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21.
Noble metals are well-known to afford highly active, selective and durable catalysts, and have thus been at the core of the development of greener processes. In recent years, however, growing concerns about their scarcity, cost and toxicity has triggered research efforts towards the development of earth-abundant catalysts. In this Current Opinion, recent examples of the use in catalysis of pure earth-abundant metals, earth-abundant metals with minute quantities of noble metals, or earth-abundant metals activated by light are presented. This highlight article showcases the current trends in sustainable organic transformations, catalyzed by nanomaterials. 相似文献
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23.
Petit A Vincent SJ Zwahlen C 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,156(2):313-317
A two-dimensional HSQC-based NMR method, (15)N-COSMO-HSQC, is presented for the rapid determination of homonuclear (3)J(HNHalpha) couplings in (15)N-labeled proteins in solution. Scalar couplings are extracted by comparing the intensity of two separate datasets recorded with and without decoupling of the (3)J(HNHalpha) during a preparation period. The scalar couplings are introduced through a cosine modulation of the peak intensities. The experiment relies on a BIRD sandwich to selectively invert all amide protons H(N) and is very simple to implement. (3)J(HNHalpha) couplings were determined using both the (15)N-COSMO-HSQC and quantitative-J on (15)N-labeled chemokine RANTES. The two experiments show well-correlated values. 相似文献
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25.
An efficient synthesis of o-nitrobenzylcarbonyl compounds is demonstrated through the Swern-type oxidation of readily accessible phenethanol analogues. Reductive cyclization of o-nitrobenzylcarbonyl 3 using catalytic Raney nickel gives 1H-indol-2-yl-1H-quinoline 2 in 95% yield. Hydrolysis of 2 affords the KDR kinase inhibitor 1 in quantitative yield. The examination of the reductive cyclization reaction and optimization of conditions is described. 相似文献
26.
A short and efficient synthesis of UDP-exo-galactofuranosyl-glycal is presented. This molecule displayed an interesting time-dependent inactivation of UDP-galactopyranose mutase, an essential enzyme of the mycobacterial cell wall biosynthesis. 相似文献
27.
Higgs DM Rollo AK Souza MJ Popper AN 《The Journal of the Acoustical Society of America》2003,113(2):1145-1154
Investigations of the development of auditory form and function have, with a few exceptions, thus far been largely restricted to birds and mammals, making it difficult to postulate evolutionary hypotheses. Teleost fishes represent useful models for developmental investigations of the auditory system due to their often extensive period of posthatching development and the diversity of auditory specializations in this group. Using the auditory brainstem response and morphological techniques we investigated the development of auditory form and function in zebrafish (Danio rerio) ranging in size from 10 to 45 mm total length. We found no difference in auditory sensitivity, response latency, or response amplitude with development, but we did find an expansion of maximum detectable frequency from 200 Hz at 10 mm to 4000 Hz at 45 mm TL. The expansion of frequency range coincided with the development of Weberian ossicles in zebrafish, suggesting that changes in hearing ability in this species are driven more by development of auxiliary specializations than by the ear itself. We propose a model for the development of zebrafish hearing wherein the Weberian ossicles gradually increase the range of frequencies available to the inner ear, much as middle ear development increases frequency range in mammals. 相似文献
28.
A general method for the formation of N-hydroxyindoles is demonstrated through a lead-promoted intramolecular reductive cyclization of o-nitrobenzyl ketones and aldehydes under transfer hydrogenation conditions. The N-hydroxyindoles are isolated in high purity and excellent yield (>90%) in an operationally simple procedure. This new method is exemplified by a two-step synthesis of the naturally occurring 1-methoxyindole-3-carboxaldehyde, which is pivotal in many alkaloid total syntheses. 相似文献
29.
Moores A Mézailles N Ricard L Mathey F Le Floch P 《Chemical communications (Cambridge, England)》2003,(15):1914-1915
Reaction of a tetraphenyl-1,2-diphosphinyl dianion with [FeCl2(THF)1.5] or [Ru(COD)(acac)2] yields dianionic complexes which further react with Ph3SnCl to afford the corresponding bis(1,4-diphosphabutadiene) complexes. 相似文献
30.
Audrey Hecka Benoît Maunit Frédéric Aubriet Jean‐François Muller 《Rapid communications in mass spectrometry : RCM》2009,23(6):885-898
Five well‐known active naphtodianthrone constituents of Hypericum perforatum (St John's Wort) extracts have been investigated by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI‐FTICRMS) and ESI‐FTICRMSn. The studied compounds were hypericin, pseudohypericin, protohypericin, protopseudohypericin (biosynthetic precursors of the two former compounds, respectively) and isopseudohypericin (alkaline degradation product of pseudohypericin). Dissociation mass spectrometry measurements performed on the [M–H]? ion presented a variable efficiency as a function of the used activation mode. Sustained off‐resonance irradiation collision‐induced dissociation (SORI–CID) only led to a restricted number of fragment ions. In contrast, IRMPD ensured the detection of numerous product ions. Ions detected in ESI‐FTICRMS and ESI‐FTICRMSn experiments were measured with a very high mass accuracy (typically mass error is lower than 0.5 mDa at m/z close to 500) that allowed unambiguous formulae to be assigned to each signal observed in a mass spectrum. In spite of similar structures, specific fragmentation patterns were observed for the different compounds investigated. This study may be useful in the future to characterize in natural extracts these compounds (or derivatives of these compounds) by liquid chromatography/tandem mass spectrometry (LC/MS/MS) experiments by considering the MS/MS transitions highlighted in this paper. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献