Thiacalixarene Carboxylic Acid Derivatives as Inhibitors of Lysozyme Fibrillation.

Amyloid fibroproliferation leads to organ damage and is associated with a number of neurodegenerative diseases affecting populations worldwide. There are several ways to protect against fibril formation, including inhibition. A variety of organic compounds based on molecular recognition of amino acids within the protein have been proposed for the design of such inhibitors. However, the role of macrocyclic compounds, i.e., thiacalix[4]arenes, in inhibiting fibrillation is still almost unknown. In the present work, the use of water-soluble thiacalix[4]arene derivatives for the inhibition of hen egg-white lysozyme (HEWL) amyloid fibrillation is proposed for the first time. The binding of HEWL by the synthesized thiacalix[4]arenes (logKa = 5.05-5.13, 1:1 stoichiometry) leads to the formation of stable supramolecular systems capable of stabilizing the protein structure and protecting against fibrillation by 29-45%. The macrocycle conformation has little effect on protein binding strength, and the native HEWL secondary structure does not change via interaction. The synthesized compounds are non-toxic to the A549 cell line in the range of 0.5-250 µg/mL. The results obtained may be useful for further investigation of the anti-amyloidogenic role of thiacalix[4]arenes, and also open up future prospects for the creation of new ways to prevent neurodegenerative diseases.

Synthesis of calix (4) resorcinarene based amphiphilic macrocycle as an efficient nanocarrier for Amphotericin-B to enhance its oral bioavailability.

The supramolecular-based macrocyclic amphiphiles have fascinating attention and find extensive utilization in the pharmaceutical industry for efficient drug delivery. In this study, we designed and synthesized a new supramolecular amphiphilic macrocycle to serve as an efficient nanocarrier, achieved by treating 4-hydroxybenzaldehyde with 1-bromotetradecane. The derivatized product was subsequently treated with resorcinol to cyclize, resulting in the formation of a calix(4)-resorcinarene-based supramolecular amphiphilic macrocycle. The synthesized macrocycle and intermediate products were characterized using mass spectrometry, IR, and 1H NMR spectroscopic techniques. The amphotericin-B (Amph-B)-loaded and unloaded amphiphiles were screened for biocompatibility studies, vesicle formation, particle shape, size, surface charge, drug entrapment, in-vitro release profile, and stability through atomic force microscopy (AFM), Zetasizer, HPLC, and FT-IR. Amph-B -loaded macrocycle-based niosomal vesicles were investigated for in-vivo bioavailability in rabbits. The synthesized macrocycle exhibited no cytotoxicity against normal mouse fibroblast cells and was found to be hemocompatible and safe in mice following an acute toxicity study. The drug-loaded macrocycle-based vesicles appeared spherical, nano-sized, and homogeneous in size, with a notable negative surface charge. The vesicles remained stable after 30 days of storage. The results of Amph-B oral bioavailability and pharmacokinetics revealed that the newly tailored niosomal formulation enhanced drug solubility, protected drug degradation at gastric pH, facilitated sustained drug release at the specific target site, and delayed plasma drug clearance. Incorporating such advanced niosomal formulations in the field of drug delivery systems has the potential to revolutionize therapeutic outcomes and improve the quality of patient well-being.

Smartphone-assimilated colorimetric sensor for sub-nanomolar emamectin detection via KA30 capped silver nanoparticles in food, bio-fluids and water samples.

In this report, we firstly synthesized nitro calix [4] resorcinarene compound (referred as KA30) and characterized it though proton (1H) nuclear magnetic resonance (NMR) spectroscopy, electrospray ionization mass spectrometry (ESI-MS) and Fourier Transform Infra-red (FTIR) spectroscopy. KA30 was applied as functionalizing agent for the formation of silver nanoparticles (KA30-AgNPs). These NPs were confirmed as highly selective and extremely sensitive colorimetric sensor for ultra-low level detection of emamectin (EMA) as a novel report. Significant aspect of the sensor is its unique detection range between 0.0005 and 29.5 µM via color change from yellow to colorless with hypochromic-bathochromic shift exhibiting limit of detection (LOD) and limit of quantification (LOQ) as 0.12 nM and 0.4 nM respectively. The sensor was applied to colorimetrically and optically detect EMA in real samples of serum, urine and food. The sensor was further allied with smartphone for real-time, and on-site detection of EMA and results were validated through UPLC.

Situating the phosphonated calixarene-cytochrome C association by molecular dynamics simulations.

Protein-calixarenes binding plays an increasingly central role in many applications, spanning from molecular recognition to drug delivery strategies and protein inhibition. These ligands obey a specific bio-supramolecular chemistry, which can be revealed by computational approaches, such as molecular dynamics simulations. In this paper, we rely on all-atom, explicit-solvent molecular dynamics simulations to capture the electrostatically driven association of a phosphonated calix-[4]-arene with cytochome-C, which critically relies on surface-exposed paired lysines. Beyond two binding sites identified in direct agreement with the x-ray structure, the association has a larger structural impact on the protein dynamics. Then, our simulations allow a direct comparison to analogous calixarenes, namely, sulfonato, similarly reported as "molecular glue." Our work can contribute to a robust in silico predictive tool to assess binding sites for any given protein of interest for crystallization, with the specificity of a macromolecular cage whose endo/exo orientation plays a role in the binding.

Supramolecular Chiral Binding Affinity-Achieved Efficient Synergistic Cancer Therapy.

Supramolecular chirality-mediated selective interaction among native assemblies is essential for precise disease diagnosis and treatment. Herein, to fully understand the supramolecular chiral binding affinity-achieved therapeutic efficiency, supramolecular chiral nanoparticles (WP5⊃D/L-Arg+DOX+ICG) with the chirality transfer from chiral arginine (D/L-Arg) to water-soluble pillar[5]arene (WP5) are developed through non-covalent interactions, in which an anticancer drug (DOX, doxorubicin hydrochloride) and a photothermal agent (ICG, indocyanine green) are successfully loaded. Interestingly, the WP5⊃D-Arg nanoparticles show 107 folds stronger binding capability toward phospholipid-composed liposomes compared with WP5⊃L-Arg. The enantioselective interaction further triggers the supramolecular chirality-specific drug accumulation in cancer cells. As a consequence, WP5⊃D-Arg+DOX+ICG exhibits extremely enhanced chemo-photothermal synergistic therapeutic efficacy (tumor inhibition rate of 99.4%) than that of WP5⊃L-Arg+DOX+ICG (tumor inhibition rate of 56.4%) under the same condition. This work reveals the breakthrough that supramolecular chiral assemblies can induce surprisingly large difference in cancer therapy, providing strong support for the significance of supramolecular chirality in bio-application.

Polymeric membrane potentiometric antibiotic sensors using computer-aided screening of supramolecular macrocyclic carriers.

Carrier-based polymeric membrane potentiometric sensors are an ideal tool for detecting ionic species. However, in the fabrication of these sensors, the screening of carriers still relies on empirical trial- and error-based optimization, which requires tedious and time-consuming experimental verification. In this work, computer-aided screening of carriers is applied in the preparation of polymeric membrane potentiometric sensors. Molecular docking is used to study the host-guest interactions between receptors and targets. Binding energies are employed as the standard to screen the appropriate carrier. As a proof-of-concept experiment, the antibiotic ciprofloxacin is selected as the target model. A series of supramolecular macrocyclic receptors including cyclodextrins, cucurbiturils and calixarenes are chosen as potential receptors. The proposed sensor based on the receptor calix[4]arene screened by molecular docking shows a lower detection limit of 0.5 µmol L-1 for ciprofloxacin. It can be expected that the proposed computer-aided screening technique of carriers can provide a simple but highly efficient method for the fabrication of carrier-based electrochemical and optical sensors.

Host-Guest Chemosensor Ensembles based on Water-Soluble Sulfonated Calix[n]arenes and a Pyranoflavylium Dye for the Optical Detection of Biogenic Amines.

Biogenic amines (BAs) are biologically active nitrogen-containing compounds formed during the food spoilage process and are often related as key markers of food quality, safety, and freshness. Because their presence in foods at high levels can cause significant health problems, researchers have been focused on developing novel strategies and methods for early detection and capture of these analytes. Herein, water-soluble sulfonated calix[n]arene macrocycles (SC4, SC6, and SC8) and a pH-sensitive dye (4'-hydroxy-10-methylpyranoflavylium) were investigated as host-guest systems for BA sensing. The hosts were able to bind the flavylium cation of the dye with association constants of 103 to 104 M-1. The dye complexation also allowed tuning its pKa from 6.72 (free) toward high values: 7.68 (SC4), 7.79 (SC6), and 8.45 (SC8). These data were crucial to optimize the host-guest complexes as optical sensing systems for putrescine/tyramine (pH 7.2-7.6), yielding a colorimetric redshift from yellow to red. The BA sensing was also demonstrated by fluorescence quenching for the calix[n]arene/dye complexes and fluorescence recovery after the addition of BAs. 1H NMR spectroscopy was used to demonstrate the interaction mode, confirming an encapsulation-driven mechanism. Overall, these host-guest systems demonstrated great potential for the detection of BAs, one of the main key markers of food spoilage.

Multivalent Calixarene Complexation of a Designed Pentameric Lectin.

We describe complex formation between a designed pentameric ß-propeller and the anionic macrocycle sulfonato-calix[8]arene (sclx8), as characterized by X-ray crystallography and NMR spectroscopy. Two crystal structures and 15N HSQC experiments reveal a single calixarene binding site in the concave pocket of the ß-propeller toroid. Despite the symmetry mismatch between the pentameric protein and the octameric macrocycle, they form a high affinity multivalent complex, with the largest protein-calixarene interface observed to date. This system provides a platform for investigating multivalency.

Promises of anionic calix[n]arenes in life science: State of the art in 2023.

Because they hold together molecules by means of non-covalent interactions - relatively weak and thus, potentially reversible - the anionic calixarenes have become an interesting tool for efficiently binding a large range of ligands - from gases to large organic molecules. Being highly water soluble and conveniently biocompatible, they showed growing interest for many interdisciplinary fields, particularly in biology and medicine. Thanks to their intrinsic conical shape, they provide suitable platforms, from vesicles to bilayers. This is a valuable characteristic, as so they mimic the biologically functional architectures. The anionic calixarenes propose efficient alternatives for overcoming the limitations linked to drug delivery and bioavailability, as well as drug resistance along with limiting the undesirable side effects. Moreover, the dynamic non-covalent binding with the drugs enables predictable and on demand drug release, controlled by the stimuli present in the targeted environment. This particular feature instigated the use of these versatile, stimuli-responsive compounds for sensing biomarkers of diverse pathologies. The present review describes the recent achievements of the anionic calixarenes in the field of life science, from drug carriers to biomedical engineering, with a particular outlook on their applications for the diagnosis and treatment of different pathologies.

New Carboxytriazolyl Amphiphilic Derivatives of Calix[4]arenes: Aggregation and Use in CuAAC Catalysis.

This work focuses on the synthesis of a new series of amphiphilic derivatives of calix[4]arenes for the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The aggregation properties of synthesized calix[4]arenes were studied using various techniques (fluorescence spectroscopy, nanoparticle tracking analysis, and dynamic light scattering). Increasing the length of the alkyl substituent led to stronger hydrophobic interactions, which increased polydispersity in solution. The zwitterionic nature of the synthesized calix[4]arenes was established using different types of dyes (Eosin Y for anionic structures and Rhodamine 6G for cationic structures). The synthesized calix[4]arenes were used as organic stabilizers for CuI. The catalytic efficiency of CuI-calix[4]arene was compared with that of the phase transfer catalyst tetrabutylammonium bromide (TBAB) and the surfactant sodium dodecyl sulfate (SDS). For all calixarenes, the selectivity in the CuAAC reaction was higher than that observed when TBAB and SDS were estimated.

Functionalized Calixarenes as Promising Antibacterial Drugs to Face Antimicrobial Resistance.

Since the discovery of polyphenolic resins 150 years ago, the study of polymeric compounds named calix[n]arene has continued to progress, and those skilled in the art perfectly know now how to modulate this phenolic ring. Consequently, calix[n]arenes are now used in a large range of applications and notably in therapeutic fields. In particular, the calix[4]arene exhibits multiple possibilities for regioselective polyfunctionalization on both of its rims and offers researchers the possibility of precisely tuning the geometry of their structures. Thus, in the crucial research of new antibacterial active ingredients, the design of calixarenes finds its place perfectly. This review provides an overview of the work carried out in this aim towards the development of intrinsically active prodrogues or metallic calixarene complexes. Out of all the work of the community, there are some excellent activities emerging that could potentially place these original structures in a very good position for the development of new active ingredients.

Photoswitchable Calixarene Activators for Controlled Peptide Transport across Lipid Membranes.

Supramolecular synthetic transporters are crucial to understand and activate the passage across lipid membranes of hydrophilic effector molecules. Herein, we introduce photoswitchable calixarenes for the light-controlled transport activation of cationic peptide cargos across model lipid bilayers and inside living cells. Our approach was based on rationally designed p-sulfonatocalix[4]arene receptors equipped with a hydrophobic azobenzene arm, which recognize cationic peptide sequences at the nM range. Activation of membrane peptide transport is confirmed, in synthetic vesicles and living cells, for calixarene activators featuring the azobenzene arm in the E configuration. Therefore, this method allows the modulation of the transmembrane transport of peptide cargos upon Z-E photoisomerization of functionalized calixarenes using 500 nm visible light. These results showcase the potential of photoswitchable counterion activators for the light-triggered delivery of hydrophilic biomolecules and pave the way for potential applications in remotely controlled membrane transport and photopharmacology applications of hydrophilic functional biomolecules.

Protein-macrocycle polymorphism: crystal form IV of the Ralstonia solanacearum lectin-sulfonato-calix[8]arene complex.

Controlled protein assembly and crystallization is necessary as a means of generating diffraction-quality crystals as well as providing a basis for new types of biomaterials. Water-soluble calixarenes are useful mediators of protein crystallization. Recently, it was demonstrated that Ralstonia solanacearum lectin (RSL) co-crystallizes with anionic sulfonato-calix[8]arene (sclx8) in three space groups. Two of these co-crystals only grow at pH ≤ 4 where the protein is cationic, and the crystal packing is dominated by the calixarene. This paper describes a fourth RSL-sclx8 co-crystal, which was discovered while working with a cation-enriched mutant. Crystal form IV grows at high ionic strength in the pH range 5-6. While possessing some features in common with the previous forms, the new structure reveals alternative calixarene binding modes. The occurrence of C2-symmetric assemblies, with the calixarene at special positions, appears to be an important result for framework fabrication. Questions arise regarding crystal screening and exhaustive searching for polymorphs.

Synthesis of Functionalized ABAC- and ABCD-Type Inherently Chiral Heteracalix[4]aromatics.

Despite their interesting stereochemistry and potential applications in (supramolecular) chemistry and chiroptical materials, inherently chiral macrocyclic compounds remain rare and are largely unexplored. We report herein a fragment coupling method to construct ABAC- and ABCD-type inherently chiral heteracalix[4]aromatics. The synthesis involves SNAr CuI-catalyzed Ullmann coupling and aliphatic nucleophilic substitution reactions as key steps using readily available starting materials. Postmacrocyclization functionalization reactions enabled the production of amino-substituted and (benzo[d])imidazole-2-(thi)one-bearing heteracalix[4]aromatics. Enantiopure ABCD-type macrocycles were obtained from resolution.

Probing the dynamical interaction of the para-sulfonato-calix[4]arene with an antifungal protein.

Calixarenes are hallmark molecules in supramolecular chemistry as hosts for small ligands. They have also conversely proved their interest as ligands toward assisted co-crystallization of proteins. These functionalized macrocycles target positively-charged residues, and notably surface-exposed lysines, with a site-selectivity finely characterized experimentally, but that remains to be assessed. Relying on a tailored molecular dynamics simulations protocol, we explore the association of para-sulfonato-calix[4]arenes with an antifungal protein, as a small yet most competitive system with 13 surface-exposed lysines. Our computational approach probes de novo the electrostatically-driven interaction, ruled out by a competition with salt bridges, corroborating the presence of two main binding sites probed by X-ray. The attach-pull-release (APR) method provides a very good assessment of the overall binding free energy measured experimentally (-6.42 ± 0.5 vs. -5.45 kcal mol-1 by isothermal titration calorimetry). This work also probes dynamic modifications upon ligand binding, and our computational protocol could be generalized to situate the supramolecular forces ruling out the calixarene-assisted co-crystallization of proteins.

Regioselective Radical Alkylation of Arenes Using Evolved Photoenzymes.

Substituted arenes are ubiquitous in molecules with medicinal functions, making their synthesis a critical consideration when designing synthetic routes. Regioselective C-H functionalization reactions are attractive for preparing alkylated arenes; however, the selectivity of existing methods is modest and primarily governed by the substrate's electronic properties. Here, we demonstrate a biocatalyst-controlled method for the regioselective alkylation of electron-rich and electron-deficient heteroarenes. Starting from an unselective "ene"-reductase (ERED) (GluER-T36A), we evolved a variant that selectively alkylates the C4 position of indole, an elusive position using prior technologies. Mechanistic studies across the evolutionary series indicate that changes to the protein active site alter the electronic character of the charge transfer (CT) complex responsible for radical formation. This resulted in a variant with a significant degree of ground-state CT in the CT complex. Mechanistic studies on a C2-selective ERED suggest that the evolution of GluER-T36A helps disfavor a competing mechanistic pathway. Additional protein engineering campaigns were carried out for a C8-selective quinoline alkylation. This study highlights the opportunity to use enzymes for regioselective radical reactions, where small molecule catalysts struggle to alter selectivity.

Calix[4]arene Derivative for Iodine Capture and Effect on Leaching of Iodine through Packaging.

A hydrophobic calix[4]arene derivative was investigated for its iodine (I2) capture efficiency from gaseous and liquid phase. The iodine uptake was followed by UV-vis spectroscopy. Additionally, the influence of the calix[4]arene derivative-polyolefin system on the leaching of iodine through packaging from a povidone-iodine-based (PVP-I) formulation was evaluated. In fact, iodine is a low-cost, multi-target, and broad-spectrum antiseptic. However, it is volatile, and the extended storage of I2-based formulations is challenging in plastic packaging. Here, we investigated the possibility of reducing the loss of I2 from an iodophor formulation by incorporating 4-tert-butylcalix [4]arene-tetraacetic acid tetraethyl ester (CX) and its iodine complex in high-density polyethylene (HDPE) or polypropylene (PP) via a swelling procedure. Surface and bulk changes were monitored by contact angle, thermogravimetric analysis (TGA), and UV-vis diffuse reflectance spectra. The barrier effect of the different polymeric systems (embedded with CX, iodine-CX complex, or I2) was evaluated by monitoring the I2 retention in a buffered PVP-I solution by UV-vis spectroscopy. Overall, experimental data showed the capability of the calix[4]arene derivative to complex iodine in solution and the solid state and a significant reduction in the iodine leaching by the PP-CX systems.

Recent Advancements in Ion-Pair Receptors.

Over the past two decades, non-covalent chemistry has introduced various promising artificial receptors and revolutionized the host-guest chemistry. These versatile receptors have particularly been entertained in sensing and recognizing of diverse neutral molecules and/or ionic entities (e. g. anions, cations and ion-pair) of particular interest. Notably, supramolecular chemistry had given birth to a plethora of important molecules, explored in the chemical, biological, environmental, and pharmacological world to resolve the critical issues related to the human health while keeping environmental concerns in mind. Amongst the various types of supramolecular monotopic receptors (anions, cations, and neutral molecules), heteroditopic receptors (ion-pair receptors) consisting of distinct binding sites in one system for both cation and anion, have gained much interest from the scientific community in recent past because of their unique binding abilities. Interestingly, these promising artificial receptors have shown potential applications in sensing, recognition, transport and extraction processes besides their uses in salt/waste purification. Bearing the importance of these systems in mind, we intended to report the recent developments in ion-pair chemistry. Herein, we divided the whole document into three main sections; first one describes the introduction and history of the ion-pairs receptors. The second portion highlights the synthesis and applications of ion-pair receptors in sensing, recognition, molecular machines, photoswitching behaviour, extraction and transport properties, whereas the last part of this manuscript provides concluding remarks as well as future prospects of ion-pair receptors. We hope that this manuscript will be helpful to stimulating researchers around the globe to find out the hidden opportunities in this and related areas.

Selective Metal-ion Complexation of a Biomimetic Calix[6]arene Funnel Cavity Functionalized with Phenol or Quinone.

In the biomimetic context, many studies have evidenced the importance of the 1st and 2nd coordination sphere of a metal ion for controlling its properties. Here, we propose to evaluate a yet poorly explored aspect, which is the nature of the cavity that surrounds the metal labile site. Three calix[6]arene-based aza-ligands are compared, that differ only by the nature of cavity walls, anisole, phenol or quinone (LOMe , LOH and LQ ). Monitoring ligand exchange of their ZnII complexes evidenced important differences in the metal ion relative affinities for nitriles, halides or carboxylates. It also showed a possible sharp kinetic control on both, metal ion binding and ligand exchange. Hence, this study supports the observations reported on biological systems, highlighting that the substitution of an amino-acid residue of the enzyme active site, at remote distance of the metal ion, can have strong impacts on metal ion lability, substrate/product exchange or selectivity.

Calixarene Derivatives: A Mini-Review on their Synthesis and Demands in Nanosensors and Biomedical Fields.

Nanotechnology has been widely studied in biomedical applications in the last decade. The revolution in nanotechnology triggers the fabrication of nanomaterials with novel properties and functionalities, making the research in nanosensors and biomedical rapidly expanding. Nanosensor application has improved the sensitivity by enhancing their catalytic activity, conductivity, and biocompatibility. Calixarene is excellent as a sensing element used as a sensor due to its unique host-guest properties. Three major types of calixarene which are extensively studied are calix[4]arene, calix[6]arene, and calix[8]arene. These organic nanomaterials resemble vase-like supramolecular structures and exhibit valuable properties. Calixarene's basic molecular design is the cyclic phenol tetramer with four aryl groups, perfect for molecular recognition such as cations, transition metal ions, and heavy metals. Calixarenes may form stable complexes with biomolecules in developing biosensors for protein, enzyme, and antibody sensing. Calixarene's lower rim can be modified for optimum molecular interaction with guest molecules such as anions, cations, and neutral molecules. The lower ring has welldefined conformation properties and cavities, which allow trapping guest drugs such as imatinib, paclitaxel, and temozolomide. Calixarene also possesses good biocompatibility and innocuousness and gained attention for cancer treatment due to the response to multiple stimuli, stability, avoiding non-specific cell uptake, and reaching the target for treatment effect. This review paper focuses on the synthesis and characteristics of calixarene applied in nanosensors as an ideal complex agent in drug transportation and controlled drug released for biomedical research.