Organogel Formation Research Articles

Hierarchical Self-Assembly of Achiral Amino Acid Derivatives into Dendritic Chiral Nanotwists

The organogel formation and self-assembly of a glycine-based achiral molecule were investigated. It has been found that the compound could gel organic solvents either at a lower temperature with lower concentration or at room temperature with higher concentration, which showed different self-assembled nanostructures. At a low temperature of -15 °C, the compound self-assembled into fibrous structures, whereas it formed distinctive flat microbelts at room temperature. When the organogel with nanofibers formed at -15 °C was brought into an ambient condition, chiral twist nanostructures were immediately evolved, which subsequently transferred to a giant microbelt through a hierarchical dendritic twist with the time. Although the compound is achiral, it formed chiral twist with both left- and right-handed twist structures simultaneously. When a trace analogical chiral trigger, L-alanine or D-alanine derivative, was added, a complete homochiral dendritic twist was obtained. Interestingly, a reverse process, i.e. the transformation of the microbelts into twists, could occur upon dilution of the organogel with microbelt structure. During the dilution, both left- and right-handed chiral twists could be formed again. Interestingly, the same branch from the microbelt formed the twist with the same handedness. A combination of the density functional theory (DFT), molecular mechanics (MM), and molecular dynamics (MD) simulations demonstrates that the temperature-induced twisting of the bilayer is responsible for the morphological transformation and evolution of the dendrite twist. This research sheds new light on the hierarchical transformation of the chiral structures from achiral molecules via controlled self-assembly.

The correlation of microstructure morphology with gelation mechanism for sodium soaps in organic solvents

Using sodium caprylate as a model molecule, in the present work, we unraveled the gelation mechanism of sodium soaps in organic solvents from its correlation with the microstructure morphology. It is interesting to find that both the formation of organogels and radiation-like gel fibers are controlled by Na+ concentration in the system. As the gel-activator, the sodium ions not only accelerate the gelation process and enhance the gel networks, but also induce the morphology transformation from fibers to radiative nanoribbons. TEM and XRD characterization reveals that the Na+ enhanced effect should be ascribed to the structure transformation of sodium caprylate from layers to hexagonal packing, due to its reduced inter-separation after the addition of Na+. Based on these results, the gelation mechanism of sodium soaps has been also proposed.

Large‐Scale Honeycomb Microstructures Constructed by Platinum–Acetylide Gelators through Supramolecular Self‐Assembly

A series of new platinum-acetylide complexes 4a-4c and 6a-6c were synthesized and characterized. The gelation properties of these compounds were investigated by the "stable-to-inversion-of-test-tube" method. Unlike compounds 4a-4c, amides 6b and 6c can gelate a variety of nonpolar alkyl solvents; this result indicates that the hydrogen bonds between amide groups play an important role in the formation of metallic organogels. Interestingly, compared to the typical morphologies of known organogels or metallic organogels, compounds 6b and 6c exhibited highly ordered honeycomb patterns on a large-scale (determined by SEM analysis). To investigate the driving forces for the self-assembly process, concentration-dependent (1)H NMR spectroscopy and a competitive experiment between hydrogen bonds were used to confirm that intermolecular hydrogen bonding play an essential role during the formation of supramolecular aggregates.

New Lecithin Organogels from Lecithin/Polyglycerol/Oil Systems

New liquid substances that induce the formation of lecithin organogels composed of reverse worm-like micelles were studied. The phase behavior and rheological properties of lecithin/polyglycerol (PGL)/oil systems were investigated in detail; the polymerization degrees of the glycerol residues were 3, 4, 6, 10, 20, and 40. From the partial phase diagrams of the lecithin/PGL/n-decane systems, it was apparent that highly viscoelastic reverse worm-like micelles formed upon the addition of small amounts of the PGL, except in the case of the PGL with a polymerization degree of 40. Steady-flow viscosity measurements showed that the zero-shear viscosity (η₀) of the reverse worm-like micelles rapidly increased with the concentration and polymerization degree of the PGLs, reaching a maximum value that was 750,000 times the viscosity of n-decane and thus resulting in the growth of these micelles. It is noteworthy that the η₀ values of lecithin organogels formed using PGLs were higher than the η₀ value of the lecithin organogel formed using glycerol (GL). From dynamic viscoelasticity measurements, it was shown that the viscoelastic behavior of the reverse worm-like micelles was consistent with the single Maxwell model, which is the basic model of a viscoelastic body. It follows from this study that PGLs are useful liquids because they can induce the formation of lecithin organogels with high viscoelasticity, as do other liquids such as water, glycerol, ethylene glycol, and formamide.

Estimation of organogel formation and influence of solvent viscosity and molecular size on gel properties and aggregate structures

This paper proposes a simple method for predicting organogel formation, and highlights the important role played by solvent viscosity (η) and molecular size (V) in influencing the gel properties and the aggregate structures of methyl 4,6-O-(p-chlorobenzylidene)-α-D-glucopyranoside (MPBG, a model gelator) in different solvents. The research of gelation tests shows that a Teas plot derived from solubility parameters can be used to predict the behaviour of a known gelator in untested solvents. The method has successfully been tested on eight gelators reported in the literature and on untested solvents in the gelation of MPBG. The research on solvent role reveals that the aggregate morphologies of MPBG and the main factors determining the gel properties are obviously different in monohydric alcohols and aromatic hydrocarbons. According to SEM images and X-ray diffraction patterns, in monohydric alcohols with high viscosity, the self-assembly of MPBG is a diffusion-limited aggregation process resulting from solvent viscosity. Furthermore, it is found that solvent viscosity, compared with the secondary role of polar solubility parameter (δa), plays a key role in determining the morphologies of aggregates, the sol–gel phase-transition temperature (Tgel) and the gelation number (Ngel). In contrast, for aromatic hydrocarbon gels, solvent molecular size is very important in determining Tgel and Ngel although δa is the key factor.

Development of span 80-tween 80 based fluid-filled organogels as a matrix for drug delivery

Background:Organogels are defined as 3-dimensional networked structures which immobilize apolar solvents within them. These gelled formulations are gaining importance because of their ease of preparation and inherent stability with improved shelf life as compared to the ointments.Aim:Development of span 80–tween 80 mixture based organogels for the first time by fluid-filled fiber mechanism.Materials and Methods:Span 80 and tween 80 were used as surfactant and co-surfactant, respectively. The surfactant mixtures were dissolved in oil followed by the addition of water which led to the formation of organogels at specific compositions. The formulations were analyzed by microscopy, X-ray diffraction (XRD), time-dependent stability test and accelerated thermal stability test by thermocycling method. Ciprofloxacin, a fourth-generation fluoroquinolone, was incorporated within the organogels. The antimicrobial activity of the drug loaded organogels and in vitro drug release from the gels was also determined.Results and Conclusions:Microscopic results indicated that the gels contained clusters of water-filled spherical structures. XRD study indicated the amorphous nature of the organogels. The release of the drug was found to be diffusion controlled and showed marked antimicrobial property. In short, the prepared organogels were found to be stable enough to be used as pharmaceutical formulation.

Triazole-Modified Triphenylene Derivative: Self-Assembly and Sensing Applications

Triphenylene-based discotic liquid crystal 3 bearing 1,2,3-triazole groups has been synthesized using "click" chemistry. Discotic mesogen 3 has good thermal stability, and incorporation of triazole groups results in stabilization of columnar mesophases down to room temperature and formation of organogels in cyclohexane and mixed solvents such as hexane and dichloromethane (4:1 v/v). Characterization of the organogel of 3 in cyclohexane revealed a porous network. However, presence of Cd(2+) ions in solution obstructed the self-assembly of this derivative due to preferred interactions between Cd(2+) ions and triphenylene units over π-π interactions among triphenylene groups. Further, strong emission of derivative 3 in its nonaggregated form makes it a promising fluorescence sensory material for nitroaromatic compounds.

Organogel Formation of Soybean Oil with Waxes

AbstractMany waxes including plant waxes and animal waxes were evaluated for the gelation ability toward soybean oil (SBO) and compared with hydrogenated vegetable oils, petroleum waxes and commercial non‐edible gelling agents to understand factors affecting the gelation ability of a gelator. Sunflower wax (SW) showed the most promising results and all SW samples from three different suppliers could make a gel with concentrations as low as 0.5 wt%. Candelilla wax and rice bran wax also showed good gelation properties, which, however, varied with different suppliers. Gelation ability of a wax is significantly dependant on its purity and detailed composition. A wax ester with longer alkyl chains has significantly better gelation ability toward SBO than that with shorter alkyl chains indicating that the chain length of a component in a wax such as wax ester is an important factor for gelation ability. The SW–SBO organogel showed increased melting point with increased SW content, showing the melting point range from about 47 to 65 °C with 0.5–10 wt% SW. The effects of cooling rate on crystal size and firmness of a gel were investigated. The dependence of firmness on cooling rate was so significant that the desired texture of an organogel could be achieved by controlling the cooling rate in addition to controlling the amount of gelling agent. This research reveals that a small amount of food grade plant waxes including SW may replace a large amount of the hardstock containing trans‐fat or saturated fat.

Mechanism of Organogel Formation from Mixed-Ligand Silver (I) Carboxylates

Ag(I) carboxylate gelators with mixed-ligands were systemically investigated to understand the mechanism of the organic gel formation. The gelators constructed 3-D networks of nanometer-sized thin fibers which facilitated gel formation in various aromatic organic solvents, even at very low concentrations. The loss of reflection peaks in the X-ray diffraction data indicated the reduction of strong interactions between the long alkyl chains as the Ag(I) carboxylates formed gels by maximizing their interactions with the organic solvents. The gelation temperature () was measured to explore the interaction between the gelator molecules and solvents depending on their composition and concentration. Based on the gelation phenomena, a dissociation/re-association mechanism was proposed.

New dimeric cholesteryl-based A(LS)2 gelators with remarkable gelling abilities: Organogel formation at room temperature

Three new dimeric cholesterol-based compounds of A(LS)2 type, where A stands for aromatic component, S steroid moiety, and L a linker connecting the two units, have been designed and prepared. Gelation test in 30 solvents demonstrated that the compounds can gel some of the solvents and form 37 gels, of which 16 form spontaneously at room temperature (∼25°C). These gels possess smart thixotropic properties as revealed by rheological studies. FTIR and 1H NMR measurements revealed that hydrogen bonding is an important driving force for the formation of the gel networks. XRD analysis demonstrated that unlike commonly found layered structures adopted by dimeric cholesterol-based low-molecular mass gelators (LMMGs), one of the gelators created in this study adopts a hexagonal packing structure in its benzene gel.

Hydration of Gelatin Molecules in Glycerol–Water Solvent and Phase Diagram of Gelatin Organogels

We present a systematic investigation of hydration and gelation of the polypeptide gelatin in water-glycerol mixed solvent (glycerol solutions). Raman spectroscopy results indicated enhancement in water structure in glycerol solutions and the depletion of glycerol density close to hydration sheath of the protein molecule. Gelation concentration (c(g)) was observed to decrease from 1.92 to 1.15% (w/v) while the gelation temperature (T(g)) was observed to increase from 31.4 to 40.7 °C with increase in glycerol concentration. Data on hand established the formation of organogels having interconnected networks, and the universal gelation mechanism could be described through an anomalous percolation model. The viscosity of sol diverged as η ∼ (1 - c(g)/c)(-k) as c(g) was approached from below (c < c(g)), while the elastic storage modulus grew as G' ∼ (c/c(g) - 1)(t) (for c > c(g)). It is important to note that values determined for critical exponents k and t were universal; that is, they did not depend on the microscopic details. The measured values were k = 0.38 ± 0.10 and t = 0.92 ± 0.17 whereas the percolation model predicts k = 0.7-1.3 and t = 1.9. Isothermal frequency sweep studies showed power-law dependence of gel storage modulus (G') and loss modulus (G'') on oscillation frequency ω given as G'(ω) ∼ ω(n') and G''(ω) ∼ ω(n''), and consistent with percolation model prediction it was found that n' ≈ n'' ≈ δ ≈ 0.73 close to gelation concentration. We propose a unique 3D phase diagram for the gelatin organogels. Circular dichroism data revealed that the gelatin molecules retained their biological activity in these solvents. Thus, it is shown that the thermomechanical properties of these organogels could be systematically tuned and customized as per application requirement.

Self-Assembly Fibrillar Network Gels of Simple Surfactants in Organic Solvents

The self-assembled fibrillar network (SAFIN) organogels of a simple surfactant molecule, sodium laurate (C(11)H(23)COONa, SL), in organic solvents were investigated. The sol-gel transformation temperature depended on the SL concentration, the solvent, and the concentration of Na(+) was evaluated. An important finding is that Na(+) ions play an important role in forming organogels, which was regarded as the induction factor of gelation, but other cations, for instance, Li(+), K(+), Ca(2+), and Mg(2+), do not have this capability. The observations by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) proved that the organogels were network structures with fibers and ribbons by trapping a certain amount of organic solvent. High-resolution TEM (HR-TEM) images indicated that each of the fibers or ribbons was composed of cylindrical micelles. The X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectra demonstrated that SL molecules in gels behave similarly to those in SL crystals. The mechanism of organogel formation was elaborated to provide a better understanding of fibrous surfactant gels in organic solvents.

Self-assembly of a new C60 compound with a L-glutamid-derived lipid unit: formation of organogels and hierarchically structured spherical particles

A new C60-based low-molecular weight gelator (LMWG 1) with a L-glutamid-derived lipid unit was synthesized and characterized. LMWG 1 can gel toluene, p-xylene and benzene. Moreover, its gelation ability can be further enhanced by addition of an exTTF derivative (compound 2), for which the intermolecular interaction between the C60 unit in 1 and the exTTF unit in 2 is responsible based on the absorption and NOE difference 1H-NMR spectral studies. Additionally, gelation-induced CD signals are observed for the gel with LMWG 1 and that of LMWG 1 doped with compound 2. Further studies indicate that the self-assembly structures of LMWG 1 in the gel phases can be modulated by the addition of compound 2. In addition, the self-assembly of LMWG 1 in DMSO leads to spherical particles of several microns in size, and the surfaces of these spherical particles are hierarchically structured with nano-fibers. Moreover, the thin-film of spherical particles exhibits water-repellent hydrophobicity.

Gelation and fluorescent organogels of a complex of perylenetetracarboxylic tetraacid with cationic surfactants

In the work we report the formation of fluorescent organogels in toluene of a complex of perylenetetracarboxylic tetraacid (PTCTA) with four cationic surfactants. We found that the gel formation is a function of the gelation temperature and solution concentration. The TEM characterization indicates twisted- or straight-belt aggregates formed in gel-phase or in crystals. The further XRD characterization illustrated a layered structure of complex molecules in these aggregates, mainly driven by π–π stacking of the rigid perylene cores. The UV/vis and fluorescence spectra show the H-type aggregates in the gel-phase. The changes of the aggregate morphology and molecular packing structures with the gelation temperature and solution concentration reflect a competition between gelation and crystallization under the conditions used and the details are discussed in text.

Unique Organogel Formation with Macroporous Materials Constructed by the Freeze−Drying of Aqueous Cyclodextrin Solutions

Macroporous cyclodextrin materials (MP-alpha-, beta-, and gamma-CDs) were easily fabricated by the freeze-drying of aqueous solutions of alpha-, beta-, and gamma-CDs. These MP-CDs showed the absorption ability toward various organic solvents and oils to give organogels at ambient temperature. The morphological changes of the MP-CD microstructures were observed through the absorption of organic solvents. In particular, the absorption of polar organic solvents with hydrogen-bond forming ability, including 1,4-dioxane and ethanol, by the MP-CDs caused remarkable morphological changes in the microstructures. The absorption of these polar solvents by MP-alpha- and gamma-CDs resulted in the formation of channel-type assemblies of alpha- and gamma-CDs, respectively.

A New ex-TTF-Based Organogelator: Formation of Organogels and Tuning with Fullerene

A new ex-TTF-based organogelator with L-glutamide-derived lipid unit (compound 1) was synthesized and characterized. The resulting transparent organogels can be obtained with several organic solvents such as toluene, DMSO, and ethanol. It is interesting that its gelation ability can be further enhanced by addition of C(60). The (1)H NMR and absorption spectral studies indicate that the intermolecular interaction between the ex-TTF unit in 1 and C(60) may be responsible for this phenomenon. Further studies imply that the assembly structures in the gel phases in the absence and presence of C(60) may be different. Additionally, organogels can also be prepared with compound 1 and PCBM, and the corresponding xerogel was used to modify ITO electrode. A stable and rapid photocurrent was generated after exposure of the modified ITO electrode to light. This may provide an alternative way for photocurrent generation with high energy conversion efficiency.

Counterion Effects on the Columnar Mesophases of Triphenylene‐Substituted [18]Crown‐6 Ethers: Is Flatter Better?

The twisted lateral tetraalkyloxy ortho-terphenyl units in dibenzo[18]crown-6 ethers 1a-f were readily converted into the flat tetraalkyloxytriphenylene systems 2a-f by oxidative cyclization with FeCl(3) in nitromethane. Reactions of the latter with potassium salts gave complexes KX.2, which displayed mesomorphic properties. The aromatization increased both the clearing and melting points; the mesophase stabilities, however, were mainly influenced by the respective anions upon complexation with various potassium salts. In contrast, the alkyl chain lengths played only a secondary role. Among the potassium complexes of triphenylene-substituted crown ethers KX.2, only those with the soft anions I(-) and SCN(-) displayed mesophases with expanded phase temperature ranges of 93 degrees C and 132 degrees C (for KX.2e), respectively, as compared to the corresponding o-terphenyl-substituted crown ether complexes KI.1e (DeltaT=51 degrees C) and KSCN.1e (plastic crystal phase). Anions such as Br(-), Cl(-), and F(-) decreased the mesophase stability, and PF(6)(-) led to complete loss of the mesomorphic properties of KPF(6).2 although not for KPF(6).1. For crown ether complexes KX.2 (X=F, Cl, Br, I, BF(4), and SCN), columnar rectangular mesophases of different symmetries (c2mm, p2mg, and p2gg) were detected. In contrast to findings for the twisted o-terphenyl crown ether complexes KX.1, the complexation of the flat triphenylene crown ethers 2 with KX resulted in the formation of organogels. Characterization of the organogel of KI.2e in CH(2)Cl(2) revealed a network of fibers.

Sterol-containing tetraphenylethenes: synthesis, aggregation-induced emission, and organogel formation

Cholesterol- and stigmasterol-containing tetraphenylethenes (TPEs) (TPE-Chol and TPE-Stig) are facilely synthesized in satisfactory yields by Cu (I)-catalyzed click reaction of 1,2-bis(4-azidomethylphenyl)-1,2-diphenylethene and cholesteryl-4-ethylbenoate and sigmasteryl 11-(4-ethynylphenoxy)undecanoate, respectively. Whereas they are nonluminescent in solution, they become highly emissive when aggregated in the condensed phase. The molecules of TPE-Stig can self-assemble in methanol solution, generating organogels with gelation-induced emission characteristics.

A potent triphenylbenzene-based H-bonding donor to assist formation of two-component organogels with stilbazoles

Abstract Two-component organogelators based on a discotic H-bonding donor of 1,3,5-tris(4-amidobutanoic acid)phenyl benzene ( 2 ), and acceptors of 4-(4-alkoxybenzoyloxy)-4′-stilbazole derivatives were reported. These complexes showed good gelation ability for alcohols, which are known to be unfavorable for H-bonding formation. SEM study revealed that sheet-like network, nanotapes, and nanorods were gained from the self-assembling of the complexes with small difference of the carbon chain length. Based on XRD, IR, temperature-dependent 1 H NMR, and UV–vis absorption investigations, the gel-phase materials were generated from 1D columnar-type packing of complexes facilitated by cooperative H-bonding, π-stacking, and van der Walls interactions.

Shear Nanostructuring of Monoglyceride Organogels

The aim of the present research was to study the effect of shear on the crystallization behavior of monoglyceride organogels. To this end, organogels were prepared by mixing cod liver oil and saturated monoglycerides at 80°C and then crystallizing them at 20°C under shear rates ranging from 0 to 2,000 s−1. The organogels were characterized using polarized light microscopy, Cryo-SEM, and X-ray diffraction. The rheological properties and the oil binding capacity of the different systems were also evaluated. Results obtained in this study showed that the introduction of shear during organogel formation greatly affects structure at the nano, micro, and macro levels. Solidification of the organogel under static conditions led to the formation of a strong gel network, with a high oil binding capacity. On the contrary, shear processing during crystallization led to the formation of a weak gel network with a low oil binding capacity.