关键词: 钠化合物, 催化剂, 络合物, 水解, 活性, 羧酸酯, 溶剂效应, 反应速度常数, 离解平衡, 疏水性质

The hydrolysis of p-nitrophenyl esters of carboxylic acids with various chain lengths, namely, octanoate, dodecanoate and hexadecanoate, are accelerated by sodium carboxymethylamylose (NaCMA) in Me2SO-H2O, dioxane-H2O and tert-BuOH-H2O. These NaCMA-catalyzed hydrolyses follow Michaelis-Menten saturation kinetics, even when the substrate mols. are already involved in aggregate formation, in other words, even when the substrate concns. are greater than the crit. aggregate concentration (CAgC). The dissociation constants (Kd) of the inclusion complexes of the substrates and NaCMA have been evaluated from the dependencies of the hydrolytic rate constants on the concentration of NaCMA. The fact that the smallest Kd value was found in pure water indicates that organic cosolvents always decrease the stabilities of these host-guest complexes. The order of the Kd scale, Kd(DMSO-H2O) < Kd(dioxane-H2O) < Kd(tert-BuOH-H2O), agrees with the order of lipophilicities of the organic cosolvents represented by their Rekker's constants The observed Kd values obtained with substrate concentration beyond the CAgC are larger than those obtained with substrate concns. lower than CAgC. This shows that the process of helical inclusion complex formation can compete with the process of aggregation.

Key words: SODIUM COMPOUNDS, CATALYST, COMPLEX COMPOUNDS, HYDROLYSIS, ACTIVITY, CARBOXYLIC ACID ESTER, SOLVENT EFFECT, REACTION RATE CONSTANT, DISSOCIATION EQUILIBRIUM, HYDROPHOBIC PROPERTIES