Assignments of guanosine UV resonance Raman bands on the basis of C-13, N-15 and O-18 substitution effects

UV resonance Raman spectra of guanosine and its seven isotope-substituted a nalogs (2-C-13, 2-N-15 6-O-18, 7-N-15, 8-C-13, 9-N-15 and 1'-C-13) were mea sured with 257 mn excitation in H2O and D2O solutions, In-plane vibrations of the guanine ring were selectively enhanced in the UV resonance Raman spe ctra, and most Raman bands showed significant wavenumber shifts upon isotop ic substitution. The observed isotope shifts were used to assign the Raman bands to vibrations of the peripheral sites (N1-H, C2-NH2 and C6=O), the py rimidine ring and/or the imidazole ring. Previous assignments for some Rama n bands were shown to be inconsistent with the isotopic data and they were revised. Relationships between the vibrational modes and the sensitivities to hydrogen bonding or conformation are discussed for known Raman marker ba nds. Each hydrogen bond marker arises from a vibration that involves, at le ast partly, the proton donor or acceptor atom, All the marker bands of glyc osidic bond orientation and ribose ring puckering actually involve atomic d isplacements around the N9-C1' moiety connecting the guanine ring to ribose , permitting vibrational coupling between them. The isotopic wavenumber shi fts reported here may be useful in improving the force held for the 9-subst ituted guanine ring and in interpreting the vibrational spectra of guanine nucleoside and nucleotides. Copyright (C) 1999 John Wiley & Sons, Ltd.