Initial excited-state structural dynamics of uridine from resonance Raman spectroscopy

The effect of the N1 ribose sugar on the initial excited-state structural dynamics of uridine is explored with ultraviolet resonance Raman spectroscopy. Excited-state slopes and broadening parameters were obtained by simulating the resonance Raman excitation profiles and absorption spectrum using a self-consistent, time-dependent formalism. The initial excited-state structural dynamics of uridine look similar to those of uracil, in terms of the distribution of percentage of reorganization energy along different modes, but there is an overall decrease in the excited-state slopes along most of the modes in uridine compared with uracil. Only about 30% of the total initial reorganization energy in both uracil and uridine are oriented along the photochemically reactive coordinates. The results are also similar to those of thymine and thymidine, upon attachment of the sugar. These differences between thymine, thymidine, uracil and uridine are examined, and the possible effect on the resulting differences in photochemistry is discussed.