Gelation of a Highly Fluorescent Urea‐Containing Triarylmelamine Derivative: 2,4,6‐Tris(p‐N′‐Octadecylureido‐Anilino)Triazine in Organic Solvents

A new gelator of urea‐containing triazine derivatives was synthesized and tested in order to explore the gelation potential in different organic solvents. This compound has been found to form organogels with a variety of organic solvents such as decalin and other solvents. The resulting thermo‐reversible gel was characterized by using the dropping ball method and a number of other instruments. The melting temperature of the gel increased with the gel concentration. The intermolecular hydrogen bonding of gelation was demonstrated through an FT‐IR spectrometer. UV‐Vis and fluorescence analysis showed that the gel displayed various optical effects in different organic solvents. The blue fluorescence of the gel in decalin and the quenched effect of gel in CHCl³ were displayed, respectively. Morphological features in decalin and CHCl₃ were studied by applying atomic force microscopy (AFM), and the morphological features demonstrated that there were different aggregations in different solvents. In conductivity electrolyte experiments, the organogel electrolytes indicated high conductivity (σ) comparable to the corresponding NaClO₄/THF solution. The conductivity of gel electrolytes was increased with electrolyte salt.     

Self‐Assembly of π‐Conjugated Gelators into Emissive Chiral Nanotubes: Emission Enhancement and Chiral Detection

A series of new π‐conjugated gelators that contain various aromatic rings (phenyl, naphthyl, 9‐anthryl) and amphiphilic L ‐glutamide was designed, and their gel formation in organic solvents and self‐assembled nanostructures was investigated. The gelators showed good gelation ability in various organic solvents that ranged from polar to nonpolar. Those gelator molecules with small rings such as phenyl and naphthyl self‐assembled into nanotube structures in most organic solvents and showed strong blue emission. However, the 9‐anthryl derivative formed only a nanofiber structure in any organic solvent, probably owing to the larger steric hindrance. All of these gels showed enhanced fluorescence in organogels. Furthermore, during the gel formation, the chirality at the L ‐glutamide moiety was transferred to the nanostructures, thus leading to the formation of chiral nanotubes. One of the nanotubes showed chiral recognition toward the chiral amines.     

脂肪酰谷氨酸与小分子有机凝胶

研究了脂肪酰谷氨酸作为凝胶因子在不同有机溶剂中的成胶性能。结果表明,小分子有机凝胶的形成及其稳定性与有机溶剂种类、凝胶因子浓度和凝胶因子中碳链长度密切相关。FT-IR表明,凝胶因子在有机溶剂中是通过氢键等非共价力相互作用而聚集、自我组装形成凝胶。利用光学显微镜观察发现,凝胶因子在不同有机溶剂中形成凝胶的微观结构不同。     

Pyrene‐Based Fluorescent Ambidextrous Gelators: Scaffolds for Mechanically Robust SWNT–Gel Nanocomposites

With the rapid progress in the development of supramolecular soft materials, examples of low‐molecular‐weight gelators (LMWGs) with the ability to immobilise both water and organic solvents by the same structural scaffold are very limited. In this paper, we report the development of pyrene‐containing peptide‐based ambidextrous gelators (AGs) with the ability to efficiently gelate both organic and aqueous solvents. The organo‐ and hydrogelation efficiencies of these gelators are in the range 0.7–1.1 % w/v in various organic solvents and 0.5–5 % w/v in water at certain acidic pH values (pH 2.0–4.0). Moreover, for the first time, AGs have been utilised to prepare single‐walled carbon‐nanotube (SWNT)‐included soft nanocomposites in both hydro‐ and organogel matrices. The influence of different non‐covalent interactions such as hydrogen bonding, hydrophobic, π–π and van der Waals interactions in self‐assembled gelation has been studied in detail by circular dichroism, FTIR, variable‐temperature NMR, 2D NOESY and luminescence spectroscopy. Interestingly, the presence of the pyrene moiety in the structure rendered these AGs intrinsically fluorescent, which was quenched upon successful integration of the SWNTs within the gel. The prepared hydro‐ and organogels along with their SWNT‐integrated nanocomposites are thermoreversible in nature. The supramolecular morphologies of the dried gels and SWNT–gel nanocomposites have been studied by transmission electron microscopy, fluorescence microscopy and polarising optical microscopy, which confirmed the presence of three‐dimensional self‐assembled fibrillar networks (SAFINs) as well as the integrated SWNTs. Importantly, rheological studies revealed that the inclusion of SWNTs within the ambidextrous gels improved the mechanical rigidity of the resulting soft nanocomposites up to 3.8‐fold relative to the native gels.     

Versatile supramolecular gelators that can harden water, organic solvents and ionic liquids

We developed novel supramolecular gelators with simple molecular structures that could harden a broad range of solvents: aqueous solutions of a wide pH range, organic solvents, edible oil, biodiesel, and ionic liquids at gelation concentrations of 0.1-2 wt %. The supramolecular gelators were composed of a long hydrophobic tail, amino acids and gluconic acid, which were prepared by liquid-phase synthesis. Among seven types of the gelators synthesized, the gelators containing L-Val, L-Leu, and L-Ile exhibited high gelation ability to various solvents. These gelators were soluble in aqueous and organic solvents, and also in ionic liquids at high temperature. The gelation of these solvents was thermally reversible. The microscopic observations (TEM, SEM, and CLSM) and small-angle X-ray scattering (SAXS) measurements suggested that the gelator molecules self-assembled to form entangled nanofibers in a large variety of solvents, resulting in the gelation of these solvents. Molecular mechanics and density functional theory (DFT) calculations indicated the possible molecular packing of the gelator in the nanofibers. Interestingly, the gelation of an ionic liquid by our gelator did not affect the ionic conductivity of the ionic liquid, which would provide an advantage to electrochemical applications.     

Structure-property relationship of a class of efficient organogelators and their multistimuli responsiveness

A new class of efficient low-molecular-weight gelators composed of a 2-substituted anthraquinone and a hydrazide subunit were synthesized, and the structure-property relationships with respect to their gelation abilities in organic solvents were investigated. The toluene gels showed exceptional thermal stability. Interestingly, it was also found that the ultrasound radiation could promote 1b-e to form a stable organogels instead of precipitates in polar solvent, and the ultrasound could remarkably induce changes of the morphology of the assembly in pyridine. Moreover, the reversible gel to sol phase transition could be achieved by adding TFA and TEA. The gelators 1b-e further showed selective gelation of aromatic solvents or chloroalkanes from their mixtures with water.     

Water-induced physical gelation of organic solvents by N-(n-alkylcarbamoyl)-L-alanine amphiphiles

A series of amino acid-based gelators N-(n-alkylcarbamoyl)-L-alanine were synthesized, and their gelation abilities in a series of organic solvents were tested. No gelation was observed in pure solvents employed. All the amphiphilic molecules were found to form stable organogels in the solvents in the presence of a small amount of water, methanol, or urea. The volume of solvent gelled by a given amount of the gelator was observed to depend upon the volume of added water. The gelation behavior of the amphiphiles in a given solvent containing a known volume of water was compared. The effects of chirality and substitution on the acid group on the gelation ability were examined. Although the corresponding N-(n-tetradecylcarbamoyl)-DL-alanine was found to form only weak organogel in pure solvents, the achiral amphiphilic compound N-(n-tetradecylcarbamoyl)-β-alanine, however, did not form gel in the absence of water. The methyl ester of N-(n-tetradecylcarbamoyl)-L-alanine was also observed to form gels in the same solvents, but only in the presence of water. The organogels were characterized by several techniques, including (1)H NMR, Fourier transform IR, X-ray diffraction, and field emission scanning electron microscopy. The thermal and rheological properties of the organogels were studied. The mechanical strength of the organogel formed by N-(n-tetradecylcarbamoyl)-DL-alanine was observed to increase upon the addition of water. It was concluded that water-mediated intermolecular hydrogen-bonding interaction between amphiphiles caused formation of supramolecular self-assemblies.     

Super organogelator based on tetrathiafulvalene with four amide derivatives and its F4TCNQ charge-transfer complex

A new series of tetrathiafulvalene-based organogelators endowed with four hydrophobic chains incorporating amide groups was synthesised and characterised. The resulting transparent organogels were obtained with organic solvents such as cyclohexane, carbon tetrachloride and chlorobenzene. Additionally, the length of the alkyl chain influenced the gelation ability of organogels. Considering the results, we concluded that compounds were ‘super gelators’. Interestingly, the gelators reacted with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane to form charge-transfer (CT) complexes and binary organogels. ¹HNMR and FT-IR revealed that cooperation of hydrogen bonding, π–π and CT interactions was the main driving force for formation of the native and CT gels. The scanning electron microscopy images of native xerogels revealed characteristic gelation morphologies of three-dimensional cross-linking networks, whereas the morphologies of CT complex xerogels showed amorphous rod-like aggregates. X-ray powder diffraction studies suggested that both gelator and CT complex maintained lamellar molecular packing mode in organogel phase.     

Design, synthesis and stimuli responsive gelation of novel stigmasterol-amino acid conjugates

An efficient synthesis of three novel stigmasterol-amino acid (glycine, L-leucine and L-phenylalanine) conjugates as stimuli responsive gelators is reported. The gelation properties of the prepared compounds were investigated in a variety of organic as well as aqueous solvents. The most striking finding of our investigation was that the hydrochloride salts of the prepared conjugates acted as gelators, whereas the neutral conjugates were either non-gelators or formed only a weak gel in anisole. The hydrochloride salts of stigmasteryl glycinate and L-leucinate form gels in n-alcohols (n=4-10) and in ethane-1,2-diol, and that of stigmasteryl L-phenylalaninate forms gels in aromatic solvents and in tetrachloromethane. These unique properties of the gelators were explored to prepare stimuli responsive, "acid-base" triggered reversible sol-gel transitions. The gelators and their gels were characterized by liquid and solid-state NMR as well as FT-IR. The morphology of their corresponding xerogels was investigated by SEM.     

能使有机溶剂凝胶化的凝胶因子研究进展

较系统地综述了有机凝胶因子的种类及其在有机溶剂中聚集与自我组装,形成有机凝胶的研究进展。     

反应型二烷基脲凝胶剂及有机溶剂的室温凝胶化研究

通常制备有机分子凝胶是在高温下溶解凝胶剂,凝胶剂分子在冷却过程中进行自组装并使有机溶剂凝胶化。该方法限制了某些低沸点溶剂的凝胶化。利用甲苯二异氰酸酯与烷基胺的高反应活性,制备了三种不同烷基链长的反应型凝胶剂甲苯–2, 4–二（N, N’ –烷基）脲。这种反应型凝胶剂能以较低的浓度在室温下使某些芳香族和卤代烃溶剂中形成热可逆的有机分子凝胶。不同烷基链长的亲溶剂作用以及溶剂性质对有机分子凝胶的形成有较大影响。场发射扫描电镜表明这种反应型凝胶剂在有机溶剂中自组装形成纤维状三维网络结构。烷基链长度不同,形成的纤维状聚集体的形态也不同。红外光谱（FT-IR）和核磁共振波谱（1H-NMR）研究表明分子间氢键作用是这种凝胶剂自组装的驱动力。通过X射线衍射（XRD）和分子模拟推测了其聚集体的结构形态。     

含顺反异构双胆固醇型小分子胶凝剂的合成与胶凝行为

以甘氨酸为连接臂,以顺反丁烯二酸为功能基团设计合成了两种具有不同立体异构连接臂的A(LS)2型双胆固醇类小分子胶凝剂MA-C和FA-C. 考察了MA-C和FA-C对30种常见有机溶剂中的胶凝能力. 结果表明：MA-C和FA-C的胶凝能力及其所形成凝胶的性质依赖于胶凝剂分子的立体异构. 值得一提的是,MA-C能使CCl4室温胶凝,而且所形成凝胶具有良好的热稳定性和显著的剪切触变性. 更为有趣的是,此胶凝剂还能在水/CCl4混合体系中选择胶凝有机相. 显微分析表明,凝胶中胶凝剂的聚集体形貌不仅依赖于胶凝剂分子的立体异构,胶凝剂的浓度,而且也和胶凝剂分子与溶剂分子间的相互作用有关. 变温、变浓度1H NMR研究表明胶凝剂分子间的π-π堆积和氢键作用是凝胶形成的重要驱动力. 此外,根据XRD和其它实验结果提出了MA-C在CCl4中的可能堆积模型.     

Poly(dimethylsiloxane)‐based polymer organogelators with L‐lysine derivatives as a organogelation‐causing segment

New poly(dimethylsiloxane)‐based polymer organogelators with L ‐lysine derivatives were synthesized on the basis of synthetically simple procedure, and their organogelation abilities were investigated. These polymer organogelators have a good organogelation ability and form organogels in many organic solvents. In the organogels, polymer gelators constructed a mesoporous structure with a pore size of about 1 μm formed by entanglement of the self‐assembled nanofibers. The L ‐lysine derivatives in the polymer gelators functioned as a gelation‐causing segment and the organogelation was induced by self‐assembly of the L ‐lysine segments through a hydrogen bonding interaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3817–3824, 2006     

Dipeptide-based low-molecular-weight efficient organogelators and their application in water purification

The development of new low-molecular-weight gelators for organic solvents is motivated by several potential applications of gels as advanced functional materials. In the present study, we developed simple dipeptide-based organogelators with a minimum gelation concentration (MGC) of 6-0.15 %, w/v in aromatic solvents. The organogelators were synthesized using different L-amino acids with nonpolar aliphatic/aromatic residues and by varying alkyl-chain length (C-12 to C-16). The self-aggregation behavior of these thermoreversible organogels was investigated through several spectroscopic and microscopic techniques. A balanced participation of the hydrogen bonding and van der Waals interactions is crucial for efficient organogelation, which can be largely modulated by the structural modification at the hydrogen-bonding unit as well as by varying the alkyl-chain length in both sides of the hydrophilic residue. Interestingly, these organogelators could selectively gelate aromatic solvents from their mixtures with water. Furthermore, the xerogels prepared from the organogels showed a striking property of adsorbing dyes such as crystal violet, rhodamine 6G from water. This dye-adsorption ability of gelators can be utilized in water purification by removing toxic dyes from wastewater.     

Effect of the Bulkiness of the End Functional Amide Groups on the Optical,Gelation, and Morphological Properties of Oligo(p‐phenylenevinylene) π‐Gelators

Herein, we describe the role of end functional groups in the self‐assembly of amide‐functionalized oligo(p‐phenylenevinylene) (OPV) gelators with different end‐groups. The interplay between hydrogen‐bonding and π‐stacking interactions was controlled by the bulkiness of the end functional groups, thereby resulting in aggregates of different types, which led to the gelation of a wide range of solvents. The variable‐temperature UV/Vis absorption and fluorescence spectroscopic features of gelators with small end‐groups revealed the formation of 1D H‐type aggregates in CHCl₃. However, under fast cooling in toluene, 1D H‐type aggregates were formed, whereas slow cooling resulted in 2D H‐type aggregates. OPV amide with bulky dendritic end‐group formed hydrogen‐bonded random aggregates in toluene and a morphology transition from vesicles into fibrous aggregates was observed in THF. Interestingly, the presence of bulky end‐group enhanced fluorescence in the xerogel state and aggregation in polar solvents. The difference between the aggregation properties of OPV amides with small and bulky end‐groups allowed the preparation of self‐assembled structures with distinct morphological and optical features.     

Synthesis of Fluorescent Gelators and Direct Observation of Gelation with a Fluorescence Microscope

Fluorescein‐, benzothiazole‐, quinoline‐, stilbene‐, and carbazole‐containing fluorescent gelators have been synthesized by connecting gelation‐driving segments, including l ‐isoleucine, l ‐valine, l ‐phenylalanine, l ‐leucine residue, cyclo(l ‐asparaginyl‐l ‐phenylalanyl), and trans‐(1R,2R)‐diaminocyclohexane. The emission behaviors of the gelators were investigated, and their gelation abilities studied against 15 solvents. The minimum gel concentration, variable‐temperature spectroscopy, transmission electron microscopy, scanning electron microscopy, fluorescence microscopy (FM), and confocal laser scanning microscopy (CLSM) were used to characterize gelation. The intermolecular hydrogen bonding between the N?H and C=O of amide, van der Waals interactions and π–π stacking play important roles in gelation. The colors of emission are related to the fluorescence structures of gelators. Fibrous aggregates characterized by the color of their emission were observed by FM. 3D images are produced by the superposition of images captured by CLSM every 0.1 μm to a settled depth. The 3D images show that the large micrometer‐sized aggregates spread out three dimensionally. FM observations of mixed gelators are studied. In the case of gelation, two structurally related gelators with the same gelation‐driving segment lead to the gelators build up of the same aggregates through similar hydrogen‐bonding patterns. When two gelators with structurally different gelation‐driving segments induce gelation, the gelators build up each aggregate through individual hydrogen‐bonding patterns. A fluorescent reagent that was incorporated into the aggregates of gels through van der Waals interactions was developed. The addition of this fluorescent reagent enables the successful observation of nonfluorescent gelators’ aggregates by FM.     

Noncovalent Macromolecular Architectures of Oligo(p-phenylenevinylene)s (OPVs): Role of End Functional Groups on the Gelation of Organic Solvents

Summary: Self-assembly of a few OPV derivatives having different end functional groups to aggregates, fibrous networks and organogels are discussed. OPV1 and OPV2 functionalized with ester moieties form gels in nonpolar hydrocarbon solvents whereas OPV3 with carboxylic acid groups form gel from THF and dichloromethane. OPV4 with dicyano moieties form aggregates but could not gelate solvents. AFM and TEM studies revealed considerable difference in the morphology of the self-assembled structures of OPV1-4 . From the optical, morphological and gelation data it is concluded that the nature of the end functional groups strongly influences upon the self-assembly and gelation properties of OPVs.     

A new class of low-molecular-weight amphiphilic gelators

A new powerful class of low-molecular-weight amphiphilic compounds has been synthesized and their structure-property relationships with respect to their gelation ability of organic solvents have been investigated. These compounds are able to gel organic solvents over a broad range of polarity. Especially polar solvents such as valeronitrile and gamma-butyrolactone can be gelled even at concentrations far below 1 wt %. It was found that the gelation ability of these asymmetrically substituted p-phenylendiamines depends on a well-balanced relation of the terminal head group, the units involved in hydrogen bonding (amide or urea groups), and on the length of the alkyl chain. With this class of new gelators it is possible to tailor thermal and mechanical properties in different organic solvents and open various application possibilities.     

Spectral characterization of self-assemblies of aldopyranoside amphiphilic gelators: what is the essential structural difference between simple amphiphiles and bolaamphiphiles?

An aldopyranoside-based gelators (dodecanoyl-p-aminophenyl-beta-D-aldopyranoside)s and [1,12-dodecanedicarboxylic-bis(p-aminophenyl-beta-D-aldopyranoside)]s 1-4 were synthesized, and their gelation ability was evaluated in organic solvents and water. Simple aldopyranoside amphiphiles 1 and 2 were found to gelate organic solvents as well as water in the presence of a small amount of alcoholic solvents. More interestingly, not only extremely dilute aqueous solutions (0.05 wt%) of the bolaamphiphiles 3 and 4, but solutions of 3 and 4 in several organic solvents could be gelatinized. These results indicate that 1-4 can act as versatile amphiphilic gelators. We characterized the superstructures of the aqueous gels and organogels prepared from 1-4 using SEM, TEM, NMR and IR spectroscopy, and XRD. The aqueous gels 1 and 2 formed a three-dimensional network of puckered fibrils diameters in the range 20-200 nm, whereas the aqueous gels 3 and 4 produced filmlike lamellar structures with 50-100 nm thickness at extremely low concentrations (0.05 wt%). Powder XRD experiments indicate that the aqueous gels 1 and 2 maintain an interdigitated bilayer structure with a 2.90 nm period with the alkyl chain tilted, while the organogels 1 and 2 take a loosely interdigitated bilayer structure with a 3.48 nm period. On the other hand, the aqueous- and the organogels 3 and 4 have 3.58 nm spacing, which corresponds to a monolayered structure. The XRD, 1H NMR and FT-IR results suggest that 1-4 are stabilized by a combination of the hydrogen-bonding, pi-pi interactions and hydrophobic forces.