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81.
Resibufogenin is a cytotoxic steroid isolated from the Chinese drug ChanSu. The biotransformation of resibufogenin by Mucor polymorphosporus afforded 22 products, and 15 of them were new. The transformation reactions involved hydroxylations at C-1β, C-5, C-7α, C-7β, C-12α, C-12β and C-16α, as well as epimerization or dehydrogenation of 3-OH. Hydroxylations at C-12α, C-12β and C-16α were the major reactions, each giving products in >5% yields, whereas the other products were obtained in fairly low yields. Some of the products showed decreased but still potent cytotoxicities. This investigation provided a useful approach to prepare new bufadienolides and most of them were difficult to obtain by chemical means. 相似文献
82.
A capillary zone electrophoresis-negative electrospray ionization-quadrupole time of flight-mass spectrometric method was developed for the characterization of oligonucleotides after synthesis, using model compounds. The major difficulty is the adduction of metal cations to the polyanionic backbone of the oligonucleotide sample, resulting in complex spectra and decreased sensitivity. Several approaches were investigated to circumvent this problem. Separation was performed in an ammonium carbonate buffer. During separation, the interfering metal ions were exchanged for ammonium ions, which are less tightly bound to the oligonucleotide when ionized. The influence of the addition of piperidine and imidazole or trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA) to the running buffer for further reduction of cation adduction was investigated. Addition of CDTA to the buffer system resulted in a deconvoluted spectrum with very little adducts. On-line sample stacking proved vital to preconcentrate the samples. The pH and the concentration of the ammonium carbonate buffer as well as the electrophoresis voltage were optimized to achieve the best signal response for the oligonucleotides and a maximum reduction of the cation adducts as well as a short analysis time. Finally, the sheath liquid composition was examined for further improvement of the signal. The developed method was used to analyze different oligonucleotides (5000-9200 Da) in light of its use as a final quality control method for oligonucleotides in terms of purity and sequence homogeneity of the synthesized products. In all cases, very little adducts were observed in the deconvoluted spectra, and the relative errors of the measured molecular masses ranged from 3 to 35 ppm. 相似文献
83.
A novel three-dimensional metal selenite [Fe2(H2O)4(SeO3)2] (1) has been hydrothermally synthesized and characterized by the elemental analyses, IR spectrum, TG analysis and the single crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic system, space group P21/n, with a=6.5283(13) Å, b=8.8754(18) Å, c=7.6798(15) Å, (=98.82(3)β, V=439.71(15) Å3, and Z=2. Compounds 1 exhibits interesting three-dimensional structure constructed from {FeO6} octahedra and {SeO3} pyramids linked via the corner- and/or edge-sharing mode. The most interesting structural feature of compound 1 is that the existence of multidirectional intersecting double helical chains in one compound. 相似文献
84.
A novel near infrared (NIR) modeling method—Laplacian regularized least squares regression (LapRLSR) was presented, which can take the advantage of many unlabeled spectra to promote the prediction performance of the model even if there are only few calibration samples. Using LapRLSR modeling, NIR spectral analysis was applied to the online monitoring of the concentration of salvia acid B in the column separation of Salvianolate. The results demonstrated that LapRLSR outperformed partial least squares (PLS) significantly, and NIR online analysis was applicable. 相似文献
85.
Zengshun Jiang Xingqi An Yuqin Zhang Xuan Liu Xifeng Qin Yanjie Zhao Huilin Wang Guiyuan Liu Hongsheng Song 《中国光学快报(英文版)》2021,(4):56-61
After the three-dimensional self-affine fractal random surface simulation, we use the optical scattering theory to calculate the deep Fresnel region speckle(DFRS) under consideration of the more strict shadowing effect. The evolution of DFRS with the scattering distance and the intensity probability distribution are studied. It is found that the morphology of the scatterer has an antisymmetric relationship with the intensity distribution of DFRS, and the effect of micro-lenses on the scattering surface causes the intensity probability distribution of DFRS to deviate from the Gaussian speckle in the high light intensity area. 相似文献
86.
Yu Fu Yanyan Yang Dongxue Chu Zefeng Liu Lili Zhou Xiaoyang Yu Xiaoshu Qu 《Molecules (Basel, Switzerland)》2022,27(13)
Polyoxometalates (POMs) demonstrate potential for application in the development of integrated smart energy devices based on bifunctional electrochromic (EC) optical modulation and electrochemical energy storage. Herein, a nanocomposite thin film composed of a vanadium-substituted Dawson-type POM, i.e., K7[P2W17VO62]·18H2O, and TiO2 nanowires were constructed via the combination of hydrothermal and layer-by-layer self-assembly methods. Through scanning electron microscopy and energy-dispersive spectroscopy characterisations, it was found that the TiO2 nanowire substrate acts as a skeleton to adsorb POM nanoparticles, thereby avoiding the aggregation or stacking of POM particles. The unique three-dimensional core−shell structures of these nanocomposites with high specific surface areas increases the number of active sites during the reaction process and shortens the ion diffusion pathway, thereby improving the electrochemical activities and electrical conductivities. Compared with pure POM thin films, the composite films showed improved EC properties with a significant optical contrast (38.32% at 580 nm), a short response time (1.65 and 1.64 s for colouring and bleaching, respectively), an excellent colouration efficiency (116.5 cm2 C−1), and satisfactory energy-storage properties (volumetric capacitance = 297.1 F cm−3 at 0.2 mA cm−2). Finally, a solid-state electrochromic energy-storage (EES) device was fabricated using the composite film as the cathode. After charging, the constructed device was able to light up a single light-emitting diode for 20 s. These results highlight the promising features of POM-based EES devices and demonstrate their potential for use in a wide range of applications, such as smart windows, military camouflage, sensors, and intelligent systems. 相似文献
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The (2+1)-dimensional Boiti–Leon–Manna–Pempinelli (BLMP) equation is an important integrable model. In this paper, we obtain the breather molecule, the breather-soliton molecule and some localized interaction solutions to the BLMP equation. In particular, by employing a compound method consisting of the velocity resonance, partial module resonance and degeneration of the breather techniques, we derive some interesting hybrid solutions mixed by a breather-soliton molecule/breather molecule and a lump, as well as a bell-shaped soliton and lump. Due to the lack of the long wave limit, it is the first time using the compound degeneration method to construct the hybrid solutions involving a lump. The dynamical behaviors and mathematical features of the solutions are analyzed theoretically and graphically. The method introduced can be effectively used to study the wave solutions of other nonlinear partial differential equations. 相似文献