Assignments and hydrogen bond sensitivities of UV resonance Raman bands of the C8‐deuterated guanine ring

Isotope-edited Raman spectroscopy, a combination of site-selective isotopic labeling and Raman difference spectroscopy, is a useful method for studying the structure and interaction of individual nucleic acid residues in oligonucleotides. To obtain basic data for applying isotope-edited Raman spectroscopy to guanine residues, we studied the vibrational modes of UV resonance Raman bands of the C8-deuterated guanine ring by examining the wavenumber shifts upon seven isotopic substitutions (2-13C, 2-15N, 6-18O, 7-15N, 8-13C, 9-15N and 1′-13C). The hydrogen bond sensitivities of the Raman bands were also investigated by comparing the Raman spectra recorded in several solvents of different hydrogen bonding properties. Some of the Raman bands were found to be markers of hydrogen bonding at specific donor or acceptor sites on the guanine ring. The Raman bands, which shift on C8-deuteration, remain in the difference spectrum between the unlabeled and C8-deuterated guanine rings. Among them, a negative peak around 1525 cm−1 and a strong positive/negative peak pair around 1485/1465 cm−1 serve as markers of hydrogen bonding at N7 and C6O, respectively. Another weak positive/negative peak pair around 1025/1040 cm−1 is sensitive to hydrogen bonding at the proton donor sites (N1—H and N2—H2). The applicability of the hydrogen bond markers has been tested by using a 22-mer oligonucleotide duplex containing eight guanine residues and its analog in which a single guanine residue is C8-deuterated. The difference spectrum shows that the hydrogen bonding state of the guanine residue at the labeled position is consistent with the Watson–Crick base pair structure of DNA. Isotope-edited Raman spectroscopy is a useful tool for studying the hydrogen bonding state of selected guanine residues in oligonucleotides. Copyright © 2002 John Wiley & Sons, Ltd.