Substrate selective catalytic molecular hydrogels: the role of the hydrophobic effect

A catalytic hydrogel is reported for the substrate selective direct aldol reaction of aliphatic ketones based on their hydrophobicity and on the emergence of catalytic activity only after self-assembly of the catalyst.

(-)-Menthol based thixotropic hydrogel and its application as a universal antibacterial carrier

A kind of novel hydrogelator based on (-)-menthol, a traditional cooling compound, tailed by an amino acid derivate through an alkyl chain, has been designed and synthesized. The hydrogelator containing an l-lysine can form a stable hydrogel with thixotropic character in a large pH range. An interesting feature is that the viscoelastic character of the hydrogel can be enhanced by mechanical force. The mechanism of the self-assembly process was investigated by means of IR, SEM, AFM and X-ray diffraction. The formation of three dimensional multiporous networks through acid base interactions and strong double hydrogen bonding between amino acids is proposed to be the driving force for the construction of the stable hydrogel. As a result, the hydrogelator can further gelate aqueous solutions of some confirmed antibacterial agents such as Zn(2+) and a series of water soluble organic antibiotic medicines like lincomycin, amoxicillin, etc., in such a unique way that the concentration of the antibacterial agents loaded into the hydrogel can be tuned to a large extent. The antimicrobial susceptibility of the hydrogels loaded with Zn(2+) or lincomycin is much more effective than that of the corresponding aqueous solution tested by the Oxford cup method. Furthermore, the hydrogelator is completely innoxious to living cells by measurement of MTT assay. Thus, the hydrogel can be developed as a universal carrier for antibacterial agents and may also be widely used in the fields of cell culture, tissue engineering, or drug delivery systems.

A multistimuli-responsive photochromic metal-organic gel

A photochromic metal-organic gel with thermo-, photo-, and anion-responsive behavior is obtained. Unusually, heating of the Al-ligand solution leads to gel formation and cooling to room temperature reverses the process to reform the solution. The gel is sensitive to weakly coordinating anions. Additionally, reversible photochromic transformations take place both in the solution and gel states, accompanied by reversibly switched luminescence.

Improving Hg-triggered gelation via structural modifications

The relationship between chemical structure and gelation ability was examined for a series of nine Hg-containing compounds. Both solid-state properties (dissolution enthalpies/entropies and packing structure) and gel properties (strength, morphology, cation selectivity, and anion tolerance) were examined. Overall, the results reveal a complex relationship between chemical structure and properties. The remediation potential of these Hg-triggered gelations was also investigated, revealing that >98% of the Hg(2+) in water can be removed through gel formation.

Templating the self-assembly of pristine carbon nanostructures in water

The low solubility of carbon nanostructures (CNs) in water and the need of ordered architectures at the nanoscale level are two major challenges for materials chemistry. Here we report that a novel amino acid based low-molecular-weight gelator (LMWG) can be used to effectively disperse pristine CNs in water and to drive their ordered self-assembly into supramolecular hydrogels. A non-covalent mechanochemical approach has been used, so the π-extended system of the CNs remains intact. Optical spectroscopy and electron microscopy confirmed the effective dispersion of the CNs in water. Electron microscopy of the hydrogels showed the formation of an ordered, LMWG-assisted, self-assembled architecture. Moreover, the very same strategy allows the solubilization and self-assembly in water of a variety of hydrophobic molecules.

Wholly π-conjugated low-molecular-weight organogelator that displays triple-channel responses to fluoride ions

A novel salicylidene aniline-based wholly π-conjugated molecule that could be self-assembled into an organogel was synthesized. The rigid organogel collapsed into fluid solutions with significant changes in UV-vis absorption and fluorescence colors in response to fluoride ions. It was found that the hydroxyl group in the salicylidene aniline moiety played a key role not only in the gelation but also in fluoride ion responses.

Light-controlled formation of vesicles and supramolecular organogels by a cholesterol-bearing amphiphilic molecular switch

A new responsive material composed of an amphiphilic light-switchable dithienylethene unit functionalized with a hydrophobic cholesterol unit and a hydrophilic poly(ethylene glycol)-modified pyridinium group has been designed. This unique single-molecule system shows responsive light-switchable self-assembly in both water and organic solvents. Light-triggered reversible vesicle formation in aqueous solutions is reported. The molecule shows a different behavior in apolar aromatic solvents, in which light-controlled formation of organogel fibers is observed. The light-triggered aggregation behavior of this molecule demonstrates that control of a supramolecular structure with light can be achieved in both aqueous and organic media and that this ability can be present in a single molecule. This opens the way toward the effective development of new strategies in soft nanotechnology for applications in controlled chemical release systems.

N-Alkylamido-d-glucamine-based gelators for the generation of thixotropic gels

Hydrogels made from new gelators exhibit thixotropic properties, whereas hydrogels formed with structurally similar N-alkyl-d-glucamide have a tendency to crystallize.

Co-assembly of tetrapeptides into complex pH-responsive molecular hydrogel networks

Here we prepare pH-responsive complex molecular hydrogels from oppositely charged tetrapeptidic components that can be pH-tuned resulting in interconversion between different networks.

Using gel morphology to control pore shape

Polymerisation of methyl methacrylate supramolecular gels followed by removal of the gelator imprints the gel morphology into the covalent polymer.

Onset of mixing-induced thixotropy in hydrogels by mixing two homologues of low-molecular-weight hydrogelators

We determined the onset of thixotropy in hydrogels when two homologues of low-molecular-weight hydrogelators, N-alkyl-d-glucamides (CnNG), were mixed.

Photoresponsive metallo-hydrogels based on visual discrimination of the positional isomers through selective thixotropic gel collapse

Incorporating the visual discrimination of 2,2′-bipyridine and self-healing properties, a novel photo-switchable metallo-hydrogel system is fabricated using a pincer-type Cu(ii) complex and 2,2′-azopyridine.

Creation of thixotropic multicomponent alkylamide organogels containing non-volatile oil as potential drug release host materials

Multicomponent alkylamide organogels containing non-volatile oils were generated as potential thixotropic host materials for medicinal applications such as ointments.

New triangular steroid-based A(LS)3 type gelators for selective fluoride sensing application

A new series of triangular steroid-based A(LS)₃ type gelators has been developed which exhibited selective fluoride sensing abilities. The gelation, self-assembly and anion sensing properties of these gelators could be controlled by systematically altering their molecular structures.

A new composite thixotropic hydrogel composed of a low-molecular-weight hydrogelator and a nanosheet

New composite comprised of low-molecular-weight hydrogelator and the nanosheet Laponite®, showed thixotropic behaviour.

Revealing strong nanocomposite hydrogels reinforced by cellulose nanocrystals: insight into morphologies and interactions

Understanding the reinforcement mechanism by dispersing nanoscale particles into a polymer matrix is a critical challenge toward refining control of the composite properties. In this paper, the morphologies and interactions of cellulose nanocrystal/poly(acrylic acid) (CNC/PAA) nanocomposite hydrogels are demystified based on a facile synthetic platform. Two sources of CNCs with different aspect ratios are applied to model the reinforcement process, and the uniaxial tensile measurements indicate that the CNC aspect ratio and the nanocomposite mechanical behaviors are coupled, where the values of aspect ratios and nonpermanent interactions between the fillers and matrix dominate the reinforcement. Dynamic mechanical analysis is performed to examine the nature of the constrained polymer as the semicrystalline fractions, and the results indicate that polymer chain mobility in the vicinity of CNC surfaces is significantly reduced, providing new insight into the origin of the reinforcement mechanism. Rheological analysis and transmission electron microscopy observations show that both stepwise dissociation and polymer chain rearrangements contribute to the viscoelastic behaviors of the nanocomposite hydrogels. The increased modulus of the hydrogels is correlated to the volume of the constrained polymer, where the CNCs impart significant enhancement to the entanglement network. This study of the structure-property relationship deepens the understanding of the filler reinforcement mechanism and provides valuable knowledge for designing high performance nanocomposite hydrogels from cellulose as a raw material.

A novel glucose/pH responsive low-molecular-weight organogel of easy recycling

A new phenylboronic acid based gelator was developed to prepare low-molecular-weight organogel (LMOG), which could interact with several solvents to assemble into a three-dimensional nanofiber network. (1)H NMR spectroscopy study suggests that the driving force for the gelation includes hydrogen bonding and π-π stacking. Evaluated by UV-spectroscopy, the gel showed a prompt initial response to glucose at low concentration of 0.012 mmol/mL, which is a critical concentration of venous plasma glucose for diabetes. Significantly, this organogel exhibits excellent sensitivity to glucose among seven sugars tested (i.e., mannitol, galactose, lactose, maltose, sucrose, and fructose). The proposed formation of hydrogen-bonded complexes during the glucose sensing was supported by our energy calculation. Meanwhile, this organogel exhibits pH-response. Importantly, this LMOG could be conveniently recycled and thus be reused.

In situ formation of steroidal supramolecular gels designed for drug release

In this work, a steroidal gelator containing an imine bond was synthesized, and its gelation behavior as well as a sensitivity of its gels towards acids was investigated. It was shown that the gels were acid-responsive, and that the gelator molecules could be prepared either by a conventional synthesis or directly in situ during the gel forming process. The gels prepared by both methods were studied and it was found that they had very similar macro- and microscopic properties. Furthermore, the possibility to use the gels as carriers for aromatic drugs such as 5-chloro-8-hydroxyquinoline, pyrazinecarboxamide, and antipyrine was investigated and the prepared two-component gels were studied with regard to their potential applications in drug delivery, particularly in a pH-controlled drug release.

Control of molecular gelation by chemical stimuli

Molecular gels are formed by the self-assembly of low-molecular weight compounds by weak non-covalent interactions and thus, they may be easily disassembled in response to external stimuli. Chemically sensitive gels can be prepared by introducing in the molecular design functional groups that may interact either by covalent or non-covalent forces with other molecules present in the medium. Functional molecular gels have been reported that are sensitive to acids, bases, ions, redox-active compounds, neutral species, reactive compounds and enzymes. Here we present a broad revision of the different chemical inputs that can be used to tune gel properties through some appealing application-based selected examples.