Encapsulation-driven protonation

We conclude that the neutral substrate enters 1 to form a host-guest complex, leading to the observed substrate saturation. The encapsulated substrate then undergoes encapsulation-driven protonation, presumably by deprotonation of water, followed by acid-catalyzed hydrolysis inside 1, during which two equivalents of the corresponding alcohol are released. Finally, the protonated formate ester is ejected from 1 and further hydrolyzed by base in solution. The reaction mechanism (Scheme 7.7) shows direct parallels to enzymes that obey Michaelis-Menten kinetics due to the initial pre-equilibrium followed by a first-order rate-limiting step. 

A [5]rotaxane 10, based on a meso-tetraphenyl porphyrin and synthesized in 85% yield, showed similar pH-driven switching properties, depicted in Scheme 14.5. When all the nitrogen atoms of the amino groups are protonated, CB[6] prefers to encapsulate the protonated diaminotriazole site (state I) because of the strong ion-dipole interactions between ammonium ions and carbonyl functions at the portal of CB[6]. On the other hand, after complete deprotonation of the molecule, CB[6] resides mostly on the relatively more hydrophobic benzyl part, thanks to hydrophobic effect (state II). 

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