Responsive Self-Assembly of Supramolecular Hydrogel Based on Zwitterionic Liquid Asymmetric Gemini Guest

Click Chemoselective Probe with a Photoswitchable Handle for Highly Sensitive Determination of Steroid Hormones in Food Samples

Residues of endocrine disrupting steroid hormones in food might cause various diseases like cardiovascular diseases and breast and prostate cancers. Monitoring steroid hormone levels plays a vital role in ensuring food safety and exploring the pathogenic mechanism of steroid hormone-related diseases. Based on the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction, a novel chemoselective probe, Azo-N3, which contains a reactive site N3, an imidazolium salt-based MS tag, and an azobenzene-based photoswitchable handle, was designed and synthesized to label ethynyl-bearing steroid hormones. The probe Azo-N3 was applied for the highly selective and sensitive detection of four ethynyl-bearing steroid hormones in food samples (milk, egg, and pork) by using ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The ionization efficiency of the labeled analytes could be increased by 6-105-fold, and such a labeled method exhibited satisfactory detection limits (0.04-0.2 μg/L), recovery (80.6-122.4%), and precision (RSDs% lower than 6.9%). Interestingly, the efficient immobilization of the probe Azo-N3 onto α-cyclodextrin (α-CD)-modified magnetic particles to construct a solid supported chemoselective probe Fe3O4-CD-Azo-N3 and UV light-controlled release of the labeled analytes from a magnetic support can be achieved by taking advantage of the photoswitched host-guest inclusion between the azobenzene unit and α-CD. The potential applications of Fe3O4-CD-Azo-N3 for labeling, capturing, and the photocontrolled release of the labeled steroid hormones were fully investigated by mass spectrometry imaging analysis. This work not only provides a sensitive and accurate method to detect steroid hormones in food but also opens a new avenue in designing solid supported chemoselective probes.

Rheological behavior of thread-like fiber solutions formed from a rosin-based surfactant with two head groups

Wormlike micelles are conventional aggregates that exist in viscoelastic solutions. However, to achieve a solution with prominent viscoelasticity, rather high concentrations of surfactants are usually required due to the flexibility of aggregates in solution. If thread-like aggregates with rigidity can be formed by surfactants, the solutions are expected to show strong viscoelasticity at very low surfactant concentrations. Herein, A novel rosin-based quaternary ammonium surfactant with two head groups (abbreviated as R-11-3-DA) was synthesized. Cryogenic transmission electron microscopy (Cryo-TEM) images showed that flexible nanofibers with diameters of about 7-8 nm and lengths of over 1 μm were formed in the 1 : 1.5 R-11-3-DA : SL solutions. The rigidity of the aggregates seems to be inherited from the rigidity of the surfactant molecules. The novel aggregates endow the solutions with remarkable viscoelasticity at very low concentrations, with a critical overlap concentration of 0.01 wt% and a critical gelling concentration of 0.58 wt%. The rheological behavior of the solutions also shows excellent shear resistance and weak sensitivity to temperature below the critical gelation temperature (T_gel). This work reveals the advantages of viscoelastic solutions containing flexible nanofibers. The design principles of new molecular structures and system compositions can be applied to the preparation of smart soft materials based on the self-assembly of molecules.

Azobenzene Based Photo-Responsive Hydrogel: Synthesis, Self-Assembly, and Antimicrobial Activity

A new azobenzene-based symmetric amphiphile was synthesized and characterized using ¹H NMR spectroscopy. Its self-assembly behavior as well as photo-responsive behavior in its solution and gel states were investigated. Such a compound can self-assemble into fiber mesophases in water solvent. After irradiation of the gels with UV light, the trans isomer of the compound rapidly photoisomerized to the cis isomer, which resulted in a rapid destruction of the gel. High temperature also caused a rapid drop in viscosity. To verify the antimicrobial activity of the hydrogel, live and death assays of human fibroblasts L929 properties were used for in vitro cell viability studies. The compound was converted to the terminal tertiary amine in a quaternary ammonium salt molecule by using hydrochloric acid. This azobenzene quaternary ammonium salt has a relatively better antimicrobial effect biocidal activity that was demonstrated when challenged against Escherichia coli on in vitro conditions.

Multicharged cyclodextrin supramolecular assemblies

Multicharged cyclodextrin (CD) supramolecular assemblies, including those based on positively/negatively charged modified mono-6-deoxy-CDs, per-6-deoxy-CDs, and random 2,3,6-deoxy-CDs, as well as parent CDs binding positively/negatively charged guests, have been extensively applied in chemistry, materials science, medicine, biological science, catalysis, and other fields. In this review, we primarily focus on summarizing the recent advances in positively/negatively charged CDs and parent CDs encapsulating positively/negatively charged guests, especially the construction process of supramolecular assemblies and their applications. Compared with uncharged CDs, multicharged CDs display remarkably high antiviral and antibacterial activity as well as efficient protein fibrosis inhibition. Meanwhile, charged CDs can interact with oppositely charged dyes, drugs, polymers, and biomacromolecules to achieve effective encapsulation and aggregation. Consequently, multicharged CD supramolecular assemblies show great advantages in improving drug-delivery efficiency, the luminescence properties of materials, molecular recognition and imaging, and the toughness of supramolecular hydrogels, in addition to enabling the construction of multistimuli-responsive assemblies. These features are anticipated to not only promote the development of CD-based supramolecular chemistry but also contribute to the rapid exploitation of these assemblies in diverse interdisciplinary applications.

Stimuli-Responsive Biomolecule-Based Hydrogels and Their Applications

This Review presents polysaccharides, oligosaccharides, nucleic acids, peptides, and proteins as functional stimuli-responsive polymer scaffolds that yield hydrogels with controlled stiffness. Different physical or chemical triggers can be used to structurally reconfigure the crosslinking units and control the stiffness of the hydrogels. The integration of stimuli-responsive supramolecular complexes and stimuli-responsive biomolecular units as crosslinkers leads to hybrid hydrogels undergoing reversible triggered transitions across different stiffness states. Different applications of stimuli-responsive biomolecule-based hydrogels are discussed. The assembly of stimuli-responsive biomolecule-based hydrogel films on surfaces and their applications are discussed. The coating of drug-loaded nanoparticles with stimuli-responsive hydrogels for controlled drug release is also presented.

Wholly Visible-Light-Responsive Host-Guest Supramolecular Gels Based on Methoxy Azobenzene and β-Cyclodextrin Dimers

Much attention has been paid to construct photoresponsive host-guest supramolecular gels; however, red-shifting the responsive wavelength remains a formidable challenge. Here, a wholly visible-light-responsive supramolecular gel was fabricated through the host-guest interaction between a β-cyclodextrin (β-CD) dimer and a tetra-ortho-methoxy-substituted azobenzene (mAzo) dimer (binary gelator) in DMSO/H₂O (V/V = 8/2). The minimum gelation concentration of the low-molecular-weight binary gelator was 6 wt % measured via the tube inversion method. The substituted methoxy groups shifted the responsive wavelengths of trans-mAzo and cis-mAzo to the green and blue light regions, respectively. The host-guest interaction between mAzo and β-CD as the driving force for gelation was confirmed using the ¹H-NMR and 2D ¹H NOESY spectra. The supramolecular gel showed good self-supporting ability with a storage modulus higher than 10⁴ Pa. The release of Rhodamine B loaded in the gel as a model drug could be controlled by green light irradiation. We envisioned the potential applications of the wholly visible-light-responsive supramolecular compounds ranging from biomedical materials to smart materials.

Dynamic Assemblies of Molecular Motor Amphiphiles Control Macroscopic Foam Properties

Stimuli-responsive supramolecular assemblies controlling macroscopic transformations with high structural fluidity, i.e., foam properties, have attractive prospects for applications in soft materials ranging from biomedical systems to industrial processes, e.g., textile coloring. However, identifying the key processes for the amplification of molecular motion to a macroscopic level response is of fundamental importance for exerting the full potential of macroscopic structural transformations by external stimuli. Herein, we demonstrate the control of dynamic supramolecular assemblies in aqueous media and as a consequence their macroscopic foam properties, e.g., foamability and foam stability, by large geometrical transformations of dual light/heat stimuli-responsive molecular motor amphiphiles. Detailed insight into the reversible photoisomerization and thermal helix inversion at the molecular level, supramolecular assembly transformations at the microscopic level, and the stimuli-responsive foam properties at the macroscopic level, as determined by UV-vis absorption and NMR spectroscopies, electron microscopy, and foamability and in situ surface tension measurements, is presented. By selective use of external stimuli, e.g., light or heat, multiple states and properties of macroscopic foams can be controlled with very dilute aqueous solutions of the motor amphiphiles (0.2 weight%), demonstrating the potential of multiple stimuli-responsive supramolecular systems based on an identical molecular amphiphile and providing opportunities for future soft materials.

Visible light-triggered gel-to-sol transition in halogen-bond-based supramolecules

Photoresponsive supramolecular gels have aroused continuous attention because of their extensive applications; however, most studies utilize UV light, which inevitably brings about some health and environmental issues. The halogen bond is an important driving force for constructing supramolecules due to its high directionality, tunable strength, good hydrophobicity, and large size of the halogen atoms. Yet, it still remains a formidable challenge to utilize halogen bonds as a driving force to fabricate a visible light responsive gel. In this work, to fabricate such a gel, azopyridine-containing Azopy-C_n (n = 8, 10, 12) was selected as a halogen bond acceptor, while 1,2-bis(2,3,5,6-tetrafluoro-4-iodophenyl)diazene (BTFIPD) was chosen as both the halogen bond donor and visible light responsive moiety. The visible light response of BTFIPD resulted from the significant separation of n-π* energy levels between trans and cis isomers due to the introduction of an electron-withdrawing group (fluorine) to azobenzene at the ortho-position. Interestingly, the gel exhibited a good gel-to-sol transition behavior upon green light irradiation. At the same time, the morphologies varied from uniform narrow flakes to broad sheets with increasing illumination time. We provide an environmentally-friendly visible light-triggered method to regulate the phase transition of supramolecular materials in applications ranging from energy conversion to information storage.