Orientation of Pyrylium Guests in Cucurbituril Hosts

Host-Guest Complexation of Cucurbit[7]Uril and Cucurbit[8]Uril with the Antineoplastic and Multiple Sclerosis Agent Mitoxantrone (Novantrone)

The nature of interactions between the neutral/protonated mitoxantrone and the cucurbit[n]uril (n = 7, 8) host system was analyzed by employing density functional theory calculations. A comparison between the inclusion complexes of CB[7] and CB[8] shows various subtle differences in the complexation thermodynamics, given as changes in the Gibbs energy. Doubly and quadruply charged mitoxantrone (MX) molecules spontaneously form complexes in a water solvent, which are modeled using the polarizable continuum model approach. Both CB[7] and CB[8] complexes are stable as the geometry of the cavity allows for electrostatic interactions between the charged MX arms and the rim of the CB cavity. CB[8] also forms a stable complex with two mitoxantrone molecules with their aromatic rings stacked inside the cavity. Both CB[7] and CB[8] show properties that can be utilized in drug delivery.

Inclusion and Charge Transfer Interaction of a Multi-Redox Active 1,3,5-Triazine Derivative by Cucurbit[7,8]urils

The redox active 1,3,5-triazine derivative (MPT) was used as a guest to study host-guest, charge transfer interaction with CB[7,8] in water. The multi-redox active MPT undergoes four chemically and electrochemically reversible one electron redox states in organic media, but in water, the fourth redox state shows an unstable nature. As a guest, the host-guest interaction of MPT was studied with two macrocyclic cucurbit[7,8]uril (CB[7,8]) hosts in water; resulting supramolecular complexes were characterized by NMR, ESI-MS, UV-vis, ITC, and cyclic voltammetric studies.

Interaction of Phenyl-Substituted Diazaperylenium with Cucurbit[n]uril: Complex versus Supramolecular Polymer

A phenyl-substituted diazaperylenediium dication (DAP) was synthesized that shows concentration-dependent aggregation in water. The host-guest complexation of DAP was studied with the macrocyclic host cucurbit[n]uril (n = 7, 8) in water. With CB[7], it forms a 1:2 complex by placing two aryl substituents inside the CB[7]; whereas, with CB[8], a supramolecular polymer is formed. The resulting complex and supramolecular polymer have been characterized by ITC (isothermal titration calorimetry), ESI-MS (electrospray ionization mass spectrometry), 1H NMR (proton nuclear magnetic resonance), 2D NOESY (two-dimensional nuclear Overhauser enhancement spectroscopy), and DOSY (diffusion-ordered spectroscopy) spectra.

Construction of protein assemblies by host–guest interactions with cucurbiturils

Protein assembly is important in nature and bionics. Herein, we have reviewed the recent progress in protein assemblies induced by cucurbituril-based supramolecular interactions and their applications.

Air-oxidation of phenolic resin aerogels: backbone reorganization, formation of ring-fused pyrylium cations, and the effect on microporous carbons with enhanced surface areas

Air-oxidation at 240 °C, followed by pyrolytic carbonization, revealed that carbons from phenolic resins contain fused pyrylium rings and phenoxides.

Host-Guest Complexes of Flavylium Cations and Cucurbit[7]uril: The Influence of Flavylium Substituents on the Structure and Stability of the Complex

The host-guest complexes formed from six differently substituted flavylium cations and cucurbit[7]uril (CB7) have been characterized by UV/Vis absorption, fluorescence emission and ¹ H NMR spectroscopy. It was observed that all flavylium cations form 1:1 inclusion complexes with association constants that depend on the nature and position of the substituents. The results indicate that CB7 displays higher affinity for more hydrophobic flavylium compounds and for those bearing amino substituents. ¹ H NMR spectroscopy was used to elucidate the structure of the complexes. While for 7-hydroxyflavylium and 4-methyl-7-hydroxyflavylium the phenyl group (ring B) is included within the host's cavity leaving the benzopyrilium group (rings A and C) outside, in 4',7-dihydroxyflavylium and 3',4',7-trihydroxyflavylium the macrocycle shuttles between rings A and B. For compounds with amino substituents it was found that CB7 is attracted towards these groups regardless of their position in ring A or B. In addition, it was observed that the dimethylamino group tends to be positioned near the carbonyl-decorated portal while the diethylamino motif prefers the hydrophobic cavity of CB7.

Predicting the properties of a new class of host–guest complexes: C60 fullerene and CB[9] cucurbituril

DFT, semi-empirical and classical molecular dynamics methods were used to describe the structure and stability of the inclusion complex formed by the fullerene C₆₀ and the cucurbituril CB[9].

Pseudopolyrotaxanes based polyhedral oligomeric silsesquioxanes and cucurbit[7]uril

Pseudopolyrotaxanes (POSS/CB[7]) were synthesized using octaimidazolium-based polyhedral oligomeric silsesquioxanes (POSS) and cucurbit[7]uril (CB[7]) in aqueous solution. The binding interactions were monitored by (1)H NMR. Their regular octahedral morphologies were confirmed by TEM. The POSS/CB[7] was also characterized by FT-IR, thermogravimetric analysis (TGA), and elemental analysis. The TGA results show that the thermal stabilities of POSS/CB[7] can be improved by the threading of CB[7].

Theoretical prediction of the complexation behaviors of antitumor platinum drugs with cucurbiturils

The inclusion complex formation ability between CB[n] (n = 6-9) and Pt-drugs (oxaliplatin, nedaplatin, carboplatin, and cisplatin) in gas phase as well as water phases has been investigated using the using density functional theory. The results reveal the existence of several stable inclusion complexes in aqueous solution with high solvation energies compared to the guest and host molecule. It has been shown that the formation of complexes between CB[6] and Pt-drugs resulted in structural change in the CB[6], with the calculated deformation energies being higher for the inclusion complexes. The inclusion complexes are stabilized by the hydrogen bonding and the charge transfer between the Pt-drugs and the CB[n] host. Calculated enthalpy and Gibbs free energy of formation in aqueous solution revels that the formation of CB[7]-oxaliplatin is spontaneous, and hence its experimental synthesis is feasible. Among the CB's studied, CB[8]-Pt-drug inclusion complexes have exothermic enthalpy and low Gibbs free energy of formation. Computed (1)NMR spectra in CB[7]-oxaliplatin showed high chemical shielding for the cyclohexane ring, indicating the existence of charge transfer in the inclusion complex. The amine protons in the guest Pt-drugs are shielded due to the hydrogen bonding interaction with CB's oxygen portal.