Cucurbituril-Oriented Nanoplatforms in Biomedical Applications

Efficient anticancer drug delivery using nano-colloids self-assembled with an unconventional amphiphile bearing pumpkin-shaped host molecule

A new type of amphiphiles bearing macrocycle such as cucurbit[7]uril (CB[7]) spontaneously forms a nanomaterial in water, specifically vesicles (tACB[7] vesicles) with a positive surface charge, verified through various analytical techniques including TIRF, DLS and TEM. Functional validation not only reveals the accessibility of the CB[7] portal on these vesicles allowing CB[7]-based host-guest interactions with various functional guest molecules such as fluorescein isothiocyanate conjugated adamantylammonium and spermine (FITC-AdA and FITC-SPM, respectively) using confocal laser scanning microscopy, but also showcases the effective internalization of tACB[7] vesicles into cancer cells with the anticancer drug oxaliplatin (OxPt), as a guest to CB[7], through in vitro cell experiments. Hence, this study provides a blueprint to impart amphiphilic properties to CB[7] through synthetic design and highlights the potential of CB[7] derivatives as a new class of unconventional amphiphiles self-assembling into functional nanomaterials for advanced drug delivery.

Tetramethyl Cucurbit[6]uril-Porphyrin Supramolecular Polymer Enhances Photosensitization

Porphyrins serve as photosensitizers (PS) in the realm of cancer photodynamic therapy (PDT). Upon excitation by laser light, porphyrins are capable of converting molecular oxygen into highly cytotoxic singlet oxygen (1O2). However, the rigid π-conjugated structure of porphyrins frequently results in the formation of aggregates in aqueous solutions, which leads to the self-quenching of the excited state. Cucurbit[n]urils exhibit the capacity to stably bind with porphyrins via host-guest interactions, effectively inhibiting their aggregation and potentially enhancing the therapeutic efficacy of PDT. In this study, water-soluble tetramethyl cucurbit[6]uril (TMeQ[6]) was selected as the host, while four propionic acid group-appended porphyrin cationic (TPPOR) was utilized as guests to construct a supramolecular photosensitizer (TPPOR-2TMeQ[6]) in a molar ratio of 2:1. Further experimental findings demonstrate that the presence of TMeQ[6] inhibits the aggregation of TPPOR through non-covalent interactions. This inhibition reduces the energy difference between the excited singlet and triplet states, thereby enhancing the conversion efficiency of 1O2. Moreover, TPPOR-2TMeQ[6] exhibits favorable biocompatibility and minimal dark toxicity against breast cancer cells (4T1). Upon intracellular excitation, the levels of reactive oxygen species (ROS) significantly increase, inducing oxidative stress in 4T1 cells and leading to apoptosis. Consequently, the findings of this study suggest that the enhanced photosensitization achieved through this supramolecular approach is likely to promote the anticancer therapeutic effects of PDT, thereby broadening the application prospects of porphyrins within PDT systems.

Investigating Nanoscale Interactions of Host-Guest Complexes Formed Between CB[7] and Atenolol by Quantum Chemistry and Ultrasensitive Vibrational Spectroscopy

In addition to the course of over 20 years of cucurbit-7-uril (CB[7]) in the pharmaceutical industry, the present study brings together the most recent observations from the perspective of ultrasensitive Raman spectroscopy and Density Functional Theory (DFT) related to the interaction of this molecule with atenolol (Ate) enantiomers during the formation of these host-guest complexes. Quantum chemistry calculations based on DFT were first used to understand the interaction geometry between CB[7] and Ate. These results were further confirmed by ultrasensitive vibrational spectroscopy. The spectral features associated with each enantiomer in the presence of CB[7] were analyzed by means of SERS, highlighting distinct interaction profiles. These experimental findings validated quantum chemical calculations, offering a comprehensive understanding of the host-guest interactions at the nanoscale level.

Supramolecular complexation of phenylephrine by cucurbit[7]uril in aqueous solution

Cucurbiturils (CBn) are known to establish stable host-guest complexes with a variety of drug molecules. Herein, the supramolecular complexation between cucurbit[7]uril (CB7) and phenylephrine hydrochloride is reported in aqueous solution. Phenylephrine forms inclusion complex with CB7 with high binding affinity (Kaffinity = 4.0 × 106 M-1), which allows for the development of a fluorescence-based sensing assay applying the dye displacement strategy. The structure of the host-guest inclusion complex is investigated by 1H NMR spectroscopy, in which complexation-induced chemical shifts indicate the immersion of the aromatic ring inside the hydrophobic cavity of CB7. Density functional theory (DFT) calculations support the 1H NMR results, and reveal that the complex is stabilized through intermolecular interactions between the polar groups on the phenylephrine and the carbonyl rims of CB7, as well as the hydrophobic effect. Moreover, preferential binding of phenylephrine in its protonated over the neutral form results in a complexation-induced pKa shift.

Cucurbit[8]uril Binds Nonterminal Dipeptide Sites with High Affinity and Induces a Type II β-Turn

In an effort to target polypeptides at nonterminal sites, we screened the binding of the synthetic receptor cucurbit[8]uril (Q8) to a small library of tetrapeptides, each containing a nonterminal dipeptide binding site. The resulting leads were characterized in detail using a combination of isothermal titration calorimetry, 1H NMR spectroscopy, electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS), and X-ray crystallography. The equilibrium dissociation constant values determined for the binding of Q8 to nonterminal dipeptide sites Lys-Phe (KF) and Phe-Lys (FK) were 60 and 86 nm, respectively. These are to the best of our knowledge the highest affinities reported to date for any synthetic receptor targeting a nonterminal site on an unmodified peptide. A 0.79 Å resolution crystal structure was obtained for the complex of Q8 with the peptide Gly-Gly-Leu-Tyr-Gly-Gly-Gly (GGLYGGG) and reveals structural details of the pair-inclusion motif. The molecular basis for recognition is established to be the inclusion of the side chains of Leu and Tyr residues, as well as an extensive network of hydrogen bonds between the peptide backbone, the carbonyl oxygens of Q8, and proximal water molecules. In addition, the crystal structure reveals that Q8 induces a type II β-turn. The sequence-selectivity, high affinity, reversibility, and detailed structural characterization of this system should facilitate the development of applications involving ligand-induced polypeptide folding.

Overcoming barriers with non-covalent interactions: supramolecular recognition of adamantyl cucurbit[n]uril assemblies for medical applications

Adamantane, a staple in medicinal chemistry, recently became a cornerstone of a supramolecular host-guest drug delivery system, ADA/CB[n]. Owing to a good fit between the adamantane cage and the host cavity of the cucurbit[n]uril macrocycle, formed strong inclusion complexes find applications in drug delivery and controlled drug release. Note that the cucurbit[n]uril host is not solely a delivery vehicle of the ADA/CB[n] system but rather influences the bioactivity and bioavailability of drug molecules and can tune drug properties. Namely, as host-guest interactions are capable of changing the intrinsic properties of the guest molecule, inclusion complexes can become more soluble, bioavailable and more resistant to metabolic conditions compared to individual non-complexed molecules. Such synergistic effects have implications for practical bioapplicability of this complex system and provide a new viewpoint to therapy, beyond the traditional single drug molecule approach. By achieving a balance between guest encapsulation and release, the ADA/CB[n] system has also found use beyond just drug delivery, in fields like bioanalytics, sensing assays, bioimaging, etc. Thus, chemosensing in physiological conditions, indicator displacement assays, in vivo diagnostics and hybrid nanostructures are just some recent examples of the ADA/CB[n] applicability, be it for displacements purposes or as cargo vehicles.

Stability and pKa Modulation of Aminophenoxazinones and Their Disulfide Mimics by Host-Guest Interaction with Cucurbit[7]uril. Direct Applications in Agrochemical Wheat Models

Aqueous solubility and stability often limit the application of aminophenoxazinones and their sulfur mimics as promising agrochemicals in a sustainable agriculture inspired by allelopathy. This paper presents a solution to the problem using host-guest complexation with cucurbiturils (CBn). Computational studies show that CB7 is the most suitably sized homologue due to its strong affinity for guest molecules and its high water solubility. Complex formation has been studied by direct titrations monitored using UV-vis spectroscopy, finding a preferential interaction with protonated aminophenoxazinone species with high binding affinities (CB7·APOH⁺, K_a = (1.85 ± 0.37) × 10⁶ M^-1; CB7·DiS-NH₃⁺, K_a = (3.91 ± 0.53) × 10⁴ M^-1; and DiS-(NH₃⁺)₂, K_a= (1.27 ± 0.42) × 10⁵ M^-1). NMR characterization and stability analysis were also performed and revealed an interesting pK_a modulation and stabilization by cucurbiturils (2-amino-3H-phenoxazin-3-one (APO), pK_a = 2.94 ± 0.30, and CB7·APO, pK_a = 4.12 ± 0.15; 2,2'-disulfanediyldianiline (DiS-NH₂), pK_a = 2.14 ± 0.09, and CB7·DiS-NH₂, pK_a = 3.26 ± 0.09), thus favoring applications in different kinds of crop soils. Kinetic studies have demonstrated the stability of the CB7·APO complex at different pH media for more than 90 min. An in vitro bioassay with etiolated wheat coleoptiles showed that the bioactivity of APO and DiS-NH₂ is enhanced upon complexation.

Supramolecular host-guest interaction-driven electrochemical recognition for pyrophosphate and alkaline phosphatase analysis

Herein, we report an electrochemical biosensor based on the supramolecular host-guest recognition between cucurbit[7]uril (CB[7]) and L -Phenylalanine-Cu(II) Complex for pyrophosphate (PPi) and alkaline phosphatase (ALP) analysis. First, L -Phe-Cu(II) Complex is simply synthesized by the complexation of Cu(II) (metal node) with L -Phe (bioorganic ligand), which can be immobilized onto CB[7] modified electrode via host-guest interaction of CB[7] and L -Phe. In this process, the signal of the Complex triggered electro-catalytic reduction of H 2 O 2 can be captured. Next, in the view of strong chelation between PPi and Cu(II), a biosensing system of the model "PPi and Cu(II) premixing, then adding L -Phe" is designed and the platform can be applied for PPi analysis well by hampering the formation of L -Phe-Cu(II) Complex. Along with ALP introduction, PPi can be hydrolyzed into orthophosphate (Pi), where abundant Cu(II) ions are released to form L -Phe-Cu(II) Complex, which gives rise to the catalytic reaction of Complex to H 2 O 2 reduction. The quantitative analysis of H 2 O 2 , PPi and ALP activity is achieved successfully and the detection of limits are 0.067 μM, 0.42 μM and 0.09 mU/mL ( S / N =3), respectively. With the merits of high sensitivity and selectivity, cost-effectiveness, and simplification, our developed analytical system has great potential to act on diagnosis and treatment of ALP-related diseases.