Acetonitrile cyclodextrin inclusion complexes with

In 1980, Breslow (3) made the dramatic observation that the reaction of cyclopentadiene with butenone in water was more than 700 times faster than the same reaction in isooctane. The reaction rate in methanol is comparable to that in a hydrocarbon solvent. Such an unusual acceleration of the Diels-Alder reaction by water was attributed to the "hydrophobic effect (4) in which the hydrophobic interactions brought together the two nonpolar groups in the transition state. The use of P-cyclodextrin, which simultaneously forms an inclusion complex with the dioie and dienophile, and the use of 4.86 M LiCl aqueous solution as solvent, which salts out nonpolar materials dissolved in water (5), further enhanced the rate of aqueous Diels-Alder reactions. The second-order rate constant of the reaction between hydroxymethylanthiaceneandN-ethylmaleimideinwaterat 45°C was over 200 times larger than in acetonitrile (eq. 1). 

The modular NESI-chip system was used (i) to qualitatively as well as quantitatively study two well-known supramolecular systems, i.e. the Zn-porphyrin complexation with nitrogen-containing ligands in acetonitrile and the inclusion of small organic molecules into the cavity of (5-cyclodextrin in water,41 and (ii) to study the kinetics of the reaction of 4-nitro-7-piperazino-2,l,3-benzoxadiazole (NBDPZ) with isocyanates as a model system.42... 

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