We demonstrate here a novel method for the design of liquid crystals (LCs) via the cyclization of mesogens by flexible chains. For two azobenzene-4,4′-dicarboxylate derivatives, the cyclic dimer, cyclic bis(tetraethylene glycol azobenzene-4,4′-dicarboxylate) (CBTAD), shows LC properties with smectic A phase, while its linear counterpart, bis(2-(2′-hydroxyethyloxy)ethyl azobenzene-4,4′-dicarboxylate (BHAD), has no LC phase. The difference is ascribed to the shackling effect from the cyclic topology, which leads to the much smaller entropy change during phase transitions and increases the isotropic temperature greatly for cyclics. In addition, the trans-to-cis isomerization of azobenzene groups under UV-light is also limited in CBTAD. With the reversible isomerization of azobenzene groups, CBTAD showed interesting isothermal phase transition behaviors, where the LC phase disappeared upon photoirradiation of 365 nm UV-light, and recovered when the UV-light was off. Combined with the smectic LC nature, a novel UV-light tuned visible light regulator was designed, by simply placing CBTAD in two glass plates. The scattered phase of smectic LC was utilized as the “OFF” state for light passage, while the UV-light induced isotropic phase was utilized as the “ON” state. The shackling effect outlined here should be applicable for the design of cyclic LC oligomers/polymers with special properties.
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Two unknown solution degradants were found during the dissolution testing in 0.1-M HCl for olmesartan medoxomil (OLM) tablets. The structure of the degradants was identified and characterized by liquid chromatography–ultraviolet (LC–UV), liquid chromatography with tandem mass spectrometry (LC–MS/MS), and nuclear magnetic resonance (NMR) and demonstrated to be cyclization of tetrazole and benzene in the olmesartan (OL) and OLM structures. A series of studies including stress studies, simulation studies, and mechanism-based studies were performed to reveal the potential mechanisms that lead to the formation of the unknown degradants. The study results demonstrated that the degradation was catalyzed with radicals that originated from the metal ions leached from the inner surface of high-performance liquid chromatography (HPLC) glass vials with dissolved oxygen under acidic condition. Prerinsing the glass vials with acidic solution dissolved with EDTA can effectively avoid the generation of such oxidative impurities. The present work provides new insights into the understanding of degradation pathways of OLM, which might support the development of OLM tablets. 相似文献
An advanced dual pH- and temperature-sensitive hydrogel (NASH2.5) was optimally synthesized through modification of N-isopropylacrylamide (NIPAM) hydrogel with introducing 5 mol% acrylic acid (AA) and 2.5 wt% sewage sludge ash (SSA). The swelling kinetic results showed that NASH2.5 exhibited both high equilibrium swelling ratio and swelling rate, which was attributed to the higher porous structure as shown in scanning electron microscope, and the more hydrogen bonding formed inside of the hydrogel as investigated in Fourier transform infrared spectrometer. In addition, its curve was better fitted to the pseudo-second-order model, indicating that the water absorption process was dominated by chemisorption through forming the hydrogen bonding among the water molecules and carboxyl/silanol groups of the hydrogel. Compared with the pure NIPAM hydrogel, the water transport mechanism switched from Case I diffusion to Case II diffusion by introduction of AA and further SSA. Furthermore, through the results of the deswelling kinetics in pH value change (from 9 to 4 and 2, respectively), temperature value change (from 25 to 40, 50, and 60°C, respectively), and dual pH and temperature values changes, NASH2.5 not only presented a high pH sensitivity, but also showed high sensitive to temperature by achieving high water recovery ratio in rapid dehydrated rate. Therefore, the dual stimuli-sensitive hydrogel with the simultaneously high performance of swelling and deswelling would provide a suitable alternative for specific applications such as pollutant adsorption. 相似文献