides elaborating on the merits of supramolecular biofunctional materials (mainly in the form of hydrogels and/or nanoscale assemblies) resulting from noncovalent interactions, we also discuss the advantages of small peptides as a prevalent molecular platform to generate a wide range of supramolecular biofunctional materials for the applications in drug delivery, tissue engineering, immunology, cancer therapy, fluorescent imaging, and stem cell regulation. This review aims to provide a brief synopsis of recent achievements at the intersection of supramolecular chemistry and biomedical science in hope of contributing to the multidisciplinary research on supramolecular biofunctional materials for a wide range of applications. We envision that supramolecular biofunctional materials will contribute to the development of new therapies that will ultimately lead to a paradigm shift for developing next generation biomaterials for medicine.

Preparation and investigation of temperature-responsive calix[4]arene-based molecular gels

Higher temperature enhances the strength and the toughness of the gel comprised of kerosene and a tetracholesteryl derivative based on calix[4]arene.

Integrating Enzymatic Self-Assembly and Mitochondria Targeting for Selectively Killing Cancer Cells without Acquired Drug Resistance

Targeting organelles by modulating the redox potential of mitochondria is a promising approach to kill cancer cells that minimizes acquired drug resistance. However, it lacks selectivity because mitochondria perform essential functions for (almost) all cells. We show that enzyme-instructed self-assembly (EISA), a bioinspired molecular process, selectively generates the assemblies of redox modulators (e.g., triphenyl phosphinium (TPP)) in the pericellular space of cancer cells for uptake, which allows selectively targeting the mitochondria of cancer cells. The attachment of TPP to a pair of enantiomeric, phosphorylated tetrapeptides produces the precursors (L-1P or D-1P) that form oligomers. Upon dephosphorylation catalyzed by ectophosphatases (e.g., alkaline phosphatase (ALP)) overexpressed on cancer cells (e.g., Saos2), the oligomers self-assemble to form nanoscale assemblies only on the surface of the cancer cells. The cancer cells thus uptake these assemblies of TPP via endocytosis, mainly via a caveolae/raft-dependent pathway. Inside the cells, the assemblies of TPP-peptide conjugates escape from the lysosome, induce dysfunction of mitochondria to release cytochrome c, and result in cell death, while the controls (i.e., omitting TPP motif, inhibiting ALP, or removing phosphate trigger) hardly kill the Saos2 cells. Most importantly, the repeated stimulation of the cancers by the precursors, unexpectedly, sensitizes the cancer cells to the precursors. As the first example of the integration of subcellular targeting with cell targeting, this study validates the spatial control of the assemblies of nonspecific cytotoxic agents by EISA as a promising molecular process for selectively killing cancer cells without inducing acquired drug resistance.

Self-assembled peptide nanostructures for functional materials

Nature is an important inspirational source for scientists, and presents complex and elegant examples of adaptive and intelligent systems created by self-assembly. Significant effort has been devoted to understanding these sophisticated systems. The self-assembly process enables us to create supramolecular nanostructures with high order and complexity, and peptide-based self-assembling building blocks can serve as suitable platforms to construct nanostructures showing diverse features and applications. In this review, peptide-based supramolecular assemblies will be discussed in terms of their synthesis, design, characterization and application. Peptide nanostructures are categorized based on their chemical and physical properties and will be examined by rationalizing the influence of peptide design on the resulting morphology and the methods employed to characterize these high order complex systems. Moreover, the application of self-assembled peptide nanomaterials as functional materials in information technologies and environmental sciences will be reviewed by providing examples from recently published high-impact studies.

Design and Synthesis of Nanofibers of Self-assembled de novo Glycoconjugates towards Mucosal Lining Restoration and Anti-Inflammatory Drug Delivery

The medical practice for IBD is solely based on anti-inflammatory drugs, but the outcome is far from ideal. Our long-term research goal is to seek a better clinical outcome by combining the anti-inflammatory therapy with physical mucus layer restoration. As the first step towards that objective, we choose to develop self-assembled hydrogels of de novo glycoconjugates that consist of anti-inflammatory drugs and glycopeptides. By covalently linking peptides (e.g., nap-phe-phe-lys), saccharides (e.g., glucosamine), and an anti-inflammatory drug (i.e., olsalazine), we have demonstrated that the obtained molecules self-assemble in water to form hydrogels composed of 3D networks of the nanofibers under acidic conditions. We also confirmed that the resulting glycoconjugates are cell compatible. However, the preliminary assessment of the efficacy of the hydrogels on the murine model is inconclusive, which warrants further investigation and molecular engineering.

Supramolecular Self-Assembly of Histidine-Capped-Dialkoxy-Anthracene: A Visible-Light-Triggered Platform for Facile siRNA Delivery

Supramolecular self-assembly of histidine-capped-dialkoxy-anthracene (HDA) results in the formation of light-responsive nanostructures. Single-crystal X-ray diffraction analysis of HDA shows two types of hydrogen bonding. The first hydrogen bond is established between the imidazole moieties while the second involves the oxygen atom of one amide group and the hydrogen atom of a second amide group. When protonated in acidic aqueous media, HDA successfully complexes siRNA yielding spherical nanostructures. This biocompatible platform controllably delivers siRNA with high efficacy upon visible-light irradiation leading up to 90 % of gene silencing in live cells.

Two Gelation Mechanisms of Deoxycholate with Inorganic Additives: Hydrogen Bonding and Electrostatic Interactions

This work describes the gelation behaviors of a biological amphiphile, deoxycholate (DC(-)), in aqueous solution by adding inorganic salts and modulating pH. Electrostatic interaction and hydrogen bonding can separately act as the controlling interaction for the hydrogel formation. The hydrogels formed at higher pH (about 8.5) through introducing monovalent inorganic cations (Na(+)) are mainly driven by electrostatic interaction between deoxycholate species and Na(+) ions. When pH is decreased, with the formation of DCA molecules, hydrogen bonding between DC(-) and DCA come into being another leading role to construct the hydrogels, which can induce the gels within an appropriate pH region (6.7-7.3) without inorganic cations. Gels constructed through the self-assembly of deoxycholate present diverse properties according to the difference in the main driving force. Moreover, the combination of the two important interactions can significantly enhance the gelation ability.