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Research on the structural responses to thermal stimuli for crystalline energetic materials is crucial to their practical applications. DAP-4 is a metal-free molecular perovskite high-energetic material attracting increasing attentions on its application potential as heat-resistant explosive. In order to reveal its structural responses to thermal stimuli, herein we investigated the structural phase transitions and thermal expansion of DAP-4 by DSC, single-crystal X-ray diffraction, and variable-temperature capillary powder X-ray diffraction. The results show that DAP-4 undergoes two-step reversible phase transitions at 300.4/298.9 K and 548.4/547.7 K, respectively, which are caused by two-step order-disorder transition of the molecular components during a heating/cooling cycle. The axial and the volumetric expansion coefficients of DAP-4 are estimated based on the temperature-dependent cell parameters obtained by Pawley refinement in a large temperature range of 173–353 K, and they are close to those estimated for β-HMX. Notably, although a volume change of 0.77% occur in the near-room-temperature phase transition, all the crystalline phases of DAP-4 possess cubic structures with isotropic expansibility, rather than the commonly-observed anisotropic one in the most of known energetic crystals, which may be propitious to reduce the adverse effect of its volume change on the formulation design.

The incidence and severity of Clostridium difficile infection (CDI) in North America and Europe has increased significantly since the 2000s. However, CDI is not widely recognized in China and other developing countries due to limited laboratory diagnostic capacity and low awareness. Most published studies on laboratory workflows for CDI diagnosis are from developed countries, and thus may not be suitable for most developing countries. Therefore, an alternative strategy for developing countries is needed. In this study, we evaluated the performance of the Glutamate Dehydrogenase (GDH) test and its associated workflow on 416 fecal specimens from suspected CDI cases. The assay exhibited excellent sensitivity (100.0%) and specificity (92.8%), compared to culture based method, and thus could be a good screening marker for C. difficile but not for indication of toxin production. The VIDAS CDAB assay, which can detect toxin A/B directly from fecal specimens, showed good specificity (99.7%) and positive predictive value (97.2%), but low sensitivity (45.0%) and negative predictive value (88.3%), compared with PCR-based toxin gene detection. Therefore, we propose a practical and efficient GDH test based workflow strategy for the laboratory diagnosis of CDI in developing countries like China. By applying this new workflow, the CDI laboratory diagnosis rate was notably improved in our center, yet the increasing cost was kept at a minimum level. Furthermore, to gain some insights into the genetic population structure of C. difficile isolates from our hospital, we performed MLST and PCR toxin gene typing.