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81.
The reaction of linear (Si(n)Cl(2)(n)(+2); n = 3-5) and cyclic (Si(5)Cl(10)) perchloropolysilanes with 1 or 2 equiv of LiN(SiMe(3))(2) results in the formation of the bis(trimethylsilyl)amino derivatives (Me(3)Si)(2)NSi(3)Cl(7) (1), (Me(3)Si)(2)NSi(4)Cl(9) (2), (Me(3)Si)(2)N(SiCl(2))(n)N(SiMe(3))(2) (n = 3, 4; n = 4, 5; n = 5, 6), cyclo-(Me(3)Si)(2)NSi(5)Cl(9) (7), and cyclo-[(Me(3)Si)(2)N](2)Si(5)Cl(8) (8). 1-8 easily can be hydrogenated with LiAlH(4) to give the corresponding amino and diamino polysilanyl hydrides. The monosubstituted and cyclic compounds 1, 2, 7, and 8 additionally afford Si-Si bond scission products, which cannot be separated in all cases. Chloro- and dichloro derivatives of Si(3)H(8), n-Si(4)H(10), and n-Si(5)H(12) are obtained from the corresponding aminosilanes and dry HCl. All compounds were characterized by standard spectroscopic techniques. For Si-H derivatives the coupled (29)Si NMR spectra were analyzed to obtain an unequivocal structural proof. 相似文献
82.
France S Shah MH Weatherwax A Wack H Roth JP Lectka T 《Journal of the American Chemical Society》2005,127(4):1206-1215
We report a mechanistically based study of bifunctional catalyst systems in which chiral nucleophiles work in conjunction with Lewis acids to produce beta-lactams in high chemical yield, diastereoselectivity, and enantioselectivity. Chiral cinchona alkaloid derivatives work best when paired with Lewis acids based on Al(III), Zn(II), Sc(III), and, most notably, In(III). Homogeneous bifunctional catalysts, in which the catalyst contains both Lewis acidic and Lewis basic sites, were also studied in detail. Mechanistic evidence allows us to conclude that the chiral nucleophiles form zwitterionic enolates that react with metal-coordinated imines. Alternative scenarios, which postulated metal-bound enolates, were disfavored on the basis of our observations. 相似文献
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86.
Harald Schfer 《无机化学与普通化学杂志》1982,489(1):154-160
Structure and Properties of Cesium Hydroxide Monohydrate, a Compound Characterized by Layered [H3O2?] Polyanions in its High Temperature Form Cesium hydroxide monohydrate, which was formed at the synthesis of cesium hydride as a by-product, was obtained in form of single crystals by recrystallization from ammonia in high pressure autoclaves. Temperature dependent X-ray structure investigations and measurements of the specific heat show the occurance of several modifications. At 293 K X-ray data prove that it is possible to distinguish between OH? ions and H2O molecules. This can also be confirmed by IR spectroscopy. At 355 K and 400 K the investigations on single crystals show layered [H3O2?] polyanions, which are separated by layers of cesium ions in a hexagonal unit cell. 相似文献
87.
Equilibrium Measurements by the Transport Method. Determination of the Enthalpie of Formation ΔH°(NbOCl2,f) by Chemical Transport in the Diffusion Tube By means of chemical transport in an ampoule with a well defined diffusion path the equilibrium NbOCl2,s + NbCl5,g ? NbOCl3,g + NbCl4,g has been investigated. Introducing a reaction entropy ΔS = 45 cl one gets ΔH = 38(±2) kcal/formula weight and ΔH0(NbOCl2,s)= ?187,6 kcal/mol. 相似文献
88.
The stability constants and the partial molal volume and isentropic partial molal compressibility changes of complex formation between cations and crown ethers in water at 25°C are presented. The cations involved are Na+, K+, Rb+, Cs+, Ca2+, and Ba2+, and the crown ethers are 12-crown-4, 15-crown-5, and 18-crown-6. Values of V of complex formation have been discussed in terms of two simple models, one based on the scaled particle theory, and the others on the Drude-Nernst continuum model. The results indicate that the charge of the potassium cation in 18-crown-6 is especially well screened from the water. On this basis hydration numbers of complexed cations have been calculated. This shows that the size of the cation compared to the crown ether hole is important for the contacts between complexed cations and water. 相似文献
89.
PRIMARY DNA DAMAGE, HPRT MUTATION AND CELL INACTIVATION PHOTOINDUCED WITH VARIOUS SENSITIZERS IN V79 CELLS 总被引:1,自引:0,他引:1
Barbara B. Noodt Egil Kvam Harald B. Steen Johan Moan 《Photochemistry and photobiology》1993,58(4):541-547
DNA strand breaks and hypoxanthine guanine phosphoribosyl transferase (HPRT) mutants were measured in parallel in photochemically treated (PCT) cells and compared at the same level of cell survival. Chinese hamster fibroblasts (V79 cells) were either incubated with the lipophilic dyes tetra(3—hydroxyphenyl)porphyrin (3THPP) and Photofrin II (PII), the anionic dye meso -tetra(4—sulfonatophenyl)porphine (TPPS4 ) or the cationic dye meso -tetra( N -methyl-4-pyridyl)porphine ( p -TMPyPH2 before light exposure. In the cells, the lipophilic dyes were localized in membranes, including the nuclear membrane, while the hydrophilic dyes were taken up primarily into spots in the cytoplasm. In addition, the hydrophilic TPPS4 was distributed homogeneously throughout the whole cytoplasm and nucleoplasm. According to the HPRT mutation test, the mutagenicity of light doses survived by 10% of the cells was a factor of six higher in the presence of 3THPP than of PII, whereas for X-rays it was a factor of three higher than for PCT with 3THPP. Light exposure in the presence of the hydrophilic dyes TPPS4 and p -TMPyPH2 was not significantly mutagenic. There was no correlation between the induced rates of HPRT mutants and of DNA strand breaks. Thus, TPPS4 was the most efficient sensitizer with regard to DNA strand breaks when compared at the same level of cell survival, followed by 3THPP, PII and p -TMPyPH2 . Hence, the rate of DNA strand breaks cannot be used to predict the mutagenicity of PCT. 相似文献
90.
Prof. Dr. Maximilian Pöhm Harald Kolassa Kurt Jentzsch 《Monatshefte für Chemie / Chemical Monthly》1977,108(2):393-395
It is well known that in the ergot alkaloids of the peptide type the proline appears in thel-configuration. Different methods of acid hydrolysis may lead to various cleavage products; hydrolysis by HCl yieldsd-proline, on the other hand hydrolytic cleavage by means of strongly acid cation exchange resin preserved the orginall-configuration.
Teilveröffentlichung der Dissertation vonH. Kolassa, Univ. Wien, 1973. 相似文献
Teilveröffentlichung der Dissertation vonH. Kolassa, Univ. Wien, 1973. 相似文献