A powerful chiral counterion strategy for asymmetric transition metal catalysis     

Hamilton GL  Kang EJ  Mba M  Toste FD 《Science (New York, N.Y.)》2007,317(5837):496-499

Traditionally, transition metal-catalyzed enantioselective transformations rely on chiral ligands tightly bound to the metal to induce asymmetric product distributions. Here we report high enantioselectivities conferred by a chiral counterion in a metal-catalyzed reaction. Two different transformations catalyzed by cationic gold(I) complexes generated products in 90 to 99% enantiomeric excess with the use of chiral binaphthol-derived phosphate anions. Furthermore, we show that the chiral counterion can be combined additively with chiral ligands to enable an asymmetric transformation that cannot be achieved by either method alone. This concept of relaying chiral information via an ion pair should be applicable to a vast number of metal-mediated processes.  相似文献   

Comment on "A persistent oxygen anomaly reveals the fate of spilled methane in the deep Gulf of Mexico"     

Joye SB  Leifer I  MacDonald IR  Chanton JP  Meile CD  Teske AP  Kostka JE  Chistoserdova L  Coffin R  Hollander D  Kastner M  Montoya JP  Rehder G  Solomon E  Treude T  Villareal TA 《Science (New York, N.Y.)》2011,332(6033):1033; author reply 1033

Kessler et al. (Reports, 21 January 2011, p. 312) reported that methane released from the 2010 Deepwater Horizon blowout, approximately 40% of the total hydrocarbon discharge, was consumed quantitatively by methanotrophic bacteria in Gulf of Mexico deep waters over a 4-month period. We find the evidence explicitly linking observed oxygen anomalies to methane consumption ambiguous and extension of these observations to hydrate-derived methane climate forcing premature.  相似文献   

The evolution of modern eukaryotic phytoplankton   总被引：1，自引：0，他引：1  

Falkowski PG  Katz ME  Knoll AH  Quigg A  Raven JA  Schofield O  Taylor FJ 《Science (New York, N.Y.)》2004,305(5682):354-360

The community structure and ecological function of contemporary marine ecosystems are critically dependent on eukaryotic phytoplankton. Although numerically inferior to cyanobacteria, these organisms are responsible for the majority of the flux of organic matter to higher trophic levels and the ocean interior. Photosynthetic eukaryotes evolved more than 1.5 billion years ago in the Proterozoic oceans. However, it was not until the Mesozoic Era (251 to 65 million years ago) that the three principal phytoplankton clades that would come to dominate the modern seas rose to ecological prominence. In contrast to their pioneering predecessors, the dinoflagellates, coccolithophores, and diatoms all contain plastids derived from an ancestral red alga by secondary symbiosis. Here we examine the geological, geochemical, and biological processes that contributed to the rise of these three, distantly related, phytoplankton groups.  相似文献   

Pest management programmes in vineyards using male mating disruption   总被引：1，自引：0，他引：1  

Harari AR  Zahavi T  Gordon D  Anshelevich L  Harel M  Ovadia S  Dunkelblum E 《Pest management science》2007,63(8):769-775

Israeli vine growers have been reluctant to adopt the mating disruption technique for control of the European vine moth, Lobesia botrana Den. & Schiff. Since the chemically controlled honeydew moth, Cryptoblabes gnidiella Mill., coexists with the European vine moth, growers have maintained that the use of mating disruption would fail to bring about a significant reduction in pesticide use. In this study, the efficacy of mating disruption techniques against C. gnidiella was tested, as well as the effect of these methods on pesticide use and damage to clusters when the method was employed against both of the pests in wine grapes. Comparisons were made between plots treated with (1) L. botrana mating disruption pheromone, (2) L. botrana and C. gnidiella mating disruption pheromones and (3) control plots. A significant difference in the number of clusters infested with the developmental stages of the moths was seen between pheromone-treated plots and controls, while no such difference was observed between plots treated with one versus two pheromones. A similar pattern was observed in the number of insecticide applications; the greatest number of applications was used in control plots, followed by plots treated with L. botrana mating disruption pheromone and by plots treated with pheromones against both pests, in which no pesticides were applied.  相似文献