The pH‐Dependence of the Hydration of 5‐Formylcytosine: an Experimental and Theoretical Study

5‐Formylcytosine is an important nucleobase in epigenetic regulation, whose hydrate form has been implicated in the formation of 5‐carboxycytosine as well as oligonucleotide binding events. The hydrate content of 5‐formylcytosine and its uracil derivative has now been quantified using a combination of NMR and mass spectroscopic measurements as well as theoretical studies. Small amounts of hydrate can be identified for the protonated form of 5‐formylcytosine and for neutral 5‐formyluracil. For neutral 5‐formylcytosine, however, direct detection of the hydrate was not possible due to its very low abundance. This is in full agreement with theoretical estimates.