Cytosine Raman spectra

The SERS spectrum of methylated DNA shows new Raman bands at 656 cm , 700 cm and 1360 cm" which correspond to characteristic vibrations of 7-MeGua residues in adsorbed methylated DNA (cf. Table 4). Furthermore, the decrease of the band at 1200 cm and the 13(K)cm" shoulder of the band centered at 1332 cm" in the SERS spectrum of native DNA upon methylation can be related to a conformational change of DNA at the location of modified nucleic base pairs 7-MeGua-cytosine. Thus, at a rather positively charged surface, the SERS spectra reveal substantial changes in the adsorption behaviour of methylated DNA. 

Distinct differences between the Raman spectra of the two forms are evident in Fig. 20.10. In particular, the phosphodiester vibration of the backbone at a frequency of 824 cm is characteristic for the C2 -endo pucker of the ribose rings in the B conformation. In the spectrum of the Z conformation, this band is downshifted to 786 cm and overlaps a cytosine ring breathing vibration. 

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