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211.
The "epimerisation" of UDP-GlcNAc to ManNAc, the first step in the biosynthesis of sialic acids, is catalyzed by UDP-GlcNAc 2-epimerase. In this paper we report the synthesis of transition state based inhibitors of this enzyme. To mimic the assumed first transition state of this reaction (TS 1), we designed and synthesized the novel UDP-exo-glycal derivatives 1-4. We also report herein the synthesis of 5 and 6, the first C-glycosidic derivatives of 2-acetamidoglucal, and the synthesis of the ketosides 7 and 8, which were designed as bis-substrate analogue and bis- product analogue, respectively, to mimic the second step of the reaction via the assumed second transition state TS 2. 相似文献
212.
213.
N. Rösch P. Sandl P. Knappe A. Görling B. I. Dunlap 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1989,12(1-4):547-550
LCGTO Xα model cluster calculations have been carried out to rationalize the shape of the CO 1π band of the chemisorption system CO/Ni(111) observed in angular resolved photoemission. The splitting induced by substrate interaction at twofold bridging sites (0.4 eV) is much smaller than the value deduced from experiment (1.2 eV). From calculations on (CO) n clusters lateral adsorbate interaction is estimated to cause a sizable broadening of the 1π band (1.2eV, in satisfactory agreement with experiment), but essentially no splitting (?0.1 eV). Therefore, rehybridisation due to local interaction does not seem to suffice as an explanation for the observed shape of the CO 1π band. 相似文献
214.
Zusammenfassung Mit einer Drahtexplosion von Silberdraht in einer Brom/Argon-Atmosphäre wurde AgBr-Aerosol hergestellt und auf einer Quarzglasplatte niedergeschlagen. Bei Bestrahlung der so gebildeten Schicht im UV-Spektralbereich von 300–400 nm ergab sich eine Schwärzung, die nach Unterbrechung der Einstrahlung wieder zurückging (Phototropie), wenn die Schicht mit Bromdampf in Berührung stand. Mit Laserlichtbeleuchtung wurde an mehreren Schichten der zeitliche Verlauf der Remission gemessen und dabei Bestrahlungsstärke, Bromdampfdichte und Belegungsdichte der Schicht variiert. Zunehmender Bromgehalt hat aufhellende Wirkung. Die gemessenen Schwärzungs- und Regenerationszeiten sind etwa 10mal kleiner als die von handelsüblichen phototropen Gläsern. Zur phänomenologischen Deutung der Ergebnisse wurde ein einfaches reaktionskinetisches Modell aufgestellt, das 4 Konstanten enthält, die aus dem Experiment bestimmt wurden. Dabei wurde die Konzentrationsabhängigkeit der die Remission kennzeichnendenKubelka-Munk-Funktion herangezogen.Summary A silver wire exploding in an atmosphere of bromine and argon provides the generation of a silver bromide aerosol which is precipitated on a quartz glass plate. As the layer formed in this way is submitted to ultraviolet radiation ranging from 300 to 400 nm, a blackening occurs which, after interruption of the emitted radiation, decreases again (phototropy) when the layer is in contact with the bromine vapor. A laser beam is used to measure the development with time of the reflectance of various layers. For this the irradiante, bromine vapor concentration, and surface density of the layer are being varied. The increase in the content of bromine causes the blackening to attenuate. Both the measured blackening and regeneration durations are approximately ten times shorter than those of commercially available phototropec glasses. In order to explain these phenomena as well as the relating results, a simple kinetic model was established including four constants which were determined from the experiment. For this theKubelka-Munk function was used characterizing the reflectance as a function of concentration.
Mit 10 Abbildungen 相似文献
Mit 10 Abbildungen 相似文献
215.
The half-sandwich type compounds C5H5Rh[P(OR)3]2 (R = CH3, C2H5, C6H5, p-CH3C6H4, p-ClC6H4) have been prepared from [(P(OR)3)2RhCl]2 and NaC5H5. The NMR. data as well as the IR. and mass spectra of the new compounds will be discussed. The preparation of C5H5Rh(CO)P(OC2H5)3 is also reported. 相似文献
216.
E. Ziegler Th. Kappe H. G. Foraita L. F. Werner 《Monatshefte für Chemie / Chemical Monthly》1970,101(3):923-931
Zusammenfassung Die Darstellung von polymeren Indigofarbstoffen (PI) nach dem Verfahren vonZiegler undKappe
2, 3 wird beschrieben. Ausgehend von Benzidin (1 a) und Tolidin (1 b) erhält man so diePI
6 a bzw.6 b. In analoger Weise wird aus Tetrahydrochinoxalin (7), der N,N-überbrücktePI
12 gewonnen.
Aus den Dissertationen vonH. G. Foraita undL. F. Werner, Universität Graz, Januar bzw. Juni 1963. 相似文献
Syntheses of heterocycles, CXLVI: The synthesis of polymeric indigos with potential semiconductor properties
The synthesis of polymeric indigos (PI) according to the procedure ofZiegler andKappe 2, 3 is described. Starting with benzidine (1 a) or tolidine (1 b) thePI 6 a and6 b, resp., are obtained. In a similar way the N,N-bridgedPI 12 is synthesized from tetrahydroquinoxaline (7).
Aus den Dissertationen vonH. G. Foraita undL. F. Werner, Universität Graz, Januar bzw. Juni 1963. 相似文献
217.
To avoid changes in the original As species distribution in natural water after sampling, a method of immediate separation
of As(V) by anion exchange at the sampling site was developed. The procedure consists of two steps. The total concentration
of arsenic is determined in one part of the water sample acidified on site. Another part of the water samples is pressed through
a column filled with an anion exchanger. The As(III) species that is not redox-stable remains in the effluent of the sorbents
column and can be analyzed with conventional methods after stabilization by addition of conc. HNO3. As(V) is sorbed by the exchanger material. The As(V) concentration can be calculated as the difference between Assol and As(III), neglecting very low contents of methylated species.
Oxidation of Fe(II) by air followed by co-precipitation of arsenic with iron hydroxide was applied in field experiments to
minimize the As concentration in seepage and mining water. 相似文献
218.
A method is described which uses the ammonium salt of 2,2′-azino-di-[3-ethyl-benzothiazoline-(6)-sulphonic acid] as a redox indicator for the photometric determination of glucose with glucose oxidase and peroxidase. The sensitivity of this method is more than four times better than the method using o-dianisidine. The test solution including all reagents necessary for the determination of glucose is highly stable. 相似文献
219.
The azavinylidene osmium complex [(mes)Os(=N=CPh2(PiPr3)]PF6 (3; MES = 1.3.5-C6H3Me3), which was prepared in two steps from [(mes)OsCl2(PiPr3], CH3CO2Na/KPF6 and HN=CPh2, has been shown to react with trifluoracetic acid to give the isomeric heterocycle [(mes)
6H4)(Pi Pr3)]PF6 (4) in almost quantitative yield. With CF3CO2D, the monodeuterated compound 4-d4,containing a N---D unit in the five-membered ring, is obtained. An analogue of 4 with the composition [(mes)
6H4)(PMe3)]X(X = PF6 14a, SbF6 14b) has been made both from [(mes)Os(=N=CPh2)(PMe3)]PF6 12 and CF3CO2H and from [(mes)OsCl(NH= CPh2(PMe3)]SbF6 (13) and CF3CO2Ag. The reaction of 4 with NaH or KOtBu gives the uncharged heterocycle [(mes)
6 H4)(PiPr3)] (15), while treatment of [(mes)OsCl 2(NH=CPh2)] (19) with NaStBu gives the related complex [(mes)
6H4)(St Bu)] (20). The crystal structure of 4 has been determined. kw]Osmium; Azavinylidene; Cyclometallation; Crystal structure; Arene complexes 相似文献
220.
The PF6 salts of the new cationic hexamethylborazinerhodium(I) complexes of general formula [Rh(Me3B3N3Me3)(LL′)]+ (LL′= 1,5-cyclooctadiene, norbornadiene, tetrafluorobenzobarrelene, trimethyltetrafluorobenzobarrelene, L = L′ = ethylene, CO) have been prepared from the reaction between [RhCl(LL′)]2, Me3B3NMe3, and AgPF6 in dichloromethane. These complexes are very labile, undergoing rapid ring ligand exchange in solution with σ and π-donor ligands. The synthesis of [Rh(η6-naphthalene)(COD)]PF6 is also described. The properties and NMR and IR spectroscopic characteristics of the new compounds are briefly discussed. 相似文献