Kinetics and activation parameter analyses of hydrolysis and interconversion of 2′,5′- and 3′,5′-linked dinucleoside monophosphate at extremely high temperatures

Abstract

Kinetic analysis of hydrolytic stability of 2′,5′- and 3′,5′-linked dinucleoside monophosphate (N 2′pN and N 3′pN) was successfully performed in aqueous solution at 175–240 °C using a new real-time monitoring method for rapid hydrothermal reactions. The half-lives of NpN were in the range 2–8 s at 240 °C and apparent activation energy decreases in the order U 2′pU>A 2′pA>G 2′pG>U 3pU∼C 3′pC>A 3pA. The stability of phosphodiester bond was dependent on the types of base moiety and phosphodiester linkages, but no systematic correlation was found between the structure and stability. The interconversion of 2′,5′-adenylyladenosine monophosphate (A 2′pA) and 3′,5′-adenylyladenosine monophosphate (A 3′pA) was enhanced in the presence of d- or l-histidine. The rate constants of degradation of NpN were dissected into the rate constants of hydrolysis and interconversion between N 2′pN and N 3′pN using a computer program SIMFIT. Kinetic analysis supports the mechanism that imidazolium ion and imidazole catalyze interconversion and hydrolysis even under hydrothermal environments. The activation parameters for the hydrolysis and interconversion of NpN were systematically determined for the first time from the temperature dependence of the rate constants, where both Δ H app ≠ and Δ S app ≠ for 2′,5′-linked NpN are larger than those for 3′,5′-linked NpN. These parameters support the pseudorotation mechanism through pentacoordinate intermediate from 2′,5′- and 3′,5′-linked NpN, where the average value of Δ H ≠ (pseudorotation) was estimated to be 30±18 kJ mol −1 at 175–240 °C.