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31.
Hubert Maehr Hilda V. Cuellar Joanne Smallheer Thomas H. Williams Gino J. Sasso Julius Berger 《Monatshefte für Chemie / Chemical Monthly》1979,110(3):531-540
Streptomyces sp. XT-11989 produces a mixture of two antibiotics with litmus-like indicator properties. One of them was shown to be identical with granaticin, the other was identified as [1S,3S,4S,7R,9R,10S,13R]-4,7,9,10-tetrahydro-5,12-dioxo-4, 6,10,11,13-pentahydroxy-1,9-dimethyl-(1H,3H)-7,10-ethanonaphtho[2,3-c: 6,7-c]dipyran-3-acetic acid and termed granaticinic acid. Microbial production and nuclear magnetic resonance data of these antibiotics are discussed and the antibacterial properties of the antibiotics are compared.
Mikrobielle produkte. II. Granaticinsäure, ein neues Antibiotikum von einem thermophilen Streptomyceten
Zusammenfassung Der Streptomycetenstamm XT-11989 produziert eine Mischung von zwei Antibiotika mit Lakmus-ähnlichen Indikatoreigenschaften. Eines dieser Antibiotika erwies sich als Granaticin, das andere wurde als [1S,3S,4S,7R,9R,10S,13R]-4,7,9,10-tetrahydro-5,12-dioxo-4,6,10,11,13-pentahydroxy-1,9-dimethyl-(1H,3H)-7,10-ethanonaphto[2,3-c: 6,7-c]dipyran-3-essigsäure identifiziert und Granaticinsäure benannt. Mikrobiologische Produktion und Kernresonanzdaten dieser antibiotika werden besprochen und ihre antibakteriellen Eigenschaften verglichen.相似文献
32.
Mark J. Ablowitz Gino Biondini Sarbarish Chakravarty Rudy L. Horne 《Optics Communications》1998,150(1-6):305-318
Collision-induced timing shifts in a wavelength-division multiplexed soliton system are computed when damping, amplification, filtering and positive dispersion management following the loss profile are included. A statistical analysis is presented which takes into account the resulting effect of the large number of collisions occurring in the fiber. Analytic expressions are derived for the root mean square timing jitter and the maximum length of error-free transmission with an arbitrary number of channels. An extensive analysis of system performance corresponding to situations with and without filters and/or dispersion management is carried out. 相似文献
33.
Peak assignment is a complex but important task for analyzing the vibration spectra of surface-bound molecules. Here we describe a simple approach for calculating infrared and Raman spectra for surface-bound molecules using a cluster model approach with quantum capping potentials (QCPs). The utility of the approach is demonstrated by comparisons to the measured high resolution electron energy loss spectra for ethylene on clean silicon. By capping the silicon cluster with QCPs we computed spectra that agree very well with the HREEL spectrum, allowing us to easily assign the experimental peaks. QCPs are similar to effective core potentials, can be used with any ab initio technique and most computational chemistry packages, and their use requires no special expertise. 相似文献
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Gino Bontempelli Salvatore Daniele Gilberto Schiavon Mario Fiorani 《Transition Metal Chemistry》1987,12(4):292-295
Summary Evidence for the ability of the electrogenerated cationic nickel(I) complex [Ni(PPh3)4]+ to promote the isomerization of allylbenzene is reported. However, the corresponding triethylphosphitenickel(I) complex displays no catalytic activity, apparently due to the poor leavinggroup character exhibited by the phosphite. The involvement of a -allylnickel hydride in the isomerization reaction is inferred from a comparison of the results obtained with those for the same reaction promoted by nickel hydride. 相似文献
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We show that the proton can be made absolutely stable, without introducing superheavy bosons, by imposing a global U(1) color symmetry on the Higgs couplings of the theory. Vector-like SU(5) and SU(6) models are discussed in detail. 相似文献
40.
In solution, the self-exchange reactions for oxygen-centered pi-radicals, e.g., PhO. + PhOH <==>PhOH + PhO., are known to occur with low activation enthalpies (E(a) approximately equal to 2 kcal/mol). For the PhO./PhOH couple and, we conclude, for other O-centered pi-radicals, exchange occurs by proton-coupled electron transfer (PCET) with the proton transferred between oxygen electron pairs while the electron migrates between oxygen orbitals orthogonal to the -O- - -H- - -O- transition state plane (Mayer et al. J. Am. Chem. Soc. 2002, 123, 11142). Iminoxyls, R(2)C=NO., are sigma-radicals with substantial spin density on the nitrogen. The R(2)C=NO./R(2)C=NOH self-exchange has a significant E(a) (Mendenhall et al. J. Am. Chem. Soc. 1973, 95, 627). For this exchange, DFT calculations have revealed a counterintuitive cisoid transition state in which the seven atoms, >C=NO- - -H- - -ON=C<, lie in a plane (R = H, Me) or, for steric reasons, two planes twisted at 45.2 degrees (R = Me(3)C). The planar transition state has the two N-O dipoles close to each other and pointing in the same direction and an O- - -H- - -O angle of 165.4 degrees . A transoid transition state for R = H lies 3.4 kcal/mol higher in energy than the cisoid despite a more favorable arrangement of the dipoles and a near linear O- - -H- - -O. It is concluded that iminoxyl/oxime self-exchange reactions occur by a five-center, cyclic PCET mechanism with the proton being transferred between electron pairs on the oxygens and the electron migrating between in-plane orbitals on the two nitrogens (R(N-N) = 2.65 A). The calculated E(a) values (8.8-9.9 kcal/mol) are in satisfactory agreement with the limited experimental data. 相似文献