Homotropic cooperativity of cyclodextrin dimer as an artificial hydrolase

Abstract: Three kinds of cyclodextrin (CD) dimer (one homo-dimer of β-CD and two types of hetero-dimer of α-CD and β-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°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 (βCβH 5) gave a sigmoidal curve, whereas the reaction with either of the hetero-dimers gave a simple hyperbolic curve. Only βCβH 5 showed homotropic cooperativity, with a Hill constant of 1.8. [Copyright &y& Elsevier]