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101.
β-Trifluoroacetyl vinyl ethers ROCHCHCOCF3 react smoothly as dienophiles with α,β-unsaturated carbonyl compounds to give the unexpected 2-alkoxyl-5-trifluoroacetyl-3,4-dihydro-2H pyrans. These products are formed by elimination and addition of the alcohol to the products of the normal hetero Diels-Alder reaction (2-alkoxyl-3-trifluoroacetyl-2,3-dihydro-2H pyrans). In contrast, 1,3-dipolar cycloaddition of ROCHCHCOCF3 with ArCHN(O)Me proceeds via a Z-endo transition state to give regio- and stereospecific 4-trifluoroacetyl substituted isoxazolidines and their derivatives. 相似文献
102.
Chemodynamic therapy(CDT) is an emerging endogenous stimulation activated tumor treatment approach that exploiting iron-containing nanomedicine as catalyst to convert hydrogen peroxide(H_2O_2)into toxic hydroxyl radical(·OH) through Fenton reaction.Due to the unique characteristics(weak acidity and the high H_2O_2 level) of the tumor microenvironment,CDT has advantages of high selectivity and low side effect.However,as an important substrate of Fenton reaction,the endogenous H_2O_2 in tumor is still insufficient,which may be an important factor limiting the efficacy of CDT.In order to optimize CDT,various H_2O_2-generating nanomedicines that can promote the production of H_2O_2 in tumor have been designed and developed for enhanced CDT.In this review,we summarize recently developed nanomedicines based on catalytic enzymes,nanozymes,drugs,metal peroxides and bacteria.Finally,the challenges and possible development directions for further enhancing CDT are prospected. 相似文献
103.
The carbohydrate chains decorating cell membranes and secreted proteins participate in a range of important biological processes. However, their ultimate significance and possible therapeutic potential have not been fully explored due to the lack of economical methods for their production. This study is an example of the use of a genetically engineered bacterial strain in the preparation of diverse oligosaccharides. Based on an ex vivo biosynthetic pathway, an artificial gene cluster was constructed by linking the genes of five associated enzymes on a plasmid vector. This plasmid was inserted into the E. coli NM522 strain to form globotriose-producing cells ('superbug' pLDR20-CKTUF). The specific strain was conveniently applied to the synthesis of globotriose trisaccharide and its derivatives, as potential neutralizers for Shiga toxin. This work demonstrates a novel and economical method for generating ligand diversity for carbohydrate drug development. 相似文献
104.
105.
In this report, we describe our attempt to understand the photochemical interactions that occur between dihydroxybenzophenone (DHB)-based UV screens and lignin when high-yield pulps are treated with such materials. Milled wood lignin (MWL) and filter paper were used as models, and various irradiation protocols were carried out in the presence and absence of UV screens. After irradiation, the lignin and the UV screen were extracted and the products analyzed. These experiments showed that upon irradiation, fragments of MWL-containing chromophores were linked to cellulose via an acid-labile linkage. In the presence of UV screens, these reactions were minimized. Molecular weight measurements of the extracted lignin showed that the MWL is degraded upon solid-state irradiation. The samples that contained UV screens showed a reduced tendency to degrade. Using quantitative 31P NMR, it was possible to probe further the detailed structural changes that occurred in MWL during irradiation. In general, DHB-based UV screens and derivatives were found to interact actively with MWL when irradiated. 相似文献
106.
Mn2P2S6 single-crystal nanorods with diameters 20-40 nm and lengths up to 1 microm and nanotubes with diameters 40-50 nm and lengths ranging between 110 and 170 nm have been prepared through a low-temperature solvothermal method. They have been characterized by X-ray diffraction, transmission electron microscopy (TEM), high-resolution (HR) TEM, electron diffraction, energy-dispersive spectrometry analysis, X-ray photoelectron spectroscopy, and Raman spectroscopy. 相似文献
107.
Changlun Shao Zhiyong Guo Hong Peng Guangtian Peng Zhongjing Huang Zhigang She Yongcheng Lin Shining Zhou 《Chemistry of Natural Compounds》2007,43(4):377-380
A new isoprenyl phenyl ether, 3-hydroxy-4-(3-methylbut-2-enyloxy)benzoic acid methyl ester (1), together with 4-hydroxybenzoic acid (2), 2-hydroxy-6-methylbenzoic acid (3), and 4-hydroxy-3-methoxybenzoic acid (4) were isolated from Mangrove fungus (No. B60) from the South China Sea. The structures of the compounds were established
on the basis of NMR spectroscopic and mass spectrometric data. In the preliminary bioassay, compound 1 exhibited antibacterial and antifungal activities. Compound 1 also inhibited cytotoxicity to the hepG2 cell line with an IC50 value of 10.0 μg/mL.
Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 313–314, July–August, 2007. 相似文献
108.
Ge JP Wang J Zhang HX Wang X Peng Q Li YD 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(6):1889-1894
Three-dimensional, orthogonal lead sulfide (PbS) nanowire arrays and networks have been prepared by using a simple, atmospheric pressure chemical vapor deposition (APCVD) method. These uniform nanowires (average diameter 30 nm) grow epitaxially from the surface of the initial PbS crystal seeds and form orthogonal arrays and networks in space. The growth mechanism has been explored, and the process was classified as homogeneous, epitaxial growth in the 200 directions. Furthermore, Raman spectra of PbS nanowires are reported here, and their characteristic Raman peak (190 cm(-1), no shoulder) could be used as a unique probe for the study of PbS nanomaterials. 相似文献
109.
C. T. Peng S.-F. Ding R.-L. Hua 《Journal of Radioanalytical and Nuclear Chemistry》1988,123(2):411-420
Retention indexes (RI's) on SE-30 and Carbowax 20M columns are characteristic and can be used for identification purposes. A method for predicting RI on the basis of the number of atoms and contributions from substituents and functional groups is discussed. This method establishes a structure retention index relationship (SRIR), capable of relating structure to RI and is useful for suggesting structure to match with radioactive peaks. Examples of labeled side products tentatively identified in this manner are given. 相似文献
110.
库仑滴定法测定有机硅样品中的氮含量 总被引:3,自引:0,他引:3
本文利用库仑滴定法研究了高分子和低分子硅氮化合物及含氮有机硅样品中氮含量的测定,并研究和讨论了影响测定结果准确性的因素。 相似文献