Hydrolysis of phosphate esters with polymer-supported catalysts containing cyclodextrin pendant group

Polymer-supported catalysts of several kinds, including beta-cyclodextrin (P-CD), beta-cyclodextrin-diethylenetriamine (P-CD-DETA), and beta-cyclodextrin-N-methylhydroxamate (P-CD-NMHA)-containing polymers, as well as their corresponding metal complexes, were synthesized and examined as catalysts for the hydrolysis of phosphate esters, The kinetic measurements were performed in a phosphate buffer (0.05 M, pH 8.2) at a temperature of 25.0 +/- 0.1 degrees C. Each kinetic run was initiated on introducing ester stock solution (0.13 ml) containing diphenyl p-nitrophenyl phosphate (DPPhTPP) in dioxane (0.010 M). The rate of hydrolysis of DPPNPP was evaluated by measuring the absorbance of liberated p-nitrophenol at 402 nm. The dissociation constants between DPPNPP and the polymers P-CD, P-CD-DETA and P-CD-NMHA obtained from Eadie-type plots were 16.8, 16.4 and 8.0 (x 10(-3) M) and the acceleration factors were 1.5, 2.8 and 8.6 respectively. Hence P-CD-NMHA is the most promising catalyst. The activation parameters, preexponential factor (A) and activation energy using P-CD-NMHA as catalyst, are A = 1.2 x 10(9) min(-1) and E(a) = 43 kJ/mol respectively; the latter was about 12 kJ/mol lower than the activation energy of spontaneous hydrolysis. The results indicate that the catalytic power of P-CD-NMHA may reflect the combined behavior of molecular recognition and nucleophilicity.