The chiral interfaces fabricated by d/l-alanine-pillar[5]arenes for selectively adsorbing ctDNA

Rim-differentiated pillar[5]arene-modified surfaces for rapid PFOA/PFOS detection

A new rim-differentiated pillar[5]arene (RD-P5) has been synthesized and immobilized onto an Al2O3 surface for the rapid detection of perfluoroalkyl acids. This P5-Al2O3 surface provides a novel approach for measuring perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) using contact angle measurements, with limits of detection down to 10 ng L-1.

Preparation and evaluation of two chiral stationary phases based on imidazolyl-functionalized bromoethoxy pillar[5]arene-bonded silica

Chiral pillar[5]arene-based mesoporous silica, an emerging class of chiral structure, possesses excellent characteristics such as abundant chiral active sites, encapsulated cavity and excellent chiral modification, which make them a promising candidate as new chiral stationary phases (CSPs) in enantioseparation. In this study, two imidazole-containing (S)-1-(4-phenyl-1H-imidazol-2-yl)ethanamine and (S)-Histidinol were respectively modified to bromoethoxy pillar[5]arene-bonded silica to construct new chiral stationary phases (sPIE-BP5-Sil and sHol-BP5-Sil) for the separation and analysis of enantiomers. The separation conditions such as mobile phase composition, flow rate and temperature were optimized. Under optimal conditions, both sPIE-BP5-Sil and sHol-BP5-Sil showed good separation performance for different types of enantiomers. Interestingly, sPIE-BP5-Sil and sHol-BP5-Sil showed better enantioselectivity for chiral aromatic compounds and chiral aliphatic compounds, respectively. This enantioseparation result was closely related to the presence of additional aromatic rings and abundant hydroxyl groups in the side chains of the two chiral groups. In addition, the enantioseparation process was further studied by molecular docking simulation. Therefore, this work provided a new strategy for the preparation and application of imidazolyl-derived pillar[5]arene-based chiral stationary phases, which can be efficiently used for screening and separating enantiomers.

Applications of macrocycle-based solid-state host-guest chemistry

Macrocyclic molecules have been used in various fields owing to their guest binding properties. Macrocycle-based host-guest chemistry in solution can allow for precise control of complex formation. Although solution-phase host-guest complexes are easily prepared, their limited stability and processability prevent widespread application. Extending host-guest chemistry from solution to the solid state results in complexes that are generally more robust, enabling easier processing and broadened applications. Macrocyclic compounds in the solid state can encapsulate guests with larger affinities than their soluble counterparts. This is crucial for use in applications such as separation science and devices. In this Review, we summarize recent progress in macrocycle-based solid-state host-guest chemistry and discuss the basic physical chemistry of these complexes. Representative macrocycles and their solid-state complexes are explored, as well as potential applications. Finally, perspectives and challenges are discussed.

Electrochemical DNA-Sensor Based on Macrocyclic Dendrimers with Terminal Amino Groups and Carbon Nanomaterials

The assembling of thiacalix[4]arene-based dendrimers in cone, partial cone, and 1,3-alternate configuration on the surface of a glassy carbon electrode coated with carbon black or multiwalled carbon nanotubes has been characterized using cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. Native and damaged DNA were electrostatically accumulated on the modifier layer. The influence of the charge of the redox indicator and of the macrocycle/DNA ratio was quantified and the roles of the electrostatic interactions and of the diffusional transfer of the redox indicator to the electrode interface indicator access were established. The developed DNA sensors were tested on discrimination of native, thermally denatured, and chemically damaged DNA and on the determination of doxorubicin as the model intercalator. The limit of detection of doxorubicin established for the biosensor based on multi-walled carbon nanotubes was equal to 1.0 pM with recovery from spiked human serum of 105-120%. After further optimization of the assembling directed towards the stabilization of the signal, the developed DNA sensors can find application in the preliminary screening of antitumor drugs and thermal damage of DNA. They can also be applied for testing potential drug/DNA nanocontainers as future delivery systems.

Enantioselective Labeling of Zebrafish for D-Phenylalanine Based on Graphene-Based Nanoplatform

Enantioselective labeling of important bioactive molecules in complex biological environments by artificial receptors has drawn great interest. From both the slight difference of enantiomers' physicochemical properties and inherently complexity in living organism point of view, it is still a contemporary challenge for preparing practical chiral device that could be employed in the model animal due to diverse biological interference. Herein, we introduce γ-cyclodextrin onto graphene oxide for fabricating γ-cyclodextrin and graphene oxide assemblies, which provided an efficient nanoplatform for chiral labelling of D-phenylalanine with higher chiral discrimination ratio of KD/KL = 8.21. Significantly, the chiral fluorescence quenching effect of this γ-CD-GO nanoplatform for D-phenylalanine enantiomer in zebrafish was 7.0-fold higher than L-isomer, which exhibiting real promise for producing practical enantio-differentiating graphene-based systems in a complex biological sample.

Decasubstituted Pillar[5]arene Derivatives Containing L-Tryptophan and L-Phenylalanine Residues: Non-Covalent Binding and Release of Fluorescein from Nanoparticles

Sensitive systems with controlled release of drugs or diagnostic markers are attractive for solving the problems of biomedicine and antitumor therapy. In this study, new decasubstituted pillar[5]arene derivatives containing L-Tryptophan and L-Phenylalanine residues have been synthesized as pH-responsive drug nanocarriers. Fluorescein dye (Fluo) was loaded into the pillar[5]arene associates and used as a spectroscopic probe to evaluate the release in buffered solutions with pH 4.5, 7.4, and 9.2. The nature of the substituents in the pillar[5]arene structure has a huge influence on the rate of delivering. When the dye was loaded into the associates based on pillar[5]arene derivatives containing L-Tryptophan, the Fluo release occurs in the neutral (pH = 7.4) and alkaline (pH = 9.2) buffered solutions. When the dye was loaded into the associates based on pillar[5]arene with L-Phenylalanine fragments, the absence of release was observed in every pH evaluated. This happens as the result of different packing of the dye in the structure of the associate. This fact was confirmed by different fluorescence mechanisms (aggregation-caused quenching and aggregation-induced emission) and association constants. It was shown that the macrocycle with L-Phenylalanine fragments binds the dye more efficiently (lgK_a = 3.92). The experimental results indicate that the pillar[5]arene derivatives with amino acids fragments have a high potential to be used as a pH-responsive drug delivery devices, especially for promoting the intracellular delivering, due to its nanometric size.

Guest-Induced Planar-Chiral Pillar[5]arene Surface for Selectively Adsorbing Protein Based on Host-Guest Chemistry

In living systems, the adsorption of a protein on biointerfaces is a universal phenomenon, such as the specific binding of an antibody and antigen, which plays an important role in body growth and life maintenance. The exploration of a protein-selective adsorption on the biointerface is of great significance for understanding the life process and treatment in vitro. Herein, on the basis of biomimetic strategies, we fabricated a planar-chiral NH₂-pillar[5]arene modified silicon surface (pR-/pS-NP5 surfaces) for a highly enantioselective adsorption of protein by taking advantage of the guest-induced planar chirality of pillar[5]arenes. Results from practical experiments and theoretical calculations show that the pR-NP5 surface possesses a high adsorption capacity and chiral selectivity for bovine serum albumin (BSA). Moreover, it was identified that the guest-induced chiral effect the generation and amplification of planar chirality, which was much beneficial for enhancing the interaction between planar-chiral pillar[5]arene host and BSA. The binding capacity of pR-NP5 and BSA is stronger than that of pS-NP5, thus promoting the chiral selective adsorption of BSA. This work affords a deeper understanding of the chiral influence of protein adsorption on biointerfaces and meanwhile provides a new perspective for chiral-sensing applications.

Chiral pillar[5]arene-functionalized silica microspheres: synthesis, characterization and enantiomer separation

Chiral pillar[5]arene-functionalized silica microspheres were prepared and characterized for the first time, which can be used as a new kind of chiral stationary phases for effective enantioseparation under reversed-phase and...

Electrochemical Sensing of Interactions between DNA and Charged Macrocycles

In this work, we investigated aggregation of native DNA and thiacalix[4]arene derivative bearing eight terminal amino groups in cone configuration using various redox probes on the glassy carbon electrode. It was shown that sorption transfer of the aggregates on the surface of the electrode covered with carbon black resulted in changes in electrostatic interactions and diffusional permeability of the surface layer. Such changes alter the signals of ferricyanide ion, methylene green and hydroquinone as redox probes to a degree depending on their specific interactions with DNA and own charge. Inclusion of DNA in the surface layer was independently confirmed by scanning electron microscopy, electrochemical impedance spectroscopy and experiments with doxorubicin as a model intercalator. Thermal denaturing of DNA affected the charge separation on the electrode interface and the signals of redox probes. Using hydroquinone, less sensitive to electrostatic interactions, made it possible to determine from 10 pM to 1.0 nM doxorubicin (limit of detection 3 pM) after 10 min incubation. Stabilizers present in the commercial medications did not alter the signal. The DNA sensors developed can find future application in the assessment of the complexes formed by DNA and macrocycles as delivery agents for small chemical species.

Recent advances in chiral discrimination on host-guest functionalized interfaces

Chiral discrimination has gained much focus in supramolecular chemistry, since it is one of the fundamental processes in biological systems, enantiomeric separation and biochemical sensors. Though most of the biochemical processes can routinely recognize biological enantiomers, enantioselective identification of chiral molecules in artificial systems is currently one of the challenging topics in the field of chiral discrimination. Inaccuracy, low separation efficiency and expensive instrumentation were considered typical problems in artificial systems. Recently, chiral recognition on the interfaces has been widely used in the fields of electrochemical detection and biochemical sensing. For the moment, a series of macrocyclic host functionalized interfaces have been developed for use as chiral catalysts or for enantiomeric separation. Here, we have briefly exposited the most recent advances in the fabrication of supramolecular functionalized interfaces and their application for chiral recognition.

Electrochemical Polymerization Induced Chirality Fixation of Crystalline Pillararene-Based Polymer and Its Application in Interfacial Chiral Sensing

A new strategy has been developed for the direct chirality fixation, which is induced by electrochemical polymerization, of macrocyclic hosts pillar[5]arene. Taking advantage of electrochemical polymerization, thiophene-modified pillar[5]arene monomers (Th-P[5]A) have been regularly arranged under the action of an electric field to form chiral nanofiber-like crystalline pillar[5]arene-based polymers (poly-Th-P[5]A), showing a significant circular dichroism (CD) signal. With the active photochemical properties, poly-Th-P[5]A is first used as a photoelectrochemical (PEC) chiral sensor for the identification and determination of l- and d-ascorbic acid (l-AA, d-AA) without adding any extra photoactive probes. Importantly, the chiral recognition between poly-Th-P[5]A and l-AA also triggers a polarity conversion for the photocurrent of the polymer, and it greatly results in a broad chiral detection range for l-AA, crossing 6 orders of magnitude. This work provides a promotional strategy for building a PEC chiral recognition platform based on pillararenes.

Solvent-Driven Chirality Switching of a Pillar[4]arene[1]quinone Having a Chiral Amine-Substituted Quinone Subunit

Several new chiral pillar[4]arene[1]quinone derivatives were synthesized by reacting pillar[4]arene[1]quinone (EtP4Q1), containing four 1,4-diethoxybenzene units and one benzoquinone unit, with various chiral amines via Michael addition. Due to the direct introduction of chiral substituents on the rim of pillar[n]arene and the close location of the chiral center to the rim of EtP4Q1, the newly prepared compounds showed unique chiroptical properties without complicated chiral resolution processes, and unprecedented high anisotropy factor of up to −0.018 at the charge transfer absorption band was observed. Intriguingly, the benzene sidearm attached pillar[4]arene[1]quinone derivative 1a showed solvent- and complexation-driven chirality inversion. This work provides a promising potential for absolute asymmetric synthesis of pillararene-based derivatives.

Simultaneous determination of Acetaminophen and dopamine based on a water-soluble pillar[6]arene and ultrafine Pd nanoparticle-modified covalent organic framework nanocomposite

A novel electrochemical sensing platform for the simultaneous determination of AP and DA based on a water-soluble pillar[6]arene and ultrafine Pd nanoparticle-modified covalent organic framework nanocomposite.

Nanocomposite Based on Organic Framework-Loading Transition-Metal Co Ion and Cationic Pillar[6]arene and Its Application for Electrochemical Sensing of l-Ascorbic Acid

In this study, we constructed a highly sensitive and selective electrochemical sensing strategy for l-ascorbic acid (AA) based on a covalent organic framework (COF)-loading non-noble transition metal Co ion and macrocyclic cationic pillar[6]arene (CP6) nanocomposite (CP6-COF-Co). The COF plays a crucial role in anchoring the Co ion according to its crystalline porous and multiple coordination sites and has an outstanding performance for building an electrochemical sensing platform based on a unique two-dimensional structure. Accordingly, the transition-metal Co ion can be successfully anchored on the framework of COF and shows strong catalytic activity for the determination of AA. Moreover, introduction of host-guest recognition based on CP6 and AA can bring new properties for enhancing selectivity, sensitivity, and practical application in real environment. Host-guest interactions between CP6 and AA were evaluated by the ¹H NMR spectrum. When compared with other literatures, our method displayed a lower determination limit and broader linear range. To the best of our knowledge, this is the first study carried out for the non-noble transition-metal Co ion, COF, and pillar[6]arene hybrid material in sensing field, which has a potential value in sensing, catalysis, and preparation of advanced multifunction materials.

Self-Assembly of Supramolecular Architectures by the Effect of Amino Acid Residues of Quaternary Ammonium Pillar[5]arenes

Novel water-soluble multifunctional pillar[5]arenes containing amide-ammonium-amino acid moiety were synthesized. The compounds demonstrated a superior ability to bind (1S)-(+)-10-camphorsulfonic acid (S-CSA) and methyl orange dye depending on the nature of the substituent, resulting in the formation one-to-one complexes with both guests. The formation of host-guest complexes was confirmed by ultraviolet (UV), circular dichroism (CD) and 1H NMR spectroscopy. This work demonstrates the first case of using S-CSA as a chiral template for the non-covalent self-assembly of architectures based on pillar[5]arenes. It was shown that pillar[5]arenes with glycine or L-alanine fragments formed aggregates with average hydrodynamic diameters (d) of 165 and 238 nm, respectively. It was established that the addition of S-CSA to the L-alanine-containing derivative led to the formation of micron-sized aggregates with d of 713 nm. This study may advance the design novel stereoselective catalysts and transmembrane amino acid channels.

Wettability read-out strategy for aptamer target binding based on a recognition/hydrophobic bilayer surface

We established a wettability read-out strategy for an aptasensor with a bilayer surface, using hydrophobicity reduction as the signal. The signal was induced by a fracture of the nanoneedle layer resulting from recognition by the supporting aptamer layer. The kinetics and influencing factors of this process were investigated with time curves.

Cell adhesion and proliferation in chiral pores triggered by polyoxometalates

The chirality of polyoxometalate anchoring in the cavity of pitted films was demonstrated to strongly influence the adhesion and proliferation of E. coli cells.