Low-molecular-mass Organic Gelators Research Articles

Inorganic Subnanometer Nanowire-Based Organogels: Trends, Challenges, and Opportunities.

Organogels exhibit many excellent properties and multiple functions. Conventionally, polymers and low-molecular-mass organic gelators (LMOGs) are used for preparing organogels, showing potential applications. Recently, a subnanometer nanowire (SNW) gelator applicable for various organic liquids emerged, which has potential for semi-solidification, safe storage, and transportation of organic liquids and oil spill recovery. This perspective summarizes and compares these three kinds of organogels. Through this perspective, the challenges and opportunities for SNW-based organogels are made clearer. Regulating functions of gels by controlling the structure and composition of SNWs and developing other subnanometer material gelators may be further research directions.

Synthesis and organogelating behaviour of urea- and Fmoc-containing diphenylalanine based hexaamide

A new low molecular mass organic gelator based on tri-tert-butylates Glu-Urea-Lys and Fmoc-capped di-L-Phe-containing hexaamide (tri-tert-butyl (10S,13S,31S,35S)-10,13-dibenzyl-1-(9H-fluoren-9-yl)-3,9,12,15,18,25,33-heptaoxo-2-oxa-4,8,11,14,19,26,32,34-octaazaheptatriacontane-31,35,37-tricarboxylate, 9) was synthesized and examined for the ability to gelate various organic solvents (dichloromethane (DCM), chlorophorm, methanol, acetonitrile and acetonitrile/water mixtures, ethyl acetate). The microstructure of the obtained gels was studied using scanning electron microscopy (SEM). It was shown that the morphologies of the xerogels, formed by the slow drying of the corresponding organogels, differ for different solvents. For example, xerogels from DCM showed the layered slab structures with widths and lengths to hundreds of micrometers, but xerogels in ethanol exhibit networks composed of entwined fibers. Based on FTIR, 1H NMR and UV-vis data, the gelator molecules are aggregate via N–H/O hydrogen bonding, hydrophobic interaction and π-π-staking.

An organogel library for solution NMR analysis of nanoparticle suspensions in non-aqueous samples

Surface contrast solution NMR methods (scNMR) are emerging as powerful tools to investigate the adsorption of small molecule ligands to the surface of nanoparticles (NP), returning fundamental insight into the kinetics and thermodynamics of sorption, as well as structural information on the adsorbed species. A prerequisite for the acquisition of high quality solution NMR data is the preparation of homogeneous and stable samples that return consistent NMR spectra and allow extensive signal averaging. Unfortunately, this condition does not apply to NMR samples containing NPs that often show a tendency to sediment and accumulate at the bottom of the NMR tube over the course of the experiment. We have recently shown that preparing NMR samples in an agarose gel matrix inhibits sedimentation and allows the characterization of small molecule-NP interactions by scNMR. Unfortunately, as the agarose gel only forms in aqueous solution, this sample preparation method cannot be used to stabilize NP suspensions in a non-aqueous environment. Here, we introduce a library of 48 organogels, based on low molecular-mass organic gelators (LMOGs), to prepare NMR samples of small molecule/NP systems in a wide range of organic solvents. In addition, we present a simple method that takes advantage of 1H transverse relaxation (1H-R2) measurements to screen the library and identify the best gelator to characterize the small molecule-NP interaction of interest in the solvent of choice. We expect the results of this study will enable the preparation of homogeneous and stable samples of NPs in non-aqueous environments, therefore dramatically increasing the applicability of scNMR to the characterization of heterogeneous interactions and to the investigation of the role played by solvent molecules in regulating the kinetics and thermodynamics of sorption.

Organogelator based on long alkyl chain attached excimer precursor: Two channels of TICT, highly efficient and switchable luminescence

A low molecular mass organic gelator (LMOG) T16 was obtained by introducing a long alkyl chain into an excimer precursor α–CN–TPA. Immobile organogels of T16 exhibiting both thermochromic and mechanochromic fluorescence switching between blue and green could be formed. Far more than expected, the long alkyl chain endows T16 with unique two channels of twisted intramolecular charge transfer (TICT) emission in solution and highly luminescent properties in both a gel and solid state (crystal). The fluorescence distribution ratio of the two channels is dependent on irradiation wavelength and solvent polarity, leading to distinct effects of aggregation induced enhanced emission (AIEE) and gelation induced enhanced emission (GIEE), respectively. The fluorescent quantum efficiency of T16 is increased more than 380 times in xerogel and almost 500 times in the crystal compared with that of α–CN–TPA crystal, though both molecules have the same conjugated unit. The radiant transition is found to be transformed from a forbidden state in α–CN–TPA to the allowed state in T16, owing to the incorporation of a long alkyl chain which influences the self-assembly structure and intermolecular interactions. Antiparallel molecular H-stacking and multi-layered self-assembly are constructed in T16 under the driving force of π−π, electrostatic and long alkyl-alkyl chain interactions. These findings offer a simple and interesting platform for manipulating the fluorescence radiation characteristics.

Fluorenone-based organogel and self-assembled fibrous film: Synthesis, optical properties and reversible detection of aniline vapor

Two new low-molecular mass organic gelators (LMOGs) based on fluorenone and 3,4,5-tris(dodecyloxy)benzamide auxiliary group (SOF and DOF) were synthesized and characterized. Their photophysical properties were investigated systematically via spectroscopic and theoretical methods. Both compounds exhibit 1π,π* transitions in the UV region, and broad, structureless intramolecular charge transfer (1ICT) absorption bands in the visible spectral region. Both compounds are emissive in solution at room temperature, which can be attributed to 1ICT state. In addition, the gel properties of the two compounds in 10 solvents was studied. Compared to SOF with a single auxiliary group, DOF bearing two auxiliary groups are easier to form gels in different solvents. Fluorescence behavior and sensing performance studies of DOF xerogel film obtained by self-assembling demonstrated that this film is chemically stable, and reversible and selective to the presence of aniline vapor through the photoinduced electron transfer (PET) mechanism. The self-assembled properties of the LMOGs will be more conducive to the functionalization of photofunctional materials.

Aggregation-Induced Enhanced Emission (AIEE) from N,N-Octyl-7,7′-diazaisoindigo-Based Organogel

A new kind of low molecular-mass organic gelator (LMOG) π-electron-deficient N,N-octyl-7,7'-diazaisoindigo (1) with aggregation-induced enhanced emission (AIEE) phenomenon is described. This organogel is capable of self-assembling through intermolecular H-bonding and π−π interactions between diazaisoindigo molecules. Its rheological properties, X-ray diffraction pattern, optical properties and theoretical calculations were investigated. The AIEE effect is exhibited in fluorescence during the formation of the supramolecular organogel, which persisted in the xerogel state, the spectral red-shifts suggest the formation of J-type aggregates during the gelation process via - interactions in microbelts or 3D networks. Fluorescence lifetime and quantum yield significantly increases from dilute solution to the aggregate state. From a theoretical perspective, the effect of the aggregation of 1 on the photophysical properties was also studied by means of the Density Functional Theory (DFT). In this sense, the low...

Molecular Gels as Intermediates in the Synthesis of Porous Materials and Fluorescent Films: Concepts and Applications.

Low-molecular-mass organic gelator (LMOG)-based molecular gels are known as one of the most attractive soft materials and have received great attention since the early 1990s. In the last few decades, many LMOGs have been synthesized, and a series of theories have been proposed to better understand molecular gels. However, only limited applications of LMOGs have been realized for a variety of reasons, such as their lack of stability compared to chemical gels. Therefore, efforts to explore the applications of these materials are especially meaningful. As an example, this feature article mainly introduces studies on the application of LMOGs as intermediates in porous materials and fluorescent sensing films. Particular attention will be paid to gelator design, LMOG emulsion preparation, solid surface modification, and the practical application of the obtained materials. Concepts that are related to these studies, such as organic gel-water interface equilibria and molecular gel strategies, will be comprehensively illustrated. Finally, we will conclude with a study of LMOG-based intermediates. Some challenges and future perspectives related to these research areas will also be presented. It is anticipated that this feature article will not only contribute to the further understanding of LMOG-based intermediates but also will help to promote the practical application of molecular gels and facilitate development in related research areas.

Organogel materials: Preparation and biomedical applications

Event Abstract Back to Event Organogel materials: Preparation and biomedical applications Sophie Franceschi1 and Emile Perez1 1 Universite Paul Sabatier, Chimie Moleculaire et Supramoleculaire, France Organogels are soft materials, which result from the immobilisation of an organic liquid or oil in a three dimensional network by a gelator. The organogels in this study were obtained from an organic liquid and a low molecular mass organic gelator (LMOG). In vegetable oils, 12-hydroxystearic acid (HSA) self assemble by non-covalent interactions to form fibrous structures responsible for the gelation phenomenon. We elaborated original soft materials from organogels, characterized them by different techniques and developed original materials for biomedical applications. Starting from the self-assembly of HSA in soybean oil, we prepared microporous organogels, and water dispersion of gelled nanoparticles: Microporous organogels were elaborated by a particulate leaching technique. Sugar, salt or powdered sugar templates were used to introduce a controlled porosity inside the organogels. The obtained porous materials are used as artificial matrices for tissue engineering. Water dispersion of gelled particles were obtained by an hot emulsification (T > Tgel), with a stabilizing agent (surfactant or polymer), and a cooling at room temperature (T < Tgel). The dispersions are very stable, and the gelled particles are able to encapsulate hydrophobic drugs for a controlled delivery. Figure: Electron microscopy images of organogels a) and b) TEM observations of fibrils and fibers of HSA self-assembled in soybean oil. c) SM of a microporous organogel obtained with sugar porogen and HSA/soybean oil as gel phase. d) TEM of organogel nanoparticles HSA/soybean oil.

Gelation Properties of Aprotic Low-Molecular-Mass Organic Gelators Based on a Gemini 4-[2-(Perfluoroalkyl)ethylsulfanyl]phenoxy Derivative Unit

Abstract Gelation properties of aprotic low-molecular-mass organic gelators (LMOGs) based on a gemini 4-[2-(perfluoroalkyl)ethylsulfanyl]phenoxy derivative unit are described. These LMOGs without hydrogen-bonding functional groups produced physical gels in several organic solvents such as ethanol, 1-octanol, acetonitrile, DMF, DMSO, propylene carbonate, and γ-butyrolactone at low concentration below 1 wt %. From the results of microscope observation and nuclear magnetic resonance spectroscopy, these aprotic LMOG molecules were aggregated into tape-shaped molecular nanofibers, and formed three-dimensional networks. In addition, the self-diffusion coefficient of the solvent molecules in these networks was similar to that of neat, although these solvent molecules have non-fluidity by gelation.

Methyl Cinnamate-Derived Fluorescent Rigid Organogels Based on Cooperative π-π Stacking and C═O···π Interactions Instead of H-Bonding and Alkyl Chains.

A new class of rigid low-molecular-mass organic gelators (LMOGs) was synthesized by McMurry and Heck reactions, and their gels and photophysical properties were investigated. The LMOGs lacked alkyl chain and H-bonding units and produced good gelation ability in selected mixed organic solvents facilitated by cooperative π-π stacking and C═O···π interactions. Sensitive gel-sol transformation by molecular aggregation and disaggregation was easily achieved upon heating and cooling. H-H 2D NOESY and X-ray diffraction (XRD) patterns showed the π-π stacking and C═O···π interactions between tiny methyl acrylate groups as "tails". Importantly, this soft interaction model offers a useful tool for the future design and construction of supramolecular structures. At present, the LMOGs reported herein offer a sensitive gel-formation ability and aggregation-induced emission (AIE) property and thus have promising application potentials as functional soft matter in amorphous materials, photoelectric materials, and so on.

Gelation by Novel Aprotic Low-molecular-mass Organic Gelators Based on a Gemini 4-[2-(Perfluorobutyl)ethylthio]phenoxy Unit

Abstract We found novel aprotic low-molecular-mass organic gelators (LMOGs) with simple molecular structure based on a gemini 4-[2-(perfluorobutyl)ethylthio]phenoxy unit. These aprotic LMOGs formed a physical gel with a thermally reversible sol–gel phase transition in a wide variety of alcoholic and polar solvents such as 1-octanol and propylene carbonate at concentrations below 1 wt %.

Novel Tri-Cholesteryl Derivatives-Based Low Molecular Mass Organic Gelators with Multi-Stimuli Responsive Properties

Two novel tri-cholesteryl derivatives 1 and 2 have been designed and prepared. Gelation tests in 30 liquids revealed that 1 is a more efficient gelator than 2. Interestingly, the gel of 1/cyclohexane shows a reversible sol–gel phase transition in response to a variety of disparate stimuli such as temperature, stress, and HCl gas. In particular, a fully reversible thixotropic property was observed, which has been rarely reported before. Fourier transform infrared spectroscopy and 1H NMR measurements revealed that hydrogen bonding is an important driving force for the formation of the gel networks. The network structures of 1 and 2 in their cyclohexane gels were studied by scanning electron microscopy and X-ray diffraction analyses, and possible packing models were proposed accordingly. The findings demonstrated in the present work suggest that there is a big potential for developing tri-cholesteryl derivatives into extraordinary low molecular mass gelators.

Morphology and Wettability Tunable Organogel System Based on An 1,3,4-Oxadiazole Derivative

A new low molecular mass organic gelator (LMOG) bearing 1,3,4-oxadiazole and azobenzene groups, namely N-(3,4,5-octanoxyphenyl)-N’-4-[(4-hydroxyphenyl)azophenyl] 1,3,4-oxadiazole (AOB-t8), was designed and synthesized. The organogelator has shown great ability to gel a variety of organic solvents to form stable organogels with the critical gelation concentration as low as 5.0 × 10−4 M and, therefore, can be considered a supergelator. It has been demonstrated that the aggregation morphology and surface wettability produced by organogels strongly depend on the nature of gelling solvents. A structure of uptwisting fibers on the substrate and superhydrophobicity were observed in the xerogel formed from 1,2-dichloroethane. The wettability of the xerogel could also be tuned by applying a sol-gel process with different solvents. Cooperation of hydrogen bonding, π-π interaction, and Van der Waals force are suggested to be the main contribution for this self-assembled structure. The unique and tunable surface properties such as superhydrophobicity distinguish the obtained organogels as a novel class of functional materials.

Small-angle X-ray scattering structural study of the nanofiber self-assembly process in supramolecular gels based on glucopyranosides

This paper reports a study of the supramolecular self-assembly process of low molecular mass organic gelators in the formation of nanofiber networks. Methyl 4,6-O-benzylidene-α-D-glucopyranoside derivative compounds were designed to investigate the effect of substituents on the molecules' self-assembly properties. Gelators were prepared using two different substituent groups at position 4 of the aromatic ring: an electron-donating series (with n-alkoxyl groups) and an electron-withdrawing series (with n-alkoxycarbonyl groups), where n = 2, 3, 4, 8 and 16 C atoms. The gelation process in several gelator concentrations was studied in polar and apolar organic solvents. Differential scanning calorimetry revealed that the gelation temperature increases with the molar concentration and decreases with alkyl chain size in both series of gelators. Scanning electron microscopy images of the xerogel showed cylindrical aggregates. In situ small-angle X-ray scattering analysis corroborated a model of self-assembly based on one-dimensional nanofiber growth in a two-phase gel system, while X-ray powder diffraction revealed partial crystallization for the gelator compounds and for some gel samples. The infrared analyses of gels indicated that molecules undergo a self-assembly process via hydrogen bonding, suggesting that both OH groups are involved for samples of the n-alkoxycarbonyl series. On the other hand, the n-alkoxyl series aggregation process depends on the size of the alkyl chain. The compound with the smallest group, n-propoxyl, also undergoes self-assembly using both OH groups. Conversely, the rest of the n-alkoxyl series uses only one hydroxyl group.

Insights into low molecular mass organic gelators: a focus on drug delivery and tissue engineering applications

In recent years low molecular mass organic gelators (LMOGs) have gained increasing interest as an alternative biomaterial to polymer derived gels, with potential applications in drug delivery and tissue engineering. LMOGs are small organic molecules which self-assemble in water or organic solvents forming a 3D network that entraps the liquid phase resulting in gel formation. In this review, we report the classification of LMOGs into hydrogelators and gelators of organic solvents and we discuss the techniques commonly used to characterise the gels of these gelators with particular reference to specific applications of LMOGs in drug delivery and tissue engineering.

Spacer effect on nanostructures and self-assembly in organogels via some bolaform cholesteryl imide derivatives with different spacers

In this paper, new bolaform cholesteryl imide derivatives with different spacers were designed and synthesized. Their gelation behaviors in 23 solvents were investigated, and some of them were found to be low molecular mass organic gelators. The experimental results indicated that these as-formed organogels can be regulated by changing the flexible/rigid segments in spacers and organic solvents. Suitable combination of flexible/rigid segments in molecular spacers in the present cholesteryl gelators is favorable for the gelation of organic solvents. Scanning electron microscopy and atomic force microscopy observations revealed that the gelator molecules self-assemble into different aggregates, from wrinkle and belt to fiber with the change of spacers and solvents. Spectral studies indicated that there existed different H-bond formations between imide groups and assembly modes, depending on the substituent spacers in molecular skeletons. The present work may give some insight into the design and character of new organogelators and soft materials with special molecular structures.

Self-assembly of organogels via new luminol imide derivatives: diverse nanostructures and substituent chain effect

Luminol is considered as an efficient sycpstem in electrochemiluminescence (ECL) measurements for the detection of hydrogen peroxide. In this paper, new luminol imide derivatives with different alkyl substituent chains were designed and synthesized. Their gelation behaviors in 26 solvents were tested as novel low molecular mass organic gelators. It was shown that the length and number of alkyl substituent chains linked to a benzene ring in gelators played a crucial role in the gelation behavior of all compounds in various organic solvents. Longer alkyl chains in molecular skeletons in present gelators are favorable for the gelation of organic solvents. Scanning electron microscope and atomic force microscope observations revealed that the gelator molecules self-assemble into different micro/nanoscale aggregates from a dot, flower, belt, rod, and lamella to wrinkle with change of solvents. Spectral studies indicated that there existed different H-bond formations and hydrophobic forces, depending on the alkyl substituent chains in molecular skeletons. The present work may give some insight to the design and characteristic of new versatile soft materials and potential ECL biosensors with special molecular structures.

Applications of Supramolecular Gels in Catalyzing Organic Reactions

Supramolecular gels are the self-assembly of low molecular-mass organic gelators through non-bonding interactions to form a 3D entangled fiberous network which immobilizes liquids.This paper reviewed the application of supramolecular gels for catalyzing organic reactions which is a new extended application of supramolecular gels.Recent development of using supromolecular gels as catalysts was summarized and classified according to the gelator structures and reaction types,and particular attentions were given to the unique features of catalysis by the supramolecular system.The challenges and perspectives in this field were discussed.

Supramolecular gels based on monopyrrolotetrathiafulvalene and its TCNQ charge-transfer complex

A novel series of monopyrrolotetrathiafulvalene (monopyrrolo-TTF)-based low molecular-mass organic gelators (LMOGs) were synthesized and characterized. Electrochemical investigations exhibited two reversible one-electron redox couples. The gelators could gelate some saturated hydrocarbons and alcohols. The FE-SEM images of xerogels revealed the characteristic gelation morphologies of microporous structures. The gelators reacted with tetracyano-p-quinodimethane (TCNQ) to form the charge-transfer (CT) complexes and the binary organogels, and the morphologies of binary gels changed to regular network and fiber in cyclohexane and n-hexane, respectively. XRD studies suggest that both the gelator and the CT complex maintain the lamellar molecular-packing mode in the organogel phase. The gel–sol transition of the organogel and the CT complex gel could be stimulated by fluorine and chlorine ions.

Applications of Supramolecular Gels in Catalyzing Organic Reactions

Supramolecular gels are the self-assembly of low molecular-mass organic gelators through non-bonding interactions to form a 3D entangled fiberous network which immobilizes liquids.This paper reviewed the application of supramolecular gels for catalyzing organic reactions which is a new extended application of supramolecular gels.Recent development of using supromolecular gels as catalysts was summarized and classified according to the gelator structures and reaction types,and particular attentions were given to the unique features of catalysis by the supramolecular system.The challenges and perspectives in this field were discussed.