On the Normal Modes of Vibration in the Uracil Residue—The Use of 15N-Isotope Effects

Abstract

β-Uridine-5′-phosphoric acid-¹⁵N₂ has been prepared from ¹⁵N-RNA of baker’s yeast which was grown in (¹⁵NH₄)₂SO₄ as the sole nitrogen source. Its Raman spectrum has been observed both in ¹H₂O and ²H₂O solutions. On the basis of the observed ¹⁵N isotope effects on the Raman spectra and on the basis of other data previously obtained, normal modes of vibration have been discussed for six Raman bands of the uracil residue that are considered to be in resonance with its electronic transition at 260 nm. The result has led to a conclusion that C⁵=C⁶ is longer and C⁴–C⁵ is shorter in the excited electronic state à (260 nm) than those in the ground electronic state \~{X}.