Tracking of Proton Transfer Reaction in Supercooled RNA Nucleoside

In this paper we address a longstanding debate concerning the proton transfer reaction of DNA and RNA compounds. The sample tested is β-uridine, one of the four basic components of RNA, which has been suggested to have the capacity to adopt lactam and lactim tautomeric forms. The essential biological importance of this RNA nucleoside has motivated a number of experimental and theoretical investigations in the past. However, the kinetics of the proton transfer reaction of this compound has not been examined. Herein, we employ dielectric spectroscopy and refractive index measurements to experimentally characterize lactam-lactim transformation in the supercooled liquid state. We quantify the kinetics of β-uridine tautomerization and suggest a mechanism for the configurational changes. The obtained data are compared to quantum chemical calculations. Finally the biological importance of our results is discussed.