Novel organogelators based on pyrazine-2,5-dicarboxylic acid derivatives and their mesomorphic behaviors

A series of new low molecular organogelators (LMOGs) with thermotropic mesophase were synthesized via the reaction of 3,6-dimethyl-pyrazine-2,5-dicarboxylic acid with p-alkoxyl anilines. These compounds readily formed stable gels in a variety of organic solvents and their self-assembly behavior, structure–property relationship were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), ¹H nuclear magnetic resonance (¹H NMR), Fourier transform infrared spectroscopy (FTIR) and ultra-violet–visible spectroscopy (UV). The results showed a combination of intra-hydrogen bonding, π–π stacking and van der Waals interaction resulted in the aggregation of the organogelators to form three-dimension fibrous networks. The gels formed were multi-responsive to environmental stimuli, such as temperature, fluorinion, and shear stress. More importantly, all the organogelators exhibited thermotropic hexagonal column mesophase as revealed by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and variable temperature XRD studies. A control compound was synthesized and its gelling ability was also checked.     

Synthesis and characterization of d-glucosamine-derived low molecular weight gelators

Carbohydrate-based low molecular weight gelators are an interesting class of molecules with many potential applications. Previously, we have found that certain esters and carbamates of 4,6-O-benzylidene-α-d-methyl-glucopyranoside are low molecular weight gelators for a variety of solvents, including water. In order to obtain effective and robust sugar-based organogelators and understand the structure and gelation relationship, we extended our studies using 4,6-O-benzylidene-α-d-methyl-2-deoxy-2-amino-glucopyranoside as the headgroup. A series of amides and ureas were prepared from the protected d-glucosamine and the corresponding isocyanates or acid chlorides, in good yields. The self-assembling properties of these compounds were studied in several solvents, including water and aqueous solutions. Comparing to the ester and carbamate derivatives previously prepared from d-glucose, the amides and urea derivatives afforded more robust gels at lower concentrations typically. Most of these compounds were found to be efficient low molecular weight hydrogelators (LMHGs) for aqueous solutions at concentrations lower than 0.5 wt %. The preparation and characterization of these compounds are reported here.     

Synthesis and Self-assembling of Coumarin-based Low-molecular Weight Organogelators

Four coumarin derivatives(4a―4d) with different alkoxy chains were synthesized. It was found that compound 4d showed a better gelation ability than the other compounds, for example, it could self-assemble into organogels in various organic fluids via ultrasound treatment or heating-cooling process, whereas compound 4c could only gel in a few mixed solvents and compounds 4a, 4b could not form organogel. The results from fluorescent and FT-IR spectra indicate that π-π interaction had an effect on the formatio...     

A family of strong low-molecular-weight organogelators based on aminoacid derivatives

A new family of potent aminoacid-type organogelators obtained via an easy and unexpensive way is described. We demonstrated that structural variations onto the side chains of the aminoacid derivatives allowed modulations of the gelation properties. The organogelators bearing a benzyl or an isopropyl group (compounds 1e, 2a, and 2c) are able to provide gelation of apolar solvents at very low concentration (0.2 wt %) and to form thermostable gels.     

A phase-selective,bis-urea organogelator with a curved bis-naphthalene core

A phase-selective,bis-urea organogelator with a curved bis-naphthalene core was synthesized and characterized.This gelator is capable of gelating a variety of hydrocarbons and oils.The resulting gels have been characterized by rheology,SEM,and molecular modelling.The gelator can be applied in the powder form for the recovery of a thin layer of petrol oil spill in water.     

Gelation-induced emission enhancement in a “butterfly”-shaped π-conjugated organogelator and its reversible response to acid/base

In this work, we find that a new “butterfly”-shaped π-conjugated molecule, namely SY1, has the ability to undergo gelatinization in several solvents. Even though the SY1 moiety is not modified by normal auxiliary groups, the gel formation/dissolution process is reversible for many cycles upon heating and cooling processes, indicating that the gel of SY1 has reliable stability during gelation. Results also demonstrate that the gel of SY1 exhibits bright orange emission with the gelation-induced emission enhancement character. Interestingly, the gel shows reversible response upon acid/base treatment. After addition of normal acid, the gel turns into darker colour and its fluorescence undergoes quenching. Increasing pH value of the system by adding NaOH aq. leads to fluorescence emission recovery. Therefore, SY1 represents a π-conjugated organogelator without normal auxiliary groups, and exhibits gel-induced emission enhancement as well as reversible response to acid/base. The findings in this work enrich our fundamental understanding of the organogel system.     

The role of protecting groups in the formation of organogels through a nano-fibrillar network formed by self-assembling terminally protected tripeptides

A series of eight synthetic self-assembling terminally blocked tripeptides have been studied for gelation. Some of them form gels in various aromatic solvents including benzene, toluene, xylene, and chlorobenzene. It has been found that the protecting groups play an important role in the formation of organogels. It has been observed that, if the C-terminal has been changed from methyl ester to ethyl ester the gelation property does not change significantly (keeping the N-terminal protecting group same), while the change of the protecting group from ethyl ester to isopropyl ester completely abolishes the gelation property. Similarly, keeping the identical C-terminal protecting group (methyl ester) the results of the gelation study indicate that the substitution of N-terminal protection Boc- (tert-butyloxycarbonyl) to Cbz- (benzyloxycarbonyl) does change the gelation property insignificantly, while the change from Boc- to pivaloyl (Piv-) or acetyl (Ac-) group completely eliminates the gelation property. Morphological studies of the dried gels of two of the peptides indicate the presence of an entangled nano-fibrillar network that might be responsible for gelation. FTIR studies of the gels demonstrate that an intermolecular hydrogen bonding network is formed during gelation. Results of X-ray powder diffraction studies for these gelator peptides in different states (dried gels, gel, and bulk solids) reflected that the structure in the wet gel is distinctly different from the dried gel and solid state structures. Single crystal X-ray diffraction studies of a non-gelator peptide, which is structurally similar to the gelator molecules reveal that the peptide forms an antiparallel β-sheet structure in crystals.     

Synthesis,self-assembly and optical properties of novel fluorescent alkoxy-substituted fluoroaryl 1, 3, 4-oxadiazole organogelator

Aromatic nucleophilic substitution (S_NAr) reactions have been known to be regioselective to the para position on a variety of substituted perfluorobenzenes. In the current study, a series of fluoroaryl 1, 3, 4-oxadiazole derivatives substituted with different para terminal ethers were synthesized using S_NAr chemistry to afford fluorescent and thermally reversible low molecular weight organogelators (LMWOs). S_NAr was used to synthesize these highly fluorinated organogelators in high purity and good yields starting from pentafluorobenzoic acid and 4′-hydroxy-4-biphenylcarbonitrile. These fluorinated 1, 3, 4-oxadiazole derivatives were characterized by elemental analysis, FTIR, and ¹H, ¹³C, and ¹⁹F NMR spectroscopy. The photophysical properties of those organogelators were described. Both UV–visible absorption and fluorescence spectral profiles displayed a solvatochromic and solvatofluorochromic properties. The absorption maxima for the developed organogelators were monitored in the range of 260–289 nm, whereas the emission maxima were monitored in the range of 278–305 nm. The best gelation properties were monitored for the hexyloxy-substituted 2-(biphenylyl)-5-(perflurophenyl)-1, 3, 4-oxadiazole gelator in different solvents with critical gel concentrations in the range of 1.86–5.07 mM. The self-assembly process was monitored to occur via van der Waals forces and π-π stacks to result in gelation of solvents. Scanning electron microscope (SEM) demonstrated nanofiber-like structures (350–550 nm). The thermal stability of the hexyloxy-substituted organogel was monitored at 48 °C. Both cytotoxicity and antimicrobial activity of the produced fluoroaryl 1, 3, 4-oxadiazole derivatives were explored to verify their potential use for biomedical applications, such as drug delivery and bioimaging.     

Hydrophobic and oleophobic surface modification using fluorinated bis-urea and bis-amide gelators

A series of fluorinated bis-urea and bis-amide derivatives were synthesized from fluorinated amines and explored as surface modifiers for nonwoven substrates. A majority of these derivatives showed excellent gelation properties both in organic solvents as well as in supercritical carbon dioxide (scCO₂) at concentrations ranging from 0.3 to 3 wt%. Gelation in the presence of a nonwoven substrate led to a gel-impregnated surface, which upon drying produced a composite with porous microstructure morphology on the surface. The composites thus produced showed high water and hexadecane contact angles, indicative of excellent hydrophobic and lyophobic properties. The superior hydrophobic and oleophobic behaviors observed in these composites are attributed to a combination of increased surface roughness and the presence of fluoroalkyl functionalities in the gelator backbone.     

Phase selective amphiphilic supergelators for oil spill solidification and dye removal

Four glucose-based phase selective organogelators were designed and synthesized from low-cost and readily available starting materials. Our rapid acting supergelators were able to gelate a wide spectrum of solvents in mono- or biphasic systems, at very low concentration. They were shown to solidify oil spills at room temperature, in the form of a semi-dried gel, within 90 min. It was also revealed that their n-butanol gel could effectively absorb pollutant dyes from aqueous media. As novel smart materials, these gelators are potentially applicable to remove contaminants including aromatic solvents, oil spills, and toxic dyes from water resources. The gelators have been well characterized using spectroscopic, microscopic, and rheological studies.