Acyclic Cucurbit[n]uril Receptors Function as Solid State Sequestrants for Organic Micropollutants.

The accumulation of organic micropollutants (OMP) in aquatic systems is a major societal problem that can be addressed by approaches including nanofiltration, flocculation, reverse osmosis and adsorptive methods using insoluble materials (e.g. activated carbon, MOFs, nanocomposites). More recently, polymeric versions of supramolecular hosts (e.g. cyclodextrins, calixarenes, pillararenes) have been investigated as OMP sequestrants. Herein, we report our study of the use of water insoluble dimethylcatechol walled acyclic cucurbit[n]uril (CB[n]) hosts as solid state sequestrants for a panel of five OMPs. A series of hosts (H1 - H4) were synthesized by reaction of glycoluril oligomer (monomer - tetramer) with 3,6-dimethylcatechol and fully characterized by spectroscopic means and x-ray crystallography. The solid hosts sequester OMPs from water with removal efficiencies exceeding 90% in some cases. The removal efficiencies of the new hosts parallel the known molecular recognition properties of analogous water soluble acyclic CB[n]. OMP uptake by solid host occurs rapidly (≈120 seconds). Head-to-head comparison with CB[6] in batch-mode separation and DARCO activated carbon in flow-through separation mode show that tetramer derived host (H4) performs very well under identical conditions. The work establishes insoluble acyclic CB[n]-type receptors as a promising new platform for OMP sequestration.

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.

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.

DNA Strand Displacement Driven by Host-Guest Interactions.

Base-pair-driven toehold-mediated strand displacement (BP-TMSD) is a fundamental concept employed for constructing DNA machines and networks with a gamut of applications─from theranostics to computational devices. To broaden the toolbox of dynamic DNA chemistry, herein, we introduce a synthetic surrogate termed host-guest-driven toehold-mediated strand displacement (HG-TMSD) that utilizes bioorthogonal, cucurbit[7]uril (CB[7]) interactions with guest-linked input sequences. Since control of the strand-displacement process is salient, we demonstrate how HG-TMSD can be finely modulated via changes to the structure of the input sequence (including synthetic guest head-group and/or linker length). Further, for a given input sequence, competing small-molecule guests can serve as effective regulators (with fine and coarse control) of HG-TMSD. To show integration into functional devices, we have incorporated HG-TMSD into machines that control enzyme activity and layered reactions that detect specific microRNA.

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.

New Synthetic Route to Water-Soluble Prism[5]arene Hosts and Their Molecular Recognition Properties.

We report that the direct macrocyclization of naphthalene monomers bearing ethyl ester functional groups delivers prism[5]arene derivatives, which can be deprotected to yield water-soluble prism[5]arenes (H1 and H3). 1 H NMR spectroscopy showed that dicationic guests bind with the hydrophobic cores buried inside the anisotropic magnetically shielding cavity. Isothermal titration calorimetry measurements showed that H1 and H3 are high-affinity hosts in PBS-buffered water with Ka values exceeding 109  M-1 for a select guest. The complexation events are driven by the non-classical hydrophobic effect, CH⋅⋅⋅π interactions, and electrostatic interactions. Host H1 displays somewhat higher affinity toward a common guest than pillar[6]arene bearing carboxylic acid functional groups but is significantly less potent than pillar[6]arene bearing sulfate groups. H1 and H3 should be considered alongside other high affinity hosts for a variety of chemical and biological applications.

Double-Cavity Nor-Seco-Cucurbit[10]uril Enables Efficient and Rapid Separation of Pyridine from Mixtures of Toluene, Benzene, and Pyridine.

Benzene, toluene and pyridine are widely used as essential raw materials in industry and laboratory research, with stringent purity requirements. Herein, we show that solid double-cavity host nor-seco-cucurbit[10]uril (ns-Q[10]) functions as an efficient adsorption separator for pyridine; benzene and toluene can be obtained in >99.9 % purity by this method. Thermal removal of pyridine from ns-Q[10]⋅Py2 allows 10 separation cycles without erosion of performance. The geometry of the ns-Q[10]⋅Py2 ternary complex was established by single-crystal X-ray diffraction methods. The ns-Q[10] cage facilitates the removal of pyridine from toluene and benzene, with >99.9 % purity for the separated compounds.

Voltage-Gated Membranes Incorporating Cucurbit[n]uril Molecular Containers for Molecular Nanofiltration.

Smart voltage-gated nanofiltration membranes have enormous potential for on-demand and precise separation of similar molecules, which is an essential element of sustainable water purification and resource recovery. However, the existing voltage-gated membranes are hampered by limited selectivity, stability, and scalability due to electroactive monomer dimerization. Here, for the first time, the host-guest recognition properties of cucurbit[7]uril (CB[7]) are used to protect the viologen derivatives and promote their assembly into the membrane by interfacial polymerization. Viologen functions as a voltage switch, whereas CB[7] complexation prevents its dimerization and improves its redox stability. The inhibited diffusion of the CB[7]-viologen complex enables the precise patterning of the surface structure. The resultant voltage-gated membrane displays 80% improved rejection performance, excellent recovery accuracy for similar molecules, and anti-fouling properties. This work not only provides an innovative strategy for the preparation of voltage-gated smart nanofiltration membranes but also opens up new avenues for ion-selective transmission in water treatment, bionic ion channels, and energy conversion.

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 Ka values in the 104 - 109 M-1 range driven by favorable enthalpic contributions. This thermodynamic dataset serves as blinded data for the SAMPL9 challenge.

Anthracene-Walled Acyclic CB[n] Receptors: in†vitro and in†vivo Binding Properties toward Drugs of Abuse.

We report studies of the interaction of six acyclic CB[n]-type receptors toward a panel of drugs of abuse by a combination of isothermal titration calorimetry and 1 H NMR spectroscopy. Anthracene walled acyclic CB[n] host (M3) displays highest binding affinity toward methamphetamine (Kd =15 nM) and fentanyl (Kd =4 nM). Host M3 is well tolerated by Hep G2 and HEK 293 cells up to 100 µM according to MTS metabolic and adenylate kinase release assays. An in vivo maximum tolerated dose study with Swiss Webster mice showed no adverse effects at the highest dose studied (44.7 mg kg-1 ). Host M3 is not mutagenic based on the Ames fluctuation test and does not inhibit the hERG ion channel. In vivo efficacy studies showed that pretreatment of mice with M3 significantly reduces the hyperlocomotion after treatment with methamphetamine, but M3 does not function similarly when administered 30 seconds after methamphetamine.

Binding Methylarginines and Methyllysines as Free Amino Acids: A Comparative Study of Multiple Host Classes.

Methylated free amino acids are an important class of targets for host-guest chemistry that have recognition properties distinct from those of methylated peptides and proteins. We present comparative binding studies for three different host classes that are each studied with multiple methylated arginines and lysines to determine fundamental structure-function relationships. The hosts studied are all anionic and include three calixarenes, two acyclic cucurbiturils, and two other cleft-like hosts, a clip and a tweezer. We determined the binding association constants for a panel of methylated amino acids using indicator displacement assays. The acyclic cucurbiturils display stronger binding to the methylated amino acids, and some unique patterns of selectivity. The two other cleft-like hosts follow two different trends, shallow host (clip) following similar trends to the calixarenes, and the other more closed host (tweezer) binding certain less-methylated amino acids stronger than their methylated counterparts. Molecular modelling sheds some light on the different preferences of the various hosts. The results identify hosts with new selectivities and with affinities in a range that could be useful for biomedical applications. The overall selectivity patterns are explained by a common framework that considers the geometry, depth of binding pockets, and functional group participation across all host classes.

In Vitro and In Vivo Sequestration of Methamphetamine by a Sulfated Acyclic CB[n]-Type Receptor.

We report the synthesis of two new acyclic sulfated acyclic CB[n]-type receptors (TriM0 and Me4 TetM0) and investigations of their binding properties toward a panel of drugs of abuse (1-13) by a combination of 1 H NMR spectroscopy and isothermal titration calorimetry. TetM0 is the most potent receptor with Ka ≥106  M-1 toward methamphetamine, fentanyl, MDMA and mephedrone. TetM0 is not cytotoxic toward HepG2 and HEK 293 cells below 100 µM according to MTS metabolic and adenylate kinase release assays and is well tolerated in vivo when dosed at 46 mg kg-1 . TetM0 does not inhibit the hERG ion channel and is not mutagenic based on the Ames fluctuation test. Finally, in vivo efficacy studies show that the hyperlocomotion of mice treated with methamphetamine can be greatly reduced by treatment with TetM0 up to 5 minutes later. TetM0 has potential as a broad spectrum in vivo sequestrant for drugs of abuse.

Self Assembled Cages with Mechanically Interlocked Cucurbiturils.

We report preparation of (bis)aniline ligand 4 which contains a central viologen binding domain and its subcomponent self-assembly with aldehyde 5 and Fe(OTf)2 in CH3CN to yield tetrahedral assembly 6. Complexation of ligand 4 with CB[7] in the form of CB[7]•4•2PF6 allows the preparation of assembly 7 which contains an average of 1.95 (range 1-3) mechanically interlocked CB[7] units. Assemblies 6 and 7 are hydrolytically unstable in water due to their imine linkages. Redesign of our system with water stable 2,2'-bipyridine end groups was realized in the form of ligands 11 and 16 which also contain a central viologen binding domain. Self-assembly of 11 with Fe(NTf2)2 gave tetrahedral MOP 12 as evidenced by 1H NMR, DOSY, and mass spectrometric analysis. In contrast, isomeric ligand 16 underwent self-assembly with Fe(OTf)2 to give cubic assembly 17. Precomplexation of ligands 11 and 16 with CB[7] gave the acetonitrile soluble CB[7]•11•2PF6 and CB[7]•16•2PF6 complexes. Self-assembly of CB[7]•11•2PF6 with Fe(OTf)2 gave tetrahedron 13 which contains on average 1.8 mechanically interlocked CB[7] units as determined by 1H NMR, DOSY, and ESI-MS analysis. Self-assembly of CB[7]•16•2PF6 with Fe(OTf)2 gave cube 13 which contains 6.59 mechanically interlocked CB[7] units as determined by 1H NMR and DOSY measurements.

Acyclic Cucurbituril Featuring Pendant Cyclodextrins.

We report the design and synthesis of the acyclic cucurbit[n]uril-ß-cyclodextrin chimeric host H1. The goal of the study is to deepen the cavity of the receptor to allow ß-CD complexation of moieties on the guest (especially fentanyl) that protrude from the cavity of the primary acyclic CB[n] binding site to enhance binding affinity and deliver new supramolecular antidotes for fentanyl intoxication. 1H NMR spectroscopy was used to deduce the geometry of the complexes between H1 and H2 and the guest panel (G1 - G8 and fentanyl) whereas isothermal titration calorimetry was used to determine the thermodynamic parameters of complexation. Hosts H1 and H2 retain the essential molecular recognition features of CB[n] receptors, but chimeric host H1 binds slightly stronger toward the guest panel than H2 for reasons that remain unclear. Compared to tetraanionic hosts M1 and M2, the dianionic hosts H1 and H2 are less potent receptors which reflects the importance of electrostatic (ion-ion and ion-dipole) interactions in this series of hosts. The work highlights the challenges inherent in the optimization of binding affinity of hosts as potential supramolecular antidotes.

Self-assembled, optically-active {naphthalene diimide}U{cucurbit[8]uril} ensembles in an aqueous environment.

Naphthalene diimides (NDIs) are shown to arrange spontaneously co-facially with cucurbit[8]uril (CB[8]) in an aqueous environment through purely non-covalent interactions. The resultant 2 : 2 supramolecular complex of NDI and CB[8] is highly fluorescent (>30 times more than the constituent NDIs) due to the formation of NDI-NDI excimers within the supramolecular complex.

Chiroptical sensing of amino acids, amines, amino alcohols, alcohols and terpenes with π-extended acyclic cucurbiturils.

The efficiency and scope of two acyclic π-wall extended cucurbiturils, M2 and M3, exhibiting rapidly interconverting helical conformers for chiroptical sensing of amines, amino acids, alcohols, and terpenes at micromolar concentrations in water is evaluated. The formation of 1 : 1 host-guest complexes results in spontaneous induction of circular dichroism signals that can be used for accurate determination of the absolute configuration and enantiomeric composition of the analyte based on a simple mix-and-measure protocol.

In Vitro and In Vivo Sequestration of Phencyclidine by Me4 Cucurbit[8]uril*.

We report investigations of the use of cucurbit[8]uril (CB[8]) macrocycles as an antidote to counteract the in vivo biological effects of phencyclidine. We investigate the binding of CB[8] and its derivative Me4 CB[8] toward ten drugs of abuse (3-9, 12-14) by a combination of 1 H NMR spectroscopy and isothermal titration calorimetry in phosphate buffered water. We find that the cavity of CB[8] and Me4 CB[8] are able to encapsulate the 1-amino-1-aryl-cyclohexane ring system of phencyclidine (PCP) and ketamine as well as the morphinan skeleton of morphine and hydromorphone with Kd values ≤50 nm. In vitro cytotoxicity (MTS metabolic and adenylate kinase cell death assays in HEK293 and HEPG2 cells) and in vivo maximum tolerated dose studies (Swiss Webster mice) which were performed for Me4 CB[8] indicated good tolerability. The tightest host⋅guest pair (Me4 CB[8]⋅PCP; Kd =2 nm) was advanced to in vivo efficacy studies. The results of open field tests demonstrate that pretreatment of mice with Me4 CB[8] prevents subsequent hyperlocomotion induction by PCP and also that treatment of animals previously dosed with PCP with Me4 CB[8] significantly reduces the locomotion levels.

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.

Acyclic Cucurbit[n]uril-Type Receptors: Aromatic Wall Extension Enhances Binding Affinity, Delivers Helical Chirality, and Enables Fluorescence Sensing.

We report the linear extension from M1 to M2 to anthracene walled M3 which adopts a helical conformation (X-ray) to avoid unfavorable interactions between sidewalls. M3 is water soluble (=30 mm) and displays enhanced optical properties (ϵ=1.28×105 m-1 cm-1 , λmax =370 nm) relative to M2. The binding properties of M3 toward guests 1-29 were examined by 1 H NMR and ITC. The M3⋅guest complexes are stronger than the analogous complexes of M2 and M1. The enhanced binding of M3 toward neuromuscular blockers 25, 27-29 suggests that M3 holds significant promise as an in vivo reversal agent. The changes in fluorescence observed for M3⋅guest complexes are a function of the relative orientation of the anthracene sidewalls, guest concentration, Ka , and guest electronics which rendered M3 a superb component of a fluorescence sensing array. The work establishes M3 as a next generation sequestering agent and a versatile component of fluorescence sensors.