Donal H. Macartney

Cucurbit[7]uril host–guest complexes of the histamine H2-receptor antagonist ranitidine

The macrocyclic host cucurbit[7]uril forms very stable complexes with the diprotonated (K(CB[7])(1) = 1.8 x 10(8) dm(3) mol(-1)), monoprotonated (K(CB[7])(2) = 1.0 x 10(7) dm(3) mol(-1)), and neutral (K(CB[7])(3) = 1.2 x 10(3) dm(3) mol(-1)) forms of the histamine H(2)-receptor antagonist ranitidine in aqueous solution. The complexation behaviour was investigated using (1)H NMR and UV-visible spectroscopy as a function of pH and the pK(a) values of the guest were observed to increase (DeltapK(a1) = 1.5 and DeltapK(a2) = 1.6) upon host-guest complex formation. The energy-minimized structures of the host-guest complexes with the cationic guests were determined and provide agreement with the NMR results indicating the location of the CB[7] over the central portion of the guest. The inclusion of the monoprotonated form of ranitidine slows the normally rapid (E)-(Z) exchange process and generates a preference for the (Z) isomer. The formation of the CB[7] host-guest complex greatly increases the thermal stability of ranitidine in acidic aqueous solution at 50 degrees C, but has no effect on its photochemical reactivity.

Host—Guest Complexes and Pseudorotaxanes of Cucurbit[7]uril with Acetylcholinesterase Inhibitors

Pseudorotaxanes may be assembled in aqueous solution using dicationic acetylcholinesterase inhibitors, such as succinylcholine, BW284c51, and alpha,omega-bis(trialkylammonium)alkane dications (or their phosphonium analogues), as bolaform axles and cucurbit[7]uril (CB[7]) as the wheel. With the exceptions of the shorter [(CH(3))(3)N(CH(2))(n)N(CH(3))(3)](2+) (n = 6, 8) dications, the addition of a second CB[7] results in the translocation of the first CB[7], such that the hydrophobic -NR(3)(+) and -PR(3)(+) end groups (R = Me or Et) are located in the cavities of the wheels, while the central portion of the axles extend through the CB[7] portals into the bulk solvent. In the case of the [Quin(CH(2))(10)Quin](2+) (Quin = quinuclidinium) dication, the CB[7] host(s) resides only on the quinuclidinium end group(s). The 1:1 host-guest stability constants range from 8 x 10(6) to 3 x 10(10) M(-1) and are dependent on both the nature of the end group as well as the length and hydrophobicity of the central linker. The magnitude of the stability constants for the 2:1 complexes closely follow the trend observed previously for CB[7] binding with the NR(4)(+) and PR(4)(+) cations.

A green to blue fluorescence switch of protonated 2-aminoanthracene upon inclusion in cucurbit[7]uril

The inclusion of protonated 2-aminoanthracene in the cavity of cucurbit[7]uril increases its pKa values in the ground and excited states, resulting in the disappearance of the green emission of the neutral excited state and the significant enhancement of the blue emissions from the protonated excited state guest.

In vivo reversal of general anesthesia by cucurbit[7]uril with zebrafish models

A general anesthetic is a drug that brings about a reversible loss of consciousness, during a surgical or therapeutic procedure to render the patient free of pain and anxiety. However, the effect of anesthetics may linger far beyond the necessary time required and induce adverse effects. In addition, many surgical patients need to recover to a conscious state that allows them to make important decisions soon after their surgery. Unfortunately, there are currently no clinically-available anti-dotes to reverse the effects of anesthetics. In this study, we demonstrate the in vitro supramolecular host–guest complexations between macrocyclic cucurbit[7]uril (CB[7]) and a commonly used general anesthetic in fish, tricaine mesylate (TM), and we report for the first time the in vivo reversal effect of CB[7] to general anesthesia induced by TM with zebrafish models. These findings might lead to a new approach that may allow patients to regain lucidity much faster than their natural recovery from general anesthesia, and may also be used to reverse potentially life-threatening toxic effects encountered by some patients in response to general anesthesia.

Developmental and organ-specific toxicity of cucurbit(7)uril: in vivo study on zebrafish models†

The macrocyclic molecular container cucurbit[7]uril (CB[7]), the most water-soluble homologue in the cucurbit[n]uril family (n = 5–8, 10, 14), has been evaluated for its in vivo toxicity profile, including its developmental toxicity such as its effect on hatching, growth and survival, as well as its potential organ-specific toxicities such as cardiotoxicity, hepatotoxicity, and locomotion and behavioral toxicity, using zebrafish models. The results revealed that CB[7] has measureable cardiotoxicity and locomotion and behavioral toxicity at concentrations of ∼500 μM or higher, and negligible developmental and hepatotoxicity at concentrations up to 750 μM, although extended exposure to CB[7] in the 500–750 μM concentration range induced the mortality of tested fish. These results demonstrate for the first time with live in vivo animal models that CB[7] has relatively low developmental and organic specific toxicity, and support further exploration of the use of CB[7] in biomedical research at sub-toxic concentrations.

Enhanced in vitro and in vivo uptake of a hydrophobic model drug coumarin-6 in the presence of cucurbit[7]uril

This report describes, for the first time, cucurbit[7]uril-assisted quantitative in vitro and in vivo uptake of a hydrophobic model drug, coumarin-6, by both an epithelial cell model and a zebrafish model. The transcellular delivery pathway study suggested multiple mechanisms involved, including macropinocytosis, clathrin and lipid raft-mediated endocytosis/exocytosis.

Encapsulation of Vitamin B1 and Its Phosphate Derivatives by Cucurbit[7]uril: Tunability of the Binding Site and Affinity by the Presence of Phosphate Groups

Vitamin B1 (1) and its phosphate derivatives, thiamine monophosphate (2) and thiamine pyrophosphate (3), are shown to form stable 1:1 host-guest complexes with cucurbit[7]uril (CB[7]) in aqueous solution. The binding sites of CB[7] on these guests shift from the ethylthiazolium region of 1 to the pyrimidine moiety of 2 and 3 due to the presence of phosphate groups, leading to variations of binding affinities as well as C(2)-H/D exchange rate constants and C(2)-H pKa values with these guest molecules.

Cucurbit[n]uril type hosts for the reversal of steroidal neuromuscular blocking agents

The ideal neuromuscular blocking agent (NMBA) is regarded as being a non-depolarizing equivalent of succinylcholine, having a rapid onset and short duration of action, with minimal side effects. In the absence of a single drug, the administration of an aminosteroid NMBA, such as rocuronium, followed by reversal using an acetylcholinesterase inhibitor, such as neostigmine, is commonly employed. A different and safer approach to rapidly reversing the action of the NMBA, by encapsulating it with a macrocyclic or acyclic host molecule, such as the cyclodextrin sugammadex or more recently, cucurbituril-type hosts such as cyclic cucurbit[7]uril and the acyclic glycoluril tetramer calabadion 1, is described.

The self-assembly of α-cyclodextrin rotaxanes of μ-(1,1″-(α,ω-alkanediyl)bis-(4,4′-bipyridinium))bis[pentacyanoferrate-(II)] complexes

Abstract The rapid, quantitative complexation reactions of labile [Fe(CN)5-OH2]3- ions with α-cyclodextrin (α-CD) threaded 1,1″-(α,ω-alkanediyl)-bis(4,4′-bipyridinium) dicationic ligands yield stable, self-assembled metal rotaxane complexes, [(NC)5Fe{bpy(CH2) n bpy•α-CD}Fe(CN)5]4- (n=8–12), in aqueous solution. The {bpy(CH2)nbpy•α-CD}2+ inclusion complexes and the metal rotaxanes have been characterized by their 1H and 13C NMR spectra, which display pairs of proton and carbon resonances for symmetry-related nuclei upon inclusion in the asymmetric α-CD cavity. The stability constants and the associated thermodynamic parameters for the {bpy(CH2) n bpy•α-CD}2+ inclusion complexes have been determined by 1H NMR. The kinetics of the ligand substitution processes involved in the self-assembly of the metal rotaxane complexes from α-CD and [(NC)5Fe(bpy(CH2) n bpy)Fe(CN)5]4- have been measured using visible and 1H NMR spectroscopy. The kinetic and activation parameters are consistent with a rate-limiting dissociat...

High-affinity host–guest complex of cucurbit[7]uril with a bis(thiazolium) salt

A biologically- and pharmaceutically-relevant bis(thiazolium) dication model compound, α,α′-bis(thiazolium)-p-xylene (BTX2+), forms a strong 1 : 1 host–guest inclusion complex with cucurbit[7]uril (CB[7]). The complexation stoichiometry, binding affinity and geometry were studied via 1H NMR and UV-visible titrations, ESI-MS, and molecular modeling (ab initio calculations). The hydrogen/deuterium exchange reactions of the C(2)-proton of BTX2+ were conducted in the absence and presence of CB[7] in D2O at 25 °C and at an ionic strength of 0.20 M. The inhibition of C(2)-H/D exchange of the guest bis(thiazolium) dication upon complexation with CB[7] exhibited a second-order rate constant that decreased by more than four-fold in the presence of CB[7]. The supramolecular-controlled stability of thiazolium cations through complexation with CB[7] host molecules is anticipated to have applications for stability enhancement of thiazolium based drugs and to potentially draw interest in the application of CB[n] host molecules with regard to the formulation and delivery of these drugs.