5-Formylcytosine (5fC) is identified as one of the key players in active DNA demethylation and also as an epigenetic mark in mammals, thus representing a novel attractive target to chemical intervention. The current study represents an attempt to develop a reversible 5fC-targeted intervention tool. A supramolecular aldehyde reactive probe was therefore introduced for selective conversion of the 5fC to 5fC-AD nucleotide. Using various methods, we demonstrate that cucurbit[7]uril (CB7) selectively targets the 5fC-AD nucleotide in DNA, however, the binding of CB7 to 5fC-AD does not affect the hydrogen bonding properties of natural nucleobases in duplex DNA. Importantly, CB7-driven host-guest chemistry has been applied for reversible intervention of a variety of 5fC-targeted biochemical reactions, including restriction endonuclease digestion, DNA polymerase elongation, and polymerase chain reaction. On the basis of the current study, the macrocyclic CB7 creates obstructions that, through steric hindrance, prevent the enzyme from binding to the substrate, whereas the CB7/5fC-AD host-guest interactions can be reversed by treatment with adamantanamine. Moreover, fragment- and site-specific identification of 5fC modification in DNA has been accomplished without sequence restrictions. These findings thus show promising potential of host-guest chemistry for DNA/RNA epigenetics.

As the host possessing the largest cavity in the cucurbit[n]uril (CB[n]) family, CB[10] has previously displayed unusual recognition and assembly properties with guests but much remains to be explored. Herein, we present the recognition properties of CB[10] toward a series of bipyridinium guests including the tetracationic cyclophane known as blue box along with electron-rich guests and detail the influence of encapsulation on the charge-transfer interactions between guests. For the mono-bipyridinium guest (methylviologen, MV ), CB[10] not only forms 1:1 and 1:2 inclusion complexes, but also enhances the charge-transfer interactions between methylviologen and dihydroxynaphthalene (HN) by mainly forming the 1:2:1 packed "sandwich" complex (CB[10]⋅2 MV ⋅HN). For guest 1 with two bipyridinium units, an interesting conformational switching from linear to "U" shape is observed by adding catechol to the solution of CB[10] and the guest. For the tetracationic cyclophane-blue box, CB[10] forms a stable 1:1 inclusion complex; the two bipyridinium units tilt inside the cavity of CB[10] according to the X-ray crystal structure. Finally, a supramolecular "Russian doll" was built up by threading a guest through the cavities of both blue box and CB[10].

No abstract

No abstract

As the cucurbit[n]uril (CB[n]) homologue with the largest cavity size, cucurbit[10]uril (CB[10]) can encapsulate big guests to form interesting host-guest complexes/assemblies. Herein, we report the preparation and fluorescence properties of CB[10]-based [2]rotaxane (CB[10]·1) formed from cucurbit[10]uril and dumbbell-like guest 1. This [2]rotaxane (CB[10]·1) is assembled by C═O···N ion-dipole interactions between oxygen atoms of the carbonyl fringed portals of CB[10] and the positively charged pyridinium units of 1 via the slipping method under heating at 95 °C in DMSO. In contrast, other cucurbit[n]uril (CB[n], n = 6-8) homologues cannot form rotaxanes with 1 due to their smaller cavities. The dumbbell-like guest 1 is a poor emitter in DMSO. Interestingly, the formation of CB[10]·1 renders the restriction of intramolecular rotation of TPE, which features a strong fluorescent intensity, long lifetime, and high quantum yield. Furthermore, CB[10]·1 is shown to aggregate plate-like structures with various sizes in different solvents (DMSO, THF, or CHCl), resulting in a stepwise aggregation-induced emission enhancement effect. This kind of CB[10]-based [2]rotaxane may be used to fabricate luminescent systems with unique emission properties.