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排序方式: 共有950条查询结果,搜索用时 531 毫秒
851.
Arnold Brossi Fu-Lian Hsu Kenner C. Rice Maria D. Rozwadowska Helmut Schmidhammer Charles D. Hufford Chian Chian Chiang Isabella L. Karle 《Helvetica chimica acta》1981,64(5):1672-1681
Bromination of (?)-4-hydroxy-N-methylmorphinan-6-one ( 3 ), prepared from natural morphine, with 1 mol of bromine in acetic acid, afforded the 1-bromo ketone 5 . The structure of 5 was assigned by 13C-NMR.spectroscopy, and confirmed by X-ray diffraction analysis of its hydrobromide salt. It is suggested that monobromination of synthetic (±)-2,4-dihydroxy-N-formylmorphinan-6-one ( 7 ) takes in principle a similar course, although the 13C-NMR.spectrum of the primary reaction product 9 could not be measured because of insolubility in commonly used solvents. Monobromination of (?)-4-acetoxy-N-formylmorphinan-6-one ( 12 ) of the natural series, and of (±)-2,4-diacetoxy-N-formylmorphinan-6-one ( 8 ) of the synthetic series, followed by treatment of the monobrominated ketones with potassium carbonate in methanol resulted in closure of the O-bridge, and afforded after acid hydrolysis, the corresponding 4,5-epoxy-morphinan-6-ones (?)- 16 and (±)- 17 respectively. This variation of the ring closure reaction represents a novel and convenient method to convert 4-hydroxymorphinan-6-ones into their corresponding 4,5-epoxymorphinan-6-ones, without involving aromatic bromination and with only 1 mol of bromine. 相似文献
852.
Robert E. Linder Günter Barth Edward Bunnenberg Carl Djerassi Lloyd Seamans Albert Moscowitz 《Chemical physics letters》1976,39(3):411-415
The vapor phase magnetic circular dichroism spectrum of the 520 nm band system of glyoxal is reported. The vibrational analysis of this spectrum, and its temperature dependence, extend and confirm the assignments made by Ramsay and his collaborators from magnetic rotation and emission data. 相似文献
853.
854.
Dupont A Eastoe J Barthélémy P Pucci B Heenan R Penfold J Steytler DC Grillo I 《Journal of colloid and interface science》2003,261(1):184-190
Dilute aqueous phase behavior of a novel tris(hydroxymethyl)acrylamidomethane (THAM)-derived telomer bearing a perfluorohexyl hydrophobic chain, F6THAM6, has been investigated. Fluorinated polyhydroxy surfactants of this kind find use in emerging biomedical applications. Neutron reflection (NR) and drop volume surface tension (DVT) methods have been used to determine the critical micelle concentration (cmc=4.7 x 10(-4) mol x dm(-3)) and surface adsorption parameters (at the cmc NR gives a molecular area a(cmc)=67.4 and 62 A(2) and surface excess gamma(cmc)=2.46 x 10(-6) mol x m(-2)). The aggregation structures were determined by small-angle neutron scattering (SANS), indicating globular (polydisperse spheres) micelles of radius approximately 30 A are present. These findings are compared with literature on surfactants with related structures, to identify how the unusual molecular structure of F6THAM6 affects surfactant properties. 相似文献
855.
Endocytosis at reduced temperature has been used to define and characterize endosome subpopulations. Thus, the temperature sensitivity of endosome subpopulations involved in transport to lysosomes and transcytosis in rat hepatocytes was analyzed applying endosome labeling in the isolated perfused rat liver with route-specific ligands in combination with temperature shift protocols. Free-flow electrophoresis (FFE) that separates membranes and organelles based on their surface charge was then applied to isolate functional endosomes. Using asialoorosomucoid (ASOR) and polymeric immunoglobulin A (pIgA) as specific ligands of the lysosomal and transcytotic route, respectively, two distinct endosome subpopulations along either pathway were separated by FFE. Upon a short (1-3 min) internalization at 37 degrees C, 125I-ASOR and fluorescein isothiocyanate (FITC)-pIgA were colocalized in common early endosomes. Following a 5-10 min chase of the ligands at 37 degrees C endosomes labeled with 125I-ASOR were separated from endosomes labeled with FITC-pIgA, indicative of two distinct late compartments along the lysosomal and transcytotic route. Internalization at 16 degrees C resulted in accumulation of both ligands in common early endosomes and, consequently, in inhibition of transport to lysosomes and transcytosis. When 125I-ASOR or 125I-pIgA were first chased into late compartments at 37 degrees C and the temperature was subsequently lowered to 16 degrees C, biliary secretion of 125I-ASOR-derived counts was arrested, while biliary output of 125I-pIgA continued. In summary, ASOR en route to lysosomes can be blocked in early as well as in late endosomes at 16 degrees C, while biliary secretion of pIgA cannot be prevented by temperature reduction once the ligand had been transferred from early to late compartments. 相似文献
856.
E. J. Vandenberg W. R. Diveley L. J. Filar S. R. Patel H. G. Barth 《Journal of polymer science. Part A, Polymer chemistry》1989,27(11):3745-3757
Poly[N,N′-(sulfo-phenylene)phthalamid]es and poly[N,N′-(sulfo-p-phenylene)pyromellitimide] were prepared in water-soluble form and were found to have unique solution properties, similar in some respects to xanthan. The polymer most investigated, poly[N,N′-(sulfo-p-phenylene)terephthalamide] (PPT-S), is produced as the dimethylacetamide (DMAC) salt by the solution polymerization of 2,5-diaminobenzenesulfonic acid with terephthaloyl chloride in DMAC containing LiCl. The isolated polymer requires heating in water to dissolve; the resulting cooled solutions are viscous or gels at concentrations as low as 0.4%. They are highly birefringent, exhibit circular dichroism properties, and are viscosity-sensitive to salt. Solutions of this polymer mixed with those of guar or hydroxyethyl cellulose give significantly enhanced viscosity. The polymer is relatively low molecular weight, ca. 5000 estimated from viscosity data. Some meta and para isomeric analogs of PPT-S were prepared; these polymers have similar properties except they are more soluble in water, and higher concentrations are required to obtain significant viscosity. Poly[N,N′-(sulfo-p-phenylene) pyromellitimide] (PIM-S) was prepared similarly from 2,5-diaminobenzenesulfonic acid and pyromellitic dianhydride. Its aqueous solution properties are similar to those of PPT-S. It appears that these relatively low-molecular-weight rigid-chain polymers associate in water to form a network that results in viscous solutions at low concentrations. 相似文献
857.
Pierluigi Mercandelli Angelo Sironi Isabella Camurati 《Journal of organometallic chemistry》2007,692(21):4784-4791
Polypropene and poly(1-butene) have been synthesized under very similar experimental conditions with a series of MAO-activated C2-symmetric and C1-symmetric ansa-zirconocenes. The C1-symmetric zirconocenes bearing the bilaterally symmetric fluorenyl or bis(2-methylthieno)cyclopentadienyl ligand connected through a dimethylsilyl bridge to substituted indenyl ligands produce isotactic polybutene of similar or higher molecular mass and with noticeably higher isotacticity, compared to isotactic polypropene prepared with the same catalysts under comparable conditions. Structural and mechanistic reasons for such behavior are discussed on the basis of QM/MM calculations. 相似文献
858.
Ramon Subiros-Funosas Vivian Cheuk Lam Ho Nicole D. Barth Lorena Mendive-Tapia Morena Pappalardo Xavier Barril Ruoyu Ma Cheng-Bin Zhang Bin-Zhi Qian Miquel Sintes Ouldouz Ghashghaei Rodolfo Lavilla Marc Vendrell 《Chemical science》2020,11(5):1368
Keratin 1 (KRT1) is overexpressed in squamous carcinomas and associated with aggressive pathologies in breast cancer. Herein we report the design and preparation of the first Trp-based red fluorogenic amino acid, which is synthetically accessible in a few steps and displays excellent photophysical properties, and its application in a minimally-disruptive labelling strategy to prepare a new fluorogenic cyclopeptide for imaging of KRT1+ cells in whole intact tumour tissues.Trp(redBODIPY) is the first red-emitting Trp-based amino acid for the preparation of fluorogenic peptides with retention of target binding affinity. 相似文献
859.
P. V. Chliapnikov L. N. Gerdyukov G. N. Khromova A. I. Kurnosenko V. N. Riadovikov G. I. Sorokin V. F. Tchunikhin V. A. Uvarov A. P. Vorobjev M. Barth E. A. De Wolf F. Verbeure F. Grard K. Kesteman CERN-USSR Collaboration 《Zeitschrift fur Physik C Particles and Fields》1982,12(2):99-103
New experimental results are presented on inclusive production properties of \(\bar \Sigma ^{ * + } \) (1385) and \(\bar \Sigma ^{ * + } \) (1385) inK + p interactions at 32 GeV/c. The analysis is based on significantly larger statistics than previously available. A comparison is also made of invariantx-distributions ofK 0/ \(\bar K^0 \) , \(\bar \Lambda \) and \(\bar \Xi ^ + \) and of \(\bar \Sigma ^{ * \pm } \) (1385) andK *+(892). These spectra exhibit regularities expected from the quark-recombination picture when it is assumed that the strange mesons and antibaryons are produced off the strange \(\bar s\) -valence-quark in the incidentK + meson. Transverse momentum distributions are also presented forK *+(892) and \(\bar \Sigma ^{ * \pm } \) (1385) and found to be very similar. The results on strange antibaryon average multiplicities disagree strongly with a recent version of the additive quark model. 相似文献
860.
M. Barth A. E. De Wolf D. P. Johnson P. Theocharopoulos H. Drevermann Y. Goldschmidt-Clermont J. P. Porte R. T. Ross S. Squarcia C. Caso R. Contri F. Fontanelli R. Monge U. Trevisan J. F. Baland J. Beaufays J. Hanton F. Grard P. A. van der Poel L. Gatignon D. J. Schotanus A. Stergiou R. T. Van de Walle V. V. Brizgalov P. V. Chliapnikov A. B. Fenyuk I. A. Gritsaenko O. V. Kasian V. M. Kubic S. B. Lugovsky V. I. Nikolaenko Y. L. Petrovykh V. M. Ronjin V. A. Yarba 《Zeitschrift fur Physik C Particles and Fields》1982,16(2):111-117
Results are presented onK + p elastic scattering and on the reactionK + p→K + pπ+π? at 70 GeV/c. For the elastic channel, we measured the total ((2.29±0.04)mb) and differentialdσ/dt cross sections. The reactionK + p→K + pπ+π? has a total cross section of (470±23) μb and is shown to be dominated by diffractive dissociation processes. The contributions of the quasi-two-body channels $$K^ + p \to K*^0 (890)\Delta ^{ + + } (1,236)$$ and $$K^ + p \to K*^0 (1,430)\Delta ^{ + + } (1,236)$$ and of the Double-Pomeron Exchange (DPE) processes are estimated. 相似文献