Electroactive Organic Dye Incorporating Dipeptides in the Formation of Self-Assembled Nanofibrous Hydrogels

Low molecular weight self-assembling peptide-based materials for cell culture, antimicrobial, anti-inflammatory, wound healing, anticancer, drug delivery, bioimaging and 3D bioprinting applications

In this review, we have focused on the design and development of low molecular weight self-assembling peptide-based materials for various applications including cell proliferation, tissue engineering, antibacterial, antifungal, anti-inflammatory, anticancer, wound healing, drug delivery, bioimaging and 3D bioprinting. The first part of the review describes about stimuli and various noncovalent interactions, which are the key components of various self-assembly processes for the construction of organized structures. Subsequently, the chemical functionalization of the peptides has been discussed, which is required for the designing of self-assembling peptide-based soft materials. Various low molecular weight self-assembling peptides have been discussed to explain the important structural features for the construction of defined functional nanostructures. Finally, we have discussed various examples of low molecular weight self-assembling peptide-based materials for cell culture, antimicrobial, anti-inflammatory, anticancer, wound healing, drug delivery, bioimaging and 3D bioprinting applications.

Beyond Fmoc: a review of aromatic peptide capping groups

Self-assembling short peptides have attracted widespread interest due to their tuneable, biocompatible nature and have potential applications in energy materials, tissue engineering, sensing and drug delivery. The hierarchical self-assembly of these peptides is highly dependent on the selection of not only amino acid sequence, but also the capping group which is often employed at the N-terminus of the peptide to drive self-assembly. Although the Fmoc (9H-fluorenylmethyloxycarbonyl) group is commonly used due to its utility in solid phase peptide synthesis, many other aromatic capping groups have been reported which yield functional, responsive materials. This review explores recent developments in the utilisation of functional, aromatic capping groups beyond the Fmoc group for the creation of redox-responsive, fluorescent and drug delivering hydrogel scaffolds.

Construction of self-assembled nanostructure-based tetraphenylethylene dipeptides: supramolecular nanobelts as biomimetic hydrogels for cell adhesion and proliferation

A novel TPE-YY peptide hydrogelator self-assembled to form twisted nanobelts at neutral pH, upon cultured with 3A6 cells showed selective cell adhesion and growth.

Robust supramolecular nanocylinders of naphthalene diimide in water

Long and robust NDI-containing nanocylinders formed by supramolecular self-assembly via hydrogen bonds and aromatic interactions in aqueous medium.

Redox-Active Peptide-Functionalized Quinquethiophene-Based Electrochromic π-Gel

An electrochromic system based on a self-assembled dipeptide-appended redox-active quinquethiophene π-gel is reported. The designed peptide-quinquethiophene consists of a symmetric bolaamphiphile that has two segments: a redox-active π-conjugated quinquethiophene core for electrochromism, and peptide motif for the involvement of molecular self-assembly. Investigations reveal that self-assembly and electrochromic properties of the π-gel are strongly dependent on the relative orientation of peptidic and quinquethiophene scaffolds in the self-assembly system. The colors of the π-gel film are very stable with fast and controlled switching speed at room temperature.

Redox-sensitive reversible self-assembly of amino acid-naphthalene diimide conjugates

Peptide and low molecular weight amino acid-based materials that self-assemble in response to environmental triggers are highly desirable candidates in forming functional materials with tunable biophysical properties. In this paper, we explore redox-sensitive self-assembly of cationic phenylalanine derivatives conjugated to naphthalene diimide (NDI). Self-assembly of the cationic Phe-NDI conjugates into nanofibrils was induced in aqueous solvent at high ionic strength. Under reducing conditions, these self-assembled Phe-NDI conjugate fibrils underwent a morphological change to non-fibril aggregates. Upon reoxidation, the initially observed fibrils were reformed. The study herein provides an interesting strategy to effect reversible switching of the structure of supramolecular materials that can be applied to the development of sophisticated stimulus-responsive materials.

Two-Component Fluorescent-Semiconducting Hydrogel from Naphthalene Diimide-Appended Peptide with Long-Chain Amines: Variation in Thermal and Mechanical Strengths of Gels

Two-component fluorescent hydrogels have been discovered, containing the mixtures of naphthalene diimide (NDI)-conjugated peptide-functionalized bola-amphiphile and primary amines with long alkyl chains at physiological pH 7.46. The aggregation-induced enhanced emission associated with an NDI-appended peptide in aqueous medium is rare, as water is known to be a good quencher of fluorescence. In this study, an NDI-containing gelator peptide forms a highly fluorescent aggregate in aqueous medium. Absorption and emission spectroscopic techniques reveal the formation of J-aggregates among the chromophoric moieties in their aggregated state in aqueous medium. However, this NDI-containing peptide does not form any gel in aqueous medium. In the presence of the primary amines with long alkyl chains in the buffer solution, it forms two-component fluorescent hydrogels exhibiting bright yellow fluorescence under a UV lamp (365 nm). Probably, the acid-amine interaction between the amines and the bola-amphiphile triggers the gel formation, as evident from Fourier transform infrared data, indicating the presence of a carboxylate group (-COO^-) and an ammonium species (NH₃⁺) in the coassembled two-component gel system. Low- and wide-angle powder X-ray diffraction and small-angle X-ray scattering further support the fact that the coassembled state in the gel form is produced by the supramolecular interaction between the NDI-based bola-amphiphile and the long-chain amines. Field-emission scanning electron microscopy and high-resolution transmission electron microscopy images reveal that the π-conjugated coassembled hydrogels exhibit nanofibrillar network morphologies. Interestingly, the coassembled hydrogels exhibit an enhanced fluorescence emission, excited-state lifetime, and quantum yield when compared with those of the NDI-containing amphiphile alone in its self-assembled state in aqueous medium. Moreover, the thermal stability and mechanical strength of these gels have been successfully tuned by varying the alkyl chain length of the corresponding amine. Moreover, these NDI-peptide-conjugated soft materials exhibit semiconducting behavior in their respective coassembled states. This holds future promise to use these peptide-appended NDI-based coassembled soft materials for applications in optoelectronic and other devices.

Functional Supramolecular Polymers: A Fluorescent Microfibrous Network in a Supramolecular Hydrogel for High-Contrast Live Cell-Material Imaging in 3D Environments

A new bottom-up strategy based on aromatic peptide amphiphile is developed for a high-contrast visualization of 3D live cell-material imaging-something that has been difficult to achieve previously because of the problems associated with the diffraction of light by the nanosized peptide materials and the aggregation-caused quenching of aggregated π-conjugated fluorophores in the nanostructures. This study reports an example of a novel supramolecular hydrogelator, naphthaleneimide-phenylalanine (NI-Phe), which forms a self-supporting hydrogel displaying a unique microfibrous network and promising aggregation-induced emission characteristics at pH 7.4. The storage modulus of the NI-Phe gel supports the mass of a cell for 3D cell culturing. This work illustrates a new dopant-free supramolecular approach, complementary to well-established doping procedures that should facilitate the development of live cell imaging in 3D scaffolding materials.

Effect of Peptide Sequences on Supramolecular Interactions of Naphthaleneimide/Tripeptide Conjugates

In this study, we reported a significant difference in the supramolecular hydrogelation of newly discovered NI-GFF (NI-Gly-l-Phe-l-Phe) and NI-FFG (NI-l-Phe-l-Phe-Gly) on the basis of their phase diagrams. With a small difference in the peptide chain between NI-GFF and NI-FFG, we observed a significant difference in their self-assembly properties; NI-GFF formed a stable gel at neutral pH, whereas NI-FFG did not, under the same conditions. From spectroscopic and computational studies, intermolecular π-π interactions and extended hydrogen bonding interactions might reinforce the intermolecular interactions of NI-GFF, which may facilitate the formation of the self-assembled nanostructures and the hydrogel. In addition, the aggregation-induced emission (AIE)-active NI-GFF reveals relatively good biocompatibility compared with that of NI-FFG for two commonly used cell lines, suggesting that it is a promising candidate for use as a supramolecular material in biomedical applications. Our results highlight the importance of tripeptide sequences in a self-assembling hydrogel system.

H-bonding directed programmed supramolecular assembly of naphthalene-diimide (NDI) derivatives

In this review we have collated various supramolecular designs, all surrounding H-bonding among well-known functional groups (peptides, nucleic acids, amides, ureas, carboxylic acids, pyridine-hydroxyls, urethanes, imides and others), to dictate self-assembly of naphthalenediimide (NDI) π-systems (both small molecules and polymeric building blocks) that exhibit several exciting features including strong propensity for π-π interactions, π-acidity, excellent n-type semiconductivity, CT-complexation, ion-π interactions, ring-substitution dependent redox properties and photophysical properties. This article reveals that H-bonding can indeed serve as a very powerful and versatile tool to programmed self-assembly of a single or multiple dye system producing a wide range of tailored soft materials, including fibrillar gels, chromonic mesophases, foldamers, nanotubes, vesicles, reverse micelles and polymersomes, both in water and organic medium with distinct photophysical properties, charge transport properties, conductivity properties and functional group displays that are highly relevant in the fields of biology and organic electronics.

Nanofibrous hydrogels self-assembled from naphthalene diimide (NDI)/amino acid conjugates

A new approach is proposed for the design of NDI-capped supramolecular hydrogels.

A supramolecular hydrogel self-assembled from pentafluorobenzyl-dipeptide

We report a new aromatic-capped peptide amphiphile which is able to form a supramolecular hydrogel under neutral pH.

Remarkable influence of alkyl chain lengths on supramolecular hydrogelation of naphthalene diimide-capped dipeptides

The influence of aliphatic chain lengths on supramolecular hydrogelation of naphthalene diimide-capped dipeptides is described.