Figure 1.

Comparison of 1D ¹³C NMR spectra of nucleic acid bases and related molecules incubated in concentrated sulfuric acid for two different time periods. The intensity (y-axis) is shown as a function of spectral shift in parts per million (ppm) (x-axis). Each compound’s NMR spectrum is shown in an individual subfigure. Within each subfigure, we compare the NMR spectrum of the year-long incubation (colored lines) to the NMR spectrum collected after ~30–48 h (dashed grey line spectra from [14]). For clarity, the ~30–48 h spectra are displayed with a slight vertical offset. From top to bottom within each subpanel, we show the NMR spectra of compounds dissolved in different concentrations (by weight) of sulfuric acid in water: 98% D₂SO₄/2% D₂O; 94% D₂SO₄/6% D₂O; 88% D₂SO₄/12% D₂O; 81% D₂SO₄/19% D₂O with DMSO-d₆ as a reference and at room temperature. All peaks are consistent, with the molecules being stable and the structure not being affected by the concentrated sulfuric acid solvent. The one-year spectra and the ~30–48 h spectra look virtually identical for all tested concentrations, demonstrating the year-long stability of the compounds in the concentrated sulfuric acid solvent.