Minimum Gelation Concentration Research Articles

Extraction, characterization, and utilization of mung bean starch as an edible coating material for papaya fruit shelf‐life enhancement

AbstractThis research was aimed to investigate the utilization of mung bean starch as an innovative edible coating material to enhance the shelf‐life of cut papaya fruits. The study focused on the extraction process of mung bean starch and its subsequent characterization through various analyses. Particle size (142.3 ± 1.24 nm), zeta potential (−25.52 ± 1.02 mV), morphological images, Fourier transform infrared (FTIR) spectra, and thermal stability (68.36 ± 0.15°C) were assessed to determine the mung bean starch properties. The functional properties, such as bulk density (0.51 ± 0.004 g/cm3) and tapped density (0.62 ± 0.010 g/cm3), angle of repose (21.61°), swelling power (12.26 ± 0.25%), and minimum gelation concentration (4.01 ± 1.25%), were examined to detect its potential as a coating base material. Subsequently, the prepared mung bean starch coating solution (1%, 2%, 3%, 4%, and 5%) was applied to papaya fruits and the coated fruits' physicochemical characteristics evaluated during storage. These characteristics encompassed color, weight loss, pH shifts, total soluble solids, titratable acidity, vitamin C content, fruit firmness, microbial analysis, and sensory attributes. The results revealed that starch coating on papaya maintained its color, reduced weight loss, preserved vitamin C, and delayed firmness loss, enhancing shelf‐life when compared to control sample. These findings demonstrated the effectiveness of mung bean starch coatings in preserving papaya fruits. The research made a significant contribution to the use of mung bean starch as a potential coating material for improving the shelf‐life of papaya fruits. This finding has great promise for the field of food preservation and quality control.

Techno-functional and physicochemical properties of corn flours as potential food ingredients

Background and Objectivescorn plays a crucial role in food security and nutrition. This study aimed to assess the impact of three corn cultivars (Advanta, Leptra, and Porva) and varying particle sizes of flours on estimated glycemic index (eGI), techno-functional properties, and rheological behaviors, crucial in defining their technological properties. FindingsWAI and WSI presented differences among particle sizes for Advanta and Leptra corn flours, whereas Porva flour displayed consistent results regardless of particle sizes. Notably, while Advanta and Leptra did not showed differences in eGI and its fractions, Advanta (174.4 µm) demonstrated the lowest eGI at 32.21, alongside higher water-holding capacity (WHC) compared to wheat flours. Further findings included an initial Emulsification Activity Index (EAI) of 40.55 m2/g and a minimum gelation concentration (LGC) of 12 %. Additionally, rheological characterization indicated a non-Newtonian and pseudoplastic behavior. Conclusionsthis study presented a corn flour with high resistant starch content and low glycemic index with functional properties that could be applied to manufacture healthy food requiring high water solubility, greater emulsification capacity, and water retention capacity greater than conventional flours. Significance and Noveltythe study on intrinsic and extrinsic factors that can modulate the glycemic index of corn becomes crucial. This exploration holds the potential to design healthy commercially viable products.

N-Hydroxyalkanamide Based Organo/hydrogels as Novel Scaffolds for pH-Dependent Metronidazole and Theophylline Release.

The traditional delivery of metronidazole and theophylline presents challenges like bitter taste, variable absorption, and side effects. However, gel-based systems offer advantages including enhanced targeted drug delivery, minimized side effects, and improved patient compliance, effectively addressing these challenges. Consequently, a cost-effective synthesis of N-hydroxyalkanamide gelators with varying alkyl chain lengths was achieved in a single-step reaction procedure. These gelators formed self-assembled aggregates in DMSO/water solvent system, resulting in organo/hydrogels at a minimum gelation concentration of 1.5% w/v. Subsequently, metronidazole and theophylline were encapsulated within the gel core and released through gel-to-sol transition triggered by pH variation at 37 °C, while maintaining the structural-activity relationship. UV-vis spectroscopy was employed to observe the drug release behavior. Furthermore, in vitro cytotoxicity assays revealed cytotoxic effects against A549 lung adenocarcinoma cells, indicating anti-proliferative activity against human lung cancer cells. Specifically, the gel containing theophylline (16HAD+Th) exhibited cytotoxicity on cancerous A549 cells with IC50 values of 19.23 ± 0.6 µg/mL, followed by the gel containing metronidazole (16HAD+Mz) with IC50 values of 23.75 ± 0.7 µg/mL. Moreover, the system demonstrated comparable antibacterial activity against both gram-negative (E. coli) and gram-positive bacteria (S. aureus).

Cationic Azobenzenes as Light-Responsive Crosslinkers for Alginate-Based Supramolecular Hydrogels.

Azobenzene photoswitches are fundamental components in contemporary approaches aimed at light-driven control of intelligent materials. Significant endeavors are directed towards enhancing the light-triggered reactivity of azobenzenes for such applications and obtaining water-soluble molecules able to act as crosslinkers in a hydrogel. Here, we report the rational design and the synthesis of azobenzene/alginate photoresponsive hydrogels endowed with fast reversible sol-gel transition. We started with the synthesis of three cationic azobenzenes (AZOs A, B, and C) and then incorporated them in sodium alginate (SA) to obtain photoresponsive supramolecular hydrogels (SMHGs). The photoresponsive properties of the azobenzenes were investigated by UV-Vis and 1H NMR spectroscopy. Upon irradiation with 365 nm UV light, the azobenzenes demonstrated efficient trans-to-cis isomerization, with complete isomerization occurring within seconds. The return to the trans form took several hours, with AZO C exhibiting the fastest return, possibly due to higher trans isomer stability. In the photoresponsive SMHGs, the minimum gelation concentration (MGC) of azobenzenes was determined for different compositions, indicating that small amounts of azobenzenes could induce gel formation, particularly in 5 wt% SA. Upon exposure to 365 nm UV light, the SMHGs exhibited reversible gel-sol transitions, underscoring their photoresponsive nature. This research offers valuable insights into the synthesis and photoresponsive properties of cationic, water-soluble azobenzenes, as well as their potential application in the development of photoresponsive hydrogels.

Properties of soybean oil oleogels produced from sophorolipid‐derived hydroxy fatty acids, methyl esters and hydrogenated Lesquerella seed oil

AbstractSophorolipids (SL) are glycolipids composed of a sophorose head‐group linked to a hydroxy‐fatty acid tail which makes them a potential source of structurally unique biobased hydroxy fatty acids. Furthermore, Lesquerella is a native southwestern plant that has been commercially cultivated as a replacement for castor seed oil due to high seed oil concentrations of 14‐hydroxy‐eicosenoic acid (14‐OH‐C20:1c11). In this study, SL‐derived hydroxy fatty acids and methyl esters containing 15‐hydroxy‐palmitic acid (15‐OH‐C16), 17‐hydroxy‐stearic acid (17‐OH‐C18), 15‐hydroxy‐palmitic acid methyl ester (15‐OH‐C16ME), 17‐hydroxy‐stearic acid methyl ester (17‐OH‐C18ME), and 13‐hydroxy‐behenic acid methyl ester (13OH‐C22ME) were obtained from the SL produced by two yeast strains. In addition, hydrogenated Lesquerella oil (HLO) was made with ~62% 14‐OH‐eicosanoic (C20) acid (14‐OH‐C20). These materials, along with 12‐hydroxy‐stearic acid (12‐OH‐C18) as a standard for comparison were used to make soybean oil oleogels, and their properties determined. The minimum gelation concentration (MGC) of 12‐OH‐C18 was 1% (wt/wt), while the MGC of 15‐OH‐C16 and 17‐OH‐C18 were 5% and 10%, respectively. The MGC for 15‐OH‐C16ME was 5%, but 17‐OH‐C18ME was unable to form a stable gel at concentrations up to 10%. HLO formed a viscous solution rather than an oleogel, but its crystal morphology underwent a large transformation during storage over a 2.5‐month period, after which it was able to form a stable gel. SL‐based hydroxy fatty acids were able to form oleogels in soybean oil and have the potential to be considered as a new source of low‐molecular weight oleogelators as well as biobased hydroxy fatty acids.

Preparation and Characterization of 3D Printed Objects Based on Different Kefir Gels

AbstractIn this study, kefir-containing healthy snacks were produced by using 3D food printing technique. Although kefir has many important health benefits, its consumption is quite low. It was thought that kefir-containing snacks in attractive shapes produced with a 3D food printer could increase the kefir consumption. For this purpose, disintegrated kefir gels prepared with starch, gelatin and alginate were used as inks. First, the minimum gelation concentration (C*) of each gelator was determined. Then, disintegrated gels with concentrations of C*, C*+1%, and C*+2% were prepared with each gelator and the effect of gelator concentration on printing quality was investigated for each gelator. Printing quality was associated with storage modulus, loss factor and flow behavior, and the minimum gelator concentration required for a suitable formulation for 3D printing (highest printability and dimensional stability) was determined as 5%, 6% and 3% for starch, gelatin and alginate, respectively. Lactobacillus spp. and Lactococcus spp. contents of the starch-based sample were found to be significantly lower than those of fresh kefir and gelatin and alginate-based samples. Sensory properties and consumer appreciation were lower for the gelatin-based sample. Due to the high printing quality (98% printability and 99% dimensional stability), high probiotic content (7.81 and 8.13 log cfu/ml Lactobacillus spp. and Lactococcus spp. content, respectively) and high consumer appreciation (4.71 out of 5 for general acceptance), alginate-based sample (containing 3% alginate) was chosen as the best sample. In conclusion, new, chewable, alive, alternative kefir products were successfully developed for consumers seeking new ways of kefir consumption.

Acid-induced pea protein gels pretreated with media milling: Gelling properties and the formation mechanism

This study explored the effect of stirred media mill (SMM) processing on the acid-induced gelling properties of pea protein. Results showed that SMM treatment enhanced the gel strength from 75.06 g to 183.89 g and increased the water holding capacity from 46.64 % to 73.50 %. The minimum gelation concentration achieved for SMM-treated pea protein was 4 %, significantly lower than that of heat-pretreated pea protein (9 %). SMM decreased protein aggregate size from 104 μm to 180 nm. Microscopy analysis revealed that the small aggregates facilitated the formation of uniform gel networks with tight connections. Linear rheology indicated that small protein aggregates resulted in slower gelation rates with a higher Gʹ for the formed gels. The SMM-pretreated protein gel showed strain hardening, shear thinning behaviors, and satisfactory stability to withstand large-amplitude oscillatory shear. Overall, SMM emerges as a promising technology for producing protein gel products with strong mechanical attributes and customizable rheological properties.

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.

Supramolecular Organo/hydrogel-Fabricated Long Alkyl Chain α-Amidoamides as a Smart Soft Material for pH-Responsive Curcumin Release.

Low-molecular-mass gelators, due to their excellent biocompatibility, low toxicological profile, innate biodegradability and ease of fabrication have garnered significant interest as they self-assemble through non-covalent interactions. In this study, we have designed and synthesized a series of six α-amidoamides by varying the hydrophobic alkyl chain length (C12-C22), which were well characterized using different spectral techniques. These α-amidoamides formed self-assembled aggregates in a DMSO/water solvent system affording organo/hydrogels at 0.66% w/v, which is the minimum gelation concentration (MGC) making them as remarkable supergelators. The various functionalities present in these gelators such as amides and alkyl chain length pave the way toward excellent gelation mechanism through hydrogen bonding and van der Waals interaction as evidenced from FTIR spectroscopy. Notably, as the chain length increased, organo/hydrogels became more thermally stable. Rheological results showed that the stability and strength of these gelators were considerably impacted by variations in chain length. The SEM morphology revealed dense sheet architectures of the organo/hydrogel samples. Organo/hydrogels have a significant impact on the advancement of innovative drug delivery systems that respond to various stimuli, ushering in a new era in pharmaceutical technology. Inspired by this, we encapsulated curcumin, a chemopreventive medication, into the gel core and further released via gel-to-sol transition induced by pH variation at 37 °C, without any alteration in structure-activity relationship. The drug release behavior was observed by UV-vis spectroscopy. Moreover, cell viability and cell invasion experiments demonstrate that the gel formulations exhibit high biocompatibility and low cytotoxicity. Among the tested formulations, 5e+Cur exhibited remarkable efficacy in controlling A549 cell migration, suggesting significant potential for applications in the pharmaceutical industry.

(N-Alkyloxalamido)-Amino Acid Amides as the Superior Thixotropic Phase Selective Gelators of Petrol and Diesel Fuels.

(N-Alkyloxalamido)-amino acid amides 9-12 exhibit excellent gelation capacities toward some lipophilic solvents as well as toward the commercial fuels, petrol and diesel. Gelator 10 exhibits an excellent phase-selective gelation (PSG) ability and also possesses the highest gelation capacity toward petrol and diesel known to date, with minimum gelation concentration (MGC) values (%, w/v) as low as 0.012 and 0.015, respectively. The self-assembly motif of 10 in petrol and toluene gel fibres is determined from xerogel X-ray powder diffraction (XRPD) data via the simulated annealing procedure (SA) implemented in the EXPO2014 program and refined using the Rietveld method. The elucidated motif is strongly supported by the NMR (NOE and variable temperature) study of 10 toluene-d8 gel. It is shown that the triple unidirectional hydrogen bonding between gelator molecules involving oxalamide and carboxamide groups, together with their very low solubility, results in the formation of gel fibres of a very high aspect ratio (d = 10-30 nm, l = 0.6-1.3 μm), resulting in the as-yet unprecedented capacity of gelling commercial fuels. Rheological measurements performed at low concentrations of 10 confirmed the strength of the self-assembled network with the desired thixotropic properties that are advantageous for multiple applications. Instantaneous phase-selective gelation was obtained at room temperature through the addition of the 10 solution to the biphasic mixture of diesel and water in which the carrier solvent was congealed along with the diesel phase. The superior gelling properties and PSG ability of 10 may be used for the development of more efficient marine and surface oil spill recovery and waste water treatment technologies as well as the development of safer fuel storage and transport technologies.

Self-gelation techniques for amoxicillin: formulation and characterization

Self-assembled hydrogels without structural alterations have been a topic of considerable interest. Here, a novel self-assembled amoxicillin hydrogel devoid of any gelling substances or structural modifications was formulated with high stability. The minimum gelator concentration (MGC) was 7.14 wt.% and the gel dissociation temperature (Tgel) was found to be 43.1 °C. The formulated gel was further characterized using FE-SEM, 1H NMR, FT-IR, XRD, rheology, and contact angle measurements, which provided strong evidence in favor of the formation of hydrogel. Furthermore, computational study of gel network formation and kinetic study of amoxicillin release found that the gel exhibited an excellent release rate.

Synthesis and gelation character of photothermal responsive methylcoumarinotripeptidospiropyran

Hydrogel of methylcoumarino-tripeptidospiropyran (MC-TPSP) with a conformational transition at the C-terminus of the peptide was synthesised in this study. This LMWG can be shifted between gel and solution due to the isomerization of spiropyran- and merocyanine-typed MC-TPSP and MC-TPMC, respectively. UV was used to investigate the isomerisation process, and SEM was used to characterise the morphology of the MC-TPMC. The transition temperature was determined to be 75 °C, and the minimum gel concentration was 14.5 mM. On account of its structural biocompatibility and responsive regulatory mechanism, it is anticipated that it will develop into an outstanding bio-functional material.

Development of Thixotropic Molecular Oleogels Comprising Alkylanilide Gelators by Using a Mixing Strategy.

Molecular oleogels have the potential to be used as materials in healthcare applications. However, their design and synthesis are complex, thus requiring simple and effective methods for their preparation. This paper reports on alkylanilides that are low molecular-weight organogelators, which when appropriately mixed with different alkyl chain lengths could result in the formation of mixed molecular gels that exhibit excellent gel-forming ability and mechanical properties. In addition, the single and mixed molecular organogel systems were found to be applicable as single and mixed molecular oleogel systems capable of gelling oils such as olive oil and squalane. This has been found to be true, especially in molecular oleogel systems consisting of squalane, which is used as solvents in healthcare. The mixed squalene-molecular oleogel systems showed an increase in the critical (minimum) gelation concentration from 1.0 to 0.1 wt.% in the single system and an improvement in the thixotropic behavior recovery time. The thixotropic behavior of the molecular oleogels in the mixed system was quantitatively evaluated through dynamic viscoelasticity measurements; however, it was not observed for the single-system molecular oleogels. Scanning electron microscopy of the xerogels suggested that this behavior is related to the qualitative improvement of the network owing to the refinement of the mesh structure. These mixed molecular oleogels, composed of alkylanilides displaying such thixotropic behavior, could be used as candidates for ointment-base materials in the healthcare field.

Self-Healing Oxalamide Organogelators of Vegetable Oil.

The aim of this study was to assess the gelling potential of chiral oxalamide derivatives in vegetable oils. Special emphasis was given to the potential applications of the examined oil gels as sustained delivery systems and as fat substitutes in food products. The applicability of oil gelators is envisaged in food, cosmetics, and the pharmaceutical industry. The regulations requiring the elimination of saturated fats and rising concerns among consumers health motivated us to investigate small organic molecules capable of efficiently transforming from liquid oil to a gel state. The oxalamide organogelators showed remarkable gelation efficiency in vegetable oils, thermal and mechanical stability, self-healing properties, and a long period of stability. The physical properties of the gels were analysed by TEM microscopy, DSC calorimetry, and oscillatory rheology. The controlled release properties of acetylsalicylic acid, ibuprofen, and hydrocortisone were analysed by the LC-MS method. The influence of the oil type (sunflower, soybean, and olive oil) on gelation efficiency of diverse oxalamide derivatives was examined by oscillatory rheology. The oxalamide gelators showed thermoreversible and thixotropic properties in vegetable oils with a minimum gelation concentration of just 0.025 wt%. The substitution of palm fats with gelled sunflower oil applied in cocoa and milk spreads at gelator concentrations lower than 0.2 wt% have shown promising viscoelastic properties compared to that of the original food products.

Amino Acid- and Dipeptide Amphiphile-Based Supramolecular Eutectogels: Soft Materials for Drug Entrapment–Release and Wastewater Treatment

Supramolecular gels prepared in solvents of extreme polarities have received widespread importance across scientific disciplines. In this regard, soft materials based on deep eutectic solvents (DESs) have been receiving notable attention owing to their low toxicity, low volatility, and ability to solubilize hydrophobic drugs and natural products. A DES is a mixture of two or more compounds having a melting point lower than that of the individual components. Reports on supramolecular eutectogels derived from small molecules are very few and serendipitous. Therefore, designing a low-molecular-weight eutectogelator (LMWEG) remains challenging and demands comprehensive structure–property correlation. To this end, we have developed amino acid- and dipeptide amphiphile-based LMWEGs that immobilized choline chloride/phenylacetic acid-based DES with a minimum gelation concentration (MGC) of 0.5–10.0%, w/v. Variation of amino acids, protecting groups at the N-terminal, and hydrophobic chain length of the gelator delineated the crucial influence of the hydropathy index of amino acids and thereby the hydrophilic–lipophilic balance in eutectogelation. Replacement of the aromatic moiety in the gelator and/or in the DES with an aliphatic one ascertained the optimal necessity of aromaticity for efficient eutectogelation. Eutectogels were thermoreversible and showed considerable thermal stability (Tgel ∼ 50–70 °C). Spectroscopic and microscopic studies confirmed the fiber-like morphology of the eutectogels and the participation of hydrogen bonding in eutectogelation. Newly derived eutectogels exhibited considerably good mechanical strength (γc ∼ 7.5–16.5%) and interesting injectable as well as thixotropic properties. The ability to adsorb cationic and anionic dyes by the eutectogels ensured their potential in wastewater treatment. Importantly, these supramolecular eutectogels can be used in drug delivery owing to their ability to entrap the hydrophobic drug curcumin and subsequently its pH-dependent sustained release.

Structural modification induced hydrogelation and antibacterial properties in supramolecular gels

Low molecular weight N-oxide hydrogelators were synthesized by incorporating N-oxide moieties into hydrazone/semicarbazone groups, which was obtained by the modification of the pyridyl functional groups of hydrazone/semicarbazone compounds. The properties of the N-oxide compounds were compared with the pyridyl compounds, and the results showed that the structural modification of the pyridyl-hydrazides to pyridyl-N-oxide hydrazides enhanced the water solubility of the hydrazone gelator. The relative stability of the gels was analyzed by minimum gelation concentration, gel-to-sol transition temperature and rheology, and the morphologies were analyzed by scanning electron microscope (SEM). The stimuli-responsive properties of the gels in the presence of various salts were analyzed by adding different potassium salts, and the hydrazone gels showed a selective response towards cyanide ion. The hydrazone gels displayed antibacterial activity against both Gram-positive and Gram-negative bacteria, whereas semicarbazone gels were inactive. Furthermore, the gels were found to be biocompatible, which can be used as antibacterial agents.

A Heat Transfer Model and Supporting Experiments to Guide the Uniform Gelation of Molecular Oleogels During Scale-up.

The quest for novel vegetable oil structuring strategies has been progressing since the discovery of the deleterious impacts of trans fats. Although oleogelation using bioderived molecular gelators has been proven to be successful as an alternative to traditional hydrogenation methods, efforts are needed to meet the industrial requirements. A major constraint during the fabrication of oleogels is to achieve consistency in physical properties during scale-up. Experiments showed that gelation fails to occur when larger volumes were prepared based on the minimum gelation concentration (MGC) of gelators, determined using the smallest oil volume (1 mL), a general laboratory practice. This observation was consistent with all the molecular gelators used in this study; sorbitol dioctanoate, mannitol dioctanoate, and 12-hydroxystearic acid. To understand this behavior, a mathematical model was developed since gelator network propagation is governed by the cooling rate. The model indicates that maintenance of a minimal thermal gradient via uniform heat dissipation and gelation time is necessary to achieve homogeneous gel propagation across the vial. With these predictions, we hypothesized and confirmed that oleogels with constant surface area-to-volume ratio could result in identical gelation times and consistent physical properties (MGC, melting temperature, melting enthalpy, yield stress, solid phase content, and oil binding capacity) during scale-up.

Self-assembled Trehalose Amphiphiles as Molecular Gels: A Unique Formulation to Wax-free Cosmetics.

Trehalose has been used as an emollient and antioxidant in cosmetics. However, we aimed to explore trehalose amphiphiles as oil structuring agents for the preparation of gel-based lip balms as part of wax-free cosmetics. This article describes the synthesis of trehalose fatty acyl amphiphiles and their corresponding oleogel-based lip balms. Trehalose dialkanoates were synthesized by esterifying the two primary hydroxyls of trehalose with fatty acids (C4-C12) using a facile, regioselective lipase catalysis. The gelation potential of as-synthesized amphiphiles was evaluated in organic solvents and vegetable oils. Stable oleogels were subjected to X-ray diffraction (XRD), thermal (DSC), and rheological studies and further used for the preparation of lip balms. Trehalose dioctanoate (Tr8), trehalose didecanoate (Tr10) were found to be super gelators as their minimum gelation concentration is ≤ 0.2 wt%. XRD studies revealed their hexagonal columnar molecular packing while forming the fibrillar networks. Rheometry proved that the fatty acyl chain length of amphiphiles can influence the strength and flow properties of oleogels. Further rheometry (at 25 °C, 37 °C, and 50 °C) and DSC studies have validated that Tr8- and Tr10-based oleogels are stable for commercial applications. Tr8- and Tr10-based olive oil oleogels were used for the preparation of lip balms. The preliminary results suggested that the cumulative effect of trehalose's emolliency and vegetable oil gelling nature can be achieved with trehalose amphiphiles, specifically, Tr8 and Tr10. This study has also demonstrated that Tr8- and Tr10-based lip balms can be used as an alternative to beeswax and plant wax lip balms, indicating their huge potential to succeed as a new paradigm to formulate wax-free cosmetics.

An Amino Acid‐Based Thixotropic Hydrogel: Tuning of Gel Recovery Time by Mechanical Shaking

AbstractFmoc‐Trp‐OH (Fmoc: N‐fluorenylmethoxycarbonyl; Trp‐OH: L‐Tryptophan) undergone hydrogelation at 50 mM phosphate buffer saline of pH 7.4 with a minimum gelation concentration (MGC) of 0.25 % w/v after 12 to 15 hours. However, the hydrogel formation kinetics can be faster just by mechanical hand shaking of the hydrogelator solution during the hydrogel preparation procedure. The shake hydrogel is thermally and mechanically more stable than the non‐shake hydrogel. These hydrogels have been characterized thoroughly by Tgel estimations, UV‐Vis spectroscopy, Fluorescence spectroscopy, Fourier Transform‐Infra Red (FT‐IR) Spectroscopy, X‐ray diffractions (XRD), Field Emission Scanning Electron Microscopy (FE‐SEM) and rheology. This amino acid‐based hydrogel is thixotropic in nature and interestingly without doping any foreign materials into the hydrogel, the gel reformation kinetics can be faster just by number of times breaking of the hydrogel by mechanical hand shaking followed by keeping the hydrogel glass vial at rest. This holds future promise to develop supramolecular mechanocatalyst for various functional group transformation reactions in water through green and sustainable chemistry pathways.

Stimuli-Responsive Properties of Supramolecular Gels Based on Pyridyl-N-oxide Amides

The nature of functional groups and their relative position and orientation play an important role in tuning the gelation properties of stimuli-responsive supramolecular gels. In this work, we synthesized and characterized mono-/bis-pyridyl-N-oxide compounds of N-(4-pyridyl)nicotinamide (L1-L3). The gelation properties of these N-oxide compounds were compared with the reported isomeric counterpart mono-/bis-pyridyl-N-oxide compounds of N-(4-pyridyl)isonicotinamide. Hydrogels obtained with L1 and L3 were thermally and mechanically more stable than the corresponding isomeric counterparts. The surface morphology of the xerogels of di-N-oxides (L3 and diNO) obtained from the water was studied using scanning electron microscopy (SEM), which revealed that the relative position of N-oxide moieties did not have a prominent effect on the gel morphology. The solid-state structural analysis was performed using single-crystal X-ray diffraction to understand the key mechanism in gel formation. The versatile nature of N-oxide moieties makes these gels highly responsive toward an external stimulus, and the stimuli-responsive behavior of the gels in water and aqueous mixtures was studied in the presence of various salts. We studied the effect of various salts on the gelation behavior of the hydrogels, and the results indicated that the salts could induce gelation in L1 and L3 below the minimum gelator concentration of the gelators. The mechanical properties were evaluated by rheological experiments, indicating that the modified compounds displayed enhanced gel strength in most cases. Interestingly, cadmium chloride formed supergelator at a very low concentration (0.7 wt% of L3), and robust hydrogels were obtained at higher concentrations of L3. These results show that the relative position of N-oxide moieties is crucial for the effective interaction of the gelator with salts/ions resulting in LMWGs with tunable properties.