SERS of cytosine and its methylated derivatives on gold sols

SERS spectra of cytosine, 1‐methylcytosine, 5‐methylcytosine and 1,5‐dimethylcytosine on a gold colloid are reported. A tentative assignment of Raman bands is made by comparison with the normal Raman spectra in aqueous solution. This analysis reveals a preferred non‐planar orientation of cytosine and 1‐methylcytosine and a more planar orientation of 5‐methylcytosine and 1,5‐dimethylcytosine with respect to the metal surface, the C=O group being determinant in the interaction. A comparative study using the result obtained previously using silver and copper colloids as supports shows important differences in the electrodynamic behaviour of these molecules which depend on the presence of the methyl substituents and the nature of the metal on which they adsorb.