Guest Moieties Research Articles

Modular and Photoreversible Polymer-Nanoparticle Hydrogels via Host-Guest Interactions.

Polymer-nanoparticle (PNP) hydrogels are a class of nanocomposite materials showing potential as injectable platforms for biomedical applications. Their design is limited by incomplete knowledge of how the binding motif impacts the viscoelastic properties of the material and is generally constrained to non-responsive supramolecular interactions. Expanding the scope of available interactions and advancing the understanding of how defined interactions influence network formation would accelerate PNP hydrogel design. To address this gap in the design of PNP hydrogels, the study designs and investigates a tunable platform based on beta-cyclodextrin (βCD) host-guest cross-links between functionalized polymers and nanoparticles. A host-functionalized polymer (βCD hyaluronic acid) and guest harboring block co-polymer (poly(ethylene glycol)-b-poly(lactic acid)) NPs are synthesized. The presence and accessibility for binding of the host and guest moieties are characterized via isothermal titration calorimetry. PNP hydrogels with varying concentrations of functionalized polymer and NPs reveal a limited window of concentrations for gelation. It is hypothesized that network formation is governed by the capacity of polymer chains to effectively bridge NPs, which is related to the host-guest ratios present in the system. Further, photo-responsive guests are incorporated to engineer photoreversible gelation of PNP hydrogels via exposure to specific wavelengths of light.

Reversible Control of Gene Expression by Guest-Modified Adenosines in a Cell-Free System via Host-Guest Interaction.

Gene expression technology has become an indispensable tool for elucidating biological processes and developing biotechnology. Cell-free gene expression (CFE) systems offer a fundamental platform for gene expression-based technology, in which the reversible and programmable control of transcription can expand its use in synthetic biology and medicine. This study shows that CFE can be controlled via the host-guest interaction of cucurbit[7]uril (CB[7]) with N6-guest-modified adenosines. These adenosine derivatives were conveniently incorporated into the DNA strand using a post-synthetic approach and formed a selective and stable base pair with complementary thymidine in DNA. Meanwhile, alternate addition of CB[7] and the exchanging guest molecule induced the reversible formation of a duplex structure through the formation and dissociation of a bulky complex on DNA. The kinetics of the reversibility was fine-tuned by changing the size of the modified guest moieties. When incorporated into a specific region of the T7 promoter sequence, the guest-modified adenosines enabled tight and reversible control of in vitro transcription and protein expression in the CFE system. This study marks the first utility of the host-guest interaction for gene expression control in the CFE system, opening new avenues for developing DNA-based technology, particularly for precise gene therapy and DNA nanotechnology.

Self-Aggregation, Enhanced Guest-Binding Behavior, and Anion-Induced Agglutination of Cyclophane Dimers Linked with Florescent Perylene Diimide.

Cationic, anionic, and nonionic cyclophane dimers, 1a, 1b, and 1c, covalently linked with fluorescent perylene diimide were synthesized, respectively, as a host for aggregation-induced multivalent effects on guest-binding. These PDI-linked cyclophane dimers 1a and 1b, especially 1c, formed self-aggregates in H2O-rich solvents through π-stacking interactions. Critical aggregation concentrations of 1a, 1b, and 1c in H2O were 4.0 × 10-6, 4.0 × 10-6, and less than 0.1 × 10-6 M, respectively. The self-aggregates of the PDI-linked cyclophane dimers in H2O were several hundred nanometers in size by DLS and TEM measurements. In an aggregated state, 1a exhibited guest-binding abilities toward hydrophobic guests, such as 6-p-toluidinonaphthalene-2-sulfonate and 6-anilino-naphthalene-2-sulfonate. Moreover, anion-induced agglutination of 1a was observed upon the addition of phosphate ions, and its effectiveness was as follows: ATP > ADP > H2P2O72- > AMP ≈ PO43- > HPO42- > H2PO4-. The contribution of the adenine base of the nucleotides as a guest moiety used for effective agglutination was confirmed by 1H NMR spectroscopy.

Microinterfaces in biopolymer-based bicontinuous hydrogels guide rapid 3D cell migration

Cell migration is critical for tissue development and regeneration but requires extracellular environments that are conducive to motion. Cells may actively generate migratory routes in vivo by degrading or remodeling their environments or instead utilize existing extracellular matrix microstructures or microtracks as innate pathways for migration. While hydrogels in general are valuable tools for probing the extracellular regulators of 3-dimensional migration, few recapitulate these natural migration paths. Here, we develop a biopolymer-based bicontinuous hydrogel system that comprises a covalent hydrogel of enzymatically crosslinked gelatin and a physical hydrogel of guest and host moieties bonded to hyaluronic acid. Bicontinuous hydrogels form through controlled solution immiscibility, and their continuous subdomains and high micro-interfacial surface area enable rapid 3D migration, particularly when compared to homogeneous hydrogels. Migratory behavior is mesenchymal in nature and regulated by biochemical and biophysical signals from the hydrogel, which is shown across various cell types and physiologically relevant contexts (e.g., cell spheroids, ex vivo tissues, in vivo tissues). Our findings introduce a design that leverages important local interfaces to guide rapid cell migration.

An Overview on Cyclodextrin and Its Derivatives Encapsulated Inclusion Complex: Preparation Methods and Influencing Factors

Inclusion Complex formation is supported by non-covalent interaction between host and guest molecules. Cyclodextrins are supramolecular hosts with distinct structural characteristics that can enclose a diverse spectrum of viable compounds. The toroidal shape of CD offers the hydrophobic environment in the cavity where the guest moieties are entrapped which undergoes the physicochemical transformation and results into a superior physical, chemical and biological profiles. This review describes the chemical behavior of pharmaceuticals, both natural and synthetic, as well as other related compounds complexed with cyclodextrins. The study focuses on the commonly employed preparation methods of inclusion complexes and influencing factors to demonstrate host-guest interaction. The study demonstrates the possible stoichiometric combinations of cyclodextrins with the active pharmaceutical and organic molecules. The review also provides instances of synthetic pharmaceuticals that have combined with cyclodextrin to create inclusion products, demonstrating how cyclodextrins can be exploited to create biological substances with novel features and advance therapeutic research.

Synthetic Receptors for Early Detection and Treatment of Cancer.

Over recent decades, synthetic macrocyclic compounds have attracted interest from the scientific community due to their ability to selectively and reversibly form complexes with a huge variety of guest moieties. These molecules have been studied within a wide range of sensing and other fields. Within this review, we will give an overview of the most common synthetic macrocyclic compounds including cyclodextrins, calixarenes, calixresorcinarenes, pillarenes and cucurbiturils. These species all display the ability to form a wide range of complexes. This makes these compounds suitable in the field of cancer detection since they can bind to either cancer cell surfaces or indeed to marker compounds for a wide variety of cancers. The formation of such complexes allows sensitive and selective detection and quantification of such guests. Many of these compounds also show potential for the detection and encapsulation of environmental carcinogens. Furthermore, many anti-cancer drugs, although effective in in vitro tests, are not suitable for use directly for cancer treatment due to low solubility, inherent instability in in vivo environments or an inability to be adsorbed by or transported to the required sites for treatment. The reversible encapsulation of these species in a macrocyclic compound can greatly improve their solubility, stability and transport to required sites where they can be released for maximum therapeutic effect. Within this review, we intend to present the use of these species both in cancer sensing and treatment. The various macrocyclic compound families will be described, along with brief descriptions of their synthesis and properties, with an outline of their use in cancer detection and usage as therapeutic agents. Their use in the sensing of environmental carcinogens as well as their potential utilisation in the clean-up of some of these species will also be discussed.

Ni4 complex anchored porous silica for enhanced adsorption of organic pollutants in the wastewater.

In the current study, tetranuclear Ni complex [Ni4(LH)4]·CH3CN (1) (LH3=(E)-2-(hydroxymethyl)-6-(((2-hydroxyphenyl)imino)methyl)phenol) was prepared and incorporated in sulfonic acid functionalized MCM-48 material. This composite nanoporous material was investigated for the adsorption of toxic cationic water pollutant dyes like crystal violet (CV) and methylene blue (MB) from the water solution. Thorough characterization was carried out using a variety of techniques, including NMR, ICP, powder XRD, TGA, SEM, BET, and FT-IR, to verify the phase purity, existence of guest moiety, material morphology, and other crucial variables. The adsorption property was increased with the metal complex immobilization on the porous support. The effect of various parameters on the adsorption process was discussed, including adsorbent dosage, temperature, pH, NaCl concentration, and contact time. Maximum dye adsorption was found at 0.2 mg/ml adsorbent dosage, 10 ppm dye concentration, 6-7 pH, 25 °C temperature, and 15 minutes of contact time. The adsorption of MB (methylene blue) and CV (crystal violet) dyes by Ni complex integrated MCM-48 was effective, with over 99% adsorption achieved in 15 minutes. A recyclability test was also performed, and the material is reusable up to the third cycle, with no notable decline in adsorption found. From the previous literature survey, it is clear that very high adsorption efficiency was achieved using MCM-48-SO3-Ni in considerably short contact time which proves the novelty and effectiveness of the modified material. Ni4 was prepared, characterized, and immobilized in sulfonic acid functionalized MCM-48, and this robust and reusable adsorbent was highly effective for the adsorption of methylene blue and crystal violet dyes with >99% adsorption efficiency in short duration.

Synthesis and characterization of novel binuclear zinc complex, immobilization in nano-porous support, and its catalytic application

Binuclear zinc complex, [Zn2(L)(I)2(CH3CN)] (I) (LH2 = 1,2-phenylenebis(azaneylylidene))bis(methaneylylidene))bis(2-methoxyphenol)) was prepared and single-crystal X-ray diffraction was used to establish the structure of complex assembly. Organic acid and base were used to functionalize the nano-porous material and then binuclear Zn complex was grafted into the modified materials. Brunauer-Emmett-Teller isotherm (BET), Nuclear Magnetic Resonance (NMR), Inductively Coupled Plasma analysis (ICP), X-ray Diffraction (XRD), Fourier transform infrared spectra (FT-IR), thermogravimetric analysis (TG), Scanning electron microscope (SEM), etc., were used to characterized the synthesized nano-catalysts to check for existence of guest moiety, structural stability of the parent and modified catalysts. Catalytic performance was noticeably enhanced post modification; without catalyst, acid/base functionalized, Zn2 immobilized catalyst. Binuclear zinc immobilized on acid/base silica catalyst exhibited a maximum 95%, 89% conversion of piperidine, and 87% and 86% conversion of aniline respectively. Prior to the theoretical investigation the bond parameters of the binuclear zinc complex were measured experimentally. Time-dependent Density Functional Theory (TD-DFT) and Density Functional Theory (DFT) methods were used to calculate the molecule's UV–Vis absorption spectra at B3LYP as well as LANL2DZ and 6–31G(d)). LUMOs and HOMOs energy gap were determined from the electronic transitions to determine electrophilicity index (ω), softness (S), electronegativity (χ), hardness value (Ƞ), and chemical potential (μ), etc.

Multistep sequence-controlled supramolecular polymerization by the combination of multiple self-assembly motifs

The precise sequence control of polymer chain is an important research topic of polymer chemistry. Although some methods such as iterative synthesis and supramolecular polymerization have been developed to fabricate sequence-controllable polymer, it is still a great challenge to consecutively prepare multiple supramolecular polymers with different sequence structures. In this work, through the reasonable utilization of assembly motifs, we integrated multiple host-guest recognitions and metal coordination interactions to prepare different sequence-controlled supramolecular polymers by a multistep assembly strategy. This research provides inspiration for the design and preparation of supramolecular polymers with different sequence structures.

Weak Affinity Chromatography Using Organic Solvents on Cyanopropyl- and Arene-Modified Silica-Gel Columns—Structural Demands for Host and Guest Moieties and Effect of Solvents

Abstract Weak affinity chromatography (WAC) is effective for isolating target compounds from analogous compounds with similar functional groups. Previously, a few chromatographic behaviors based on WAC using organic solvents were observed in a series of cyclic multiporphyrin systems on cyanopropyl-modified silica gel (CN-MS). Here, three cyclic porphyrin trimers with various rigidity were examined on CN-MS to understand the mechanism of the specific interactions between porphyrin derivatives and functional groups on modified silica gel. In addition to CN-MS, six modified silica-gel columns were tested to compare their retention abilities for a cyclic nickel porphyrin dimer (C4Ni2MsCP2). We examined the cosolvent effects of the pyridine eluents for C4Ni2MsCP2. Apparent dissociation constants of C4Ni2MsCP2 with functional groups on the MS columns and effective amounts of the functional groups were estimated by frontal affinity chromatography (FAC). 1H NMR titrations of acetonitrile and nitrobenzene to C4Ni2MsCP2 were conducted to compare their association constants with movable guest molecules to the dissociation constants with immobilized functional groups obtained in FAC. We found rigidity of cyclic porphyrin derivatives and immobilization of functional groups on silica gel is necessary for significant retentions using WAC. The affinity interaction does not occur at the center of C4Ni2MsCP2, but probably occurs on the surface composed of a bipyridyl moiety and the adjacent edges of the two porphyrins. Polar solvents, such as nitrobenzene, acetonitrile, and methanol, weakened the interaction. Although C4Ni2MsCP2 dissolves well in chloroform, the interactions between C4Ni2MsCP2 and the MS columns are considerably strengthened in the presence of chloroform. The competitiveness of solvents and cosolvents with the interaction of the porphyrin on WAC is independent of the solubility of the analyte.

Solid-State Self-Assembly of Heteroditopic Copillar[5]arenes

Self-assembly is a fundamental bottom-up tool for the construction of living or synthetic materials. Owing to the specific, definite, and directional host–guest interactions, heteroditopic monomers has become one of the classic models as building blocks in self-assembly investigation. Driven by the unique multiple CH···π interactions between the pillar[5]arene cavity and the linear n-alkyl group, copillar[5]arenes have become one of the simplest and optimal models for the construction of heteroditopic monomers in recent years. Here, by comparison of the reported crystal structures of heteroditopic copillar[5]arenes with six new ones (P6Br, P8Br, P6Im, P10Im, P4 ⊃ acetonnitrile, and P8Br ⊃ succinonitrile), we found that their self-assembly manner in the solid state was primarily decided by the competition of the pillar[5]arene cavity between the threading guest moiety and the solvent molecules (or external competitors). When the competitor had much higher affinity to the pillar[5]arene cavity, a traditional host–guest complex would be formed in the solid state. When the threading guest moiety showed much higher affinity, [cn]daisy chains (normally [c2]) would be formed. It was further found that only when they had similar bonding abilities with the pillar[5]arene cavity, [an]daisy chains could be formed in the solid state.

Size-matched hydrogen bonded hydroxylammonium frameworks for regulation of energetic materials

Size matching molecular design utilizing host-guest chemistry is a general, promising strategy for seeking new functional materials. With the growing trend of multidisciplinary investigations, taming the metastable high-energy guest moiety in well-matched frameworks is a new pathway leading to innovative energetic materials. Presented is a selective encapsulation in hydrogen-bonded hydroxylammonium frameworks (HHF) by screening different sized nitrogen-rich azoles. The size-match between a sensitive high-energy guest and an HHF not only gives rise to higher energetic performance by dense packing, but also reinforces the layer-by-layer structure which can stabilize the resulting materials towards external mechanic stimuli. Preliminary assessment based on calculated detonation properties and mechanical sensitivity indicates that HHF competed well with the energetic performance and molecular stability (detonation velocity = 9286 m s−1, impact sensitivity = 50 J). This work highlights the size-matched phenomenon of HHF and may serve as an alternative strategy for exploring next generation advanced energetic materials.

Stimulus-Responsive, Gelatin-Containing Supramolecular Nanofibers as Switchable 3D Microenvironments for Cells.

Polymer- and/or protein-based nanofibers that promote stable cell adhesion have drawn increasing attention as well-defined models of the extracellular matrix. In this study, we fabricated two classes of stimulus-responsive fibers containing gelatin and supramolecular crosslinks to emulate the dynamic cellular microenvironment in vivo. Gelatin enabled cells to adhere without additional surface functionalization, while supramolecular crosslinks allowed for the reversible switching of the Young’s modulus through changes in the concentration of guest molecules in culture media. The first class of nanofibers was prepared by coupling the host–guest inclusion complex to gelatin before electrospinning (pre-conjugation), while the second class of nanofibers was fabricated by coupling gelatin to polyacrylamide functionalized with host or guest moieties, followed by conjugation in the electrospinning solution (post-conjugation). In situ AFM nano-indentation demonstrated the reversible switching of the Young’s modulus between 2–3 kPa and 0.2–0.3 kPa under physiological conditions by adding/removing soluble guest molecules. As the concentration of additives does not affect cell viability, the supramolecular fibers established in this study are a promising candidate for various biomedical applications, such as standardized three-dimensional culture matrices for somatic cells and the regulation of stem cell differentiation.

Cover Feature: Temperature‐Triggered Structural Dynamics of Non‐Coordinating Guest Moieties in a Fluorescent Actinide Polyrotaxane Framework (Chem. Eur. J. 34/2021)

Cover Feature: Temperature‐Triggered Structural Dynamics of Non‐Coordinating Guest Moieties in a Fluorescent Actinide Polyrotaxane Framework (Chem. Eur. J. 34/2021)

Temperature-Triggered Structural Dynamics of Non-Coordinating Guest Moieties in a Fluorescent Actinide Polyrotaxane Framework.

We present here the synthesis of a novel fluorescent actinide polyrotaxane compound URCP1 through the utilization of an end-cutting pseudorotaxane precursor with only the cucurbit[6]uril (CB[6]) macrocyclic components acting as linking struts. The non-coordinating guest motif in the obtained polyrotaxane, with increased freedom and structural flexibility, can display intriguing temperature-triggered conformational variations inside the cavity of CB[6], which was clearly evidenced by crystallographic snapshots at different temperatures. Notably, this observation of temperature-triggered structural dynamics in URCP1 represents the first report of actinide polyrotaxane with such feature in solid-state. Moreover, URCP1 has a high photoluminescence quantum yield (PLQY) of 49.8 %, comparable to other luminescent uranyl compounds, and can work as a fluorescent probe to selectively detect Fe3+ over other eight competing cations in aqueous solution, with the limit of detection being as low as 4.4×10-3 ppm.

Thermally Activated Delayed Fluorescence Benzyl Cellulose Derivatives for Nondoped Organic Light-Emitting Diodes

Thermally activated delayed fluorescence (TADF) benzyl cellulose derivatives (TBC-X), which contained both carbazole (host) and phthalimide-based TADF dye (guest) moieties, were prepared from 2,3-d...

A Self-Cross-Linking Supramolecular Polymer Network Enabled by Crown-Ether-Based Molecular Recognition.

Supramolecular polymers based on host-guest molecular recognition have emerged as promising platforms for the development of smart materials. However, the studies on them are primarily conducted in solution and/or in the gel state. In contrast, little is known about dynamic properties and applications of supramolecular polymers in bulk. Herein, we present a self-cross-linking supramolecular polymer network (SPN) as a model system to understand the bulk properties controlled by noncovalent interactions. Specifically, the SPN monomer is composed of two benzo-21-crown-7 (B21C7) host units and two dialkylammonium salt guest moieties on a four-arm core, wherein complementary host-guest complexation drives the formation of the SPN with [2]pseudorotaxane linkages between B21C7 and ammonium motifs. The dynamic and reversible behaviors of the linkages are evaluated by measurement of viscoelasticity. The results indicate that the host-guest molecular recognition becomes highly dynamic at elevated temperature. Moreover, the relatively high activation energy of the SPN manifests itself as a new type of thermoplastic material with network topology freezing glass transition. Finally, we demonstrate how these findings provide insights into the malleability and processability of the SPN by simple demos. The fundamental understanding gained from the research on this SPN in bulk will facilitate the advancement and application of supramolecular materials.

A Bispyrazole Based Porous 2D Luminescent MOF for the Turn‐Off Detection of Pd(II) Ions

AbstractA novel bispyrazole based porous MOF ({[Zn(MBPz)(Ene)0.5]⋅2DMF⋅2H2O}n (1)) with open alkene (‐HC=CH‐) and nitrogen sites has been synthesized, as an efficient fluorescent sensor for Pd(II) ions. The MOF exhibits 3D supramolecular structure with open channels having 27.2% porosity. The unsaturated ‐CH=CH‐ moieties are present along the walls of open channels which is favorable for interaction with guest moieties. The cation sensitivity of 1 was evaluated using a series of transition metal ions in DMF. The fluorescence quenching of 1 was demonstrated by an approximately 94% reduction in the emission intensity upon binding to Pd2+ ions. The emission intensity of 1 at 414 nm has shown a linear response to Pd(II) ion concentration with a detection limit of 4.7 x 10−7 M. The sensing property of 1 towards Pd(II) ions is attributed to the π electron donation from the alkene bonds present in the ligand (Ene).

Ring–Chain Competition in Supramolecular Polymerization Directed by Molecular Recognition of the Bisporphyrin Cleft

Increasing interest in innovative supramolecular materials has spurred efforts to develop head-to-tail monomers possessing a host moiety as a head and a guest moiety as a tail, making them capable ...

Revealing the assembly mechanism of an octadecylamine based supramolecular complex on mild steel in condensate water: Correlative experimental and theoretical studies

The corrosion inhibition and interfacial assembling mechanism of a supramolecular complex (CDOD) based on octadecylamine (ODA) and β-cyclodextrin (β-CD) towards mild steel in the condensate water were revealed through multitudinous experiments and theoretical calculations. The optimized configuration of CDOD in aqueous solution is also disclosed. The results of dynamic weight loss show that CDOD can efficiently retard the corrosion of mild steel in the condensate water yielding a maximum inhibition efficiency of 94.21% with 1 mM dosage at 308 K. The electrochemical results indicate CDOD performs as a mixed type inhibitor and significantly promotes the surface polarization resistance of steel due to strong adsorption. The protective effects of CDOD are also observed by the morphologies from SEM and AFM. The data of contact angles, XPS and ATR-FTIR collectively point out that ODA (guest moiety) can be released from the assembly at the metal/solution interface and solely adsorbed on the steel surface. The adsorption of ODA on steel surface conforms to Langmuir adsorption isotherm. Molecular dynamics simulation vividly evidences the assembly behaviour of CDOD on steel surface and reveals the tilted adsorption orientation of ODA, which is further supported by quantum chemical calculations.