Multivalent Supramolecular Self-Assembly between β-Cyclodextrin Derivatives and Polyoxometalate for Photodegradation of Dyes and Antibiotics

Study on the anti-retrogradation of wheat amylopectin by addition of alkali-soluble glutenin

The retrogradation of wheat amylopectin during cold storage is the main reason for the increasing hardness of flour products such as steamed bread, bread and pastries, etc. Addition of gluten protein components is a green, safe, cheap and efficient method to inhibit the retrogradation of wheat amylopectin. In this paper, as being stored at 4 °C for 7 d, retrogradation rate of wheat amylopectin decreased from 55.02 % to 14.37 % after it was mixed with 20 % alkali-soluble glutenin (ASG) at 30 °C for 90 min, a 73.8 % reduction. The infrared results showed that the intensity of bending vibration of water molecules and intra-molecular β-sheet content of ASG decreased during the interaction between amylopectin and ASG. Meanwhile, intermolecular β-sheet and random coil contents of ASG increased. The results of 13C Solid-state NMR indicated that Qβ, Pγ and Lγ of ASG involved in interaction of wheat amylopectin, ASG and molecule of water. Under the optimal conditions, the interaction of wheat amylopectin and ASG began to form spheres containing disulfide bonds, resulting in the attenuation or disappearance of the diffraction peak at 2θ 19.7°, which may be marked as the criterion for the best mixing time of wheat amylopectin and ASG. The retrogradation kinetic index (n) of wheat amylopectin decreased significantly with the addition of ASG and formation of disulfide bond was the key factor. ASG could be potentially used as an anti-retrogradation agent for amylopectin.

Switchable Redox and Thermo-Responsive Supramolecular Polymers Based on Cyclodextrin-Polyoxometalate Tandem

Supramolecular polymers built from stimuli-responsive host-guest interactions represent an attractive way of tailoring smart materials. Herein, we exploit the chaotropic effect of polyoxometalates and related host-guest properties to design unconventional polymer systems with reversible redox and thermo-responsive sol-gel transition. These supramolecular networks result from the association of cyclodextrin-based oligomers and Keggin-type POMs acting as electro-active crosslinking agents. The structure and the dynamics of such self-assembly systems have been investigated using a multiscale approach involving MALDI-TOF, viscosity measurements, cyclic voltammetry, 1 H-NMR (1D and DOSY), and Small-Angle X-ray Scattering. Our results reveal that the chaotropic effect corresponds to a powerful and efficient force that can be used to induce responsiveness in hybrid supramolecular oligomeric systems.

A Nickel-Containing Polyoxomolybdate as an Efficient Antibacterial Agent for Water Treatment

In view of the water pollution issues caused by pathogenic microorganisms and harmful organic contaminants, nontoxic, environmentally friendly, and efficient antimicrobial agents are urgently required. Herein, a nickel-based Keggin polyoxomolybdate [Ni(L)(HL)]₂H[PMo₁₂O₄₀] 4H₂O (1, HL = 2-acetylpyrazine thiosemicarbazone) was prepared via a facile hydrothermal method and successfully characterized. Compound 1 exhibited high stability in a wide range of pH values from 4 to 10. 1 demonstrated significant antibacterial activity, with minimum inhibitory concentration (MIC) values in the range of 0.0019–0.2400 µg/mL against four types of bacteria, including Staphylococcus aureus (S. aureus), Bacillus subtilis (B. subtilis), Escherichia coli (E. coli), and Agrobacterium tumefaciens (A. tumefaciens). Further time-kill studies indicated that 1 killed almost all (99.9%) of E. coli and S. aureus. Meanwhile, the possible antibacterial mechanism was explored, and the results indicate that the antibacterial properties of 1 originate from the synergistic effect between [Ni(L)(HL)]⁺ and [PMo₁₂O₄₀]³⁻. In addition, 1 presented effective adsorption of basic fuchsin (BF) dyes. The kinetic data fitted a pseudo-second-order kinetic model well, and the maximum adsorption efficiency for the BF dyes (29.81 mg/g) was determined by the data fit of the Freundlich isotherm model. The results show that BF adsorption was dominated by both chemical adsorption and multilayer adsorption. This work provides evidence that 1 has potential to effectively remove dyes and pathogenic bacteria from wastewater.

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.

Lanthanide Luminescence Supramolecular Switch Based on Photoreactive Ammonium Molybdate

Lanthanide supramolecular assemblies as photoswitches have attracted much attention in the fields of cellular imaging and light-emitting materials. However, the regulation of lanthanide luminescence behavior by redox of metal ions is rare. Herein, we constructed a lanthanide luminescence supramolecular switch, that is, a binary assembly constructed by mono-(6-ethylenediamine-6-deoxy)-β-cyclodextrin (ECD) and ammonium molybdate tetrahydrate ((NH₄)₆Mo₇O₂₄·4H₂O, Mo₇), and further assembled into ternary assemblies with polyoxometalate Na₉[XW₁₀O₃₆]·32H₂O (X-POM, X = Eu and Dy), which was comprehensively characterized by UV-vis, fluorescence, NMR, Fourier transform infrared, dynamic light scattering, scanning electron microscopy, and ζ potential. Thanks to the oxygen-shielding effect of secondary supramolecular assembly, the photoreduction process of Mo₇ (VI) could occur rapidly and efficiently. Due to the high Förster resonance energy transfer (FRET) efficiency of X-POM and Mo₇ (V) in supramolecular assembly, the photoreduction process is accompanied by fluorescence quenching. In addition, the oxidation process of the Mo₇ (V) could be rapidly promoted by heating, which allowed the X-POM fluorescence to recover. Interestingly, ECD-mediated ternary supramolecular assemblies not only tune the lanthanide luminescence but also strongly increase the lanthanide luminescence behavior, leading to the emission of strong narrow red light at ⁵D₀-⁷F₄, which can be successfully applied to two-dimensional code anticounterfeiting. In this study, a new approach is provided for the construction of lanthanide luminescence supramolecular switches tuned by photoreactive polyoxometalate.

Cyclodextrin-Cross-Linked Hydrogels for Adsorption and Photodegradation of Cationic Dyes in Aqueous Solution

Possessing three-dimensional porous structures and tunable mechanical strengths, cyclodextrin-containing polymeric hydrogels are one of the most promising water-based adsorbent materials due to their easy availability, simple chemical modification and environmental friendliness. In this work, two kinds of hydrogels were prepared via the copolymerization with acrylic acid and vinyl-derivatized β-cyclodextrins in water. These two gels have showed good adsorption performance towards cationic dyes through the noncovalent interactions with their anionic backbones and porous network. Meanwhile, pseudo-second-order model was selected to clarify the adsorption kinetics process. Moreover, nano-scaled TiO₂ was doped into these resultant cyclodextrins-based hydrogels to achieve efficient degradation of dyes upon light irradiation. The obtained TiO₂ -loaded hydrogels could exhibit improved adsorption performance and make the adsorbed dyes photo-degraded with the decolorization rates above 95%. It can be envisioned that such cyclodextrin-based soft materials may find applications in dye clearance and water treatment.

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

Due to the unique characteristics of macrocycles (e.g., the ease of modification, hydrophobic cavities, and specific guest recognition), they can provide a suitable environment to realize photocatalysis via noncovalent interactions with different substrates. In this minireview, we emphasized the photochemical transformation and catalytic reactivity of different guests based on the binding with various macrocyclic hosts as well as on the role of macrocyclic-hosts-assisted hybrid materials in energy transfer. To keep the clarity of this review, the macrocycles are categorized into the most commonly used supramolecular hosts, including crown ethers, cyclodextrins, cucurbiturils, calixarenes, and pillararenes. This minireview not only summarizes the role that macrocycles play in photocatalytic reactions but also clarifies the photocatalytic mechanisms. Finally, the future research efforts and new pathways to apply macrocycles and supramolecular hybrid materials in photocatalysis are also discussed.

Photocatalytic remediation of organic waste over Keggin-based polyoxometalate materials: A review

Photocatalytic remediation of industrial water pollution has courted intense attention lately due to its touted green approach. In this respect, Keggin-based polyoxometalates (POMs) as green solid acids in photocatalytic reaction possess superior qualities, viz. unique photoinduced charge-transfer properties, strong photooxidative-photoreductive ability, high chemical and thermal stability, and so forth. Unfortunately, it suffers from a large bandgap energy, low specific surface area, low recoverability, and scarce utilization in narrow absorption range. Therefore, the pollutant degradation performance is not satisfactory. Consequently, multifarious research to enhance the photocatalytic performance of Keggin-based POMs were reported, viz. via novel modifications and functionalizations through a variety of materials, inclusive of, inter alia, metal oxides, transition metals, noble metals, and others. In order to advocate this emerging technology, current review work provides a systematic overview on recent advancement, initiated from the strategized synthetic methods, followed by hierarchical enhancement and intensification process, at the same time emphasizes on the fundamental working principles of Keggin-based POM nanocomposites. By reviewing and summarizing the efforts adopted global-wide, this review is ended with providing useful outlooks for future studies. It is also anticipated to shed light on producing Keggin-based POM nanocomposites with breakthrough visible- and solar-light-driven photocatalytic performance against recalcitrant organic waste.

Self-Assembled Nano-Fe3C Embedded in Reduced Graphene Oxide Aerogel with Efficient Fenton-Like Catalysis

Aiming at the removal of refractory organic pollutants in aqueous solution, self-assembled nano-Fe3C embedded in reduced graphene oxide (nano-Fe3C@RGO) aerogel was prepared by hydrothermal synthesis and high temperature treatment, and characterized by SEM, HRTEM, pore size distribution, XRD, XPS and FTIR. The results showed that the aerogel was porous, and most of the Fe3C particles were less than 100 nm in size. They were evenly dispersed and embedded in the RGO aerogel. Furthermore, the mapping images confirmed that the elements of carbon, nitrogen and iron were homogeneously distributed. Moreover, the specific surface area of the aerogel was up to 324.770 m2/g and most of the pore sizes were between 5 and 10 nm. The formation of nano-Fe3C was identified by XRD pattern and HRTEM. Analysis of an XPS spectrum indicates that the nano-Fe3C was embedded in the graphene layer. The aerogel contained a large number of functional groups, including -NH2-NH and -C=O, etc., which greatly strengthened the adsorption of organics. Finally, the Fenton-like catalytic degradation properties of the self-assembled nano-Fe3C@RGO aerogel were investigated by testing the removal of methyl orange from the aqueous solution. The results showed that the value of Ct/C0 decreased to 0.050 after 240 min, suggesting a high degradation rate was obtained. Meanwhile, the chemical reaction was verified in accordance with the first-order kinetic model, and the higher temperature was beneficial to the catalytic degradation. At the same time, methyl orange was degraded into small molecules by the hydroxyl and superoxide radicals generated during the reactions. Therefore, the self-assembled nano-Fe3C@RGO aerogel, as a novel Fenton-like catalyst, introduces a new approach in the field of treatment of refractory organic wastewater.

Selective Decoating-Induced Activation of Supramolecularly Coated Toxic Nanoparticles for Multiple Applications

In spite of the rapid emergence of numerous nanoparticles (NPs) for biomedical applications, it is often challenging to precisely control, or effectively tame, the bioactivity/toxicity of NPs, thereby exhibiting limited applications in biomedical areas. Herein, we report the construction of hyaluronic acid (HA)-laminated, otherwise toxic methylviologen (MV), NPs via ternary host-guest complexation among cucurbit[8]uril, trans-azobenzene-conjugated HA, and MV-functionalized polylactic acid NPs (MV-NPs). The high, nonspecific toxicity of MV-NPs was effectively shielded (turned off) by HA lamination, as demonstrated in cells, zebrafish, and mouse models. The supramolecular host-guest interaction-mediated HA coating offered several HA-MV-NP modalities, including hyaluronidase locally and photoirradiation remotely, to precisely remove HA lamination on demand, thereby endowing materials with the capability of selective decoating-induced activation (DIA) for applications as a user-friendly herbicide, a selective antibacterial agent, or an anticancer nanomedicine. This work offers facile supramolecular coating and DIA strategies to effectively tame and precisely control the bioactivity and toxicity of functional nanomaterials for diverse applications.

A dual surface inorganic molecularly imprinted Bi2WO6-CuO/Ag2O heterostructure with enhanced activity-selectivity towards the photocatalytic degradation of target contaminants

The proposed mechanism reveals that under visible light, MG and AO dyes can be selectively degraded by produced radicals at the surface of the inorganic molecularly imprinted Ag₂O-CuO-Bi₂WO₆ heterojunction.