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141.
A series of pyrene-centered starburst oligocarbazoles (1-3) have been synthesized and well characterized. Based on photophysical, thermal and electrochemical studies in solutions and as thin films, all starburst molecules reveal a sky blue emission with a high efficiency (Φ(F) = 0.99-0.81) and excellent thermal and electrochemical stabilities. As OLED materials, these superior properties are helpful to enhance device stability and lifetime. 相似文献
142.
A simple, efficient and low-temperature approach for the assembly of hierarchical Zinc oxide (ZnO) microstructures in ionic liquid [EMIM]+[BF4]− is reported. The as-obtained ZnO superstructures are composed of microbundles of nanorods from the center points, with the diameter and length in the range of 100-150 nm and 2-4 μm, which have been characterized by X-ray diffraction, scanning and transmission electron microscopy, and photoluminescence spectroscopy. The ZnO microstructures exhibit significant defect-related green-yellow emission and high photodegradation of dye Methyl Orange (5×10−5 mol/L) under UV excitation within 80 min. 相似文献
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144.
A method, HPLC coupled with diode-array and evaporative light scattering detectors (HPLC-DAD-ELSD), was newly developed to evaluate the quality of Flos Lonicerae (FL) and Flos Lonicerae Japonicae (FLJ), through a simultaneous determination of multiple types of bioactive components. By employing DAD, the detection wavelengths were set at 240 nm for the determination of iridoids, 330 nm for phenolic acids, and 360 nm for flavonoids, respectively. While ELSD, connected in series after DAD, was applied to the determination of saponins. This assay was fully validated with respect to precision, repeatability, and accuracy. Moreover, principal component analysis (PCA) was used for the similarity evaluation of different samples, and it was proven straightforward and reliable to differentiate FL and FLJ samples from different origins. For PCA, two principal components have been extracted. Principal component 1 (PC1) influences the separation between different sample sets, capturing 54.598% variance, while principal component 2 (PC2) affects differentiation within sample sets, capturing 12.579% variance. In conclusion, simultaneous quantification of bioactive components by HPLC-DAD-ELSD coupled with PCA would be a well-acceptable strategy to differentiate the sources and to comprehensively control the quality of the medicinal plants FL and FLJ. 相似文献
145.
A high-performance liquid chromatographic method with diode array detection was developed and validated to simultaneously identify and quantify four phytoecdysones,i.e., polypodine B (1), ecdysterone (2), 25-R inokosterone (3) and 25-S inokosterone (4), in Radix Achyranthis Bidentatae. The analysis was performed using a C(18) column with 6% tetrahydrofuran aqueous and acetonitrile isocratic elution, and the detection was carried out by DAD at 242 nm. The identities of the analytes were determined by comparing the retention time and UV spectrum with those of reference compounds. The validation of the method included linearity, sensitivity, recovery and stability. All calibration curves of the four phytoecdysones showed good linear regression (r(2) >or= 0.9993). The limit of detection (S/N = 3) and limit of quantification (S/N = 10) were less than 7.5 and 12.3 ng, respectively. The method provided desirable repeatability with overall intra- and inter-day variations of less than 4.67%. The obtained recoveries varied between 95.1 and 104.4% while the relative standard deviations were below 4.85% (n = 3). The analysis results indicated that the contents of the investigated phytoecdysones in Radix Achyranthis Bidentatae from different locations were highly variant, and the genuine crude drug indigenous to Henan province did not possess the highest concentration of phytoecdysones. 相似文献
146.
Using epoxy chiral building blocks readily derived from d-gluconolactone as the source of the stereogenic centers, both (6R,8R)- and (6R,8S)-isomers of (E)-1-chlorotridec-1-ene-6,8-diol were synthesized. The vinylchloro unit was installed onto the substrate carbon chain in an approximately 9:1 (E)/(Z) ratio via a condensation of CrCl2/CHCl3 with a terminal aldehyde. A tosylation protocol featuring addition of H2O was also developed for a highly polar tetraol. The synthetic products allowed for re-acquisition of the NMR spectra of better quality and revealed some delicate yet unignorable discrepancies in the 13C NMR for the natural isomer obtained by synthesis and that isolated some 30 years ago from the marine cyanophyte. The puzzling discrepancies were eventually shown to be caused by deuteration of the hydroxyl groups. 相似文献
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A recently isolated bismonoglyceride of heptadecanedioic acid, which represents a novel type of natural monoglycerides (i.e., with two instead of only one glycerol unit in the molecular architecture), was synthesized in enantiopure forms using a chiral-pool based approach with the 17-carbon chain constructed from undec-10-enoic acid and oct-7-en-1-ol via a cross metathesis and the stereogenic centers derived from (R)-(2,2-dimethyl-1,3-dioxolan-4-yl)methanol. An analogue with a longer alkyl chain was also synthesized. The synthetic samples not only allowed for establishment of the absolute configuration but also helped to reveal some minor yet unignorable errors in the 1H NMR data for the natural product. Optical rotation and NMR data acquired in DMSO and DMSO-d6, respectively, are also presented. 相似文献
150.
在枯草杆菌细胞的培养基中加入赤霉酸,可以显著地促进α-淀粉酶的形成。环式磷酸腺苷和三磷酸腺苷能够模拟赤霉酸促进α-淀粉酶合成的作用。我们还观察了葡萄糖对α-淀粉酶产生的影响。当细菌在含有谷氨酸的培养基中生长时,加入葡萄糖能使α-淀粉酶的合成受到抑制。葡萄糖对α-淀粉酶形成的抑制作用可以被赤霉酸所消除。此外,在有赤霉酸存在时,枯草杆菌α-淀粉酶的合成受到放线菌素D的抑制。赤霉酸对α-淀粉酶合成的作用可能是在转录水平上受到环式磷酸腺苷的调节。 相似文献