Lithium chloride-induced organogel transformed from precipitate based on cyclodextrin complexes

This paper describes a novel heat-set organogel transformation which could be triggered by lithium chloride (LiCl) from precipitate for the first time. The system was prepared with β-cyclodextrin (β-CD) and triphenylphosphine (Ph₃P) in N,N-dimethylformamide (DMF). The system as an original transparent solution at room temperature could turn into precipitation by heating. Subsequently, the precipitation turned into organogel instantly based on the injection of LiCl into the system. SEM measurement revealed that the precipitate and gel systems have different microstructures. IR and XRD measurements revealed that the inclusion complexes formed by β-CDs and Ph₃P were arranged in cage structures in the precipitate and channel structures in the gel. Molecular dynamics simulations were performed both on the formation of the precipitate and gel models in this system, which were consistent with the test results.     

Rheometry of an androstanol steroid derivative paramagnetic organogel. Methodology for a comparison with a fatty acid organogel

This paper compares and contrasts the behavior of two different gelators using rheological and neutron scattering methods. The flow properties of a steroid-made paramagnetic organogel in cyclohexane are presented. The original gelator STNO is important in the class of organogels as being one of the most documented and as such is a good candidate for comparisons with another reference system, the 12-hydroxy stearic acid (HSA) gel. The linear viscoelastic regime of deformations of STNO gels is identified and analyzed in the context of self-assembled fibrillar networks. The linear elasticity scales with the concentration as G′ α C² similarly with HSA organogels, and both systems can be considered as cellular materials. Rheological and neutron scattering experiments show that the kinetics of gel formation exhibits long equilibration times corresponding to the elaboration of entangled fibrillar aggregates. Comparison of the linear elasticities between STNO and HSA gels demonstrates that HSA gels are much more stiffer (G′_HSA/G′_STNO∼2700). Contributions from the cross-sectional sizes, the mesh size of the networks, the solubility concentrations, and the Young's modulus of the materials are discussed. Non-linear flow properties are also compared using thixotropic loops. They indicate that the transduction of the chirality from the molecular to the supramolecular stages is more efficient with STNO gels having strong chiral junction zones. Simplified scattering and optical protocols are proposed to facilitate comparisons between different organogels.     

Effect of Solvent and Molecular Structure on the Enhanced Fluorescence and Supramolecular Chirality of Schiff Bases in Organogels

The structures and properties of some Schiff base compounds doped in organogels were investigated. It was found that although individual Schiff bases could not form organogels with organic solvents, they can gel by mixing with an organogelator, N,N′-bisoctadecyl-L-Boc-glutamic-diamide, which formed transparent organogels in dimethyl sulfoxide (DMSO) or toluene (Tol). The enhancement of doping Schiff bases fluorescence in the organogel was observed in comparison with that of the corresponding solution. Furthermore, in the DMSO organogel, the induced chirality was obtained from the doping Schiff base with long alkyl chain. In contrast, the Schiff bases without long alkyl chain could not form supramolecular chiral assemblies in organogel. It was suggested that through gel formation the chirality of the gelator could be transferred to the Schiff base through hydrophobic interaction among the long alkyl chains.     

Formation of hydrophobic surface using a bis-urea derived organogel

A bis-urea derived gelator 1 was synthesised with a high yield via a simple organic reaction. The gelator could form organogel in four kinds of solvents. The organogels obtained from four kinds of solvents were systematically investigated by FESEM, UV–Vis, PL, IR, XRD and water contact angle experiments. It was interesting that the self-assembly process of gelator 1 could be tuned by solvents. The film structure and fibre were formed in different solvents. At the same time, the different morphologies all displayed hydrophobicity. Especially, the contact angle of the fibre obtained from organogel in DMF was up to 147°. This research would provide a good pattern for preparation of a special hydrophobic surface through supramolecular self-assembly.     

Pyrene-containing peptide-based fluorescent organogels: inclusion of graphene into the organogel

The N-terminally pyrene-conjugated oligopeptide, Py-Phe-Phe-Ala-OMe, (Py=pyrene 1-butyryl acyl) forms transparent, stable, supramolecular fluorescent organogels in various organic solvents. One of these organogels was thoroughly studied using various techniques including transmission electron microscopy (TEM), field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), Fourier-transform infrared (FTIR) spectroscopy, photoluminescence (PL) spectroscopy, and rheology. Unfunctionalized and non-oxidized graphene was successfully incorporated into this fluorescent organogel in o-dichlorobenzene (ODCB) to form a stable hybrid organogel. Graphene is well dispersed into the gel medium by using non-covalent π-π stacking interactions with the pyrene-conjugated gelator peptide. In the presence of graphene, the minimum gelation concentration (mgc) of the hybrid organogel was lowered significantly. This suggests that there is a favorable interaction between the graphene and the gelator peptide within the hybrid organogel system. This hybrid organogel was characterized using TEM, AFM, FTIR, PL, and rheological studies. The TEM study of graphene-containing hybrid organogel revealed the presence of both graphene sheets and entangled gel nanofibers. The AFM study indicated the presence of 3 to 4 layers in exfoliated graphene in ODCB and the presence of both graphene nanosheets and the network of gel nanofibers in the hybrid gel system. The rheological investigation suggested that the flow of the hybrid organogel had become more resistant towards the applied angular frequency upon the incorporation of graphene into the organogel. The hybrid gel is about seven times more rigid than that of the native gel.     

Ultrasound induced formation of organogel from a glutamic dendron

New l-glutamic acid based dendritic compounds: N-(2-naphthacarbonyl)-l-glutamic acid diethyl ester (NGE) and N-(2-naphthacarbonyl)-1,5-bis(l-glutamic acid diethyl ester)-l-glutamic diamide (NBGE) were designed. Although NGE could not form any gels in common solvents, NBGE could form stable gels in hexane, toluene, and water under ultrasound. Three dimensional network structures composed of fibers with various diameters were observed in the gel by SEM and TEM. FTIR spectral measurement revealed that ultrasound during cooling of the solution could destroy some of the hydrogen bond interactions and caused the gel formation. In solution, no CD signal was detected because the naphthyl chromophore is far from the chiral center. In the gel, however, CD signals assigned to the naphthyl group were observed, which indicated that the chirality of the chiral center could be transferred to the chromophore in the supramolecular organogel system.     

A clickable,highly soluble oligopeptide that easily forms organogels

An artificial peptide, N₃-GVGV-OMe (G, glycine; V, valine), which mimics the repeating GAGA (A, alanine) sequence in Bombix Mori silk, was synthesised via solution-phase synthesis. Compared with N₃-GAGA-OMe sequence, N₃-GVGV-OMe showed high solubility in common organic solvents (such as CHCl₃, THF and CH₂Cl₂), and easily formed organogels simply by adding poor solvents (such as toluene or ether) to the peptide solution at room temperature. The hierarchical nanostructure of N₃-GVGV-OMe organogel was dependent on the nature of the poor solvents, although in all cases, β-sheets were formed exclusively. Gels formed in ether showed higher level hierarchical assembly, as evidenced by AFM and CD studies. Solution-state FT-IR analysis showed that the pre-organisation of the peptides in solution was not significant, and well-defined antiparallel β-sheets were formed after the addition of the poor solvent. The high solubility and strong tendency for self-assembly of N₃-GVGV-OMe, together with its terminal azide group, might facilitate the modification of functional organic molecules even macromolecules for better nanostructure control.     

Lecithin Organogels in a Hydrocarbon Oil

We demonstrated the existence of lecithin organogel at 20°C in a system containing the following components: phospholipid mixture with 40 wt % of phosphatidylcholine, hydrocarbon (vaseline) oil, and water, at phosphatidylcholine concentrations above 1.2 wt % and in the range of W = [H₂O]/[lec] values varying from 3.25 to 7.0. The dependences of the viscosity of lecithin organogels in a hydrocarbon oil on water and lecithin concentrations, as well as on temperature were established.     

Low molecular mass organogel from mesomorphic N‐(4‐hexyloxybenzoyl)‐N′‐(4′‐nitrobenzoyl)hydrazine

The mesomorphic compound N‐(4‐hexyloxybenzoyl)‐N′‐(4′‐nitrobenzoyl)hydrazine (C6‐NO₂), containing a dihydrazide unit in the rigid core, exhibited a highly stable SmA₁ phase (between 172.2 and 259.5°C) and strong gelation ability in chloroform and other non‐protonic organic solvents. Both SEM observations and X‐ray diffraction data indicated that the molecules self‐assembled into fibrous aggregates with a diameter of about 50 nm, and retained a head‐to‐tail configuration within layers. FTIR and ¹H NMR studies confirmed that intermolecular hydrogen bonding played a key role in the formation of the supra‐structures, and this was considered to be the driving force. Additionally, aggregation‐induced enhanced emission was observed in the organogels, and this was attributed to aggregation induced planarization and J‐aggregate formation.     

Confinement effects on the self-assembly of 1,3:2,4-Di-p-methylbenzylidene sorbitol based organogel

1,3:2,4-di- p-methylbenzylidene sorbitol (MDBS) is a small organic molecule that is capable of inducing self-assembly in a wide variety of organic solvents and of forming organogels. In this paper, we present a novel approach to tune the network architectures of organogels by utilizing geometric confinement while varying the gelator concentration. Self-assembly of MDBS in propylene carbonate (PC) is investigated in a series of microchannels with widths varying from 20 to 80 mum and the gelator concentration varying from 2 to 7 wt %. We demonstrate by optical microscopy and scanning electron microscopy (SEM) that a transition from fibrillar structure to sheaflike spherulite structure occurs when (a) the channel width is increased for fixed gelator concentrations and (b) gelator concentration is increased for fixed channel widths. A phase diagram is built based on these observations. Polarized microscopy and transmission electron microscopy (TEM) images are also obtained for organogel under unconfined condition to display the spherulite structures viewed under different length scales. The thermal properties of the organogel are measured by differential scanning calorimetry (DSC) to verify the structural difference obtained under confined and unconfined conditions and the structure stability. Our results provide a novel strategy to control the topological structure of self-assembled systems and to modify their thermal properties via geometric confinement.     

Coordinated organogel templated fabrication of silver/polypyrrole composite nanowires

A new method to fabricate metal/conducting polymer composite nanowires is presented by taking silver/polypyrrole composite nanowires as an example.A silver(Ⅰ)-coordinated organogel as template was prepared firstly,and redox-polymerization of pyrrole took place on the gel fiber,giving product of silver/polypyrrole nanowires.The silver/polypyrrole nanowires were characterized by multiple techniques.This strategy could be carried out in one-step procedure at room temperature,and it proves the utility of coordinated organogels in template synthesis of polymer nanostructures.     

Enantiomer separation of rac-2,2′-dihydroxy-1,1′-binaphthyl (BNO) by inclusion complexation with racemic or achiral ammonium salts and a novel transformation of a 1:1:1 racemic complex of BNO, Me4N·Cl and MeOH into a conglomerate complex in the solid state

The complete simultaneous and mutual enantiomer resolution of 2,2′-dihydroxy-1,1′-binaphthyl (BNO) and N-(3-chloro-2-hydroxypropyl)-N,N,N-trimethylammonium chloride, Me₃N⁺CH₂CH(OH)CH₂Cl·Cl⁻ into their enantiomers by inclusion complexation between their racemates in EtOH in the presence of a chiral seed crystal is reported. The enantiomer resolution of the rac-BNO was also accomplished easily by inclusion complexation with achiral ammonium salts, N-(2-hydroxyethyl)-N,N,N-trimethylammonium chloride, Me₃N⁺CH₂CH₂OH·Cl⁻ and tetramethylammonium chloride, Me₄N⁺·Cl⁻. Inclusion complexation of the rac-BNO with Me₃N⁺ CH₂CH₂OH·Cl⁻ gave only a 1:1 conglomerate inclusion complex but not a racemic complex. Recrystallization of the rac-BNO and an equimolar amount of Me₄N⁺·Cl⁻ from MeOH (7 ml) and MeOH (15 ml) gave a 1:1:1 racemic complex, BNO·Me₄N⁺·Cl⁻·MeOH and a 1:1 conglomerate complex, BNO·Me₄N⁺·Cl⁻, respectively. Novel transformation of the former racemate into the latter conglomerate occurred by heating or by exposure to MeOH vapor in the solid state.     

The visible light responsive properties of organogel based on anthracene-substituted acylhydrazone derivative

AHP-T8 exhibited a significant gelation-induced emission effect. In addition, its organogel and xerogel showed visible light responsive behaviors due to the trans-cis isomerizations of -C=N- bond. The organogel can turn into solution upon visible light irradiation.     

Heat‐Induced Supramolecular Organogels Composed of α‐Cyclodextrin and “Jellyfish‐Like” β‐Cyclodextrin–Poly(ε‐caprolactone)

In general, the complexation and gelation behavior between biocompatible poly(ε‐caprolactone) (PCL) derivatives and α‐cyclodextrin (α‐CD) is extensively studied in water, but not in organic solvents. In this article, the complexation and gelation behavior between α‐CD and multi‐arm polymer β‐cyclodextrin‐PCL (β‐CD‐PCL) with a unique “jellyfish‐like” structure are thoroughly investigated in organic solvent N,N‐dimethylformamide and a new heat‐induced organogel is obtained. However, PCL linear polymers cannot form organogels under the same condition. The complexation is characterized by rheological measurements, DSC, XRD, and SEM. The SEM images reveal that the complexes between β‐CD‐PCL and α‐CD present a novel topological helix porous structure which is distinctly different from the lamellar structure formed by PCL linear polymers and α‐CD, suggesting the unique “jellyfish‐like” structure of β‐CD‐PCL is crucial for the formation of the organogels. This research may provide insight into constructing new supramolecular organogels and potential for designing new functional biomaterials. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1598–1606     

Excess Gibbs energies of the ternary system ethanol+N,N-dimethylformamide+cyclohexane at 298.15 K

Vapour–liquid equilibrium (VLE) for the ternary system ethanol (EtOH)+N,N-dimethylformamide (DMF)+cyclohexane (Cy) and for the relevant binary mixtures containing DMF have been determined at 298.15 K by headspace gas chromatographic analysis of the vapour phase directly withdrawn from an equilibrium apparatus. Measurements of liquid–liquid equilibria in both binary DMF+Cy and ternary mixtures have been also carried out. The binary VLE data have been described with different correlation equations. The capabilities of different models of either predicting or reproducing the ternary data have been compared. Excess Gibbs energies G^E as well as activity coefficients γ_i of components have been obtained and briefly discussed. While EtOH+DMF behaves almost ideally with slightly negative G^E-values, both EtOH+Cy and DMF+Cy exhibit large positive deviations. The G^Es of the ternary system are positive with the exception of a narrow region in dilute Cy. The excess entropy and the temperature dependence of G^E and γ_i have been calculated in the whole ternary domain from the known excess enthalpy and heat capacity. The predictions by different equations of the effect of temperature on the mutual solubilities of DMF and Cy as well as on the binodal curve of EtOH+DMF+Cy have been compared with experiment.     

Combination of an aromatic core and aromatic side chains which constitutes discotic liquid crystal and organogel supramolecular assemblies

This paper reports unique and unusual formations of columnar liquid crystals and organogels by self-assembling discotic molecules, which are composed of an aromatic hexaazatriphenylene (HAT) core and six flexible aromatic side chains. In HAT derivatives 3a, with 4'-(N,N-diphenylamino)biphenyl-4-yl chains, 3b, with 4'-[N-(2-naphthyl)-N-phenylamino]biphenyl-4-yl chains, and 3c, with 4'-phenoxybiphenyl-4-yl chains, the two-dimensional hexagonal packings can be created by their self-assembling in the liquid crystalline phase, which were characterized by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction analysis. In certain solvents, HAT molecules 3a-c can form the viscoelastic fluid organogels, in which one-dimensional aggregates composed of the HAT molecules are self-assembled and entangled into three-dimensional network structures. The organogel structures were analyzed by scanning electron microscopy observation, (1)H NMR, UV-vis, and circular dichroism spectroscopy. In contrast to 3a-c, none of the liquid crystalline and organogel phases could be formed from 3d and 3e with short aromatic side chains including a phenylene spacer, and 3f (except a few specific solutions) and 3g without terminal diarylamino and phenoxy groups. In 3a-c, the aromatic side chains with terminal flexible groups make up soft regions that cooperatively stabilize the liquid crystalline and organogel supramolecular structures together with the hard regions of the hexaazatriphenylene core.     

Synthesis, crystal structures and thermal properties of new copper(I)halide 2-ethylpyrazine coordination polymers: the influence of solid-state kinetics on product formation

Three new copper(I) coordination polymers were prepared by the reaction of copper(I) chloride with 2-ethylpyrazine in water at room temperature or under solvothermal conditions. In poly[CuCl(μ₂-2-ethylpyrazine-N,N′)] (I), “zig-zag”-like CuCl chains are present, which are connected by the 2-ethylpyrazine ligand to a three-dimensional network. In comparison in catena[Cu₃Cl₃(μ₂-2-ethylpyrazine-N,N′)₂] (II) six-membered Cu₃Cl₃ rings occur, which are connected to chains by the organic ligands. In poly[Cu₂Cl₂(μ₂-2-ethylpyrazine-N,N′)] (III), CuCl double chains are found, which are linked by the ligands to form sheets. The thermal behaviour of the different compounds was investigated using simultaneous thermogravimetry, differential thermoanalysis and mass spectroscopy as well as temperature-dependent X-ray powder diffraction. Two mass steps are found upon heating compound I in a thermobalance with 1°C/min, where the first corresponds to the transformation into compound III, and the second to the loss of the remaining ligands under formation of CuCl. If the heating rate is increased to 16°C/min, compound II is formed as an intermediate in a consecutive reaction. Therefore, the product formation depends on the actual heating rate, which shows that the solid-state kinetics plays an important role in such thermal reactions.     

A new photo-responsive organogel containing benzophenone group

Benzophenone group was introduced into the gel system in order to fabricate a new ALS₂ organogel which was photo-responsive. In the gel state with mixed solvent of acetone and water (5%), helical fibres were formed. The light control on the morphological change from fibres to core–shell spheres was followed by transmission electron microscope, which supplied a new paradigm for the morphology control triggered by stimulus. Moreover, the gel could serve as light absorbent without being mixed with polymer.