Packing interactions in hydrated and anhydrous forms of the antibiotic Ciprofloxacin: a solid-state NMR, X-ray diffraction, and computer simulation study

We present an experimental NMR, X-ray diffraction (XRD), and computational study of the supramolecular assemblies of two crystalline forms of Ciprofloxacin: one anhydrate and one hydrate forming water wormholes. The resonance assignment of up to 51 and 54 distinct (13)C and (1)H resonances for the hydrate is reported. The effect of crystal packing, identified by XRD, on the (1)H and (13)C chemical shifts including weak interionic H-bonds, is quantified; (1)H chemical shift changes up to ～-3.5 ppm for CH···π contacts and ～+2 ppm (CH···O((-))); ～+4.7 ppm (((+))NH···O((-))) for H-bonds. Water intake induces chemical shift changes up to 2 and 5 ppm for (1)H and (13)C nuclei, respectively. Such chemical shifts are found to be sensitive detectors of hydration/dehydration in highly insoluble hydrates.