Screening of Indian plants for biological activity: Part VIII.

Abstract

Three main hydration sites of a ribose ring, as a model for 3‘-AMP and 5’-AMP, have been studied with the ab initio method, using an STO-3G basis set, in simulation of the proposed regiospecific solvation of O(1’) and O(5’) in 5’-AMP and 3’-AMP. This solvation, which does not occur in c-AMP, contributes to the large exothermic net solvation enthalpy of hydrolysis of c-AMP. It is concluded that the bridge position between O( 1’) and O(5’) is an important hydration site. Formation of a five- as well as a seven-membered ring with one molecule of water between O(1’) and O(5’) is possible. In addition to this effect the conformational difference of the ribose ring in c-AMP, on the one hand, and in 5’-AMP and 3‘-AMP, on the other hand, has been taken into account. It is clearly demonstrated that this difference also contributes to the overall enthalpy of hydrolysis.