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81.
Susanne Bredendiek-Kämper Holger Jenett 《Fresenius' Journal of Analytical Chemistry》1993,346(1-3):315-317
Summary The system of plasma sprayed Al2O3 on Ni substrates is investigated by means of AES/depth profiling. The influence of two process parameters — preoxidation procedure and spraying temperature — is examined. Rupture between substrate and ceramic layer occurs between a residual — or, in the case of excessive preoxidation, a superfluous — NiO layer on Ni, the thickness of the former depending on preoxidation conditions and the Al2O3 layer, the back side of which being partially covered with NiO. The thickness of this NiO layer increases up to about 1 m with the thickness of the initial NiO layer on the substrate, until this layer is about 1.3 m thick, and remains constant thereafter. The same dependence is observed for the width (0.1–1 m range) of the mixed oxide interface between the sprayed Al2O3 layer and the NiO layer below. These results represent the chemical contribution to adherence. Contrary to excessive preoxidation, an increase of the spraying temperature from 300°C to 500°C effects broader interfaces.This poster was awarded the First Prize in Poster Section C by the Deutscher Arbeitskreis für Spektroskopie (DASp) 相似文献
82.
Based on the lipase-catalysed kinetic resolution of the silyloxyalcohol (1RS,2SR)-5 by transesterification with vinyl acetate in the presence of lipase from Pseudomonas cepacia a synthesis of both enantiomers of the β-amino acid cispentacin (1R,2S)-1 and (1S,2R)-1 using simple functional group interconversions is described. 相似文献
83.
Smaragda Grammenudi Marlene Franke Fritz Vögtle Eberhard Steckhan 《Journal of inclusion phenomena and macrocyclic chemistry》1987,5(6):695-707
The tris-bipyridine ligand3a and its stoichiometric Rh3+ complex have been prepared. Cyclovoltammograms of the complex at pH 7.4 using a glassy carbon disk electrode reveal a strong reduction peak at –620 mV and two weak reduction peaks at more negative voltage. The reduction potential of the new complex is shifted by 300 mV to more positive values as compared to [Rh(bipy)3]3+. There is no reversible reoxidation peak of the Rh(I) complex formed due to the decomplexation of one of the three bipyridine units in the course of the transition Rh(III)Rh(I). The Rh(III) complex of3a was also studied with respect to its function as a possible redox mediator for the electrochemical regeneration of NADH from NAD+. The preparative electrolysis of the Rh3+ complex of3a in the presence of NAD+ yields a selective formation of NADH, whereas NAD dimers were not detected. On the other hand, a significant acceleration of this reaction compared to [Rh(bipy)3]3+ was not observed. 相似文献
84.
Supramolecular chemistry is a new area of research that has rapidly developed from pure synthetic chemistry, and its novelty has led to interdisciplinary cooperation between organic and inorganic chemistry, biochemistry, physical and theoretical chemistry, and physics. Whereas molecular chemistry essentially deals with the covalent bonding of atoms, Supramolecular chemistry is predominantly involved in the study of the weaker intermolecular interactions resulting in the association and self-organization of several components to form larger aggregates (supramolecules). The first crown ether discovered by the subsequent Nobel prizewinner Pedersen was more the fortuitous reaction product of an impurity, but nowadays, some twenty-five years later, chemists are able to tailor host molecules to special requirements. Host compounds having a cyclophane skeleton make an important contribution, since their aromatic structural units ensure the necessary rigidity of the molecular structures and thereby improve the preorganization of the coordination sites for the cooperative binding of the guests. During the course of the rapid development of Supramolecular chemistry such a large number of synthetic hosts has been developed and their interaction with guests studied in such depth that we must restrict ourselves here to a discussion of a particular group of host compounds, namely cavity-supporting macrobicyclic and macrooligocyclic phanesu, which bear a similar relation to open-chain and monocyclic hosts as the metal-complexing cryptands to the podands and crown ethers. The molecular architecture of these three-dimensionally bridged macrooligocycles is a challenge for synthetic chemistry. (Not only the size and shape of the intramolecular cavity, but also the provision of the latter with suitable coordination centers have to be included in the synthesis strategy.) The capacity for the envelopment of guests from all sides and the expedient endo functionalization often also produce a particularly strong binding of host and guest, outstanding selectivities with regards to molecular recognition, and special properties of the Supramolecular complexes. 相似文献
85.
The effect of pH on the formation and stability of phospholipid coatings in fused-silica capillaries in electrophoresis was investigated. A liposome solution consisting of 3 mM of 80:20 mol% phosphatidylcholine/phosphatidylserine (PC/PS) in N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid) (HEPES) buffer was used as coating material. The coating was prepared by a method described earlier and five steroids were used as neutral model analytes. First, the effect of pH of the coating solution on the formation and stability of phospholipid coatings was studied at pH 6.5-8.5. The pH of the background electrolyte (BGE) solution (HEPES) was either kept constant at pH 7.4 or made similar to the pH of the liposome coating solution. Results showed that attachment of the coating on the fused-silica wall mostly depends on the protonation of amines of the phospholipids and HEPES. The ability of the phospholipid coating to withstand changes in pH was then investigated by coating at pH 7.5 and separating steroids with acetic acid, 3-(cyclohexylamino)-1-propanesulfonic acid (CAPS), HEPES, or glycine BGE, adjusted to pH between 4.5 and 10.8. The results showed that with use of BGE solution at pH 10.8, the separation of steroids was not successful and the electroosmotic flow was high because of leakage of the phospholipid coating during preconditioning of the capillary with BGE solution. There was no phospholipid leakage with a BGE solution of pH 4.5, indicating that the protonated form of the functional groups of PS and HEPES participating in the attachment of the phospholipid coating to the capillary play an essential role in the success of the coating. 相似文献
86.
Donald L. Traul Gregory S. Anderson James M. Bilitz Marianne Krieg Fritz Sieber 《Photochemistry and photobiology》1995,62(4):790-799
Abstract— Simultaneous exposure to merocyanine 540 (MC540) and light of a suitable wavelength kills leukemia, lymphoma and neuroblastoma cells but is relatively well tolerated by normal pluripotent hematopoietic stem cells. This differential phototoxic effect has been exploited in preclinical models and a phase I clinical trial for the extracorporeal purging of autologous bone marrow grafts. Salicylate is known to potentiate the MC540-mediated photokilling of tumor cells. Assuming that salicylate induces a change in the plasma membrane of tumor cells (but not normal hematopoietic stem cells) that enhances the binding of dye molecules it has been suggested that salicylate may provide a simple and effective means of improving the therapeutic index of MC540-mediated photodynamic therapy. We report here on a direct test of this hypothesis in a murine model of bone marrow transplantation as well as in clonal cultures of normal murine hematopoietic progenitor cells. In both systems, salicylate enhanced the MC540-sensitized photoinactivation of leukemia cells and normal bone marrow cells to a similar extent and thus failed to improve the therapeutic index of MC540 significantly. On the basis of a series of dye-binding studies, we offer an alternative explanation for the potentiating effect of salicylate. Rather than invoking a salicylate-induced change in the plasma membrane of tumor cells, we propose that salicylate displaces dye molecules from serum albumin, thereby enhancing the concentration of free (active) dye available for binding to tumor as well as normal hematopoietic stem cells. 相似文献
87.
Phosphinophosphiniden-Phosphorane tBu2P?P = P(R)tBu2 aus Li(THF)2[η2-(tBu2P)2P] und Alkylhalogeniden
The Phosphinophosphinidene-phosphoranes tBu2P? P = P(R)tBu2 from Li(THF)2[η2-(tBu2P)2P] and Alkyl Halides We report the formation of tBu2P? P = P(R)tBu2 a and (tBu2)2PR b (with R = Me, Et, nPr, iPr, nBu, PhCH2, H2C = CH? CH2 and CF3) reactions of Li(THF)2[η2-(tBu2P)2P] 2 with MeCl, MeI, EtCl, EtBr, nPrCl, nPrBr, iPrCl, nBuBr, PhCH2Cl, H2C = CH? CH2Cl or CF3Br. In THF solutions the ylidic compounds a predominate, whereas in pentane the corresponding triphosphanes b are preferrably formed. With ClCH2? CH = CH2 only b is produced; CF3Br however yields both tBu2P? P = P(Br)tBu2 and tBu2P? P = P(CF3)tBu2, but no b . The ratio of a:b is influenced by the reaction temperature, too. The compounds tBu2P? P = P(Et)tBu2 4a and (tBu2P)2PEt 4 b , e. g., are produced in a ratio of 4:3 at ?70°C in THF, and 1:1 at 20°C; whereas 1:1 is obtained at ?70°C in pentane, and 1:2 at 20°C. Neither tBuCl nor H2C = CHCl react with 2 . The compounds a decompose thermally or under UV irradiation forming tBu2PR and the cyclophosphanes (tBu2P)nPn. 相似文献
88.
89.
Reactions of [(me3Si)2P]2PLi with Chlorophosphanes [(me3Si)2P]2PLi 1 with (C6H5)2PCl yields only a small amount of the expected [(me3Si)2P]2P–P(C6H5)2 2 ; the main products are (me3Si)2P–P(C6H5)2 3 and (C6H5)2P–P(C6H5)2 4 besides some (me3Si)3P 5 and (C6H5)2P–Sime3 6. 3 and 4 result from the metallation of (C6H5)2PCl by 1 t-buPCl2 and 1 form the P3-ring (me3Si)(me3C)P3[P(Sime3)2] 9 as main product besides some [(me3Si)2P]2P–Sime3 7 and 5. 9 is afforded by elimination of me3SiCl, from the initially formed unstable [(me3Si)2P]2P–P(Cl)Cme3 10 . Similarly 1 and PCl3 yield mainly the P3-ring (me3Si)(Cl)P3 · [P(Sime3)2] 11 due to elimination of me3SiCl from [(me3Si)2P]2P–PCl2. 相似文献
90.
Reactions of Silylphosphines with Sulphur We report about reactions of Me2P? SiMe3 2 , MeP(SiMe3)2 3 , (Me3Si)3P 4 , P2(SiMe3)4 5 , and (Me3Si)3P7 1 with elemental sulphur. Without using a solvent 2 reacts very vigorously. The reactions with 3 and 4 show less reactivity which is even more reduced with 5 and 1 . With equivalent amounts of sulphur the reactions with 2 , 3 , 4 lead to compounds with highest content of sulphur. These compounds are Me3SiS? P(S)Me2 9 from 2 , (Me3SiS)2P(S)Me 13 from 3 and (Me3SiS)3P(S) 16 from 4 . Besides, the by-products (Me3Si)2S 8 , P2Me4 7 , and Me2P(S)? P(S)Me2 11 can be obtained. The reactions of silylphosphines in a pentane solution run much slower so that the formation of intermediates can be observed. Reaction with 2 yields Me3SiS? PMe2 6 and Me2P(S)PMe2 10 , which lead to the final products in a further reaction with sulphur. From 3 (Me3SiS)(Me3Si)PMe 14 and (Me3SiS)2PMe 12 can be obtained which react with sulphur to (Me3SiS)2P(S)Me 13. 4 leads to the intermediates (Me3SiS)(Me3Si)2P 18 , (Me3SiS)2(Me3Si)P 17 , (Me3SiS)3P 15 yielding (Me3SiS)3P(S) 16 with excess sulphur. Depending on the molar ratio (P2SiMe3)4 5 reacts to (Me3Si)2P? P(SSiMe3)(Sime3), (Me3SiS)(Me3Si)P? P(SSiMe3). (Diastereoisomer ratio 10:1), (Me3SiS)2P? P(SiMe3)2 and (Me3SiS)2P? P(SSiMe3)(Sime3). With the molar ratio 1:4 the reaction yields (Me3SiS)2P? P(SSiMe3)2 (main product), (Me3SiS)3P(S) and (Me3SiS)3P. All silylated silylphosphines tend to decompose under formation of (Me3Si)2S. (Me3Si)3P7 reacts with sulphur at 20°C (15 h) under decomposition of the P7-cage and formation of (Me3SiS)3P(S). The products of the reaction of 5 with sulphur in hexane solution (molar ratio more than 1:3) undergo readily further reactions at 60°C under cleavage of P? P bonds and splitting off (Me3Si)2S, leading to (Me3SiS)3P(S) and cage molecules like P4S3, P4S7, and P4S10 and P? S-polymers. (Me3SiS)3P(S) isi thermally unstable and decomposes to P4S10 and (Me3Si)2S. Sulphur-containing silylphosphines like (Me3SiS)P(S)Me2 react with HBr at ?78°C under formation of Me3SiBr (quantitative cleavage of the Si? S bond) and Me2P(S)SH, which reacts with HBr to produce H2S and Me2P(S)Br. 相似文献