Low Molecular Weight Gelators Research Articles

Time Dependence of Gel Formation in Lyotropic Nematic Liquid Crystals: From Hours to Weeks.

The combination of lyotropic liquid crystals (LLCs) and low-molecular-weight gelators (LMWGs) for the formation of lyotropic liquid crystal gels (LLC gels) leads to a versatile and complex material combining properties of both parent systems. We gelled the calamitic nematic NC phases of a binary and ternary system using the LMWG 3,5-bis-(5-hexylcarbamoyl-pentoxy)-benzoic acid hexyl ester (BHPB-6). This binary system consists of the surfactant N,N-dimethyl-N-ethyl-1-hexadecylammonium bromide (CDEAB) and water, whereas the ternary system consists of the surfactant N,N,N-trimethyl-N-tetradecylammonium bromide (C14TAB), the cosurfactant n-decanol, and water. Though containing similar surfactants, the gelled NC phases of the binary and ternary systems show differences in their visual and gel properties. The gelled NC phase of the binary system remains clear for several days after preparation, whereas the gelled NC phase of the ternary system turns turbid within 24 h. We investigated the time evolution of the gel strength with oscillation rheology measurements (a) within the first 24 h and (b) up to two weeks after gel formation. The shape of the fibers was investigated over different time scales with freeze fracture electron microscopy (FFEM). We demonstrate that despite their similarities, the two LLC gels also have distinct differences.

3,4-Ethylenedioxythiophene Hydrogels: Relating Structure and Charge Transport in Supramolecular Gels.

Ionic charge transport is a ubiquitous language of communication in biological systems. As such, bioengineering is in constant need of innovative, soft, and biocompatible materials that facilitate ionic conduction. Low molecular weight gelators (LMWGs) are complex self-assembled materials that have received increasing attention in recent years. Beyond their biocompatible, self-healing, and stimuli responsive facets, LMWGs can be viewed as a "solid" electrolyte solution. In this work, we investigate 3,4-ethylenedioxythiophene (EDOT) as a capping group for a small peptide library, which we use as a system to understand the relationship between modes of assembly and charge transport in supramolecular gels. Through a combination of techniques including small-angle neutron scattering (SANS), NMR-based Van't Hoff analysis, atomic force microscopy (AFM), rheology, four-point probe, and electrochemical impedance spectroscopy (EIS), we found that modifications to the peptide sequence result in distinct assembly pathways, thermodynamic parameters, mechanical properties, and ionic conductivities. Four-point probe conductivity measurements and electrochemical impedance spectroscopy suggest that ionic conductivity is approximately doubled by programmable gel assemblies with hollow cylinder morphologies relative to gels containing solid fibers or a control electrolyte. More broadly, it is hoped this work will serve as a platform for those working on charge transport of aqueous soft materials in general.

Enantioseparation via Chiral Supramolecular Gels Comprising Ambidextrous Gelators Based on β-Peptide-type Primary Amines.

While β-peptides have been paid attention due to their diverse secondary structures, their application to the design of low-molecular-weight gelators (LMWGs) is less explored. In this work, chiral cyclic β-amino acid-based β-peptides were developed as ambidextrous LMWGs, wherein multiple hydrogen bonds between the amide moieties led to high gelation ability. Their molecular assembly was elucidated using spectroscopies, microscopy, and X-ray analysis. Further, the supramolecular gel was used as a platform for the enantioselective extraction of (S)-naproxen from its racemate under optimized conditions. These findings have expanded the utility of β-peptides and shown the potential of supramolecular gels as a distinct dynamic medium for enantiomer separation.

Gelation of whole macadamia butter by different oleogelators affects the physicochemical properties and applications

Previously, our team has successfully developed ultra-fine whole macadamia butter (WMB, D[4,3]＜20 μm) using a novel high energy media mill (HEMM), which showed poor storage stability. In this study, we aimed to enhance the stability of WMB by incorporating four low molecular weight gelators—monoglyceride stearate (MG), beeswax (BW), rice bran wax (RBW), γ-oryzanol and β-sitosterol mixture (SO)—based on the oleogelation mechanism. The effects of different oleogelation mechanisms on its microstructure, texture, storage stability, rheological behavior, spreadability and 3D printability were investigated. The results revealed distinct minimum gelation concentration for different gelators, with all gelators significantly improving the storage stability and hardness of WMB. At a gelator of 3.0%, the centrifugal oil yield for MG, BW, SO and RBW-based WMB decreased by 82.6%, 56.6%, 42.7% and 83.4%, respectively, which was closely related to the small particle size and more uniform distribution of protein particles within the system. Moreover, all samples exhibited a pseudoplastic fluid behavior. Additionally, the appropriate addition of gelators improved the spreadability and 3D printability of WMB. The results provide new insights for the development and application of high oil-based products.

Reversibly Tuning the Viscosity of Peptide-Based Solutions Using Visible Light.

Light can be used to design stimuli-responsive systems. We induce transient changes in the assembly of a low molecular weight gelator solution using a merocyanine photoacid. Through our approach, reversible viscosity changes can be achieved via irradiation, delivering systems where flow can be controlled non-invasively on demand.

Comparative outcomes of the voltage-dependent current density, charge transportation and rectification ratio of electronic devices fabricated using mechanically flexible supramolecular networks.

In this study, we report the synthetic method of two distinct supramolecular metallogels, namely Mn-BDA and Cd-BDA, using Mn(II) acetate tetrahydrate, Cd(II) acetate dihydrate and butane-1,4-dicarboxylic acid (BDA). DMF, a polar aprotic solvent, was immobilized in both metallogel-networks for their synthesis. The metallogelation of Mn-BDA was successfully attained through the instant mixing of a Mn(II)-source and BDA in DMF solvent media. By applying ultrasonication, a Cd-BDA metallogel was prepared. The stoichiometry of gel-forming components concerning metal salts and the LMWG are accountable to obtain respective stable metallogels. Rheological parameters such as storage modulus (G') and loss modulus (G'') explored the mechanical flexibility of the synthesized metallogels through amplitude and angular frequency sweep experiments. Both the metallogels possess significant mechanical stability, which was determined by monitoring diverse gel-to-sol transition shear strain values (γ%). Distinctive morphological visualizations of both of these metallogels (i.e., Mn-BDA and Cd-BDA) were made via field emission scanning electron microscopic (FESEM) studies, demonstrating a fibrous inter-connected network with a hierarchical self-assembled arrangement for Mn(II)-based metallogels and a typical stacked-flake-like association with hierarchical motifs for Cd(II)-based metallogels. EDAX elemental mapping substantiated the presence of metallogel-forming agents such as individual metal acetate salts, BDA acting as a low-molecular weight gelator, and gel-immobilized solvents such as DMF. Furthermore, Fourier transform infrared spectroscopy and ESI-mass spectroscopy were performed for both these supramolecular metallogels. FT-IR spectroscopic and ESI-mass spectroscopic results clearly substantiate the possible non-covalent supramolecular interactions among basic molecular repeating moieties, i.e., butane-1,4-dicarboxylic acid (the low-molecular weight gelator), individual metal salts and gel-immobilized polar aprotic solvent DMF for the construction of distinct stable supramolecular metallogel-systems. The semiconducting property of the fabricated metallogels was investigated. Two Schottky diodes (SDs) composed of ITO/Cd-BDA/Al and ITO/Mn-BDA/Al in a sandwich pattern with Al serving as the metal electrode were fabricated. Both these metallogel-based devices effectively offer significant semiconducting diode features with non-linear J-V characteristics. The non-ohmic conduction protocol of the fabricated metallogel-based devices was explored. Mn-BDA and Cd-BDA metallogel-based fabricated devices have rectification ratios of 6.67 and 23.50, respectively. The gel-based diode performances were examined by observing the voltage-dependent current density, charge transportation and rectification ratio.

Eutectic solvents and low molecular weight gelators for next-generation supramolecular eutectogels: a sustainable chemistry perspective

Immobilization of eutectic mixtures in supramolecular gels formed using low molecular weight gelators is a smart strategy to expand their design space. Advances in the last five years are reviewed from the viewpoint of sustainability.

Methods of changing low molecular weight gel properties through gelation kinetics.

Low molecular weight gels continue to attract notable interest, with many potential applications. However, there are still significant gaps in our understanding of these systems and the correlation between the pre-gel and final gel states. The kinetics of the gelation process plays a crucial role in the bulk properties of the hydrogel and presents an opportunity to fine-tune these systems to meet the requirements of the chosen application. Therefore, it is possible to use a single gelator for multiple applications. This review discusses four ways to modify the pre-gelled structures before triggering gelation. Such modifications can enhance the material's intended performance, which may result in significant advancements in high-tech areas, such as drug delivery, cell culturing, electronics, and tissue engineering.

Ultralight aerogels via supramolecular polymerization of a new chiral perfluoropyridine-based sulfonimidamide organogelator.

Chiral and enantiopure perfluorinated sulfonimidamides act as low-molecular weight gelators at low critical gelation concentration (<1 mg mL-1) via supramolecular polymerization in nonpolar organic solvents and more heterogenic mixtures, such as biodiesel and oil. Freeze-drying of the organogel leads to ultralight aerogel with extremely low density (1 mg mL-1). The gelation is driven by hydrogen bonding resulting in a helical molecular ordering and unique fibre assemblies as confirmed by scanning electron microscopy, CD spectroscopy, and computational modeling of the supramolecular structure.

Supramolecular gels - a panorama of low-molecular-weight gelators from ancient origins to next-generation technologies.

Supramolecular gels, self-assembled from low-molecular-weight gelators (LMWGs), have a long history and a bright future. This review provides an overview of these materials, from their use in lubrication and personal care in the ancient world, through to next-generation technologies. In academic terms, colloid scientists in the 19th and early 20th centuries first understood such gels as being physically assembled as a result of weak interactions, combining a solid-like network having a degree of crystalline order with a highly mobile liquid-like phase. During the 20th century, industrial scientists began using these materials in new applications in the polymer, oil and food industries. The advent of supramolecular chemistry in the late 20th century, with its focus on non-covalent interactions and controlled self-assembly, saw the horizons for these materials shifted significantly beyond their historic rheological applications, expanding their potential. The ability to tune the LMWG chemical structure, manipulate hierarchical assembly, develop multi-component systems, and introduce new types of responsive and interactive behaviour, has been transformative. Furthermore, the dynamics of these materials are increasingly understood, creating metastable gels and transiently-fueled systems. New approaches to shaping and patterning gels are providing a unique opportunity for more sophisticated uses. These supramolecular advances are increasingly underpinning and informing next-generation applications - from drug delivery and regenerative medicine to environmental remediation and sustainable energy. In summary, this article presents a panorama over the field of supramolecular gels, emphasising how both academic and industrial scientists are building on the past, and engaging new fundamental insights and innovative concepts to open up exciting horizons for their future use.

Nanoscale assembly of enantiomeric supramolecular gels driven by the nature of solvents.

Understanding the key parameters that control the self-assembly process is critical to predict self-assembly modes in multi-component systems, which will lead to the development of nanofibrous materials with tuneable properties. Enantiomeric amino acid-based low-molecular-weight gelators (LMWGs) were mixed in polar (polar protic) and aromatic apolar (aromatic) solvents and compared to their individual counterparts to probe the effect of solvent polarity on the self-assembly process. Scanning electron microscopy (SEM) reveals that xerogels of individual components display hollow needles in polar protic solvents, while chiral coils are observed in aromatic solvents. In contrast, the multi-component gel displays hollow needle morphologies in both solvents, indicating similar morphologies in polar protic solvents but an entirely different nanostructure for the individual gel networks in aromatic solvents. PXRD experiments performed on the dried gels showed that the nature of the solvents plays a vital role in the co-assembly process of multi-component gels. The self-assembly modes and the gel state structure of the gels are analysed by wide-angle X-ray diffraction (WAXS) and small-angle neutron diffraction (SANS), which reveals that the mixed gel undergoes different co-assembly modes depending on the nature of the solvent systems. This study shows that different co-assembly modes can be achieved for structurally similar components by varying the solvent polarity, demonstrating the importance of solvent choice in the self-assembly process of multi-component gels.

A Zn(ii)-metal ion directed self-healing wide bandgap semiconducting supramolecular metallohydrogel: effective non-volatile memory design for in-memory computing

5-Amino-1-pentanol was used as a low molecular weight gelator to develop a room temperature stable supramolecular hydrogel with Zn(ii)-ions, which offers an efficient resistive random access memory switching application.

Using a biocatalyzed reaction cycle for transient and pH-dependent host-guest supramolecular hydrogels.

The formation of transient structures plays important roles in biological processes, capturing temporary states of matter through influx of energy or biological reaction networks catalyzed by enzymes. These natural transient structures inspire efforts to mimic this elegant mechanism of structural control in synthetic analogues. Specifically, though traditional supramolecular materials are designed on the basis of equilibrium formation, recent efforts have explored out-of-equilibrium control of these materials using both direct and indirect mechanisms; the preponderance of such works has been in the area of low molecular weight gelators. Here, a transient supramolecular hydrogel is realized through cucurbit[7]uril host-guest physical crosslinking under indirect control from a biocatalyzed network that regulates and oscillates pH. The duration of transient hydrogel formation, and resulting mechanical properties, are tunable according to the dose of enzyme, substrate, or pH stimulus. This tunability enables control over emergent functions, such as the programmable burst release of encapsulated model macromolecular payloads.

Hybrid gels by combining low molecular weight glycolipid gelators with agarose: a promising soft material for efficient dye removal

Designing hybrid gels by combining glycolipids and polysaccharides to achieve improved characteristics. These hydrogels can serveas a highly efficient medium for the removal of Congo red.

Exploration of a wide bandgap semiconducting supramolecular Mg(II)-metallohydrogel derived from an aliphatic amine: a robust resistive switching framework for brain-inspired computing

A rapid metallohydrogelation strategy has been developed of magnesium(II)-ion using trimethylamine as a low molecular weight gelator in water medium at room temperature. The mechanical property of the synthesized metallohydrogel material is established through the rheological analysis. The nano-rose like morphological patterns of Mg(II)-metallohydrogel are characterized through field emission scanning electron microscopic study. The energy dispersive X-ray elemental mapping analysis confirms the primary gel forming elements of Mg(II)-metallohydrogel. The possible metallohydrogel formation strategy has been analyzed through FT-IR spectroscopic study. In this work, magnesium(II) metallohydrogel (Mg@TMA) based metal–semiconductor-metal structures have been developed and charge transport behaviour is studied. Here, it is confirmed that the magnesium(II) metallohydrogel (Mg@TMA) based resistive random access memory (RRAM) device is showing bipolar resistive switching behaviour at room temperature. We have also explored the mechanism of resistive switching behaviour using the formation (rupture) of conductive filaments between the metal electrodes. This RRAM devices exhibit excellent switching endurance over 10,000 switching cycles with a large ON/OFF ratio (~ 100). The easy fabrication techniques, robust resistive switching behaviour and stability of the present system makes these structures preferred candidate for applications in non-volatile memory design, neuromorphic computing, flexible electronics and optoelectronics etc.

New Ureas and Amides - An Account of Recent Trends and Developments in Low Molecular Weight Gelators

Abstract: The last 20 years have witnessed major advancements in the field of supramolecular chemistry and have brought us closer to the designing of low molecular weight gelators with desired properties and applications. In that regard, amide- and urea- based gelators comprise a unique class as they are extremely versatile in terms of molecular design and offer a wide range of applications, like anion responsive materials, selective sensing of heavy metal ions, environmental remediation and many more. Both sets of compounds have similar molecular scaffolds, making them an excellent tool to determine the relative importance of the supramolecular interactions involved in the gelation process. Besides, the concept of crystal engineering can also be employed to understand the underlying mechanism of gelation by scrutinizing the interactions and supramolecular assemblies formed by these systems. In this chapter, we focus on various supramolecular assemblies formed by various amide and urea derivatives and their recently reported applications to establish structure-property correlation and their futuristic aspects.

Synthesis and Characterization of pH Triggered Imine Functional Low Molecular Weight Hydrogel

AbstractA C‐3 symmetric imine functional nonpolymeric low molecular weight gelator is prepared using microwave assisted Schiff base reaction. The synthesized molecule forms a hydrogel at 5 wt% under slightly acidic pH. The material was characterized using an inversion tube test, thermogravimetric analysis (TGA), powder X‐ray diffraction (PXRD) and FT‐IR spectroscopy. Rheological studies show the material forms a strong hydrogel with formation of nanofibrils supported by field‐emission scanning electron microscopy (FE‐SEM). To the best of our knowledge this is the first example of imine based trigonal low molecular weight hydrogelator reported.

Cysteine-Silver-Polymer Systems for the Preparation of Hydrogels and Films with Potential Applications in Regenerative Medicine.

Herein, the problem concerning the poorer mechanical properties of gels based on low molecular weight gelators (LMWGs)-L-cysteine and silver nitrate-was solved by the addition of various polymers-polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG)-to the initial cysteine-silver sol (CSS). The physicochemical methods of analysis-viscosimetry, UV spectroscopy, DLS, and SEM-identified that cysteine-silver hydrogels (CSG) based on PVA possess the best rheological properties and porous microstructure (the average pore size is 2-10 µm) compared to gels without the polymer or with PVP or PEG. Such gels are able to form cysteine-silver cryogels (CSC) and then porous cysteine-silver films (CSF) with an average pore size of 10-20 µm and good mechanical, swelling, and adhesion to skin characteristics as long as the structure of CSS particles remains stable. In vitro experiments have shown that hydrogels are non-toxic to normal human fibroblast cells. The obtained materials could potentially be applied to regenerative medicine.

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.

Fabricating Shaped and Patterned Supramolecular Multigelator Objects via Diffusion-Adhesion Gel Assembly.

We report the use of acid-diffusion to assemble core-shell supramolecular gel beads with different low-molecular-weight gelators (LMWGs) in the core and shell. These gel beads grow a shell of dibenzylidenesorbitol-based DBS-COOH onto a core comprising DBS-CONHNH2 and agarose that has been loaded with acetic acid. Diffusion of the acid from the core triggers shell assembly. The presence of DBS-CONHNH2 enables the gel core to be loaded with metal nanoparticles (NPs) as acyl hydrazide reduces metal salts in situ. The pH-responsiveness of DBS-COOH allows responsive assembly of the shell with both temporal and spatial control. By fixing multiple gel beads in a Petri dish, the cores become linked to one another by the assembled DBS-COOH gel shell─a process we describe as diffusion-adhesion assembly. By controlling the geometry of the beads with respect to one another, it is possible to pattern the structures, and using a layer-by-layer approach, 3D objects can be fabricated. If some of the beads are loaded with basic DBS-carboxylate instead of CH3COOH, they act as a "sink" for diffusing protons, preventing DBS-COOH shell assembly in the close proximity. Those beads do not adhere to the remainder of the growing gel object and can be simply removed once diffusion-assembly is complete, acting as templates, and enabling the fabrication of 3D "imprinted" multigel architectures. Preloading the gel beads with AuNPs or AgNPs suspends these functional units within the cores at precisely defined locations within a wider gel object. In summary, this approach enables the dynamic fabrication of shaped and patterned gels with embedded metal NPs─such objects have potential next-generation applications in areas including soft nanoelectronics and regenerative medicine.