Crystal growth mechanisms govern a wide range of properties of crystalline materials. Reversed crystal growth is one of the nonclassical mechanisms observed in many materials. However, the reversed crystallization starting from amorphous aggregates and the key factors driving this growth remain elusive. Here, we describe a characteristic model of reversed crystal growth representing the inner structure and crystallinity development of aggregates studied by microscopy and nano X-ray computed tomography. By adjusting the synthesis conditions, the fundamental function of the structure-directing agent, which determines the crystallization pathway, was revealed. As a result, the crystal growth mode can be “switched” from the classical route at a low ratio of SDA/framework elements to reversed growth at a high ratio. Our findings provide further insights into crystal growth control, which is crucial for improving synthesis protocols and designing various forms of crystalline materials. 相似文献
A sensitive and simple HPLC method for simultaneous determination of PAC-1 (first procaspase-activating compound), phenol red, and permeability markers (carbamazepine and furosemide) in perfusion samples was developed and validated to assess intestinal absorption of PAC-1 using single-pass intestinal perfusion technique (SPIP) in rats. The chromatographic separation was carried out on a Kromasil C18 column (150 mm × 4.6 mm, 5 μm) with acetonitrile–methanol–30 mmol L−1 phosphate buffer (pH 3.0, 25:10:65, v/v/v) as mobile phase at a flow rate of 1.0 mL min−1, and the wavelength of the UV detector was set at 281 nm. The calibration curves were linear in the ranges of 2.40–48.0 μg mL−1 for PAC-1; 3.60–72.0 μg mL−1 for carbamazepine; 3.20–64.0 μg mL−1 for furosemide, and 4.80–96.0 μg mL−1 for phenol red (r > 0.999). Both the intra- and inter-day precisions (RSD%) of all analytes were less than 6.8 % at three concentration levels, while accuracy ranged from 95.4 to 104.5 %. Data obtained in all method validation studies indicated that the method was suitable for the intended purpose. The effective permeability values (Peff) considering water flux with the help of non-permeable marker phenol red was calculated to be 0.42 × 10−4, 0.62 × 10−4, 0.32 × 10−4 cm s−1 for PAC-1; 0.72 × 10−4, 0.77 × 10−4, 0.52 × 10−4 cm s−1 for carbamazepine; 0.20 × 10−4, 0.16 × 10−4, 0.12 × 10−4 cm s−1 for furosemide in duodenum, jejunum and ileum, respectively. The Peff value can be increased by co-perfusion with verapamil, indicating that absorption of PAC-1 is efficiently transported by P-glycoprotein (P-gp) in the gut wall.