A supramolecular polypseudorotaxane material based on novel pillar[5]arene for ultrasensitive Fe3+ reaction

In this study, a novel linear supramolecular polypseudorotaxane was synthesized using a pillar[5]arene derivative (CP5) as the host and bis-bromohexyl pillar[5]arene (DP5) as the guest, facilitated by host-guest interactions. Subsequently, these components self-assembled to create an AIE-active material (CPDP-G) through C-H⋯π interactions involving the pillar[5]arene groups. Notably, the CPDP-G fluorescence material exhibits an exceptionally sensitive response to Fe3+, with a detection limit of 0.543 nM. The fabricated CPDP-G film serves as a rudimentary kit for Fe3+ detection. Moreover, CPDP-G demonstrates robust stability under diverse conditions, including variations in temperature, exposure to KClO4, AcOH, and tetrabutylammonium hydroxide, and ultrasonic treatment. Consequently, the innovative supramolecular polypseudorotaxane material CPDP-G holds promising potential for the ultrasensitive detection of Fe3+ ions.

Ortho-Functionalization of Pillar[4]arene[1]benzoquinone Monoxime via Selective 1,4-Addition of Grignard Reagents

Ortho-functionalization of pillar[n]arenes has been a formidable challenge, partially due to the fragility of their macrocyclic skeletons. In this concise report, we describe a facile synthetic method for monoarylation/alkylation at the position ortho to the oxime functionality in pillar[4]arene[1]benzoquinone monoxime (1) via addition of Grignard reagents. The described method enables the creation of various mono-ortho-alkyl/aryl-substituted pillar[5]arene derivatives that were previously inaccessible.

The End of the Beginning of Mechanical Stereochemistry

ConspectusStereochemistry has played a key role in the development of synthetic chemistry for the simple reason that the function and properties of most molecules, from medicine to materials science, depend on their shape and thus the stereoisomer used. However, despite the potential for rotaxanes and catenanes to display unusual forms of stereochemistry being identified as early as 1961, this aspect of the mechanical bond remained underexplored and underexploited; until 2014 it was only possible to access chiral rotaxanes and catenanes whose stereoisomerism is solely attributable to the mechanical bond using chiral stationary phase high performance liquid chromatography, which limited their production on scale and thus inhibited the investigation of their properties and applications. Furthermore, the stereogenic units of such molecules and analogues were often poorly described, which made it hard to fully articulate both what had been achieved in the field and what problems were left to solve. Relatively recently, methods to access rotaxanes and catenanes that display mechanical stereochemistry selectively have been developed, making these intriguing structures available for study in a range of prototypical applications including catalysis, sensing, and as chiral luminophores.In this Account, we briefly discuss the history of mechanical stereochemistry, beginning in 1961 when the potential for mechanical stereoisomerism was first identified, before defining how mechanical stereochemistry arises from a structural point of view. Building on this, using simple stereochemical arguments, we confirm that the complete set of unique stereogenic units of two-component rotaxanes and catenanes have finally been identified and categorized unambiguously, with the last being identified only in 2024. After pausing to discuss some of the stereochemical curiosities that arise when molecules contain both covalent and mechanical stereogenic units, and the potential for stereoisomerism to arise due to co-conformational movement, we use our stereochemical framework to summarize our efforts to develop conceptually general approaches to [2]catenanes and [2]rotaxanes containing all of the possible mechanical stereogenic units. In particular, we highlight how the nature of a mechanical stereogenic unit affects the available strategies for their stereoselective synthesis. We finish by highlighting recent prototypical chemical applications of interlocked molecules that rely on their mechanical stereochemistry, before discussing future directions and challenges.Taken together, we propose that the transition of such molecules from being hard to make and poorly described, to being available in high stereopurity using clearly articulated methodological and stereochemical concepts suggests that the field is finally maturing. Thus, we are now coming to the end of the beginning of mechanical stereochemistry. The stage is now set for such molecules to play a functional role in a range of areas, indeed in any chemical or physical application where control over molecular shape is required.

Facial Selectivity in Mechanical Bond Formation: Axially Chiral Enantiomers and Geometric Isomers from a Simple Prochiral Macrocycle

In 1971, Schill recognized that a prochiral macrocycle encircling an oriented axle led to geometric isomerism in rotaxanes. More recently, we identified an overlooked chiral stereogenic unit in rotaxanes that arises when a prochiral macrocycle encircles a prochiral axle. Here, we show that both stereogenic units can be accessed using equivalent strategies, with a single weak stereodifferentiating interaction sufficient for moderate to excellent stereoselectivity. Using this understanding, we demonstrated the first direct enantioselective (70% ee) synthesis of a mechanically axially chiral rotaxane.

The Final Stereogenic Unit of [2]Rotaxanes: Type 2 Geometric Isomers

Mechanical stereochemistry arises when the interlocking of stereochemically trivial covalent subcomponents results in a stereochemically complex object. Although this general concept was identified in 1961, the stereochemical description of these molecules is still under development to the extent that new forms of mechanical stereochemistry are still being identified. Here, we present a simple analysis of rotaxane and catenane stereochemistry that allowed us to identify the final missing simple mechanical stereogenic unit, an overlooked form of rotaxane geometric isomerism, and demonstrate its stereoselective synthesis.

Pillar[4]arene[1]thioarene: Synthesis and Host-Guest Binding Properties

The synthesis and characterisation of novel class of pillar[4]arene[1]thioarenes (P[4]A[1]SMe) are reported. Synthesised via an oxidation-thionation strategy, the replacement of a single dialkoxybenzene panel from parent pillar[5]arene (P[5]A) is achieved. 1H-NMR spectroscopic titration experiments, supported by DFT computational studies, revealed that P[4]A[1]SMe show starkly modulated host-guest binding properties for electron deficient aliphatic guests.

ortho-Functionalization of Pillar[5]arene: An Approach to Mono-ortho-Alkyl/Aryl-Substituted A1/A2-Dihydroxypillar[5]arene

Despite the fact that the rim and lateral functionalizations of pillar[n]arenes have been well explored, ortho-functionalization has rarely been realized. In this work, we report a facile method of introducing a single functionality ortho to the hydroxyl group in A1/A2-dihydroxypillar[5]arene via a Grignard addition to pillar[4]arene[1]quinone followed by a dienone-phenol rearrangement. The described ortho-alkylation/arylation method allowed formation of various mono ortho-alkyl/aryl-substituted A1/A2-dihydroxypillar[5]arenes previously difficult to obtain.

Pillar[5]arene-Derived endo-Functionalized Molecular Tube for Mimicking Protein-Ligand Interactions

Artificial tubular molecular pockets bearing polar functionalities on their inner surface are useful model systems for understanding the mechanisms of protein-ligand interactions in living systems. We herein report a pillar[5]arene-derived molecular tube, [P4-(OH)BPO], whose endo conformational isomer endo-[P4-(OH)BPO] possesses an inwardly pointing hydrogen-bond (H-bond) donor (OH) in its deep cavity and a strong H-bond acceptor (C═O) on its predominantly hydrophobic inner surface, rendering it a perfect protein binding pocket mimetic. A fragment-based drug design model was established using endo-[P4-(OH)BPO] and a library of various shape-complementary fragment ligands (1-38). On the basis of the binding affinity data for "fragment-pocket" complexes G⊂endo-[P4-(OH)BPO] (G = 1-38), two rationally designed "lead molecules" (39 and 40) were identified as being able to enhance binding affinity significantly by forming H-bonds with both the donor and acceptor of endo-[P4-(OH)BPO]. The described work opens new avenues for developing pillar[n]arene-derived protein binding pocket-mimetic systems for studies of protein-ligand interactions and mechanisms of enzymatic reactions.

Supramolecular brush polymers prepared from 1,3,4-oxadiazole and cyanobutoxy functionalised pillar[5]arene for detecting Cu2+

The self-assembly of an A1/A2 disubstituted pillar[5]arene was used to construct a supramolecular brush polymer.