Cyclodextrin Inclusion Complexes Mechanism of Adduct Formation and Intermolecular Interactions

Abteilung Chemie, Max-Planck-Institut fur experimentelle Medizin, D-34 Gottingen, H. Rein Str. 3, Germany 

The inclusion complexes of cyclodextrins have been studied since about 30 years using chemical, spectroscopic, kinetic, potentiometric methods. The obtained data have led to the conclusion that the adduct formation of the cyclodextrin molecules in solution is due to their annular structure and that they provide space for the substrate molecules in their annular cavity. The only obvious requirement for inclusion is that the dimensions of the guest molecules must be small enough to fit into the cyclodextrin cavity. 

More recently, the cyclodextrins became of interest as model enzymes. It was found that they can accelerate different reactions by factors ranging from 0.3 to 400, the factor smaller than 1.0 corresponding to a deceleration [1, 6, 8, 9]. Some of these reactions and the acceleration rates are listed in Table I. The cyclodextrins not only catalyze reactions but they also mimic the reaction mechanism of enzymes as could be demonstrated for the system a-cyclodextrin - aryl benzoate [6]. In this case, benzoyl-a-cyclodextrin was observed as reaction intermediate, in direct analogy to the acylation of the active site during the cleavage of esters through a-chymotrypsin. It is not surprising that the acceleration rate of cyclodextrins of maximum 400 is modest as compared to the 10 found for catalysis with a-chymotrypsin as in one 

Pullman (ed.). Environmental Effects on Molecular Structure and Properties, 265-305. All Rights Reserved Copyright 1976 by D. Reidel Publishing Company. Dordrecht-Holland 

Catalytic effects of cyclodextrins. Data taken from References 5 and 6 

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Saenger W (1976) a-Cyclodextrin inclusion complexes mechanism of adduct formation and intermolecular interactions. Jerusalem Symp Ser 8 265 - 308... 

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