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171.
The structures and biosynthesis of the sesquiterpenoid metabolites of Botrytis cinerea and their relationship to the presilphiperfolanes are reviewed. The development of a novel strategy for the control of this phytopathogenic fungus based on analogues of these metabolites is described. There are 75 references. 相似文献
172.
Roberts TC Smith PA Cirz RT Romesberg FE 《Journal of the American Chemical Society》2007,129(51):15830-15838
The growing threat of untreatable bacterial infections has refocused efforts to identify new antibiotics, especially those acting by novel mechanisms. While the inhibition of pathogen proteases has proven to be a successful strategy for drug development, such inhibitors are often limited by toxicity due to their promiscuous inhibition of homologous and mechanistically related human enzymes. Unlike many protease inhibitors, inhibitors of the essential type I bacterial signal peptidase (SPase) may be more specific and thus less toxic due to the enzyme's unique structure and catalytic mechanism. Recently, the arylomycins and related lipoglycopeptide natural products were isolated and shown to inhibit SPase. The core structure of the arylomycins and lipoglycopeptides consists of a biaryl-linked, N-methylated peptide macrocycle attached to a lipopeptide tail, and in the case of the lipoglycopeptides, a deoxymannose moiety. Herein, we report the first total synthesis of a member of this group of antibiotics, arylomycin A2. The synthesis relies on Suzuki-Miyaura-mediated biaryl coupling, which model studies suggested would be more efficient than a lactamization-based route. Biological studies demonstrate that these compounds are promising antibiotics, especially against Gram-positive pathogens, with activity against S. epidermidis that equals that of the currently prescribed antibiotics. Structural and biological studies suggest that both N-methylation and lipidation may contribute to antibiotic activity, whereas glycosylation appears to be generally less critical. Thus, these studies help identify the determinants of the biological activity of arylomycin A2 and should aid in the design of analogs to further explore and develop this novel class of antibiotic. 相似文献
173.
174.
Szanyi J Kwak JH Kim do H Wang X Hanson J Chimentao RJ Peden CH 《Chemical communications (Cambridge, England)》2007,(9):984-986
Exposure of NO(2)-saturated BaO/gamma-Al(2)O(3) NO(x) storage materials to H(2)O vapour results in the conversion of surface nitrates to Ba(NO(3))(2) crystallites, causing dramatic morphological changes in the Ba-containing phase, demonstrating a role for water in affecting the NO(x) storage/reduction properties of these materials. 相似文献
175.
A method for the determination of colorimetric uncertainties has been developed in order to meet the requirements for accreditation by the UK accreditation service (UKAS), which include a statement of uncertainty for all certified quantities. The values of the principal sources of spectrophotometric uncertainty are first determined and are used to calculate corresponding components of colorimetric uncertainty using a simple model. The components of uncertainty analysed are 100% level (diffuse reflectance), photometric non-linearity, dark level and wavelength error. Bandwidth error is not significant for NPL surface colour standards because a small bandwidth is always used.
The gloss trap error and specular beam error are determined and corrected so that only the uncertainties after correction need be considered. These can be treated as components of dark level uncertainty. The uncertainties are determined for the following colour data: x, y, Y, u′, v′, L*, a* and b* for the CIE 10° Standard Observer and the CIE Standard Illuminant D65 for three geometries: specular included, specular excluded and 0°/45°. These are now quoted routinely on NPL certificates for ceramic colour standards, white and black ceramic tile standards and Russian opal standards. 相似文献
176.
Hanson J.D. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1999,27(6):1588-1595
Non axisymmetric correction coils can be highly effective at canceling the low order magnetic islands generated by magnetic field errors. Correction coil currents which, by themselves, mould produce an island of the same size and opposite phase as the error field, will result in cancelled magnetic islands. In computing the magnetic island sizes and toroidal phases of perturbations, the use of a straight-cylinder approximation can cause substantial error. An n=1 error with arbitrary phase can be corrected at a single resonant surface with one set of four correction coils. Correcting higher n harmonics requires more coils toroidally. Correcting same-n errors at more than one rational surface requires more correction coil sets 相似文献
177.
We report a new imaging diagnostic suitable for measurements of infrared-active molecules, namely infrared planar laser-induced
fluorescence (IR PLIF), in which a tunable infrared source is used to excite vibrational transitions in molecules and vibrational
fluorescence is collected by an infrared camera. A nanosecond-pulse Nd:YAG-pumped KTP/KTA OPO/OPA system is used to generate
12 mJ of tunable output near 2.35 μm which excites the 2ν band of carbon monoxide (CO); fluorescence resulting from excited
CO is collected at 4.7 μm by using an InSb focal plane array. Quantitative, high-SNR PLIF imaging of gas-phase CO is demonstrated
at a 10-Hz acquisition rate with a minimum detection limit of 1350 ppm at 300 K.
Received: 30 July 1999 / Published online: 16 September 1999 相似文献
178.
Michael Rhrig Eric L. Petersen David F. Davidson Ronald K. Hanson Craig T. Bowman 《国际化学动力学杂志》1997,29(10):781-789
The rate coefficient of the reaction CH+O2 → products was determined by measuring CH-radical concentration profiles in shock-heated 100–150 ppm ethane/1000 ppm O2 mixtures in Ar using cw, narrow-linewidth laser absorption at 431.131 nm. Comparing the measured CH concentration profiles to ones calculated using a detailed kinetics model, yielded the following average value for the rate coefficient independent of temperature over the range 2200–2600 K: The experimental conditions were chosen such that the calculated profiles were sensitive mainly to the reactions CH+O2 → products and CH3+M → CH+H2+M. For the methyl decomposition reaction channel, the following rate-coefficient expression provided the best fit of the measured CH profiles: Additionally, the rate coefficient of the reaction CH2+H→CH+ H2 was determined indirectly in the same system: © 1997 John Wiley & Sons, Inc. 相似文献
179.
180.
Xing Chao Guofeng Shen Kai Sun Zhenhai Wang Qinghui Meng Shengkai Wang Ronald K. Hanson 《Proceedings of the Combustion Institute》2019,37(2):1345-1353
Cavity-enhanced absorption spectroscopy (CEAS) has generated much interest in shocktube kinetics studies because of its recent success in achieving improved sensitivity and high time resolution with robust optical alignment. While recent progress demonstrated experimental schemes including off-axis scanned-wavelength approach and on-axis ps-pulsed laser approach, that both successfully suppressed the laser-cavity coupling noise, this paper develops a theoretical model to predict the CEAS sensor performance that can be used as a design tool applicable to more generalized cases. The method models the optical field in the cavity based on the decentered Gaussian beam model, from which the cavity transmission spectrum and the laser-cavity coupling noise can be numerically calculated. The simulation results predict sensor performance for different cavity configurations and laser characteristics, including various degrees of laser-cavity mode-matching, laser linewidths, scanning rates, and cavity filling conditions. Simulation with example wavelengths in the ultraviolet, near-infrared, and mid-infrared showed increasing mode-matched beam waist size for increasing wavelengths. An off-axis alignment scheme was found to be capable of suppressing the coupling noise by two orders-of-magnitude at a moderate laser linewidth of 1?GHz. Coupling noise level on the order of 1e-5 for scanned-wavelength off-axis alignment case with a narrowband mid-infrared laser was obtained by model calculation and agreed with experimental results within acceptable uncertainty range. The developed method can serve to guide future design and optimization of CEAS system in shocktube studies. 相似文献