Low Molecular Weight Gelators Research Articles

Zn(II)-based mechanically flexible metallosupramolecular network: Investigating rheology, morphology, anti-bacterial effect and semiconducting device performances

Synthesis of supramolecular Zn(II)-metallogel of succinic acid with N,N′-dimethyl formamide (DMF) solvent has been explored in this present study. Succinic acid is used as a low molecular weight gelator (LMWG) and DMF acts as a metallogel-immobilized solvent-media. Mechanical flexibility, viscous, and elastic behaviours of the metallogel are characterized by exhaustive rheological experiments. Different rheological parameters like storage modulus (G′) and loss modulus (G″) are evaluated for certain regions of shear strain and angular frequency. The morphological decoration of xerogel material obtained from Zn(II)-based metallosupramolecular gel (i.e., Zn-Succinic) has been visualized through field emission scanning electron microscope (FESEM). Energy dispersive X-ray analysis (EDX) verifies the active involvement of metallogel-forming chemical constituents. The flexible metallosupramolecular scaffold-construction strategy has been unveiled through infrared spectroscopic data and ESI-Mass investigations. The antibacterial potency of Zn(II)-directed metallogel has also been verified against several Gram-positive bacteria (i.e., Bacillus cereus (ATCC 13061), Bacillus subtilis (MTCC 121), Listeria monocytogenes (MTCC 657), Staphylococcus aureus (MTCC 96)), and two Gram-negative bacterial strains (i.e., Salmonella typhimurium (MTCC 98) and Escherichia coli (MTCC 1667)). Even, Zn-Succinic metallogel exhibits Schottky diode behaviour with a significant non-linear rectifying nature in I-V curve, proving the semiconducting diode features with electrical parameters.

Formulation and Release of Active Pharmaceutical Ingredients using a Supramolecular Self-healing Two-component Gel.

A two-component low-molecular-weight gelator (LMWG) formed from a modified amino acid and an aldehyde was formulated with active pharmaceutical ingredients (APIs). Basic APIs (propranolol, atropine) can be mixed with the LMWG prior to gel assembly while acidic APIs (naproxen, rosuvastatin) inhibit assembly by disrupting the LMWG imine bond and were loaded by diffusion after gel assembly. For diffusion-loaded gels, the API in the liquid-like phase was rapidly released, with the remainder, interacting with gel fibres, retained in the gel. Rosuvastatin release was particularly low with STD NMR indicating interactions between the aromatic ring and the self-assembled gel network. Propranolol also interacted with the gel via its aromatic unit, and its release led to gel erosion. Using agarose as a polymer gelator additive reinforced the gel, restricting erosion. In contrast, atropine was readily released over a period of hours - it is primarily in the liquid-like phase with STD NMR indicating no interactions with the gel network. The atropine-loaded gel retained its thixotropic properties. Overall, APIs must be carefully chosen to optimise formulation/release. Of the APIs investigated, atropine has most potential for further development. Atropine has applications in treating myopia, and our results suggest potential ophthalmic applications of supramolecular gels.

Fabrication of Ag Nanoparticle-Embedded Covalent Organic Frameworks for Oil Gel with Long-Term Stability and High Lubrication Performance.

In previous reports, covalent organic frameworks (COFs) have demonstrated significant potential as lubricant additives. Herein, we embedded Ag nanoparticles in the DT-COF (polycondensation polymer of 2,5-dihydroxyterephthalaldehyde and 4,4',4″-(1,3,5-triazine-2,4,6-triyl) trianiline) matrix via the ball milling method and utilized this composite (Ag@DT-COF) as an additive for supermolecule oil gel. The low molecular weight gelator effectively mitigates the dispersion challenges of COFs in lubricant oil, while the embedded Ag nanoparticles enhance the repairing effect and antipressure performance of the lubricant. The resulting Ag@DT-COF gel exhibits a reduction in the average friction coefficient and wear volume of base oil by 46.0% and 87.5%, respectively, and increases the load-carrying capacity to 750 N. The remarkable tribological properties are attributed to the easy adsorption of DT-COF, antiwear characteristic of Ag nanoparticles, and the gelator that ensures the long-term stability of oil gel.

Supramolecular gels: a versatile crystallization toolbox.

Supramolecular gels are unique materials formed through the self-assembly of molecular building blocks, typically low molecular weight gelators (LMWGs), driven by non-covalent interactions. The process of crystallization within supramolecular gels has broadened the scope of the traditional gel-phase crystallization technique offering the possibility of obtaining crystals of higher quality and size. The broad structural diversity of LMWGs allows crystallization in multiple organic and aqueous solvents, favouring screening and optimization processes and the possibility to search for novel polymorphic forms. These supramolecular gels have been used for the crystallization of inorganic, small organic compounds of pharmaceutical interest, and proteins. Results have shown that these gels are not only able to produce crystals of high quality but also to influence polymorphism and physicochemical properties of the crystals, giving rise to crystals with potential new bio- and technological applications. Thus, understanding the principles of crystallization in supramolecular gels is essential for tailoring their properties and applications, ranging from drug delivery systems to composite crystals with tunable stability properties. In this review, we summarize the use of LMWG-based supramolecular gels as media to grow single crystals of a broad range of compounds.

3D-Printing Multi-Component Multi-Domain Supramolecular Gels with Differential Conductivity.

We report the use of wet-spinning to 3D-print gels from low-molecular-weight gelators (LMWGs) based on the 1,3 : 2,4-dibenzylidenesorbitol (DBS) scaffold. Gel stripes assembled from DBS-CONHNH2 and DBS-COOH are printed, and their conductivities assessed. Printed gels based on DBS-CONHNH2 can be loaded with Au(III), which is reduced in situ to form embedded gold nanoparticles (AuNPs). The conductivity of these gels increases because of electron transport mediated by the AuNPs, whereas the conductivity of DBS-COOH, which does not promote AuNP formation, remains lower. We then fabricate multi-component gel patterns comprised of spatially well-defined domains of printed DBS-CONHNH2/AuNP (higher conductivity) and DBS-COOH (lower conductivity) resulting in soft multi-domain materials with differential conductivity. Such materials have future prospects in applications such as soft nanoelectronics or tissue engineering.

3D‐Printing Multi‐Component Multi‐Domain Supramolecular Gels with Differential Conductivity

AbstractWe report the use of wet‐spinning to 3D‐print gels from low‐molecular‐weight gelators (LMWGs) based on the 1,3 : 2,4‐dibenzylidenesorbitol (DBS) scaffold. Gel stripes assembled from DBS‐CONHNH2 and DBS‐COOH are printed, and their conductivities assessed. Printed gels based on DBS‐CONHNH2 can be loaded with Au(III), which is reduced in situ to form embedded gold nanoparticles (AuNPs). The conductivity of these gels increases because of electron transport mediated by the AuNPs, whereas the conductivity of DBS‐COOH, which does not promote AuNP formation, remains lower. We then fabricate multi‐component gel patterns comprised of spatially well‐defined domains of printed DBS‐CONHNH2/AuNP (higher conductivity) and DBS‐COOH (lower conductivity) resulting in soft multi‐domain materials with differential conductivity. Such materials have future prospects in applications such as soft nanoelectronics or tissue engineering.

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.

Chemiluminescent Reaction Induced by Mixing of Fluorescent-Dye-Containing Molecular Organogels with Aqueous Oxidant Solutions.

Chemiluminescence in solution-based systems has been extensively studied for the chemical analysis of biomolecules. However, investigations into the control of chemiluminescence reactions in gel-based systems, which offer flexibility in reaction conditions (such as the softness of the reaction environment), have only recently begun in polymer materials, with limited exploration in low-molecular-weight gelator (LMWG) systems. In this study, we investigated the chemiluminescence behaviors in the gel states using LMWG systems and evaluated their applicability to fluorescent-dye-containing molecular organogel systems/oxidant-containing aqueous systems. Using diethyl succinate organogels composed of 12-hydroxystearic acid as a molecular organogelator, we examined the fluorescent properties of various fluorescent dyes mixed with oxidant aqueous solutions. As the reaction medium transitioned from the solution to the gel state, the emission color and chemiluminescence duration changed significantly, and distinct characteristics were observed, for each dye. This result indicates that the chemiluminescence behavior differs significantly between the solution and gel states. Additionally, visual inspection and dynamic viscoelastic measurements of the mixed fluorescent dye-containing molecular gels and oxidant-containing aqueous solutions confirmed that the chemiluminescence induced by the mixing occurred within the gel phase. Furthermore, the transition from the solution to the gel state may allow for the modulation of the mixing degree, thereby enabling control over the progression of the chemiluminescence reaction.

Naphthalimide-linked carbazole derivative: Synthesis, gelation and naked eye detection of Cu2+ and Fe3+-ions under different conditions

Naphthalimide-labeled carbazole derivative NC has been synthesized, characterized, and tested for sensing of metal ions in different conditions. Compound NC acts as Low Molecular Weight Gelator (LMWG) and exhibits gelation from aqueous DMF, DMSO, and 1,4-dioxane. Morphologies of the gels are fibrous and their packing varies with the nature of the gelling solvent. All the gels reveal good viscoelastic response. Based on the different morphologies, the rheological behavior of gels differs. DMSO/H2O and DMF/H2O gels with lower tanδ values intimate considerable mechanical strength. As an application, the brown gel derived from DMF: H2O (1:1, v/v) is Cu2+ and Fe3+ responsive involving a gel-to-sol conversion, and validates the naked eye detection. The Fe3+-broken gel is is sharply distinguished from the Cu2+-broken gel by adding F− ions. In CH3CN, compound NC also shows interaction with Cu2+ and Fe3+ ions through a color change (yellow to colorless) and fluorescence quenching. The metal ions are fluorimetrically differentiated in aqueous CH3CN using F− ions although compound NC was incapable of showing selectivity in aqueous CH3CN. The detection limits for Cu2+ and Fe3+ ions are calculated using emission data as 2.02 x 10−7 M and 2.09 x 10−7 M, respectively. Compound NC also recognizes Cu2+ and Fe3+ ions through paper strips under UV light and the ions are distinguished by F− solution. The binding and spectroscopic observations are explained by theoretical calculations. The structure of the copper complex as obtained from single crystal x-ray analysis gives additional support to the observation.

Photopatterned Hybrid Supramolecular/Polymer Hydrogels for Controlled Heparin Release and Stem Cell Growth

AbstractThis paper reports hybrid gels combining a low‐molecular‐weight gelator (LMWG) and a photoinitiated crosslinked polymer gel (PG). The presence of the PG enhanced the stiffness and strength of the gel. The gels were loaded with heparin, and in the hybrid gel, the interpenetrated LMWG and PG networks somewhat restricted its release. In terms of stem cell growth, the hybrid gel significantly improved the performance of the PG because of the presence of the LMWG, which is an excellent substrate for stem cells in its own right. Furthermore, the presence of heparin in the hybrid gels also enhanced stem cell proliferation over longer timescales. Finally, these gels were photopatterned within the well‐plates used for tissue culture, with patterning helping control stem cell proliferation. In summary, these hybrid gels combine the advantageous features of both LMWG and PG: rheological performance is endowed by the PG with stem cell compatibility provided by the LMWG. The hybrid gels also control the release of the bioactive agent heparin and have capacity to be shaped and patterned. Patterned gels such as these, capable of directing stem cell growth, have potential in regenerative medicine.

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 ureabased 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 article, 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.

Self‐Gelling Quinone‐Based Wearable Microbattery

AbstractWearable power sources are envisioned since their development promises to speed up the widespread application of wearable devices in different areas, such as healthcare, smart‐city management, and robotics. Here, the 4′‐((9,10‐anthraquinone‐2‐yl)oxy)butyrate (2‐BEAQ), an anthraquinone derivative, is synthesized, and further applied for producing a redox‐active shear‐thinning hydrogel (BEAQ‐gel). The gel comprises cylindrical aggregates of 2‐BEAQ molecules dispersed within a water matrix, interconnected through ionic, ion‐dipole, and hydrogen bonding interactions. BEAQ‐gel also presents interesting rheological characteristics and composition tunability since it can be produced in a large range of concentrations. This improved redox 3D hierarchical network also makes the network capable of retaining high quantities of potassium hydroxide, thereby enhancing conductivity. By coupling BEAQ‐gel with Ferricyanide the development of a wearable battery is demonstrated, which exhibits an output voltage of 0.89 V even when bent at a 180° angle, making it suitable for powering wearable devices. This work presents an innovative alternative for the production of wearable devices, from the design of the anode and cathode materials to the wearable casing and demonstrates the use of redox‐active low‐molecular‐weight‐gel (LMWG) as an active material of a microbattery giving a valuable glimpse to the further development of wearable energy storage devices.

Development of a novel self-healing Zn(II)-metallohydrogel with wide bandgap semiconducting properties for non-volatile memory device application

A rapid and effective strategy has been devised for the swift development of a Zn(II)-ion-based supramolecular metallohydrogel, termed Zn@PEH, using pentaethylenehexamine as a low molecular weight gelator. This process occurs in an aqueous medium at room temperature and atmospheric pressure. The mechanical strength of the synthesized Zn@PEH metallohydrogel has been assessed through rheological analysis, considering angular frequency and oscillator stress dependencies. Notably, the Zn@PEH metallohydrogel exhibits exceptional self-healing abilities and can bear substantial loads, which have been characterized through thixotropic analysis. Additionally, this metallohydrogel displays injectable properties. The structural arrangement resembling pebbles within the hierarchical network of the supramolecular Zn@PEH metallohydrogel has been explored using FESEM and TEM measurements. EDX elemental mapping has confirmed the primary chemical constituents of the metallohydrogel. The formation mechanism of the metallohydrogel has been analyzed via FT-IR spectroscopy. Furthermore, zinc(II) metallohydrogel (Zn@PEH)-based Schottky diode structure has been fabricated in a lateral metal–semiconductor-metal configuration and it’s charge transport behavior has also been studied. Notably, the zinc(II) metallohydrogel-based resistive random access memory (RRAM) device (Zn@PEH) demonstrates bipolar resistive switching behavior at room temperature. This RRAM device showcases remarkable switching endurance over 1000 consecutive cycles and a high ON/OFF ratio of approximately 270. Further, 2 × 2 crossbar array of the RRAM devices were designed to demonstrate OR and NOT logic circuit operations, which can be extended for performing higher order computing operations. These structures hold promise for applications in non-volatile memory design, neuromorphic and in-memory computing, flexible electronics, and optoelectronic devices due to their straightforward fabrication process, robust resistive switching behavior, and overall system stability.

Harnessing Glycolipids for Supramolecular Gelation: A Contemporary Review.

Within the scope of this review, our exploration spans diverse facets of amphiphilic glycolipid-based low-molecular-weight gelators (LMWGs). This journey explores glycolipid synthesis, self-assembly, and gelation with tailorable properties. It begins by examining the design of glycolipids and their influence on gel formation. Following this, a brief exploration of several gel characterization techniques adds another layer to the understanding of these materials. The final section is dedicated to unraveling the various applications of these glycolipid-based supramolecular gels. A meticulous analysis of available glycolipid gelators and their correlations with desired properties for distinct applications is a pivotal aspect of their investigation. As of the present moment, there exists a notable absence of a review dedicated exclusively to glycolipid gelators. This study aims to bridge this critical gap by presenting an overview that provides novel insights into their unique properties and versatile applications. This holistic examination seeks to contribute to a deeper understanding of molecular design, structural characteristics, and functional applications of glycolipid gelators by offering insights that can propel advancements in these converging scientific disciplines. Overall, this review highlights the diverse classifications of glycolipid-derived gelators and particularly emphasizes their capacity to form gels.

Mouldable multicomponent low molecular weight supergelators

ABSTRACT A significant drawback of gels formed from low molecular weight gelators (LMWGs) is their typically poor mechanical stability due to the weak non-covalent interactions responsible for forming the gel. Here, we present a rare example of bicomponent gels prepared from LMWGs that show excellent mechanical stability even at <0.7 wt.% gelator loading. The gels can be moulded into any desired shape, without creep deformation. Dynamic diffusion of a guest, like β-carotene, from a spiked gel into its submerged solvent environment is explored through UV–vis spectrophotometry and NMR techniques, showing that the integrity of the gel network remains in the presence of the guest.

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.