Hybrid Gels Assembled from Fmoc-Amino Acid and Graphene Oxide with Controllable Properties

A Review on the Rheological Properties of Single Amino Acids and Short Dipeptide Gels

Self-assembled peptide-based hydrogels have attracted considerable interest from the research community. Particularly, low molecular weight gelators (LMWGs) consisting of amino acids and short peptides are highly suitable for biological applications owing to their facile synthesis and scalability, as well as their biocompatibility, biodegradability, and stability in physiological conditions. However, challenges in understanding the structure-property relationship and lack of design rules hinder the development of new gelators with the required properties for several applications. Hereby, in the plethora of peptide-based gelators, this review discusses the mechanical properties of single amino acid and dipeptide-based hydrogels. A mutual analysis of these systems allows us to highlight the relationship between the gel mechanical properties and amino acid sequence, preparation methods, or N capping groups. Additionally, recent advancements in the tuning of the gels' rheological properties are reviewed. In this way, the present review aims to help bridge the knowledge gap between structure and mechanical properties, easing the selection or design of peptides with the required properties for biological applications.

Bioinspired Amino Acid Based Materials in Bionanotechnology: From Minimalistic Building Blocks and Assembly Mechanism to Applications

Inspired by natural hierarchical self-assembly of proteins and peptides, amino acids, as the basic building units, have been shown to self-assemble to form highly ordered structures through supramolecular interactions. The fabrication of functional biomaterials comprised of extremely simple biomolecules has gained increasing interest due to the advantages of biocompatibility, easy functionalization, and structural modularity. In particular, amino acid based assemblies have shown attractive physical characteristics for various bionanotechnology applications. Herein, we propose a review paper to summarize the design strategies as well as research advances of amino acid based supramolecular assemblies as smart functional materials. We first briefly introduce bioinspired reductionist design strategies and assembly mechanism for amino acid based molecular assembly materials through noncovalent interactions in condensed states, including self-assembly, metal ion mediated coordination assembly, and coassembly. In the following part, we provide an overview of the properties and functions of amino acid based materials toward applications in nanotechnology and biomedicine. Finally, we give an overview of the remaining challenges and future perspectives on the fabrication of amino acid based supramolecular biomaterials with desired properties. We believe that this review will promote the prosperous development of innovative bioinspired functional materials formed by minimalistic building blocks.

Morphological Evaluation of Supramolecular Soft Materials Obtained through Co-Assembly Processes

Low-molecular-weight gelators (LMWGs) are compounds with an intrinsic tendency to self-assemble forming various supramolecular architectures via non-covalent interactions. Considering that the development of supramolecular assemblies through the synergy of molecules is not entirely understood at the molecular level, this study introduced a Fmoc-short peptide and four Fmoc-amino acids as building blocks for the self-assembly/co-assembly process. Hence, we investigated the formation of supramolecular gels starting from the molecular aggregation following two triggering approaches: solvent/co-solvent method and pH switch. The complex morphological analysis (POM, AFM, and STEM) offered an insight into the spontaneous formation of well-ordered nanoaggregates. Briefly, POM and AFM images demonstrated that self-assembled gels present various morphologies like dendrimer, spherulite, and vesicle, whereas all co-assembled supramolecular systems exhibit fibrillar morphologies as a result of the interaction between co-partners of each system. STEM study has confirmed that the molecules interact and join together, finally forming a fibrous network, an aspect seen in both self-assembled and co-assembled gels. XRD allowed the determination of the molecular arrangement. The study emphasized that the Fmoc motif protected the amino groups and facilitated gelation through additional π-π interactions.

Probing the Gelation Synergies and Anti-Escherichia coli Activity of Fmoc-Phenylalanine/Graphene Oxide Hybrid Hydrogel

The N-fluorenyl-9-methyloxycarbonyl (Fmoc)-protected amino acids have shown high antimicrobial application potential, among which the phenylalanine derivative (Fmoc-F) is the most well-known representative. However, the activity spectrum of Fmoc-F is restricted to Gram-positive bacteria only. The demand for efficient antimicrobial materials expanded research into graphene and its derivatives, although the reported results are somewhat controversial. Herein, we combined graphene oxide (GO) flakes with Fmoc-F amino acid to form Fmoc-F/GO hybrid hydrogel for the first time. We studied the synergistic effect of each component on gelation and assessed the material's bactericidal activity on Gram-negative Escherichia coli (E. coli). GO flakes do not affect Fmoc-F self-assembly per se but modulate the elasticity of the gel and speed up its formation. The hybrid hydrogel affects E. coli survival, initially causing abrupt bacterial death followed by the recovery of the surviving ones due to the inoculum effect (IE). The combination of graphene with amino acids is a step forward in developing antimicrobial gels due to their easy preparation, chemical modification, graphene functionalization, cost-effectiveness, and physicochemical/biological synergy of each component.

Effect of differential backbone di-substitution of gamma amino acid residues on the conformation and assembly of their Fmoc derivatives in solid and solution states

We studied the effect of variable backbone dimethyl-substitution of γ amino acid residues (γ 2,2 , γ 3,3 and γ 4,4 ) on the conformation and assembly, in crystals and solution of their Fmoc derivatives. Crystal structure of γ 2,2 and γ 4,4 derivatives showed distinct conformations (open/close for γ 2,2 /γ 4,4 ) that differed in torsion angles, hydrogen-bonding and most importantly the π-π Fmoc-stacking interactions (relatively favorable for γ 4,4 -close). Fmoc derivatives existed in an equilibrium between major-monomeric (low energy, non-hydrogen bonded) and minor-dimeric (high energy, hydrogen bonded) populations in solution. Rate of major/minor population exchange was dependent on the position of substitution, highest being for γ 4,4 derivative. In solution, assembly of Fmoc derivatives was solvent dependent, but it was independent of the position of geminal substitution. Crystallization was primarily governed by the stabilization of high-energy dimer by favorable π-π stacking involving Fmoc moieties. High free-energy of the dimers (γ 2,2 -close, γ 3,3 -open/close) offset favorable stacking interactions and hindered crystallization.

Chiral macrocycle-induced circularly polarized luminescence of a twisted intramolecular charge transfer dye

The host-guest binding between a chiral macrocycle and an achiral dye could suppress the twisted intramolecular charge transfer (TICT) process, leading to enhanced emission and bright circularly polarized luminescence (CPL) from the originally achiral TICT-dye.

Biosynthesis and physico-chemical characterization of high performing peptide hydrogels@graphene oxide composites

Hydrogels based on short peptide molecules are interesting biomaterials with wide present and prospective use in biotechnologies. A well-known possible drawback of these materials can be their limited mechanical performance. In order to overcome this problem, we prepared Fmoc-Phe₃self-assembling peptides by a biocatalytic approach, and we reinforced the hydrogel with graphene oxide nanosheets. The formulation here proposed confers to the hydrogel additional physicochemical properties without hampering peptide self-assembly. We investigated in depth the effect of nanocarbon morphology on hydrogel properties (i.e. morphology, viscoelastic properties, stiffness, resistance to an applied stress). In view of further developments towards possible clinical applications, we have preliminarily tested the biocompatibility of the composites. Our results showed that the innovative hydrogel composite formulation based on FmocPhe3 and GO is a biomaterial with improved mechanical properties that appears suitable for the development of biotechnological applications.

Ultrathin Supramolecular Architectures Self-Assembled from a C3-Symmetric Synthon for Selective Metal Binding

Ultrathin supramolecular nanoarchitectures are an emerging class of two-dimensional (2D) materials with dynamic features that facilitate their on-demand functions. However, facile and efficient synthesis for multiple 2D topologies by taking advantage of spontaneous self-assembly is limited. In this work, we report the synthesis of ultrathin supramolecular nanoarchitectures from the self-assembly of a π-conjugated C₃-symmetric synthon (tribenzyloxybenzoic acid, TBBA), with the benzene-1,3,5-tricarboxamide core terminated by three carboxylic acids. Supported by the carboxylic acid-amide hydrogen-bonding and π-π/CH-π interactions, TBBA self-assembles into freestanding microsheets with the thickness of around 2 nm, demonstrating considerable integrity in different solvent systems or in the presence of carboxylic acid binders such as bipyridines. The deprotonation of the carboxylic acids endows TBBA with amphiphilicity, allowing for the formation of mixed micelles that are sensitive to transition-metal ions. Selectively, TBBA^3- shows relatively strong coordination to Cu(II), giving rise to long and thin organometallic ribbons (about 3 nm thickness) with a pronounced aging process. Kinetically insufficient coordination was probed by various characterization techniques and molecular dynamics simulation, which played a vital role in directing the formation of thin ribbons. This work provides a proof-of-concept study for a feasible and versatile construction of both flexible and rigid 2D supramolecular nanostructures with promising applications.

Self-Assembly Evolution of N-Terminal Aromatic Amino Acids with Transient Supramolecular Chirality

Deep understanding and fine tailoring of spontaneous structural evolution of self-assembled arrays are pivotal in the rational design of advanced soft materials. However, an indistinct structure-property relationship and pathway complexity in self-assembly lead to a considerable challenge. Herein, we reveal the self-assembly pathway complexity in spontaneous aggregation of several N-terminated aromatic amino acids. By primarily tuning the incubation time, building blocks appended with alanine and serine selectively form 1:1 hydrated clathrates, enabling the microfiber to transition to crystals. The dynamic water intercalation process was studied by incubation time-dependent morphological changes, powder X-ray diffraction, and single-crystal structure analysis. A pronounced amino acid residue effect on the self-assembly evolution was reflected by supramolecular chirality inversion of the building block having the phenylalanine residue, accomplishing dynamic M- to P-helicity transition within a confined time scale.

Fabrication of soft-nanocomposites from functional molecules with diversified applications

With the increasing demand for new soft materials having excellent physical and biological characteristics and functionality, the design of hybrid materials offers a simple, yet versatile platform for the development of materials with specific and tunable properties. By definition a "soft-nanocomposite" is the combination of supramolecular self-assemblies with nanomaterials of different origins (inorganic/metallic nanoparticles and carbonaceous allotropes like carbon nanotubes and graphene) through covalent/non-covalent interactions. Dynamic supramolecular self-assemblies can serve as excellent hosts for the incorporation of these dimensionally different nanomaterials. Nanomaterials within the matrix of supramolecular self-assemblies can give rise to new characteristics due to the synergistic contribution of both materials. Although the very initial work intended to use molecular gels as media for the preparation and stabilization of nanoparticles, recent reports have suggested that amalgamation of different supramolecular self-assemblies with nanoparticles is advantageous for both constituents. These newly developed soft-nanocomposites have interesting properties including electrical conductivity, viscoelasticity, thermal robustness, magnetic, phase-selective, redox and near-infrared radiation sensitive properties and so on. This review will focus on some of the most recent advancements in the development of novel soft-nanocomposites. In particular, we intend to correlate various design strategies for synthesis as well as composite preparation from functional molecules with interesting applications in the area of supercapacitors, nanoelectronics, photovoltaic devices, chemical and biosensors, biomedicine and so on. We expect that this article will be a general and conceptual demonstration of various approaches to develop different soft-nanocomposites and will highlight their applications across disciplines.

A review on peptide functionalized graphene derivatives as nanotools for biosensing

Peptides exhibit unique binding behavior with graphene and its derivatives by forming bonds on its edges and planes. This makes them useful for sensing and imaging applications. This review with (155 refs.) summarizes the advances made in the last decade in the field of peptide-GO bioconjugation, and the use of these conjugates in analytical sciences and imaging. The introduction emphasizes the need for understanding the biotic-abiotic interactions in order to construct controllable peptide-functionalized graphitic material-based nanotools. The next section covers covalent and non-covalent interactions between peptide and oxidized graphene derivatives along with a discussion of the adsorption events during interfacing. We then describe applications of peptide-graphene conjugates in bioassays, with subsections on (a) detection of cancer cells, (b) monitoring protease activity, (c) determination of environmental pollutants and (d) determination of pathogenic microorganisms. The concluding section describes the current status of peptide functionalized graphitic bioconjugates and addresses future perspectives. Graphical abstractSchematic representation depicting biosensing applications of peptide functionalized graphene oxide.

Graphene oxide containing self-assembling peptide hybrid hydrogels as a potential 3D injectable cell delivery platform for intervertebral disc repair applications

Cell-based therapies have shown significant promise in tissue engineering with one key challenge being the delivery and retention of cells. As a result, significant efforts have been made in the past decade to design injectable biomaterials to host and deliver cells at injury sites. Intervertebral disc (IVD) degeneration, a major cause of back pain, is a particularly relevant example where a minimally-invasive cellular therapy could bring significant benefits specifically at the early stages of the disease, when a cell-driven process starts in the gelatinous core of the IVD, the nucleus pulposus (NP). In this present study we explore the use of graphene oxide (GO) as nano-filler for the reinforcement of FEFKFEFK (β-sheet forming self-assembling peptide) hydrogels. Our results confirm the presence of strong interactions between FEFKFEFK and GO flakes with the peptide coating and forming short thin fibrils on the surface of the flakes. These strong interactions were found to affect the bulk properties of hybrid hydrogels. At pH 4 electrostatic interactions between the peptide fibres and the peptide-coated GO flakes are thought to govern the final bulk properties of the hydrogels while at pH 7, after conditioning with cell culture media, electrostatic interactions are removed leaving the hydrophobic interactions to govern hydrogel final properties. The GO-F820 hybrid hydrogel, with mechanical properties similar to the NP, was shown to promote high cell viability and retained cell metabolic activity in 3D over the 7 days of culture and therefore shown to harbour significant potential as an injectable hydrogel scaffold for the in-vivo delivery of NP cells. STATEMENT OF SIGNIFICANCE: Short self-assembling peptide hydrogels (SAPHs) have attracted significant interest in recent years as they can mimic the natural extra-cellular matrix, holding significant promise for the ab initio design of cells' microenvironments. Recently the design of hybrid hydrogels for biomedical applications has been explored through the incorporation of specific nanofillers. In this study we exploited graphene oxide (GO) as nanofiller to design hybrid injectable 3Dscaffolds for the delivery of nucleus pulposus cells (NPCs) for intervertebral disc regeneration. Our work clearly shows the presence of strong interactions between peptide and GO, mimicking the mechanical properties of the NP tissue and promoting high cell viability and metabolic activity. These hybrid hydrogels therefore harbour significant potential as injectable scaffolds for the in vivo delivery of NPCs.

Induced Aggregation of Epoxy Polysiloxane Grafted Gelatin by Organic Solvent and Green Application

In this paper, we studied the aggregation of amphiphilic polymer epoxy-terminated polydimethylsiloxane (PDMS-E) grafted gelatin (PGG) in water induced by methanol, ethanol, 2-propanol, acetone, tetrahydrofuran (THF), and 1,4-dioxane. The aggregation pattern of the polymer was monitored by infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. It was revealed that the aggregate morphology showed clear dependence on the solvent polarity. The PGG aggregates had regular spherical morphology in polar solvents, including water, methanol, ethanol, 2-propanol, and acetone. The coating performance was evaluated by X-ray photoelectron spectroscopy and friction experiment, and PGG and acetone coating exhibited excellent coating performance on the surface of pigskin. Gel was formed in acetone and tetrahydrofuran (THF) with the slow evaporation of solvent, and this property can possibly be applied to industrial sewage treatment. White precipitate and soft film were formed in non-polar 1,4-dioxane.

Subtle chemical modification for enrichment of Fmoc-amino acid at a phospholipid interface

Amino acids including the Fmoc group (9-fluorenylmethyloxycarbonyl) are bioinspired molecules that display intriguing features in self-assembly and biological applications. The influence of a delicate chemical modification between Fmoc-F and Fmoc-Y on the interaction with a phospholipid surface was analyzed. Langmuir monolayers of the 1,2-dimyristoyl-sn-glycero-3-phosphate (DMPA) phospholipid were used to mimic the eukaryotic cell membrane. In situ Brewster angle microscopy and UV-vis reflection spectroscopy provided insights on the effect of the Fmoc-amino acid derivatives on the DMPA phospholipid. The formation of H-bonds between the Fmoc-Y and the DMPA molecules was assessed, demonstrating the crucial role of the hydroxyl group of Fmoc-Y in enhancing the interaction with biosurfaces.

A modest chemical modification of the Fmoc-amino acids led to enhanced interaction with a model surface for biomembrane.

The aromaticity of the phenyl ring imparts thermal stability to a supramolecular hydrogel obtained from low molecular mass compound

Using Fmoc-phenylalanine and Fmoc-cyclohexylalanine, we show that the aromaticity of the phenyl ring imparts significant thermal stability to a supramolecular hydrogel system and its significance depends on the method of inducing hydrogelation.

Programmable Multicomponent Self-Assembly Based on Aromatic Amino Acids

Construction of integrated self-assembly with ordered structures from two or more organic building blocks is currently a challenge, since it suffers from intrinsic systematic complexity and diverse competitive pathways. Here, it is reported that aromatic amino acid building units can be incorporated into two- or three-component coassembly driven primarily by hydrogen bonding interactions without the assistance of metal-ligand and macrocycle-based host-guest interactions. The key strategy is to employ a C₃ -symmetric molecule with alternative hydrogen bonding donor/acceptor sites that are able to bind either carboxylic acid or pyridine appended building units. Aromatic amino acids, C₃ -symmetric compound, and bipyridine unit constitute a unique ternary mutual binding system, where three coassembly pathways including two pairwise formations and one ternary combination are unveiled, giving rise to two- and three-component self-assemblies with ordered structures, respectively. The pathway complexity lies in the structural parameter of aromatic amino acids, which can be programmable by controlling substituents at the α-position of amino acids.

Selective Coassembly of Aromatic Amino Acids to Fabricate Hydrogels with Light Irradiation-Induced Emission for Fluorescent Imprint

Controlling the structural parameters in coassembly is crucial for the fabrication of multicomponent functional materials. Here a proof-of-concept study is presented to reveal the α-substituent effect of aromatic amino acids on their selective coassembly with bipyridine binders. With the assistance of X-ray scattering technique, it is found that individual packing in the solid state as well as bulky effect brought by α-substitution determines the occurrence of coassembly. A well-performed hydrogels based on the complexation between certain aromatic amino acids and bipyridine units are successfully constructed, providing unprecedented smart materials with light irradiation-triggered luminescence. Such hydrogels without the phase separation and photobleaching during light irradiation are able to behave fluorescent imprint materials. This study provides a suitable protocol in rationally designing amino acid residues of short peptides for fabricating self-assembled multicomponent materials. In addition, this protocol is useful in screening potential functional materials on account of diverse self-assembly behavior.

Understanding Pathway Complexity of Organic Micro/Nanofiber Growth in Hydrogen-Bonded Coassembly of Aromatic Amino Acids

Rational engineering of one-dimensional (1D) self-assembled aggregates to produce desired materials for versatile functions remains a challenge. In this work, we report the noncovalent modulation of 1D aggregates at the micro/nanoscale using a coassembly protocol. Aromatic amino acids were employed as the model building blocks, and melamine (Mm) behaves as a modulator to form coassembly arrays with aromatic amino acids selectively. The selective self-assembly behavior between aromatic amino acids and Mm allows distinguishing and detecting Mm and aromatic amino acids from their analogues in macroscopic and microscopic scales. Dimensions and sizes of fibrous aggregates prepared from different amino acids show two opposite pathways from pristine assemblies to coassemblies induced by the addition of Mm. This pathway complexity could be controlled by the molecular conformation determined by α-positioned substituents. The developed hypothesis presents an excellent expansibility to other substrates, which may guide us to rationally design and screen 1D materials with different dimensions and sizes including the production of high-quality self-standing hydrogels.

Functional Graphene Nanomaterials Based Architectures: Biointeractions, Fabrications, and Emerging Biological Applications

Functional graphene nanomaterials (FGNs) are fast emerging materials with extremely unique physical and chemical properties and physiological ability to interfere and/or interact with bioorganisms; as a result, FGNs present manifold possibilities for diverse biological applications. Beyond their use in drug/gene delivery, phototherapy, and bioimaging, recent studies have revealed that FGNs can significantly promote interfacial biointeractions, in particular, with proteins, mammalian cells/stem cells, and microbials. FGNs can adsorb and concentrate nutrition factors including proteins from physiological media. This accelerates the formation of extracellular matrix, which eventually promotes cell colonization by providing a more beneficial microenvironment for cell adhesion and growth. Furthermore, FGNs can also interact with cocultured cells by physical or chemical stimulation, which significantly mediate their cellular signaling and biological performance. In this review, we elucidate FGNs-bioorganism interactions and summarize recent advancements on designing FGN-based two-dimensional and three-dimensional architectures as multifunctional biological platforms. We have also discussed the representative biological applications regarding these FGN-based bioactive architectures. Furthermore, the future perspectives and emerging challenges will also be highlighted. Due to the lack of comprehensive reviews in this emerging field, this review may catch great interest and inspire many new opportunities across a broad range of disciplines.

Selective Metal-Ion-Mediated Vesicle Adhesion Based on Dynamic Self-Organization of a Pyrene-Appended Glutamic Acid

Vesicles with dynamic membranes provide an ideal model system for investigating biological membrane activities, whereby vesicle aggregation behaviors including adhesion, fusion, fission, and membrane contraction/extension have attracted much attention. In this work we utilize an aromatic amino acid (pyrene-appended glutamic acid, PGlu) to prepare nanovesicles that aggregate to form vesicle clusters selectively induced by Fe(3+) or Cu(2+), and the vesicles transform into irregular nano-objects when interacting with Al(3+). Vesicle clusters have better stability than pristine vesicles, which hinders the spontaneous morphological transformation from vesicles into lamellar nanosheets with long incubation period. The difference between complexation of Fe(3+) and Al(3+) with vesicles was studied by various techniques. On the basis of metal ion-vesicle interactions, this self-assembled nanovesicle system also behaves as an effective fluorescent sensor for Fe(3+) and Al(3+), which cause fluorescence quenching and enhanced excimer emission, respectively.

Superstructure Formation and Topological Evolution Achieved by Self-Organization of a Highly Adaptive Dynamer

The adaptive property of supramolecular building blocks facilitates noncovalent synthesis of soft materials. While it is still a challenging task, fine-tuning and precise control over topological nanostructures constructed from the self-assembly of low-molecular-weight building blocks are an important research direction to investigate the structure-property relationship. Herein, we report controlled self-assembly evolution of a low-molecular-weight building block bearing cholesterol and naphthalene-dicarboximide moieties, showing ultrasensitivity to solvent polarity. In low-polarity solvents (<4), it could form an M-type fiber-constituted organogel (supergel) with high solvent content, columnar molecular packing, and self-healing property. Highly polar solvents (>7.8) favor the formation of P-type helical nanostructures terminated by nanotoroids, having lamellar molecular packing. With a further increase in solvent polarity (up to 9.6), unilamellar and multilamellar vesicles were generated, which could undergo an aggregation-induced fusion process to form branched nanotubes tuned by the concentration. Self-attractive interactions between aggregates were found to be responsible for the formation of superstructures including helix-nanotoroid junctions as well as membrane-fused nanotubes.

Solvent-polarity-tuned nanostructures assembled from modified octadecylcarbamate with an anthracen moiety

A-9-YMOC tends to form nanofibers whereas it self-assembles in polar solvents and nanoflowers in nonpolar solvents with different molecular arrangements.

Tuning of gel morphology with supramolecular chirality amplification using a solvent strategy based on an Fmoc-amino acid building block

The self-assembly of an aromatic amino acid affords diverse aggregates from flat nanofibers to twist nanofibers with tunable supramolecular chirality.

Tailoring luminescence color conversion via affinitive co-assembly of glutamates appended with pyrene and naphthalene dicarboximide units

Co-assembled vesicles constructed from two glutamic acid derivatives display concentration-dependent energy transfer along with multiple color emissions.

Hydrogelation Induced by Fmoc-Protected Peptidomimetics

Four new low molecular weight hydrogelators (LMWGs) have been prepared in multigram scale and their attitude to form hydrogels has been tested. The gelation trigger is pH variation. The resulting gels have been characterized with several techniques: measurement of the melting points (T(gel)), transparency, gelation time, and viscoelastic properties, together with ECD analysis. Among them, Fmoc-L-Tyr-D-Oxd-OH 1 is an excellent gelator that leads to the preparation of strong, transparent, and viscoelastic gels, by pH variation. UV-visible analyses have demonstrated that the gels obtained with the LMWG 1 possess high transparency, with a transmittance up to 25.6% at a wavelength of 600 nm. Results of the amplitude sweep experiments showed that the elastic response component (G') was approximately an order of magnitude larger than the viscous component, indicating an elastic rather than viscous attitude of the gels, confirmed by the frequency independence of G' and G″ values, in the range from 0.1 to 100 rad·s(-1). The thermal behavior of gel obtained from Fmoc-L-Tyr-D-Oxd-OH 1 was characterized performing an "ad hoc" rheological temperature sweep experiment, that indicated that G' remained almost constant from 23 °C up to about 65 °C while G″ increased in the same temperature range. At higher temperatures, both G' and G″ values started to slightly decrease without displaying a crossover point.

An additional fluorenylmethoxycarbonyl (Fmoc) moiety in di-Fmoc-functionalized L-lysine induces pH-controlled ambidextrous gelation with significant advantages

In recent years, several fluorenylmethoxycarbonyl (Fmoc)-functionalized amino acids and peptides have been used to construct hydrogels, which find a wide range of applications. Although several hydrogels have been prepared from mono Fmoc-functionalized amino acids, herein, we demonstrate the importance of an additional Fmoc-moiety in the hydrogelation of double Fmoc-functionalized L-lysine [Fmoc(Nα)-L-lysine(NεFmoc)-OH, (Fmoc-K(Fmoc))] as a low molecular weight gelator (LMWG). Unlike other Fmoc-functionalized amino acid gelators, Fmoc-K(Fmoc) exhibits pH-controlled ambidextrous gelation (hydrogelation at different pH values as well as organogelation), which is significant among the gelators. Distinct fibrous morphologies were observed for Fmoc-K(Fmoc) hydrogels formed at different pH values, which are different from organogels in which Fmoc-K(Fmoc) showed bundles of long fibers. In both hydrogels and organogels, the self-assembly of Fmoc-K(Fmoc) was driven by aromatic π-π stacking and hydrogen bonding interactions, as evidenced from spectroscopic analyses. Characterization of Fmoc-K(Fmoc) gels using several biophysical methods indicates that Fmoc-K(Fmoc) has several advantages and significant importance as a LMWG. The advantages of Fmoc-K(Fmoc) include pH-controlled ambidextrous gelation, pH stimulus response, high thermal stability (∼100 °C) even at low minimum hydrogelation concentration (0.1 wt%), thixotropic property, high kinetic and mechanical stability, dye removal properties, cell viability to the selected cell type, and as a drug carrier. While single Fmoc-functionalized L-lysine amino acids failed to exhibit gelation under similar experimental conditions, the pH-controlled ambidextrous gelation of Fmoc-K(Fmoc) demonstrates the benefit of a second Fmoc moiety in inducing gelation in a LMWG. We thus strongly believe that the current findings provide a lead to construct or design various new synthetic Fmoc-based LMW organic gelators for several potential applications.

Dual-tuning multidimensional superstructures based on a T-shaped molecule: vesicle, helix, membrane and nanofiber-constructed gel

Dual-tuning self-assembly of Fmoc–Gly (a T-shape molecule) supramolecular self assembly was firstly reported here.

Hydrogels formed from Fmoc amino acids

A number of Fmoc amino acids can be effective low molecular weight hydrogelators; we compare single crystal structures to fibre X-ray diffraction data.

Controllable self-assemblies of sodium benzoate in different solvent environments

Sodium benzoate is an important and widely used food additive, however, it's self-assembly properties in diverse solvents have been rarely studied. Here, we systematically report its various self-assemblies in different solvents environments.

Reversible pH-responsive helical nanoribbons formed using camptothecin

The natural antitumor drug camptothecin was found to self-assemble into helical nanoribbons in aqueous solution. The formation and disappearance of the helical nanoribbons can be tuned reversibly through changing the pH value of the solution.