Infrared Spectra of the Thymidine ¹³ C2 and ¹³ C4 Isotopes in H ₂ O and D ₂ O

Here we report the synthesis of two new ¹³C thymidine (T) isotopes labeled at two key positions in its structure, C2═O and C4═O, and the first IR spectra of each T isotope in H₂O and in D₂O. Our experimental isotope shifts and normal mode calculations indicate some structurally sensitive modes may be more localized than previously thought, making them regiosensitive probes of thymidine's chemical environment. These results provide new physical insight into the normal modes of thymidine, and will guide future studies to determine how these structurally and environmentally sensitive probe vibrations are impacted by the duplex environment.