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31.
用双-(2-羟乙基)二硫代甲酸铵(HEDC)在反相液相色谱中作检测某些金属离子的衍生化试剂,HEDC的金属螯合物微溶于水,可直接水样注射于C18柱中进行检测,范围为0.006~10mg/L相对偏差1%~2%,检测波长254nm,金属汞的整合物在HPLC分析前进行浓缩富集检测限可低至0.06~25μg/L,相对偏差小于2%。 相似文献
32.
The hydroboration of cis-2-butene and cis-3-hexene with pure diisopinocampheylborane (IPC2BH) and monoisopinocampheylborane (IPCBH2), both prepared from (+)-α-pinene, were studied. In contrast to IPC2BH, which yielded R-(?)-2-butanol and R-(?)-3-hexanol in 98.4 and 94.5% optical purities, IPCBH2 yielded S-(+)-2-butanol and S-(+)-3-hexanol in 23.6 and 19.7% optical purifies respectively. PMR examination of the methanolyzed products were utilized to establish the species present in the freshly prepared and aged adduct from (+)-α-pinene and BH3 · THF. The results confirm the interpretation previously advanced for the major differences realized in asymmetric hydroboration with the fresh and aged adducts. 相似文献
33.
The cyclopeptide, squamtin A (1, formula: C39H60O11N8S), was found to crystallized in two pseudopolymorphisms, i.e. 1·(H2O)3.5 and 1·(H2O)3.9. The composition of the amino acids and their linkage sequences are the same. The main differences between the two kinds of crystals lie in the positions and occupancies of the water molecules, the positions of the sulfur atoms and the conformation of the side chains. The absolute configuration of 1 is established by X-ray analysis in combination with the Marfey's analysis of its hydrolysates. 相似文献
34.
The qualitative analysis of bufadienolides in the Chinese drug ChanSu was performed using high-performance liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry (APCI-MS/MS). Bufadienolides are the major bioactive constituents of ChanSu, which is used to treat heart failure and cancer in traditional Chinese medicine. The APCI-MS fragmentation behavior of bufadienolides was studied. For bufadienolides with only hydroxyl substituents, the fragmentation was characterized by successive eliminations of H(2)O and CO molecules, and the profile of MS/MS product ions was correlated with the number of hydroxyl groups. If a C-16 acetoxyl group was present, the fragmentation of [M+H](+) ions was triggered by initial loss of 60 Da (HOAc). The elimination of CO was significant for bufadienolides with a 19-formyl group, and the 19-hydroxyl group could be characterized by the loss of 30 Da (HCHO). These fragmentation rules were applied to the identification of bufadienolides in a methanolic extract of ChanSu, which was separated on a C(18) column with gradient elution. A total of 35 bufadienolides were identified, including four new constituents. The method established here facilitated the convenient and rapid quality control of ChanSu crude drug and its pharmaceutical preparations. 相似文献
35.
Designs, Codes and Cryptography - In this paper, we complete the classification of the caps in $$\text{ PG }(n,q)$$ having the property that on every tangent line L, there exists a unique point... 相似文献
36.
Shiyu Huang Yuan Chang Zhuwei Li Jiaqi Cao Yurou Song Junfeng Gao Licheng Sun Jungang Hou 《Advanced functional materials》2023,33(21):2211631
Photoredox catalysis is a green solution for organics transformation and CO2 conversion into valuable fuels, meeting the challenges of sustainable energy and environmental concerns. However, the regulation of single-atomic active sites in organic framework not only influences the photoredox performance, but also limits the understanding of the relationship for photocatalytic selective organic conversion with CO2 valorization into one reaction system. As a prototype, different single-atomic metal (M) sites (M2+ = Fe2+, Co2+, Ni2+, Cu2+, and Zn2+) in hydrogen-bonded organic frameworks (M-HOF) backbone with bridging structure of metal-nitrogen are constructed by a typical “two-in-one” strategy for superior photocatalytic C N coupling reactions integrated with CO2 valorization. Remarkably, Zn-HOF achieves 100% conversion of benzylamine oxidative coupling reactions, 91% selectivity of N-benzylidenebenzylamine and CO2 conversion in one photoredox cycle. From X-ray absorption fine structure analysis and density functional theory calculations, the superior photocatalytic performance is attributed to synergic effect of atomically dispersed metal sites and HOF host, decreasing the reaction energy barriers, enhancing CO2 adsorption and forming benzylcarbamic acid intermediate to promote the redox recycle. This work not only affords the rational design strategy of single-atom active sites in functional HOF, but also facilitates the fundamental insights upon the mechanism of versatile photoredox coupling reaction systems. 相似文献
37.
Zhongzhe Li Yufang Chen Xiaoru Yun Peng Gao Chunman Zheng Peitao Xiao 《Advanced functional materials》2023,33(32):2300502
Lithium metal batteries (LMBs), due to their ultra-high energy density, are attracting tremendous attentions. However, their commercial application is severely impeded by poor safety and unsatisfactory cycling stability, which are induced by lithium dendrites, side reactions, and inferior anodic stability. Electrolytes, as the indispensable and necessary components in lithium metal batteries, play a crucial role in regulating the electrochemical performance of LMBs. Recently, the fluorinated electrolytes are widely investigated in high-performance LMBs. Thus, the design strategies of fluorinated electrolytes are thoroughly summarized, including fluorinated salts, fluorinated solvents, and fluorinated additives in LMBs, and insights of the fluorinated components in suppressing lithium dendrites, improving anodic stability and cycling stability. Finally, an outlook with several design strategies and challenges will be proposed for novel fluorinated electrolytes. 相似文献
38.
Two novel transition metal-doped tungsten bronze oxides, Pb2.15Li0.85Nb4.85Ti0.15O15 (PLNT) and Pb2.15Li0.55Nb4.85W0.15O15 (PLNW), are synthesized by high-temperature solid-state reactions. The Rietveld method using the high-resolution synchrotron radiation indicates that PLNT and PLNW crystallize in the orthorhombic polar noncentrosymmetric space group, Pmn21 (no. 31). As a class of tungsten bronze oxide, PLNT and PLNW retain a unique rigid framework composed of d0 transition metal cation (Ti4+ or W6+)-doped highly distorted NbO6 octahedra along with the subsequently generated Pb/LiO12 and PbO15 polyhedra. Interestingly, the d0 transition metal-doped tungsten bronzes, PLNT and PLNW, exhibit extremely large second-harmonic generation (SHG) responses of 56 and 67 × KH2PO4, respectively. The observed immeasurably strong SHG is mainly attributed to a net polarization originating from the alignment of highly distorted NbO6 octahedra with doped transition metals in the frameworks. It is believed that doping transition metal cations at the B-site of the tungsten bronze structures should be an innovative strategy to develop novel high-performance nonlinear optical materials. 相似文献
39.
40.
W. Zong D. R. DeWitt R. Schuch H. Gao S. Asp E. Justiniano 《Hyperfine Interactions》1996,99(1):325-331
We report here an observation ofn=1 dielectronic recombination resonances of boron-like argon in the energy region 140–195 eV. With the cooler's electron beam as a target, a resolution of approximately 0.6 eV FWHM was obtained in the observed energy range. The energies of the doubly excited states were estimated with a Hartree-Fock calculation, which indicates that the observed resonances are from Ar13+(1s22s22p) to Ar12+(1s22s23l3l) and Ar12+(1s22s2p3l3l) transitions. 相似文献