Self-assembled sonogels formed from 1,4-naphthalenedicarbonyldinicotinic acid hydrazide.

In this paper, we report self-assembled sonogels formed from 1,4-naphthalenedicarbonyldinicotinic acid hydrazide (NDC-NN3) in some liquids including ethanol, tetrahydrofuran (THF), 1,4-dioxane, n-propanol, n-butanol and n-pentanol. When the clear solution of NDC-NN3 in the selected liquids mentioned above at a suitable concentration was irradiated with ultrasound waves at room temperature, a sonogel was formed. Upon heating, the sonogel dissolved gradually and finally became a clear solution again. Upon cooling the hot solution to room temperature, the solution state did not change even after standing for a few days. Nevertheless, if the solution underwent sonication for a certain time, a stable gel was obtained again. The critical gelation concentrations (CGCs) of NDC-NN3 in ethanol, THF, 1,4-dioxane, n-propanol, n-butanol and n-pentanol are 10, 8, 6, 8, 6 and 8 mg mL-1, respectively. The obtained sonogels display excellent mechanical properties. The crystal structure of NDC-NN3 suggests that the naphthalene ring, hydrazide group and the position of N in the pyridine ring mediate the self-assembly process. Upon sonication, the formation of suitable π-π stacking and intermolecular hydrogen bonding drives the gelator molecules to self-assemble into fibers, spheres and micro-burdock-shaped balls in various solvents, which ultimately confine the liquids.

Supramolecular gel formation regulated by water content in organic solvents: self-assembly mechanism and biomedical applications.

As one of the most important and fruitful methods, supramolecular self-assembly has a significant advantage in designing and fabricating functional soft materials with various nanostructures. In this research, a low-molecular-weight gelator, N,N'-di(pyridin-4-yl)-pyridine-3,5-dicarboxamide (PDA-N4), was synthesized and used to construct self-assembled gels via a solvent-mediated strategy. It was found that PDA-N4 could form supramolecular gels in mixed solvents of water and DMSO (or DMF) at high water fraction (greater than or equal to 50%). By decreasing the water fraction from 50% to 30%, the gel, suspension and solution phases appeared successively, indicating that self-assembled aggregates could be efficiently modulated via water content in organic solvents. Moreover, the as-prepared PDA-N4 supramolecular gels not only displayed solid-like behavior, and pH- and thermo-reversible characteristics, but also showed a solution-gel-crystal transition with the extension of aging time. Further analyses suggested that both the crystal and gel had similar assembled structures. The intermolecular hydrogen bonding between amide groups and the π-π stacking interactions between pyridine groups played key roles in gel formation. Additionally, the release behavior of vitamin B12 (VB12) from PDA-N4 gel (H2O/DMSO, v/v = 90/10) was evaluated, and the drug controlled release process was consistent with a first-order release mechanism. The human umbilical venous endothelial cell culture results showed that the PDA-N4 xerogel has good cytocompatibility, which implied that the gels have potential biological application in tissue engineering and controlled drug release.

Supramolecular organogels fabricated with dicarboxylic acids and primary alkyl amines: controllable self-assembled structures.

Supramolecular organogels are soft materials comprised of low-molecular-mass organic gelators (LMOGs) and organic liquids. Owning to their unique supramolecular structures and potential applications, LMOGs have attracted wide attention from chemists and biochemists. A new "superorganogel" system based on dicarboxylic acids and primary alkyl amines (R-NH2) from the formation of organogels is achieved in various organic media including strong and weak polar solvents. The gelation properties of these gelators strongly rely on the molecular structure. Their aggregation morphology in the as-obtained organogels can be controlled by the solvent polarity and the tail chain length of R-NH2. Interestingly, flower-like self-assemblies can be obtained in organic solvents with medium polarity, such as tetrahydrofuran, pyridine and dichloromethane, when the gelators possess a suitable length of carbon chain. Moreover, further analyses of Fourier transformation infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy reveal that the intermolecular acid-base interaction and van der Waals interaction are critical driving forces in the process of organogelation. In addition, this kind of organogel system displays excellent mechanical properties and thermo-reversibility, and its forming mechanism is also proposed.

A pH-/thermo-responsive hydrogel formed from N,N'-dibenzoyl-l-cystine: properties, self-assembly structure and release behavior of SA.

In this study, we report a pH-/thermo-responsive hydrogel formed by N,N'-dibenzoyl-l-cystine (DBC). It is difficult to dissolve DBC in water even on heating, and it exhibits no gelation ability. Interestingly, DBC is readily soluble in NaOH solution at room temperature and the self-assembled hydrogels are obtained by adjusting the basic DBC aqueous solution with HCl to achieve a given pH value (<3.5). When NaOH is added to the hydrogel (pH > 9.4), it becomes a sol again. This small-molecule hydrogel is characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, rheological measurement and differential scanning calorimetry. The results indicate that the DBC hydrogel exhibits excellent mechanical properties, thermo-reversibility, and pH-responsive properties. Fortunately, the single crystal of DBC is obtained by volatilizing its acid aqueous solution. It crystallizes in the monoclinic space group P21 (Z = 2) with lattice parameters a = 10.8180 (11) Å, b = 9.0405 (9) Å, c = 10.9871 (11) Å and ß = 90.798 (3)°. By comparing the X-ray diffraction result of the DBC single crystal with that of its xerogel, the self-assembled structure of DBC in hydrogel has been ascertained. The gelators are self-assembled via strong intermolecular hydrogen bonds linking neighboring amide and carboxyl groups, π-π stacking interactions for aromatic rings, and hydrogen bonds between water molecules. In addition, the release behavior of salicylic acid (SA) molecules from the DBC gel is also investigated taking into account the DBC concentration, phosphate buffer solution (PBS) pH and SA concentration. When the concentrations of DBC and SA are 3.0 g L-1 and 200 mg L-1, respectively, the release ratio in PBS (pH = 4.0) reaches 58.02%. The diffusion-controlled mechanism is in accordance with Fickian diffusion control within the given time range.

Self-assembled metallogels formed from N,N',N''-tris(4-pyridyl)trimesic amide in aqueous solution induced by Fe(III)/Fe(II) ions.

In this work, we report self-assembled metallogels formed from a ligand of trimesic amide, N,N',N''-tris(4-pyridyl)trimesic amide (TPTA), induced by Fe(III)/Fe(II) ions. TPTA is difficult to dissolve in water even in the presence of some metal ions such as Cu(2+), Co(2+), Ni(2+), K(+), Na(+) and Mg(2+) under heating, and it exhibits no gelation ability. Interestingly, upon heating TPTA can be dissolved easily in aqueous solution containing Fe(3+)/Fe(2+), and subsequently self-assembled into metallogels after cooling. The metallogels could also be formed in aqueous solutions of mixed metal ions containing Fe(3+)/Fe(2+), indicating that the other metal ions do not affect the formation of Fe(III)-TPTA and Fe(II)-TPTA metallogels. The high selectivity of metallogel formation to Fe(3+)/Fe(2+) may be used for application in the test of Fe(3+)/Fe(2+). The metallogels obtained are characterized by scanning electron microscopy, Fourier transform infrared spectra, nuclear magnetic resonance spectra, rheological measurements and scanning tunneling microscopy. The results indicate that TPTA can self-assemble into fibrous aggregates in Fe(3+)/Fe(2+) aqueous solution through the metal-ligand interactions and intermolecular hydrogen bonding. This kind of metallogel also possesses good mechanical properties and thermoreversibility.

A microporous hydrogen-bonded organic framework: exceptional stability and highly selective adsorption of gas and liquid.

An extremely stable hydrogen-bonded organic framework, HOF-8, was fabricated. HOF-8 is not only thermally stable but also stable in water and common organic solvents. More interestingly, desolvated HOF-8 exhibits high CO2 adsorption as well as highly selective CO2 and C6H6 adsorption at ambient temperature.

Two-component supramolecular organogels formed by maleic N-monoalkylamides and aliphatic amines.

The complexes of maleic N-monoalkylamides and aliphatic amines lead to the formation of sheet-like and fiber-shaped aggregates in diverse organic solvents. Their morphologies and microstructures were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), as well as small angle X-ray diffraction (SA-XRD). The results reveal that the alkyl chain lengths of 8-12 carbons for maleic N-monoalkylamides, and 12-18 carbons for aliphatic amines, are suitable for obtaining highly efficient two-component gelators.

Self-assembled organogels formed by monochain derivatives of ethylenediamine.

A family of low molecular weight organogelators (LMOG) based on monochain derivatives of ethylenediamine were investigated. The monochain derivatives of ethylenediamine show strong gelation ability in a number of organic solvents, including polar solvents and non-polar solvents. In gel state, molecules of monochain ethylenediamine derivatives self-assemble into ordered aggregates, which are juxtaposed and interlocked to form three-dimensional networks of fiber bundles as confirmed by scanning electron microscopy (SEM). The Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) studies demonstrate that intermolecular hydrogen bonds between neighboring molecules are critical factor in the process of organogelation.

Supramolecular organogels formed by monochain derivatives of succinic acid.

The monoalkyl chain derivatives of succinic acid self-assemble into ordered bilayer aggregates by forming dimers of hydrogen bonded carboxylic acid in a number of organic solvents and finally gelatinize the solvents. The gelation ability of each derivative was inspected. The morphologies of xerogels were investigated by scanning electron microscope (SEM). The microstructure of aggregates was studied by small angle X-ray diffraction (SA-XRD) and Fourier transform infrared spectroscopy (FT-IR). The results reveal that the intermolecular hydrogen bonds between neighboring molecules are critical factor in the process of organogelation.