5-Fluorocytosine (FC), a widely used antifungal drug, has poor physical stability under different relative humidity (RH) conditions, which may trigger serious challenges during its drug product development. In this contribution, a conjugate acid–base (CAB) cocrystal and a salt hydrate of FC were obtained with an artificial sweetener, acesulfame (AH), in molar ratios of 2:1 (FCAH21) and 1:1 (FCAH11), respectively. The resulting products were characterized by a variety of analytical methods, including single-crystal and powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and dynamic vapor sorption (DVS). 13C and 15N solid-state NMR spectra provide solid evidence for the CAB cocrystal/salt formation. At room temperature, moisture sorption data show that the new forms are nonhygroscopic/slightly hygroscopic and resistant to FC hydrate formation under high RH conditions (>80%). FCAH21 has a higher FC content and presents more favorable thermal stability than FCAH11, which make it more attractive for further pharmaceutical application.

In order to improve the solubility of diflunisal (DIF), and hence the oral bioavailability, two 2:1 diflunisal cocrystals were prepared by solution crystallization from ethanol with nicotinamide (NIC) or isonicotinamide (ISO) as coformer. The cocrystals were characterized by powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), as well as liquid- and solid-state nuclear magnetic resonance (LNMR and SSNMR). PXRD and NMR measurements indicate that the pure 2:1 cocrystals can be obtained even the DIF and coformer started from different ratios (2:1, 1:1 and 1:2). FTIR and 13C SSNMR measurements provide clues about the formation of amide–carboxylic acid heterosynthon and pyridine–carboxylic acid heterosynthon between DIF and coformer. The melting points of DIF-NIC and DIF-ISO cocrystals are 195 and 182 °C respectively, indicating their favorable thermal stability. Meanwhile, the two cocrystals exhibit faster dissolution rates and higher aqueous solubilities than the pure drug compound.

We have examined the specificity of electrosynthesized poly-o-phenylenediamine as a kind of material molecularly imprinted with metal chelates. Molecularly imprinted polymers (MIPs) were prepared in situ by an electrochemical method. The EDTA chelate complexes of Cu(II), Zn(II), Fe(III) and Cd(II) ions were used as templates of the MIPs deposited on a gold electrode of a quartz crystal microbalance (QCM). The binding ability and specificity of the MIPs were investigated via the frequency response of the QCM to the adsorption of the template chelates and their analogs. Linear relationships are observed between the frequency shift and the concentration of the template chelates over a typical range of ~10−6 to ~10−4 mol·L−1. The results reveal good binding specificity of such MIPs for their templates over structurally related analogs, but the selectivity coefficients are less significant than that for enantiomers. The results also suggest no significant correlation between binding specificity and the ionic (or atomic) radius of the investigated metal ions. The observed specificity is qualitatively attributed to the overall conformational difference of the metal-EDTA complexes resulting from their difference in both ionic radius and electronic structures.