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171.
钴(Ⅱ)-5-取代邻菲罗啉-α-氨基酸三元配合物的稳定性研究 总被引:5,自引:1,他引:5
本文在25.0±0.1℃,I=0.1mol·dm-3KNO3存在下,采用pH法测得了5-取代邻菲罗啉的质子化常数以及钴(Ⅱ)与5-取代邻菲罗啉、α-氨基酸的二元、三元配合物的稳定常数。结果表明三元配合物的稳定性与5-取代邻菲罗啉的质子化常数、取代基常数均存在直线自由能关系。并用三元配合物稳定性的表征值logKM、△logK,讨论了三元配合物的稳定性,发现钴(Ⅱ)与配体5-取代邻菲罗啉之间也存在着d-p反馈π键。该π健的强度对三元配合物稳定性有着显著影响。 相似文献
172.
The 2-methyloxazol-5-on-2-yl radical (3) and its deuterium labeled analogs were generated in the gas-phase by femtosecond electron-transfer and studied by neutralization-reionization mass spectrometry and quantum chemical calculations. Radical 3 undergoes fast dissociation by ring opening and elimination of CO and CH(3)CO. Loss of hydrogen is less abundant and involves hydrogen atoms from both the ring and side-chain positions. The experimental results are corroborated by the analysis of the potential energy surface of the ground electronic state in 3 using density functional, perturbational, and coupled-cluster theories up to CCSD(T) and extrapolated to the 6-311 ++ G(3df,2p) basis set. RRKM calculations of radical dissociations gave branching ratios for loss of CO and H that were k(CO)/k(H) > 10 over an 80-300 kJ mol(-1) range of internal energies. The driving force for the dissociations of 3 is provided by large Franck-Condon effects on vertical neutralization and possibly from involvement of excited electronic states. Calculations also provided the adiabatic ionization energy of 3, IE(adiab) = 5.48 eV and vertical recombination energy of cation 3(+), RE(vert) = 4.70 eV. The present results strongly indicate that oxazolone structures can explain fragmentations of b-type peptide ions upon electron capture, contrary to previous speculations. 相似文献
173.
174.
引言硒作为人体必需的微量元素,其主要生化作用与谷胱甘肽过氧化物酶密切相关.在体内,该酶可以催化许多过氧化物的分解,并且与谷胱甘肽一起组成一个强有力的细胞防御体系,发挥其抗氧化作用.近几年来,人们发现了一种小分子有机硒化物2-苯基-1,2-苯并异硒唑酮-3(简称Ebselen)具有类似谷胱甘肽过氧化物酶的活性.它能有效地抑制活性氧自由基的产生而引起的细胞损伤,具有良好的抗炎活性,且毒性极低(大鼠LD_(50)>6180mg/os).因而,普遍认为Ebselen及其类似物是一类具有广谱抗炎活性的潜在药物,在医药领域具有广阔的应用前景. 相似文献
175.
The synthesis of aziridines from imines and ethyl diazoacetate in room temperature ionic liquids is reported. The reactions proceed readily under mild conditions with high cis selectivities and high yields. 相似文献
176.
Synthesis and light scattering study of microgels with interpenetrating polymer networks 总被引:1,自引:0,他引:1
Monodispersed microgels composed of poly(acrylic acid) (PAAc) and poly(N-isopropylacrylamide) (PNIPAM) interpenetrating polymer networks (IPN) were synthesized by a two-step method, first preparing PNIPAM microgel and then polymerizing acrylic acid that interpenetrates into the PNIPAM network. The growth kinetics of the IPN particle formation was obtained by measuring the turbidity and particle hydrodynamic radius (Rh) as a function of reaction time. IPN and PNIPAM microgels were characterized and compared by dynamic and static light scattering techniques. The concentrated aqueous solutions of the PNIPAM-PAAc IPN microgels exhibit an inverse thermoreversible gelation. In contrast to polymer solutions of poly(NIPAM-co-AAc) that have the inverse thermoreversible gelation, our system can self-assemble into an ordered structure, displaying bright colors. Furthermore, IPN microgels undergo the reversible volume phase transitions in response to both pH and temperature changes associated with PAAc and PNIPAM networks, respectively. 相似文献
177.
Coating Carbon Nanotubes with Europium Oxide 总被引:4,自引:0,他引:4
HuiQunCAO GuangYanHONG JingHuiYAN JiLinZHANG GuiXiaLIU 《中国化学快报》2003,14(12):1293-1295
Carbon nanotubes (CNTS) coating with europium oxide by a simple method is reported in this letter for the first time. The CNTS were refluxed in a solution of nitric acid containing europium nitrate, and the pH value was subsequently ajusted with ammonia solution. At last, the mixture was filtered and annealed. The TEM micrograph showed that the CNTS were covered with a uniform thin layer with thickness of about 15 nm. The XRD results revealed that the CNTS were coated with europium oxide. 相似文献
178.
Chun‐Xiang Wang Chen‐Xia Du Zhi‐Feng Li 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(10):m488-m490
In the title compound, [Zn(C17H10N5O)2(H2O)2]·4H2O, cyclic water hexamers forming one‐dimensional metal–water chains are observed. The water clusters are trapped by the co‐operative association of coordination interactions and hydrogen bonds. The ZnII ion resides on a centre of symmetry and is in an octahedral coordination environment comprising two O atoms and two N atoms from two 2′‐(4,5‐diazafluoren‐9‐ylidene)picolinohydrazidate ligands and two water molecules. 相似文献
179.
Xiongyu Wu Xiaohong Liu Guangce Jiang Yongcheng Lin Willy Chan L. L. P. Vrijmoed 《Chemistry of Natural Compounds》2005,41(1):27-29
A novel metabolite 1, named xyloketal G, was isolated from cultures of marine derived mangrove fungus Xylaria sp. 2508. Its structure was elucidated by analysis of spectroscopic data.__________Published in Khimiya Prirodnykh Soedinenii, No. 1, pp. 22–23, January–February, 2005. 相似文献
180.
Jibo Xia Yili Chen Kathryn M. Liberatore Barry S. Selinsky 《Tetrahedron letters》2003,44(52):9295-9297
Methyl 3,3-(ethylenedioxy)-6β-fluoro-5β-cholan-24-oate has been prepared starting from hyodeoxycholic acid and 3,3-(ethylenedioxy)-7( and β)-fluorocholestan-22-al starting from stigmasterol, using diethylaminosulfur trifluoride as the fluorinating agent. These molecules will be used to synthesize analogs of the aminosterol antibiotic squalamine. 相似文献