A Systematic Study of Peripherally Multiple Aromatic Ester-Functionalized Poly(benzyl ether) Dendrons for the Fabrication of Organogels: Structure-Property Relationships and Thixotropic Property

Functional supramolecular gels based on poly(benzyl ether) dendrons and dendrimers

Supramolecular gels, as a fascinating and useful class of soft materials, constructed from low-molecular-weight gelators via noncovalent interactions have attracted increasing attention in the past few decades. Dendrimers and dendrons are highly branched and monodisperse macromolecules with a well-defined three-dimensional architecture and multiple surface functionalities. In recent years, poly(benzyl ether) dendrimers and dendrons are found to be powerful candidates for constructing gel phase materials in organic or aqueous media due to the advantages of capability of forming multiple noncovalent interactions and significant steric impact. In this Feature Article, we provide a comprehensive overview of recent progress in supramolecular gels involving poly(benzyl ether) dendritic molecules. Firstly, we outline the molecular design strategies of dendritic gelators with an emphasis on the discussion of their gelating units and position in molecular structures. Subsequently, we discuss the potential applications of dendritic gels in light harvesting, stimuli responsive materials, sensors and environmental remediation. In addition, the potential challenges and future perspectives of poly(benzyl ether) dendritic gels have also been discussed. It is hoped that this feature article will attract increasing attention and provide some valuable insights for the future design and evolution of supramolecular gels.

Quinoline-cored Poly(Aryl Ether) Dendritic Organogels with Multiple Stimuli-Responsive and Adsorptive Properties

Functional supramolecular gel materials have potential applications in sensors, optical switches, artificial antennae, drug delivery and so on. In this paper, quinoline-cored poly(aryl ether) dendritic organogelators were designed, synthesized and fully characterized. The gelation behaviour of the dendritic organogelator was tested in organic solvents, mixed solvents and ionic liquids. The dendron Q-G1 was found to be an efficient and versatile organogelator toward various apolar and polar organic solvents with the critical gelation concentrations (CGCs) approaching 1.2×10^-2  mol/L, indicating one dendritic organogelator could immobilize 1.2×10³ solvent molecules in the organogel network. Interestingly, these dendrons exhibited excellent gel formation in ionic liquids. Notably, these dendritic organogels were found to display multiple stimuli-responsive properties toward external stimuli including heat, ultrasound and shear stress, with a reversible sol-gel phase transition. In addition, the dendritic organogel could effectively adsorb heavy metals and organic dyes. The removal rate of Pb²⁺ was up to 20% and the adsorption rate for Rhodamine B was as high as 89%.

Complexation of Injectable Biphasic Calcium Phosphate with Phosphoserine-Presenting Dendrons with Enhanced Osteoregenerative Properties

Injectable biphasic calcium phosphates have been proposed as a solution in the treatment of a range of clinical applications including as fillers in the augmentation of osteoporotic bone. To date, various biodegradable natural or synthetic organics have been used as a polymer component of bone materials to increase their cohesiveness. Herein, a novel bone material was developed combining osteoconductive biphasic calcium phosphate (BCP) nanoparticles with phosphoserine-tethered generation 3 poly(epsilon-lysine) dendron (G3-K PS), a class of hyperbranched peptides previously shown to induce biomineralization and stem cell osteogenic differentiation. Strontium was also incorporated into the BCP nanocrystals (SrBCP) to prevent bone resorption. Within 24 h, an antiwashout behavior was observed in G3-K PS-integrated pure BCP group (BCPG3). Moreover, both in vitro tests by relevant cell phenotypes and an in vivo tissue regeneration study by an osteoporotic animal bone implantation showed that the integration of G3-K PS would downregulate Cxcl9 gene and protein expressions, thus enhancing bone regeneration measured as bone mineral density, new bone volume ratio, and trabecular microarchitectural parameters. However, no synergistic effect was found when Sr was incorporated into the BCPG3 bone pastes. Notably, results indicated a concomitant reduction of bone regeneration potential assessed as reduced Runx2 and PINP expression when bone resorptive RANKL and CTX-I levels were reduced by Sr supplementation. Altogether, the results suggest the potential of injectable BCPG3 bone materials in the treatment of osteoporotic bone defects.

Discotic Organic Gelators in Ion Sensing, Metallogel Formation, and Bioinspired Catalysis

Two organogelators G2 and G3 with a carboxamide group have been synthesized and characterized with different spectroscopic tools. Dimethylformamide or dimethyl sulfoxide solutions of both the compounds upon the addition of a minute quantity of water show the tendency to form gels. Supramolecular self-assembly for gel formation paves the way for aggregation-induced emission enhancement (AIEE) phenomena for both the gelator molecules. Introduction of metal ions in organogels strengthens the gel property without much affecting the fluorescence behavior. However, the introduction of Ag⁺, Fe²⁺, and Fe³⁺ ions in the G2 organogel separately results in total quenching of AIEE, making it possible to sense that particular cation in the gel state. The G3 organogel shows a similar behavior with the Fe²⁺ ion. Remarkably, other metallogels such as Ni(II)G2 and Co(II)G2 can sense sulfide ion and Cu(II)G2 can sense iodide ion by switching off the fluorescence even in multianalyte conditions. Furthermore, the copper-based metallogel Cu(II)G2 can be utilized as a catalyst and reaction medium for aerobic oxidation of catechol to quinone. To the best of our knowledge, this is the first attempt known so far to utilize a metallogel material for bioinspired catalysis such as catechol oxidation.

A class of polytriazole metallogels via CuAAC polymerization: preparation and properties

Coordination-driven polytriazole metallogels possess good self-healing abilities.

From Weakness to Strength: C-H/π-Interaction-Guided Self-Assembly and Gelation of Poly(benzyl ether) Dendrimers

The C-H/π interactions as the key driving force for the construction of supramolecular gels remain a great challenge because of their weak nature. We hereby employed for the first time weak C-H/π interactions for the construction of supramolecular dendritic gels based on peripherally methyl-functionalized poly(benzyl ether) dendrimers. Their gelation property is highly dependent on the nature of the peripheral methyl groups. Furthermore, single-crystal X-ray analysis and NMR spectroscopy revealed that multiple C-H/π interactions between the proton of the methyl group and the electron-rich peripheral methyl-substituted aryl ring played significant roles in the formation of supramolecular nanofibers and organogels. This study uncovers the critical role of weak noncovalent interactions and provides new insights into the further design of self-assembled nanomaterials.

Functional organogelators formed by liquid-crystal carbazole-containing bis-MPA dendrimers

Functional organogels based on carbazole-containing liquid crystal block codendrimers that show an increased fluorescence emission and redox properties.

Halogen-bonding for visual chloride ion sensing: a case study using supramolecular poly(aryl ether) dendritic organogel systems

A convenient and straightforward method for the visual recognition of chloride ion has been established through a chloride-responsive dendritic organogel.

Long-chain alkylamide-derived oil gels: mixing induced onset of thixotropy and application in sustained drug release

Oil gels composed of long-chain alkylamides exhibited thixotropic properties, although the same property was absent in each alkylamide.

Self-assembly of azobenzene-based two-component gels

Two-component gels were formed and their photophysical properties were dependent on the ratio of the two compounds.