Pressure Effects on the Hydrolysis of Acetanilide Catalyzed by Cyclodextrins

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Abstract
The rates of the hydrolysis of p-nitrotrifluoroacetanilide (pNFA) catalyzed by α- and β-cyclodextrins (α-, β-CD) were measured at pressures up to 2 kbar at 25 °C and at pH 6.9 in a 0.05 M Tris buffer solution. The substrate binding constants, K, and the rate constants of the acylation process, kacyl, increased monotonically up to 2 kbar. From the pressure dependence of K, the volume changes (ΔV) accompanying the formation of the inclusion complexes at 1 bar were −3±2 cm3/mol for α-CD–pNFA and −2±2 cm3/mol for β-CD–pNFA. The activation volumes (ΔV) for the cleavage of the anilide molecule in the acylation process were −25±2 cm3/mol for α-CD–pNFA and −18±2 cm3/mol for β-CD–pNFA. The reaction mechanisms of the cleavage of the anilide substrte by CDs were discussed on the basis of the volume parameters (ΔV and ΔV*).