Pillar[n]MaxQ: A New High Affinity Host Family for Sequestration in Water

Triphenylamine[3]arenes: Streamlining Synthesis of a Versatile Macrocyclic Platform for Supramolecular Architectures and Functionalities

Triphenylamine[3]arenes (TPA[3]s), featuring [16]paracyclophane backbone with alternating carbon and nitrogen bridging atoms, were synthesized through a BF3 ⋅ Et2O-catalyzed cyclization reaction using triphenylamine derivatized monomers and paraformaldehyde. This molecular design yielded a series of TPA[3] macrocycles with high efficiency, with their facile derivatizations also successfully demonstrated. On account of the strong electron-donating properties of the TPA moieties, these TPA[3]s exhibit remarkable delayed fluorescence, and possess a significant affinity for iodine. Furthermore, their inherent three-fold symmetry rendered TPA[3]s as novel building blocks for the construction of extended frameworks and molecular cages. This advancement expands the versatility of discrete macrocycles into complex architectures, enhancing their applicability across a broad spectrum of applications.

Methodological and force field effects in the molecular dynamics-based prediction of binding free energies of host-guest systems

As a contribution to the understanding and rationalization of methodological and modeling effects in recent host-guest SAMPL challenges, using an alchemical molecular dynamics technique we have examined the impact of force field parameterization and ionic strength in connection with guest charge neutralization on computed dissociation free energies in two typical SAMPL heavily charged macrocyclic hosts encapsulating small protonated amines with disparate binding affinities. We have shown that the methodological treatment for host neutralization, with explicit ions or with the background neutralizing plasma in the context of alchemical calculations under periodic boundary conditions, has a moderate effect on the calculated affinities. On the other hand, we have shown that seemingly small differences in the force field parameterization in highly symmetric hosts can produce systematic effects on the structural features that can have a significant impact on the predicted binding affinities.

Pillar[5]arenes decorated with six-membered-ring aromatics at all the substitution positions

Macrocyclic molecules have characteristic properties different from linear ones, such as high symmetry and guest-inclusion ability. To bring drastic changes to these properties, direct introduction of many substituents is a challenging but effective tool. Herein, we attain direct installation of ten six-membered-ring aromatic π-units into both rims of a pillar[5]arene. In contrast to previous pillar[n]arenes with less hindered five-membered-ring units, which showed conformational complexity and crushed crystal structures, the per-phenyl-substituted pillar[5]arene has a cylinder-shaped crystal structure with a dichloromethane inside the cavity and is obtained as a single pair of D 5-symmetric enantiomers. The average dihedral angles between the core and peripheral benzene rings sharply increase from 38° to 66°. These differences indicate the importance of local steric repulsion on both rims for determining the structures and properties of macrocycles.

Expanding the Hydrophobic Cavity Surface of Azocalix[4]arene to Enable Biotin/Avidin Affinity with Controlled Release

The development of artificial receptors that combine ultrahigh-affinity binding and controllable release for active guests holds significant importance in biomedical applications. On one hand, a complex with an exceedingly high binding affinity can resist unwanted dissociation induced by dilution effect and complex interferents within physiological environments. On the other hand, stimulus-responsive release of the guest is essential for precisely activating its function. In this context, we expanded hydrophobic cavity surface of a hypoxia-responsive azocalix[4]arene, affording Naph-SAC4A. This modification significantly enhanced its aqueous binding affinity to 1013 M-1, akin to the naturally occurring strongest recognition pair, biotin/(strept-)avidin. Consequently, Naph-SAC4A emerges as the first artificial receptor to simultaneously integrate ultrahigh recognition affinity and actively controllable release. The markedly enhanced affinity not only improved Naph-SAC4A's sensitivity in detecting rocuronium bromide in serum, but also refined the precision of hypoxia-responsive doxorubicin delivery at the cellular level, demonstrating its immense potential for diverse practical applications.

Trapping and reversing neuromuscular blocking agent by anionic pillar[5]arenes: Understanding the structure-affinity-reversal effects

Selective relaxant binding agents (SRBA) have great potential in clinical surgeries for the precise reversal of neuromuscular blockades. Understanding the relationship between the structure-affinity-reversal effects of SRBA and neuromuscular blockade is crucial for the design of new SRBAs, which has rarely been explored. Seven anionic pillar[5]arenes (AP5As) with different aliphatic chains and anionic groups at both edges were designed. Their binding affinities to the neuromuscular blocking agent decamonium bromide (DMBr) were investigated using 1H NMR, isothermal titration calorimetry (ITC), and theoretical calculations. The results indicate that the capture of DMBr by AP5As is primarily driven by electrostatic interactions, ion-dipole interactions and C-H‧‧‧π interactions. The optimal size matching between the carboxylate AP5As and DMBr was ∼0.80. The binding affinity increased with an increase in the charge quantity of AP5As. Further animal experiments indicated that the reversal efficiency increased with increasing binding affinity for carboxylate or phosphonate AP5As. However, phosphonate AP5As exhibited lower reversal efficiencies than carboxylate AP5As, despite having stronger affinities with DMBr. By understanding the structure-affinity-reversal relationships, this study provides valuable insights into the design of innovative SRBAs for reversing neuromuscular blockade.

Adamantylglycine as a high-affinity peptide label for membrane transport monitoring and regulation

The non-canonical amino acid adamantylglycine (Ada) is introduced into peptides to allow high-affinity binding to cucurbit[7]uril (CB7). Introduction of Ada into a cell-penetrating peptide (CPP) sequence had minimal influence on the membrane transport, yet enabled up- and down-regulation of the membrane transport activity.

Pillar[6]MaxQ functions as an in vivo sequestrant for rocuronium and vecuronium

The binding affinity of pillar[6]MaxQ toward a panel of neuromuscular blockers and neurotransmitters was measured in phosphate buffered saline by isothermal titration calorimetry and 1H NMR spectroscopy. In vivo efficacy studies showed that P6MQ sequesters rocuronium and vecuronium and reverses their influence on the recovery of the train-of-four (TOF) ratio.

The SAMPL9 host-guest blind challenge: an overview of binding free energy predictive accuracy

We report the results of the SAMPL9 host-guest blind challenge for predicting binding free energies. The challenge focused on macrocycles from pillar[n]-arene and cyclodextrin host families, including WP6, and bCD and HbCD. A variety of methods were used by participants to submit binding free energy predictions. A machine learning approach based on molecular descriptors achieved the highest accuracy (RMSE of 2.04 kcal mol-1) among the ranked methods in the WP6 dataset. Interestingly, predictions for WP6 obtained via docking tended to outperform all methods (RMSE of 1.70 kcal mol-1), most of which are MD based and computationally more expensive. In general, methods applying force fields achieved better correlation with experiments for WP6 opposed to the machine learning and docking models. In the cyclodextrin-phenothiazine challenge, the ATM approach emerged as the top performing method with RMSE less than 1.86 kcal mol-1. Correlation metrics of ranked methods in this dataset were relatively poor compared to WP6. We also highlight several lessons learned to guide future work and help improve studies on the systems discussed. For example, WP6 may be present in other microstates other than its -12 state in the presence of certain guests. Machine learning approaches can be used to fine tune or help train force fields for certain chemistry (i.e. WP6-G4). Certain phenothiazines occupy distinct primary and secondary orientations, some of which were considered individually for accurate binding free energies. The accuracy of predictions from certain methods while starting from a single binding pose/orientation demonstrates the sensitivity of calculated binding free energies to the orientation, and in some cases the likely dominant orientation for the system. Computational and experimental results suggest that guest phenothiazine core traverses both the secondary and primary faces of the cyclodextrin hosts, a bulky cationic side chain will primarily occupy the primary face, and the phenothiazine core substituent resides at the larger secondary face.

Delving into the Variability of Supramolecular Affinity: Self-Ion Pairing as a Central Player in Aqueous Host-Guest Chemistry

The determination of binding constants is a key matter in evaluating the strength of host-guest interactions. However, the profound impact of self-ion pairing on this parameter is often underrated in aqueous solution, leading in some cases to a misinterpretation of the true potential of supramolecular assemblies. In the present study, we aim to shed further light on this critical factor by exploring the concentration-dependent behavior of a multicharged pillararene in water. Our observations reveal an extraordinary 1-million-fold variability in the affinity of this macrocycle toward a given anion, showcasing the highly dynamic character of electrostatic interactions. We argue that these findings bring to the forefront the inherent determinism that underlies the estimation of affinity constants, a factor profoundly shaped by both the sensitivity of the instrumental technique in use and the intricacies of the experimental design itself. In terms of applications, these results may provide the opportunity to optimize the operational concentrations of multicharged hosts in different scenarios, aiming to achieve their maximum efficiency based on the intended application. Unlocking the potential of this hidden variability may pave the way for the creation of novel molecular materials with advanced functionalities.

Adaptive and Ultrahigh-Affinity Recognition in Water by Sulfated Conjugated Corral[5]arene

The pursuit of synthetic receptors with high binding affinities has long been a central focus in supramolecular chemistry, driven by their significant practical relevance in various fields. Despite the numerous synthetic receptors that have been developed, most exhibit binding affinities in the micromolar range or lower. Only a few exceptional receptors achieve binding affinities exceeding 109  M-1 , and their substrate scopes remain rather limited. In this context, we introduce SC[5]A, a conjugated corral-shaped macrocycle functionalized with ten sulfate groups. Owing to its deep one-dimensional confined hydrophobic cavity and multiple sulfate groups, SC[5]A displays an extraordinarily high binding strength of up to 1011  M-1 towards several size-matched, rod-shaped organic dications in water. Besides, its conformation exhibits good adaptability, allowing it to encapsulate a wide range of other guests with diverse molecular sizes, shapes, and functionalities, exhibiting relatively strong affinities (Ka =106 -108  M-1 ). Additionally, we've explored the preliminary application of SC[5]A in alleviating blood coagulation induced by hexadimethrine bromide in vitro and in vivo. Therefore, the combination of ultrahigh binding affinities (towards complementary guests) and adaptive recognition capability (towards a wide range of functional guests) of SC[5]A positions it as exceptionally valuable for numerous practical applications.

Water-soluble pillar[6]arene bearing pyrene on alternating methylene bridges for direct spermine sensing

This paper describes the design and synthesis of a conjugate, which is composed of a percarboxylated water-soluble pillar[6]arene and three fluorescent pyrene chromophores on alternating methylene bridges. The optical characteristics are investigated. This conjugate is capable of encapsulating polycationic guest spermine, which results in an enhancement in the fluorescence intensity of pyrene. This host-pyrene conjugate is used for direct sensing of spermine, which shows selectivity towards a variety of biological analytes. The detection of spermine is demonstrated in live cells.

A Chiral Emissive Conjugated Macrocycle for High-Affinity and Highly Enantioselective Recognition in Water

Accurately distinguishing between enantiomeric molecules is a fundamental challenge in the field of chemistry. However, there is still significant room for improvement in both the enantiomeric selectivity (KR(S) /KS(R) ) and binding strength of most reported macrocyclic chiral receptors to meet the demands of practical application scenarios. Herein, we synthesized a water-soluble conjugated tubular host-namely, corral[4]BINOL-using a chiral 1,1'-bi-2-naphthol (BINOL) derivative as the repeating unit. The conjugated chiral backbone endows corral[4]BINOL with good fluorescent emission (QY=34 % ) and circularly polarized luminescence (|glum | up to 1.4×10-3 ) in water. Notably, corral[4]BINOL exhibits high recognition affinity up to 8.6×1010  M-1 towards achiral guests in water, and manifested excellent enantioselectivity up to 18.7 towards chiral substrates, both of which represent the highest values observed among chiral macrocycles in aqueous solution. The ultrastrong binding strength, outstanding enantioselectivity, and facile accessibility, together with the superior fluorescent and chiroptical properties, endow corral[4]BINOL with great potential for a wide range of applications.

Challenges and Opportunities of Functionalized Cucurbiturils for Biomedical Applications

Cucurbit[n]uril (CB[n]) macrocycles (especially CB[5] to CB[8]) have shown exceptional attributes since their discovery in 2000. Their stability, water solubility, responsiveness to several stimuli, and remarkable binding properties have enabled a growing number of biological applications. Yet, soon after their discovery, the challenge of their functionalization was set. Nevertheless, after more than two decades, a myriad of CB[n] derivatives has been described, many of them used in cells or in vivo for advanced applications. This perspective summarizes key advances of this burgeoning field and points to the next opportunities and remaining challenges to fully express the potential of these fascinating macrocycles in biology and biomedical sciences.

Synthesis and Host-Guest Chemistry of Chiral Spirobifluorene-Based Macrocycles Soluble in Basic Aqueous Solution

Synthesis and host-guest chemistry of water-soluble (pH 12.5) chiral spirobifluorene-based macrocycles 2-[n] were carried out. Cationic guests, such as quaternary ammonium salts, were accommodated well in the hosts. Cp2Co+ was especially strongly bound in 2-[4] (Ka of up to 3.0 × 105 M-1). Enantioselective recognition with (l)-carnitine was also achieved.

Balancing on a Knife's Edge: Studies on the Synthesis of Pillar[6]arene Derivatives

Pillar[6]arenes are established as crucial building blocks in supramolecular chemistry; however, they can be difficult to synthesize, particularly in the absence of large solubilizing substituents. In this work, we explore variability in literature syntheses of pillar[6]arene derivatives and suggest that the outcome is dependent on whether oligomeric intermediates stay in solution long enough for the thermodynamically favorable macrocyclization to occur. We demonstrate that in a previously capricious BF₃·OEt₂-mediated procedure, ≤5 mol % of a Brønsted acid can slow down the reaction to favor macrocycle formation.

Water-soluble terphen[3]arene macrocycle: a versatile reversal agent of neuromuscular blockers

Herein we report the design and synthesis of a terphen[n]arene derivative functionalised with sulfate acid ester groups. This water-soluble terphen[3]arene host effectively encapsulates a multitude of neuromuscular blocking agents (NMBAs) with high affinity, showing great potential as a NMBAs reversal agent in pharmaceutical research.

Pillar[6]MaxQ: A Potent Supramolecular Host for In Vivo Sequestration of Methamphetamine and Fentanyl

Pillar[6]MaxQ (P6AS) functions as an in vivo sequestration agent for methamphetamine and fentanyl. We use 1H NMR, isothermal titration calorimetry, and molecular modelling to deduce the geometry and strength of the P6AS•drug complexes. P6AS forms tight complexes with fentanyl (Kd=9.8 nM), PCP (17.1 nM), MDMA (25.5 nM), mephedrone (52.4 nM), and methamphetamine (101 nM). P6AS has good in vitro biocompatibility according to MTS metabolic, Adenylate Kinase cell death, and hERG ion channel inhibition assays, and the Ames fluctuation test. The no observed adverse effect level for P6AS is 45 mg/kg. The hyperlocomotion of mice treated with methamphetamine (0.5 mg/kg) can be ameliorated by treatment with P6AS (35.7 mg/kg) 5-minutes later, whereas the hyperlocomotion of mice treated with fentanyl (0.1 mg/kg) can be controlled by treatment with P6AS (5 mg/kg) up to 15-minutes later. P6AS has significant potential for development as a broad spectrum in vivo sequestration agent.

Host-guest binding of tetracationic cyclophanes to photodynamic agents inhibits posttreatment phototoxicity and maintains antitumour efficacy

In the past two decades, photodynamic therapy (PDT) has become an effective method for the treatment of cancer. However, the posttreatment residue of photodynamic agents (PDAs) causes long-term skin phototoxicity. Here, we apply naphthalene-derived, box-like tetracationic cyclophanes, named NpBoxes, to bind to clinically used porphyrin-based PDAs to alleviate their posttreatment phototoxicity by reducing their free content in skin tissues and 1O2 quantum yield. We show that one of the cyclophanes, 2,6-NpBox, could include the PDAs to efficiently suppress their photosensitivity for the generation of reactive oxygen species. A tumour-bearing mouse model study revealed that, when Photofrin, the most widely used PDA in clinic, was administrated at a dose corresponding to the clinical one, 2,6-NpBox of the same dose could significantly suppress its posttreatment phototoxicity on the skin induced by simulated sunlight irradiation, without imposing a negative influence on its PDT efficacy.

Macrocycle with Equatorial Coordination Sites Provides New Opportunity for Structure-Diverse Metallacages

Reported here is the synthesis of a macrocycle with equatorial coordination sites for the construction of self-assembled metallacages. The macrocycle is prepared via a post-modification on the equator of biphen[n]arene. Utilizing this macrocycle as a ligand, three prismatic cages and one octahedral cage were synthesized by regulating the geometric structures and coordination number of metal acceptors. The multi-cavity configuration of prismatic cage was revealed by single-crystal structure. We prove that a macrocycle with equatorial coordination sites can be an excellent building block for synthesizing structure-diverse metallacages. Our results provide a typical example and a general method for the design and synthesis of metallacages.

Highly Water-Soluble Cucurbit[8]uril Derivative as a Broad-Spectrum Neuromuscular Block Reversal Agent

Broad-spectrum agents for the reversal of residual curarization induced by neuromuscular blocking agents are of great significance. Here, we report a highly water-soluble cucurbit[8]uril (CB[8]) derivative as a broad-spectrum neuromuscular block reversal agent induced by both benzylisquinolinium and aminosteroid neuromuscular block agents by the supramolecular sequestration strategy. The UV/Vis competition titration assays suggest the high binding affinity of the CB[8] derivative toward both benzylisquinolinium-type cisatracurium besylate and aminosteroid-type rocuronium, vecuronium, and pancuronium, at the level of 10⁷ M^-1. In vivo studies demonstrate that the administration of the CB[8] derivative could significantly accelerate the recovery time compared to the placebo or neostigmine groups. The reversal activity of the CB[8] derivative is comparable to or higher than that of clinically approved sugammadex. Acute toxicity evaluations reveal that the CB[8]-derivative displays outstanding biocompatibility, with the maximum tolerance dose as high as 960 mg kg^-1.

Molecular recognition of methylated amino acids and peptides by Pillar[6]MaxQ

We report the molecular recognition properties of Pillar[n]MaxQ (P[n]MQ) toward a series of (methylated) amino acids, amino acid amides, and post-translationally modified peptides by a combination of 1H NMR, isothermal titration calorimetry, indicator displacement assays, and molecular dynamics simulations. We find that P6MQ is a potent receptor for N-methylated amino acid side chains. P6MQ recognized the H3K4Me3 peptide with Kd = 16 nM in phosphate buffered saline.

Chemical Mechanism-Dominated and Reporter-Tunable Surface-Enhanced Raman Scattering via Directional Supramolecular Assembly

Molecular resonance can be strengthened by charge transfer, profiting chemical mechanism (CM)-related surface-enhanced Raman scattering (SERS). Herein a supramolecular assembly enabled SERS system is established by functionalizing para-sulfonatocalix[4]arene (pSC₄) onto Au₃Cu nanocrystals (NCs). Due to the cooperation of Au and Cu, pSC₄ is directionally assembled on the surface of Au₃Cu NCs via van der Waals force, enabling photoinduced and hydrogen bond-induced charge transfer, which remarkably enhances the Raman scattering of methylene blue (MB) captured by pSC₄. In particular, for the C-N and C-C stretching of MB, the contributions of resonance Raman scattering increase up to 80%. In addition, the SERS system is able to display affinities of different host-guest interactions, and further employed to evaluate effects of drugs for Alzheimer's disease. In this work, charge transfer is realized by performing supramolecular assembly on the surface of plasmonic nanomaterials, providing an avenue to design CM-related and reporter-tunable SERS systems.

"Rim-Differentiated" Pillar[6]arenes

A "rim-differentiated" pillar[6]arene (RD-P[6]) was obtained successfully, with the assistance of a dimeric silver trifluoroacetate template, among eight different constitutional isomers in a direct and regioselective manner. The solid-state conformation of this macrocycle could switch from the 1,3,5-alternate to a truly rim-differentiated one upon guest inclusion. This highly symmetric RD-P[6] not only hosts metal-containing molecules inside its cavity, but also can form a pillar[6]arene-C₆₀ adduct through co-crystallization on account of donor-acceptor interactions. The development of synthetic strategies to desymmetrize pillararenes offers new opportunities for engineering complex molecular architectures and organic electronic materials.

When Molecules Meet in Water-Recent Contributions of Supramolecular Chemistry to the Understanding of Molecular Recognition Processes in Water

Molecular recognition processes in water differ from those in organic solvents in that they are mediated to a much greater extent by solvent effects. The hydrophobic effect, for example, causes molecules that only weakly interact in organic solvents to stay together in water. Such water‐mediated interactions can be very efficient as demonstrated by many of the synthetic receptors discussed in this review, some of which have substrate affinities matching or even surpassing those of natural binders. However, in spite of considerable success in designing such receptors, not all factors determining their binding properties in water are fully understood. Existing concepts still provide plausible explanations why the reorganization of water molecules often causes receptor‐substrate interactions in water to be strongly exothermic rather than entropically favored as predicted by the classical view of the hydrophobic effect.

Thermodynamics of Pillararene•Guest Complexation: Blinded Dataset for the SAMPL9 Challenge

We report an investigation of the complexation between a water soluble pillararene host (WP6) and a panel of hydrophobic cationic guests (G1 - G20) by a combination of ¹H NMR spectroscopy and isothermal titration calorimetry in phosphate buffered saline. We find that WP6 forms 1:1 complexes with K_a values in the 10⁴ - 10⁹ M^-1 range driven by favorable enthalpic contributions. This thermodynamic dataset serves as blinded data for the SAMPL9 challenge.

Stabilization of Antitumor Agent Busulfan through the Encapsulation within a Water-Soluble Pillar[5]arene

The complexation of antitumor agent busulfan by negatively charged carboxylatopillar[5]arenein water is reported. The encapsulation within carboxylatopillar[5]arenein reduces the hydrolytic degradation of busulfan from 90.7 % to 25.2 % after 24 days and accordingly enhances its stability by providing a hydrophobic shelter for busulfan in water. Moreover, the complexation result in 12 times improvement of water solubility for busulfan. Our result provides a supramolecular approach for stabilizing the anticancer agent busulfan.

Photomodulation of ultrastable host–guest complexes in water and their application in light-controlled steroid release

Host–guest complexation of dithienylethene photoswitches with cucurbit[8]uril leads to photoresponsive binding pairs with picomolar affinity in water.

Analyte sensing with unselectively binding synthetic receptors: virtues of time-resolved supramolecular assays

Time-resolved supramolecular assays probe analyte-characteristic complexation and decomplexation rates. Consequently, even unselectively binding synthetic receptors can be used for analyte identification and quantification.

Flexible organic frameworks sequester neuromuscular blocking agents in vitro and reverse neuromuscular block invivo

Supramolecular sequestration and reversal of neuromuscular block (NMB) have great clinical applications. Water-soluble flexible organic frameworks (FOFs) cross-linked by disulfide bonds are designed and prepared. Different linker lengths are introduced to FOFs to give them varied pore sizes. FOFs are anionic nanoscale polymers and capable of encapsulating cationic neuromuscular blocking agents (NMBAs), including rocuronium (Roc), vecuronium (Vec), pancuronium (Panc) and cisatracurium (Cis). A host–guest study confirms that FOFs bind NMBAs in water. The multivalency interaction between FOFs and NMBAs is able to sequester NMBAs, and prevent them from escaping. These FOFs are non-toxic and biocompatible. Animal studies show that FOFs are effective for the reversal of NMB induced by Roc, Vec and Cis, which shorten the time to a train-of-four ratio of 0.9 by 2.6, 3.8 and 5.7-fold compared to a placebo, respectively.

Water-soluble flexible organic frameworks are prepared and used to sequester neuromuscular blocking agents, and reverse their neuromuscular block in vivo.

Charged Tubular Supramolecule Boosting Multivalent Interactions for the Drastic Suppression of Aβ Fibrillation

Anti-Aβ therapy has dominated clinical trials for the prevention and treatment of Alzheimer's disease (AD). However, suppressing Aβ aggregation and disintegrating mature fibrils simultaneously remains a great challenge. In this work, we developed a new strategy using a charged tubular supramolecule (CTS) with pillar[5]arene as the backbone and modifying amino and carboxyl groups at the tubular terminals (noted as CTS-A, CTS-A/C, and CTS-C, respectively) to suppress Aβ fibrillation for the first time. According to the spectroscopic and microscopic characterizations, Aβ₄₀ fibrillation can be efficiently suppressed by CTS-A in a very low inhibitor:peptide (I:P) molar ratio (1:10). A greatly alleviated cytotoxic effect of Aβ peptides after the inhibition or disaggregation process is further disclosed. The well-organized supramolecular structure drives multivalent interaction and gains enhanced efficiency on amyloid fibrillar modulation. These results open a new path for the design of supramolecules in the application of AD treatment.

Template-Directed Synthesis of Bivalent, Broad-Spectrum Hosts for Neuromuscular Blocking Agents*

We report on the synthesis of bivalent water-soluble calix[4]arene and calix[5]arene hosts, Super-sCx4 and Super-sCx5 as new broad-spectrum supramolecular binders of neuromuscular blocking agents (NMBAs). Synthesis was achieved using the target bisquaternary amine NMBAs as a template to link two highly anionic p-sulfonatocalixarene building blocks in aqueous solution. Bivalent anionic hosts Super-sCx4 and Super-sCx5 bind by engaging both quaternary amines present on a variety of NMBAs. We report low μM binding to structurally diverse alkyl, steroidal, curarine and benzylisoquinoline NMBAs with high selectivity over the neurotransmitter acetylcholine and a variety of other hydrophobic amines.

Supramolecular Host-Guest Hydrogels for Corneal Regeneration

Over 6.2 million people worldwide suffer from moderate to severe vision loss due to corneal disease. While transplantation with allogenic donor tissue is sight-restoring for many patients with corneal blindness, this treatment modality is limited by long waiting lists and high rejection rates, particularly in patients with severe tissue damage and ocular surface pathologies. Hydrogel biomaterials represent a promising alternative to donor tissue for scalable, nonimmunogenic corneal reconstruction. However, implanted hydrogel materials require invasive surgeries and do not precisely conform to tissue defects, increasing the risk of patient discomfort, infection, and visual distortions. Moreover, most hydrogel crosslinking chemistries for the in situ formation of hydrogels exhibit off-target effects such as cross-reactivity with biological structures and/or result in extractable solutes that can have an impact on wound-healing and inflammation. To address the need for cytocompatible, minimally invasive, injectable tissue substitutes, host-guest interactions have emerged as an important crosslinking strategy. This review provides an overview of host-guest hydrogels as injectable therapeutics and highlights the potential application of host-guest interactions in the design of corneal stromal tissue substitutes.

Cucurbituril-Encapsulating Metal-Organic Framework via Mechanochemistry: Adsorbents with Enhanced Performance

The first examples of monolithic crystalline host-guest hybrid materials are described. The reaction of 1,3,5-benzenetricarboxylic acid (H3 BTC) and Fe(NO3 )3 ⋅9 H2 O in the presence of decamethylcucurbit[5]uril ammonium chloride (MC5⋅2 NH4 Cl⋅4 H2 O) directly affords MC5@MIL-100(Fe) hybrid monoliths featuring hierarchical micro-, meso- and macropores. Particularly, this "bottle-around-ship" synthesis and one-pot shaping are facilitated by a newly discovered Fe-MC5 flowing gel formed by mechanochemistry. The designed MC5@MIL-100(Fe) hybrid material with MC5 as active domains shows enhanced CH4 and lead(II) uptake performance, and selective capture of lead(II) cations at low concentrations. This shows that host-guest hybrid materials can exhibit synergic properties that out-perform materials based on individual components.

Host-guest binding in water, salty water, and biofluids: general lessons for synthetic, bio-targeted molecular recognition

Synthetic molecular recognition systems are increasingly being used to solve applied problems in the life sciences, and bio-targeted host-guest chemistry has rapidly arisen as a major field of fundamental research. This tutorial review presents a set of fundamental lessons on how host-guest molecular recognition can be programmed in water. The review uses informative examples of aqueous host-guest chemistry organized around generalizable themes and lessons, building towards lessons focused on molecular recognition in salty solutions and biological fluids. It includes selected examples of macrocyclic host systems that work well, as well as common pitfalls and how to avoid them. The review closes with a survey of the most important and inspirational recent advances, which involve host-guest chemistry in living cells and organisms.

Applications of Macrocyclic Host Molecules in Immune Modulation and Therapeutic Delivery

The immune system plays a central role in the development and progression of human disease. Modulation of the immune response is therefore a critical therapeutic target that enables us to approach some of the most vexing problems in medicine today such as obesity, cancer, viral infection, and autoimmunity. Methods of manipulating the immune system through therapeutic delivery centralize around two common themes: the local delivery of biomaterials to affect the surrounding tissue or the systemic delivery of soluble material systems, often aided by context-specific cell or tissue targeting strategies. In either case, supramolecular interactions enable control of biomaterial composition, structure, and behavior at the molecular-scale; through rational biomaterial design, the realization of next-generation immunotherapeutics and immunotheranostics is therefore made possible. This brief review highlights methods of harnessing macromolecular interaction for immunotherapeutic applications, with an emphasis on modes of drug delivery.

Pillararene-based self-assemblies for electrochemical biosensors

The ingenious design and synthesis of novel macrocycles bring out renewed vigor of supramolecular chemistry in the past decade. As an intriguing class of macrocycles, pillararene and pillararene-based functional materials that are constructed through the noncovalent bond self-assembly approach have been undergoing a rapid growth, benefiting from their unique structures and physiochemical properties. This review elaborates recent significant advances of electrochemical studies based on pillararene systems. Fundamental electrochemical behavior of pillar[n]arene[m]quinone and pillararene-based self-assemblies as well as their applications in electrochemical biosensors are highlighted. In addition, the advantages and functions of pillararene self-assembly systems resulted from the unique molecular architectures are analyzed. Finally, current challenges and future development tendency in this burgeoning field are discussed from the viewpoint of both fundamental research and applications. Overall, this review not only manifests the main development vein of pillararene-based electrochemical systems, but also conquers a solid foundation for their further bioelectrochemical applications.

Molecular Recognition in Water Using Macrocyclic Synthetic Receptors

Molecular recognition in water using macrocyclic synthetic receptors constitutes a vibrant and timely research area of supramolecular chemistry. Pioneering examples on the topic date back to the 1980s. The investigated model systems and the results derived from them are key for furthering our understanding of the remarkable properties exhibited by proteins: high binding affinity, superior binding selectivity, and extreme catalytic performance. Dissecting the different effects contributing to the proteins' properties is severely limited owing to its complex nature. Molecular recognition in water is also involved in other appreciated areas such as self-assembly, drug discovery, and supramolecular catalysis. The development of all these research areas entails a deep understanding of the molecular recognition events occurring in aqueous media. In this review, we cover the past three decades of molecular recognition studies of neutral and charged, polar and nonpolar organic substrates and ions using selected artificial receptors soluble in water. We briefly discuss the intermolecular forces involved in the reversible binding of the substrates, as well as the hydrophobic and Hofmeister effects operating in aqueous solution. We examine, from an interdisciplinary perspective, the design and development of effective water-soluble synthetic receptors based on cyclic, oligo-cyclic, and concave-shaped architectures. We also include selected examples of self-assembled water-soluble synthetic receptors. The catalytic performance of some of the presented receptors is also described. The latter process also deals with molecular recognition and energetic stabilization, but instead of binding ground-state species, the targets become elusive counterparts: transition states and other high-energy intermediates.

Supramolecular hosts as in vivo sequestration agents for pharmaceuticals and toxins

Pharmaceutical agents, drugs of abuse, and toxic substances have a large impact, positive and negative, on modern society. Efforts to mitigate the side effects of pharmaceuticals and counteract the life threatening effects of drugs of abuse and toxins can occur either by pharmacodynamic (PD) approaches based on bioreceptor·drug antagonism or by pharmacokinetic (PK) approaches that seek to reduce the concentration of free drug. In this tutorial review, we present the use of supramolecular hosts (cyclodextrins, calixarenes, (acyclic) cucurbiturils, and pillararenes) as in vivo sequestration agents for neuromuscular blockers, drugs of abuse (methamphetamine and fentanyl), anesthetics, neurotoxins, the pesticide paraquat, and heparin anti-coagulants by the PK approach. The review presents the basic physical and molecular recognition features of the supramolecular hosts and some of the principles used in their selection and structural optimization for in vivo sequestration applications. The influence of host·guest complexation on other relevant in vivo properties of drugs (e.g. distribution, circulation time, excretion, redox properties) is also mentioned. The article concludes with a discussion of future directions.

Ultrasensitive Electrochemical Sensor for Luteolin Based on Zirconium Metal-Organic Framework UiO-66/Reduced Graphene Oxide Composite Modified Glass Carbon Electrode

Luteolin is a kind of natural flavonoid with many bioactivities purified from a variety of natural herbs, fruits and vegetables. Electrochemical sensing has become an outstanding technology for the detection of luteolin in low concentration due to its fast response, easy operation and low cost. In this study, electroreduced graphene oxide (ErGO) and UiO-66 were successively modified onto a glassy carbon electrode (UiO-66/ErGO/GCE) and applied to the detection of luteolin. A combination of UiO-66 and ErGO showed the highest promotion in the oxidation peak current for luteolin compared with those of a single component. The factors affecting the electrochemical behavior of UiO-66/ErGO/GCE were evaluated and optimized including pH, accumulation potential, accumulation time and scan rate. Under optimum conditions, UiO-66/ErGO/GCE showed satisfactory linearity (from 0.001 μM to 20 μM), reproducibility and storage stability. The detection limit of UiO-66/ErGO/GCE reached 0.75 nM of luteolin and was suitable for testing real samples. Stable detection could be provided at least eight times by one modified electrode, which guaranteed the practicability of the proposed sensor. The fabricated UiO-66/ErGO/GCE showed a rapid electrochemical response and low consumption of materials in the detection of luteolin. It also showed satisfactory accuracy for real samples with good recovery. In conclusion, the modification using MOFs and graphene materials made the electrode advanced property in electrochemical sensing of natural active compounds.