Same but different: structural diversity of cytidine 5′-monophosphate (CMP) (an)hydrates†

Cytidine 5′-monophosphate (CMP), despite its highly important biological function (as a basic component of nucleic acids), is one of the least studied nucleotides in terms of structural nature. In this work we present crystallographic studies of a series of CMP crystals in acidic form (the crystal structure of which has not been described in the literature). In addition to the determination of new polymorphs and varieties of hydrates and anhydrates of CMP, we describe structural changes caused by its temperature-, vacuum- and humidity-induced dehydration and rehydration. We complement the variable-temperature SC-XRD and 3D electron diffraction (3D ED) studies with thermal analysis (TGA/DTA) and variable-temperature micro-PXRD experiments. In the field of the described research results, we indicate and describe the most important types of intermolecular interactions, including hydrogen bonds and lone pair (lp)⋯π interactions. This, especially in light of dehydration, can be particularly valuable in the pharmaceutical field, and not only with regard to the nucleotide-based drugs.