Cucurbit[n]uril Host‐Guest Complexes of Acids, Photoacids, and Super Photoacids

Abstract

The supramolecular chemistry of host‐guest complexes of cucurbit[n]urils (CB[n]) with acidic guests in the ground (HG+) and excited states (HG+*) are reviewed. The effects of CB[n] complexation on the guests’ pKa and/or pKa* values are related to relative binding constants and host‐guest structures of the acid form of the guest and its conjugate base. Included are carbon acids, guests of biological and medicinal interest, dyes and related polyaromatic guests, and other organic and organometallic guests. The applications of the pKa shifts to the solubility, stability, and bioavailabilty of drug molecules, the stability and enhanced spectral properties of dyes, and in pH‐induced self‐sorting, micelle formation, host‐guest shuttling, and controlled guest release, are discussed.

Reversing Chemoselectivity: Simultaneous Positive and Negative Catalysis by Chemically Equivalent Rims of a Cucurbit[7]uril Host

“…Zuschriften the solution had to be decreased by about 1.2 pH units ( Figures S33-S37), which is in line with pK a shifts caused by this macrocycle. [15] Theo bserved reaction acceleration, however,d id not explain the chemoselectivity reversion which required much higher reaction rates.…”

“…That the hydrazone formation is acid‐catalyzed was evinced at low pH. To achieve the same acceleration as that by CB7 , the pH of the solution had to be decreased by about 1.2 pH units (Figures S33–S37), which is in line with p K a shifts caused by this macrocycle . The observed reaction acceleration, however, did not explain the chemoselectivity reversion which required much higher reaction rates.…”

Encapsulation of Metronidazole in Biocompatible Macrocycles and Structural Characterization of Its Nano Spray-Dried Nanostructured Composite

“…The acidity diminution upon embedment in CB7 originates from the stabilization of the MetH + form by cation–dipole interactions with the partial negative charge of the carbonyl-laced portals of the macrocycle. Host–guest binding induced proton release suppression was also found for various dyes, drugs and ammonium compounds [ 25 , 26 , 27 , 28 , 29 ].…”

Change of the kinetics of inclusion in cucurbit[7]uril upon hydrogenation and methylation of palmatine

“…The modification of the acidity of guests by inclusion complex formation has been reported for other amines, drugs, and dyes. [48][49][50][51] As both free and CB7-encapsulated THP + s are completely protonated at pH 4, further experiments were performed under this condition.…”