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In order to investigate the ability of bis(zinc octaethylporphyrin) (

Inherently chiral, barrel-shaped, macrocyclic hosts such as cyclohexanohemicucurbit[n]urils (cycHC[n]) bind zinc porphyrins and trifluoroacetic acid externally in halogenated solvents. In the current study, we tested a set of eighteen organic guests with various functional groups and polarity, namely, thiophenols, phenols, and carboxylic and sulfonic acids, to identify a preference toward hydrogen bond–donating molecules for homologous cycHC[6] and cycHC[8]. Guests were characterized by Hirshfeld partial charges on acidic hydrogens and their binding by 1H and 19F NMR titrations. Evaluation of association constants revealed the complexity of the system and indirectly proved an external binding with stoichiometry over 2:1 for both homologs. It was found that overall binding strength is influenced by the stoichiometry of the formed complexes, the partial atomic charge on the hydrogen atom of the hydrogen bond donor, and the bulkiness of the guest. Additionally, a study on the formation of complexes with halogen anions (Cl− and Br−) in methanol and chloroform, analyzed by 1H NMR, did not confirm complexation. The current study widens the scope of potential applications for host molecules by demonstrating the formation of hydrogen-bonded complexes with multisite hydrogen bond acceptors such as cycHC[6] and cycHC[8].

We found that cyclohexanohemicucurbit[8]uril encapsulates five- and six-membered sulfur- and oxygen-containing unsubstituted heterocycles and can be used as a selective sorption material for the extraction of sulfur-heterocycles like 1,3-dithiolane and α‑lipoic acid from water.

Here we report a study on cyclohexanohemicucurbit[8]uril (cycHC[8]) binding of sulfur-, oxygen- and nitrogen-containing heterocycles in both solid state and solution, which is investigated by single crystal X-ray diffraction, NMR spectroscopy, isothermal titration calorimetry, and thermogravimetry. Potential guests include environmental pollutants, hazardous compounds, and bioactive substances. We found that cycHC[8] encapsulates five- and six-membered sulfur- and oxygen-containing unsubstituted heterocycles and can be used as a selective sorption material for the extraction of sulfur-heterocycles from water. Both cycHC[6] and cycHC[8] can remove a substituted heterocycle, α-lipoic acid, from an aqueous solution via the formation of an external complex. The results show that cycHC[n] is a promising reusable sorbent material with the potential to be employed in molecular recognition and highly specific solid-phase extraction of sulfur-heterocycles.

This research with title "Dynamic chiral cyclohexanohemicucurbit[12]uril" is dedicated to the memory of late Professor Hans J. Reich.Abstract:NMR and DFT studies of chiral cyclohexanohemicucurbit[12]uril indicate that the macrocycle adopts a concave octagon shape with three distinct ranges of conformational flexibility in solution. Methylene bridge flipping occurs at temperatures above 265 K, while urea monomers rotate at temperatures above 308 K resulting in the loss of confined space within the macrocycle.

Solid-state reactions using mechanochemical activation have emerged as solvent-free atom-efficient strategies for sustainable chemistry. Herein we report a new mechanochemical approach for the amide coupling of carboxylic acids and amines, mediated by combination of (1-сyano-2-ethoxy-2-oxoethylidenaminooxy)dimethylaminomorpholinocarbenium hexafluorophosphate (COMU) or N,N,N′,N′-tetramethylchloroformamidinium hexafluorophosphate (TCFH) and K2HPO4. The method delivers a range of amides in high 70–96% yields and fast reaction rates. The reaction protocol is mild, maintains the integrity of the adjacent to carbonyl stereocenters, and streamlines isolation procedure for solid amide products. Minimal waste is generated due to the absence of bulk solvent. We show that K2HPO4 plays a dual role, acting as a base and a precursor of reactive acyl phosphate species. Amide bonds from hindered carboxylic acids and low-nucleophilic amines can be assembled within 90 min by using TCFH in combination with K2HPO4 or N-methylimidazole. The developed mechanochemical liquid-assisted amidation protocols were successfully applied to the challenging couplings of all six carboxylate functions of biotin[6]uril macrocycle with phenylalanine methyl ester, resulting in an 80% yield of highly pure hexa-amide-biotin[6]uril. In addition, fast and high-yielding synthesis of peptides and versatile amide compounds can be performed in a safe and environmentally benign manner, as verified by green metrics.

Cucurbituril-type hosts are highly symmetric, but there are means to break their symmetry. This review will present examples from three directions of induction of chirality in or by cucurbituril-type hosts: first, through the incorporation of stereogenic elements into host molecules; second, through complexation with achiral guests, which leads to axial supramolecular chirality and helical structures; third, through the formation of complexes with chiral guests in multi-molecule complexes and induction of supramolecular chirality. In addition, a list of chiral guests used in binding studies with cucurbiturils is collected. We would envision that encouraged by the outlined examples of outstanding applications of chiral cucurbituril-supramolecular systems, the boundaries of chiral applications of cucurbiturils would be widened.

Solvent-free, atom-efficient, and mechanochemically activated reactions have emerged as synthetic strategy for sustainable chemistry. Herein we report a new mechanochemical approach for the amide c...

Solid-phase extraction that utilizes selective macrocyclic receptors can serve as a useful tool for removal of chemical wastes. Hemicucurbiturils are known to form inclusion complexes with suitably sized anions; however, their use in selective binding of non-charged species is still very limited. In this study, we found that cyclohexanohemicucurbit[8]uril encapsulates five- and six-membered sulfur- and oxygen-containing unsubstituted heterocycles, which is investigated by single-crystal X-ray diffraction, NMR spectroscopy, isothermal titration calorimetry, and thermogravimetry. The macrocycle acts as a promising selective sorption material for the extraction of sulfur heterocycles, such as 1,3-dithiolane and α-lipoic acid, from water.