Effect of pressure on cyclodextrin-catalysed hydrolysis of nucleotide 2′:3′-cyclic monophosphates

Abstract

The effect of pressure on the cyclodextrin (CyD)-catalysed regiospecific P–O cleavage of nucleotide 2′:3′-cyclic monophosphates (cNMP) was investigated. In all cases hydrolytic reactions in the absence and the presence of CyD were accelerated by increasing pressure, indicating negative activation volume. The apparent regiospecificity seen in the cAMP–β-CyD and cCMP–α-CyD combinations, however, became less prominent at higher pressure. The apparent activation volumes of P–O(3′) cleavage of cAMP in the presence of β-CyD (6 cm³ mol^–1) was almost half that in the other cases. The CyD concentration dependence of the ratio of the apparent rate constants of P–O(2′) and P–O(3′) cleavages was studied and the activation volumes for k_c2 and k_c3 for cAMP–β-CyD were calculated as –9.7 and –14.5 cm³ mol^–1, respectively. The apparent decrease in the regiospecificity seen in the reaction cAMP +β-CyD is, therefore, responsible for the positive volume change of the complex formed from cAMP and β-CyD (∼5cm³mol^–1).

The difference in the activation volumes of the P–O(2′) and P–O(3′) cleavages of cCMP by α-CyD was also found to be ca. 4.4 cm³ mol^–1; in this case the high pressure made the reaction less regiospecific.