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81.
Ostash B Rix U Rix LL Liu T Lombo F Luzhetskyy A Gromyko O Wang C Braña AF Méndez C Salas JA Fedorenko V Rohr J 《Chemistry & biology》2004,11(4):547-555
A 3 kb DNA fragment from the Streptomyces globisporus 1912 landomycin E (LaE) biosynthetic gene cluster (lnd) was completely sequenced. Three open reading frames were identified, lndGT4, lndZ4, and lndZ5, whose probable translation products resemble a glycosyltransferase, a reductase, and a hydroxylase, respectively. Studies of generated mutants from disruption and complementation experiments involving the lndGT4 gene allowed us to determine that LndGT4 controls the terminal L-rhodinose sugar attachment during LaE biosynthesis and that LndZ4/LndZ5 are responsible for the unique C11-hydroxylation of the landomycins. Generation of the novel landomycins F, G, and H in the course of these studies provided evidence for the flexibility of lnd glycosyltransferases toward their acceptor substrates and a basis for initial structure-activity relationships within the landomycin family of antibiotics. 相似文献
82.
Uwe Klingebiel Dieter Bentmann Anton Meller 《Journal of organometallic chemistry》1978,144(3):381-388
Aminofluorsilanes are obtained by the reaction of fluorosilanes with the lithium salts of the corresponding amines. The reaction of aminofluorosilanes with butyllithium in a (2 + 2)cyclo addition reaction leads to the formation of fourmembered silicon-nitrogen ring compounds. The mechanism of the reaction is discussed, the mass, 1H and 19F NMR spectra of the compounds are reported. 相似文献
83.
Uwe Einmahl 《Probability Theory and Related Fields》1992,92(2):177-194
Summary In a previous paper we obtained upper and lower class type results refining the bounded LIL for sums of iid Hilbert space valued mean zero random variables, whose covariance operators satisfy certain regularity assumptions. We now establish precise convergence rates for the bounded LIL in the non-regular case. It turns out that the almost sure behavior in this case is entirely different from the behavior in the previous situation.Supported in part by NSF Grant DMS 90-05804 相似文献
84.
Normen Peulecke Andreas Ohff Wolfgang Baumann Rhett Kempe Vladimir V. Burlakov Uwe Rosenthal 《Journal of organometallic chemistry》1996,520(1-2):235-239
The reaction of Cp2Zr(L)(η2-Me3SiC2) (L = THF, py) with equimolar amounts of H2C = CMe-CHO at room temperature depends strongly on the ligands L and the solvents that are used. With L = THF, in the THF solution the insertion product 1 was isolated, whereas by conducting the reaction in n-hexane solution an alkyne substitution with 1,4-coordination of the methacrolein takes place and the binuclear complex [ 2 was obtained. In conttrast, with L = py (a stronger ligand) only a 1:1 ratio of 1 and 2 was observed in both THF and in n-hexane. At 50°C complex 1 was converted into 2 and the alkyne was eliminated quantitatively.
Complexes 1 and 2 were characterized by IR and NMR spectroscopical measurements and 1 by an additional X-ray structure determination. 相似文献
85.
Fluoro- und aminofluoro-silanes react with the lithium salt of N,O-bis(trimethylsilyl)hydroxylamine under LiF elimination and substitution. Alkyl- and amino-fluorosilanes give O-fluorosilyl-N,N-bis(trimethylsilyl)hydroxylamines, arylfluorosilanes give N-fluorosilyl-N,O-bis(trimethylsilyl)hydroxylamines. By the further reaction of O-difluorosilyl-N,N-bis(trimethylsilyl)hydroxylamine with the lithiated hydroxylamine, O,O′-fluoromethylsilyldi[N,N-bis(trimethylsilyl)hydroxylamine] is formed. On heating N-difluorophenylsilyl-N,O-bis(trimethylsilyl)hydroxylamine di[fluorophenylsilyl(methyl)amino]pentamethylsiloxane is formed by methyl group migration. The NMR and mass spectra of the compounds are reported. 相似文献
86.
Th. Freudenberg W. Radloff H. -H. Ritze V. Stert K. Weyers F. Noack I. V. Hertel 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1996,36(3-4):349-364
The formation of protonated and unprotonated ammonia cluster ions is studied by femtosecond two colour two photon pump-probe techniques applied to (NH3) n and (ND3) n clusters withn up to 8. The fourth harmonic (~ 200 nm, 6.2 eV, 160 fs) of a Ti: Sapphire laser pulse is used to excite the clusters in a state corresponding to theà state of NH3 while the third harmonic (267 nm, 4.65 eV) is used for the subsequent ionisation step. Employing a combination of the optical Bloch equations for the excitation process and rate equations for the cluster dynamics we calibrate the zero time delay and carefully analyse the time dependence of the pump-probe signal. Several distinct intermediate steps in the time evolution can be distinguished, having characteristic time constants ranging from 40 fs to over 100 ps. They are discussed in a consistent scheme for the excitation, ionisation and protonation dynamics, accounting also for characteristic differences observed between deuterated and undeuterated species. A particularly remarkable time dependence of the homogeneous (NH3) 2 + cluster ion signal is interpreted as a fingerprint of internally protonated neutral precursors of the type NH3NH2NH4. 相似文献
87.
Uwe Klingebiel Detlev Enterling Lutz Skoda Anton Meller 《Journal of organometallic chemistry》1977,135(2):167-172
Fluorosilyl substituted cyclosilazanes are formed by treating lithium salts of hexamethylcyclotri- and octa-methylcyclotetrasilazanes with silicon tetrafluoride and organo-substituted silicon fluorides. Disubstituted compounds are obtained by the reaction of dilithium hexamethylcyclotrisilazane with silicon fluorides or by the reaction of lithium hexamethylcyclotrisilazane with silicon fluorides at higher temperature. Cyclosilazanes with bulky ligands react with butyllithium with elimination of butane as a first step and then react further with a silicon fluoride compound, with LiF-elimination, to give a mixed substituted cyclosilazane. Ring coupling through a silicon bridge is achieved by the reaction of a fluorosilyl-substituted cyclotrisilazane with lithium hexamethylcyclotrisilazane. The mass,1H and19F NMR spectra of the compounds are reported. 相似文献
88.
Alkoxylierung von bis(trimethylsilyl)-aminofluorsilanen,sowie siloxanbildung unter äthereliminierung
Uwe Klingebiel Dietrich Fischer Anton Meller 《Journal of organometallic chemistry》1975,85(2):141-147
The reaction of bis(trimethylsilyl)aminofluorsilanes, (Me3Si)2NSiF2R (R = CH3 or F), with sodium alcoholates or sodium phenylate yields under elimination of NaF alkoxy- and aryloxy-aminofluorosilanes of the composition (Me3Si)2NSiF(R)OR′(R′ = CH3, C2H5, C3H7, C6H5). A disiloxane is formed by thermal elimination of diethyl ether from bis(trimethylsilyl)aminomethylfluoroethoxysilane. The IR, mass, 1H and 19F NMR spectra of the above-mentioned compounds are reported. ab]Die Reaktion von Bis(trimethylsilyl)-aminofluorsilanen des Typs (Me3Si)2NSiF2R (R = F, CH3) mit Natriumalkoholaten und Natriumphenolat führt unter NaF-Abspaltung zu Alkyl- und Aryloxyaminofluorsilanen der Zusammensetzung: (Me3Si)2NSiF(R)OR′ (R′ = CH3, C2H7, C6H5, C6H5). Ein Disiloxan könnte durch die thermische Eliminierung von Diäthyläther aus Bis(trimethylsilyl)aminomethyl-fluor-äthoxy-silylarnin erhalten werden.Die IR-, Massen-, 1H- und 19F-NMR-Spektren der dargestellten Verbindungen werden mitgeteilt. 相似文献
89.
Hu Xing Yiting Zhang Markus Krmer Ann-Kathrin Kissmann Marius Henkel Tanja Weil Uwe Knippschild Frank Rosenau 《Molecules (Basel, Switzerland)》2022,27(17)
Recent studies have demonstrated that changes in the abundance of the intestinal bacterium Blautia producta, a potential probiotic, are closely associated with the development of various diseases such as obesity, diabetes, some neurodegenerative diseases, and certain cancers. However, there is still a lack of an effective method to detect the abundance of B. producta in the gut rapidly. Especially, DNA aptamers are now widely used as biometric components for medical testing due to their unique characteristics, including high chemical stability, low production cost, ease of chemical modification, low immunogenicity, and fast reproducibility. We successfully obtained a high-affinity nucleic acid aptamer library (B.p-R14) after 14 SELEX rounds, which efficiently discriminates B. producta in different analysis techniques including fluorometric suspension assays or fluorescence microscopy from other major gut bacteria in complex mixtures and even in human stool samples. These preliminary findings will be the basis towards aptamer-based biosensing applications for the fast and reliable monitoring of B. producta in the human gut microbiome. 相似文献
90.
Marine Rémy Dr. Iwona Nierengarten Boram Park Dr. Michel Holler Dr. Uwe Hahn Dr. Jean-François Nierengarten 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(33):8492-8499
Stable pillar[5]arene-containing [2]rotaxane building blocks with pentafluorophenyl ester stoppers have been efficiently prepared on a multi-gram scale. Reaction of these building blocks with various nucleophiles gave access to a wide range of [2]rotaxanes with amide, ester or thioester stoppers in good to excellent yields. The rotaxane structure is fully preserved during these chemical transformations. Actually, the addition-elimination mechanism at work during these transformations totally prevents the unthreading of the axle moiety of the mechanically interlocked system. The stopper exchange reactions were optimized both in solution and under mechanochemical solvent-free conditions. While amide formation is more efficient in solution, the solvent-free conditions are more powerful for the transesterification reactions. Starting from a fullerene-functionalized pillar[5]arene derivative, this new strategy gave easy access to a photoactive [2]rotaxane incorporating a C60 moiety and two Bodipy stoppers. Despite the absence of covalent connectivity between the Bodipy and the fullerene moieties in this photoactive molecular device, efficient through-space excited state interactions have been evidenced in this rotaxane. 相似文献