Cucurbit[7]uril-Modulated H/D Exchange of α-Carbonyl Hydrogen: Deceleration in Alkali and Acceleration in Acid Conditions

Abstract

Supramolecular catalysis based on host−guest interactions has aroused much attention in past decades. Among the various strategies, modulation of the reactivity of key intermediates is an effective strategy to achieve high-efficiency supramolecular catalysis. Here, we report that by utilizing the host− guest interaction of cucurbit[7]uril (CB[7]), the reactivity of anionic enolate and cationic oxonium, the intermediates of H/D exchange of the α-carbonyl hydrogen in alkali and acid conditions, respectively, could be modulated effectively. On one hand, in alkaline conditions, both the electrostatic effect and the steric hindrance effect of CB [7] disfavored formation of the enolate anion intermediate. On the other hand, in acidic conditions, the oxonium was stabilized and the solvent effect was weakened by the electrostatic effect of CB [7]. As a result, the H/D exchange of 1-(4-acetylphenyl)-N,N,N-trimethylmethanaminium bromide is decelerated in alkaline and accelerated in acidic conditions. It is promising that the highly polar portals of CB[n] molecules together with their well-defined host−guest chemistry may be applied to modulate the reactivity of other kinds of ionic intermediates in an effective and convenient way, thus enriching the toolkit of supramolecular catalysis.

Aggregation-induced emission photosensitizer microneedles for enhanced melanoma photodynamic therapy

“…Due to the electron-rich nature of CB, it can electrostatically bind with positively charged organic photosensitizers, enhancing their performance for catalysis and PDT. [12][13][14] Meanwhile, utilizing stereoisomer engineering to explore different spatial configurations of a molecule is a clever strategy for developing desired functional molecules. In our previous work, we reported a pair of tetraphenylethene-based isomeric PSs, in which the trans isomer exhibited a higher ROS efficiency compared to the cis one.…”

pH-Triggered Transition from Micellar Aggregation to a Host–Guest Complex Accompanied by a Color Change

“…The construction of a stimuli-responsive nanosystem by the method of supramolecular assembly has attracted extensive attention benefitting from its simple composition, easy adjustment, and good repeatability. − In particular, the use of biocompatible water-soluble macrocyclic compounds, such as cyclodextrin, − p -sulfonatocalixarene, − cucurbituril, − and modified pillararene, − to construct stimuli-responsive supramolecular assemblies has shown many promising applications in the biomedical field. It is worth noting that organs, body fluids, and cell compartments have their unique pH values in living organisms.…”

Supramolecularly modulated carbon-centered radicals: toward selective oxidation from benzyl alcohol to aldehyde

“…[26][27][28][29][30] The rigid cavities provide steric hindrance, and the polar carbonyl portals induce a significant electrostatic effect. [31][32][33] These advantages permit cucurbiturils showing great potentials to appropriately modulate the reactivity of carbon-centered radicals. [34][35][36][37][38][39][40] Herein, we employ the host-guest interaction of cucurbit[7] uril (CB [7]) to modulate the reactivity of ketyl radicals and benzoyl radicals, two critical intermediates of the photo-induced oxidation of benzyl alcohol, [41][42][43][44][45][46][47] aiming to enhance the selectivity from benzyl alcohol to aldehyde.…”