Homotropic cooperativity of cyclodextrin dimer as an artificial hydrolase

Three kinds of cyclodextrin (CD) dimer (one homo-dimer of beta-CD and two types of hetero-dimer of alpha-CD and beta-CD) were synthesized as artificial hydrolases. The initial rates of the cleavage reaction of p-nitrophenyl methoxyethoxyethoxyacetate (8) by each of the three dimers were measured under the condition of excess of substrate at 25 degrees C in a pH 7.4 phosphate buffer solution. In a plot of initial rate against concentration of the substrate, the reaction with the homo-dimer (beta C beta H 5) gave a sigmoidal curve, whereas the reaction with either of the hetero-dimers gave a simple hyperbolic curve. Only beta C beta H 5 showed homotropic cooperativity, with a Hill constant of 1.8. (C) 2010 Elsevier B.V. All rights reserved.