Chiral amplification of oligopeptides in two-dimensional crystalline self-assemblies on water     

Zepik H  Shavit E  Tang M  Jensen TR  Kjaer K  Bolbach G  Leiserowitz L  Weissbuch I  Lahav M 《Science (New York, N.Y.)》2002,295(5558):1266-1269

Differences in the two-dimensional packing arrangements of racemic and enantiomeric crystalline self-assemblies on the water surface of amphiphilic activated analogs of lysine and glutamic acid have been used to prepare oligopeptides of homochiral sequence and oligopeptides of single handedness from chiral nonracemic mixtures. The crystalline structures on the water surface were determined by grazing incidence x-ray diffraction and the diastereomeric composition of the oligopeptides by matrix-assisted laser desorption time-of-flight mass spectrometry with enantio-labeling. These results suggest that reactivity of ordered clusters at interfaces might have played a role in the generation of early homochiral biopolymers.  相似文献   

Viscosity of fluids in subduction zones   总被引：2，自引：0，他引：2  

Audétat A  Keppler H 《Science (New York, N.Y.)》2004,303(5657):513-516

The viscosities of aqueous fluids with 10 to 80 weight percent dissolved silicates have been measured at 600 degrees to 950 degrees C and 1.0 to 2.0 gigapascals by in situ observation of falling spheres in the diamond anvil cell. The viscosities at 800 degrees C range from 10(-4) to 10(0.5) pascal seconds. The combination of low viscosities with a favorable wetting angle makes silicate-rich fluid an efficient agent for material transport at low-volume fractions. Our results therefore suggest that there may be a direct relationship between the position of the volcanic front and the onset of complete miscibility between water and silicate melt in the subducting slab.  相似文献   

Atmospheric methane and nitrous oxide of the Late Pleistocene from Antarctic ice cores     

Spahni R  Chappellaz J  Stocker TF  Loulergue L  Hausammann G  Kawamura K  Flückiger J  Schwander J  Raynaud D  Masson-Delmotte V  Jouzel J 《Science (New York, N.Y.)》2005,310(5752):1317-1321

The European Project for Ice Coring in Antarctica Dome C ice core enables us to extend existing records of atmospheric methane (CH4) and nitrous oxide (N2O) back to 650,000 years before the present. A combined record of CH4 measured along the Dome C and the Vostok ice cores demonstrates, within the resolution of our measurements, that preindustrial concentrations over Antarctica have not exceeded 773 +/- 15 ppbv (parts per billion by volume) during the past 650,000 years. Before 420,000 years ago, when interglacials were cooler, maximum CH4 concentrations were only about 600 ppbv, similar to lower Holocene values. In contrast, the N2O record shows maximum concentrations of 278 +/- 7 ppbv, slightly higher than early Holocene values.  相似文献   

聚氨酯防腐涂层对埋地金属构件的保护     

Gérard GAILLARD 《油气储运》2005,24(Z1)

讨论了聚氨酯的化学性质,指出聚氨酯的性能取决于它的一些特性,如附着性、抗冲击性、抗水解能力、抗化学品的性质、阴极剥离及使用寿命等,并对这些性质进行了分析和评价性试验.建议现场涂敷聚氨酯涂层时必须彻底清除掉现有的涂层,并在新涂层涂敷之前进行适当的表面处理.同时还讨论了底层温度对聚氨酯防腐层涂敷的影响.  相似文献   

A haptoglobin-hemoglobin receptor conveys innate immunity to Trypanosoma brucei in humans     

Vanhollebeke B  De Muylder G  Nielsen MJ  Pays A  Tebabi P  Dieu M  Raes M  Moestrup SK  Pays E 《Science (New York, N.Y.)》2008,320(5876):677-681

The protozoan parasite Trypanosoma brucei is lysed by apolipoprotein L-I, a component of human high-density lipoprotein (HDL) particles that are also characterized by the presence of haptoglobin-related protein. We report that this process is mediated by a parasite glycoprotein receptor, which binds the haptoglobin-hemoglobin complex with high affinity for the uptake and incorporation of heme into intracellular hemoproteins. In mice, this receptor was required for optimal parasite growth and the resistance of parasites to the oxidative burst by host macrophages. In humans, the trypanosome receptor also recognized the complex between hemoglobin and haptoglobin-related protein, which explains its ability to capture trypanolytic HDLs. Thus, in humans the presence of haptoglobin-related protein has diverted the function of the trypanosome haptoglobin-hemoglobin receptor to elicit innate host immunity against the parasite.  相似文献   

Selective and efficient platinum(0)-carbene complexes as hydrosilylation catalysts     

Markó IE  Stérin S  Buisine O  Mignani G  Branlard P  Tinant B  Declercq JP 《Science (New York, N.Y.)》2002,298(5591):204-206

The hydrosilylation reaction enables the production of silicon polymers. Platinum-carbene complexes are reported that catalyze the hydrosilylation reaction of alkenes with remarkable efficiency and exquisite selectivity and avoid the formation of platinum colloids. By-products, typically encountered with previous catalytic systems, are suppressed with these platinum derivatives.  相似文献   

Long road to reform in France     

Brézin E  Triller A 《Science (New York, N.Y.)》2008,320(5884):1695

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Deep human genealogies reveal a selective advantage to be on an expanding wave front     

Moreau C  Bhérer C  Vézina H  Jomphe M  Labuda D  Excoffier L 《Science (New York, N.Y.)》2011,334(6059):1148-1150

Since their origin, human populations have colonized the whole planet, but the demographic processes governing range expansions are mostly unknown. We analyzed the genealogy of more than one million individuals resulting from a range expansion in Quebec between 1686 and 1960 and reconstructed the spatial dynamics of the expansion. We find that a majority of the present Saguenay Lac-Saint-Jean population can be traced back to ancestors having lived directly on or close to the wave front. Ancestors located on the front contributed significantly more to the current gene pool than those from the range core, likely due to a 20% larger effective fertility of women on the wave front. This fitness component is heritable on the wave front and not in the core, implying that this life-history trait evolves during range expansions.  相似文献   

Microinjection of a conserved peptide sequence of p34cdc2 induces a Ca2+ transient in oocytes   总被引：3，自引：0，他引：3  

A Picard  J C Cavadore  P Lory  J C Bernengo  C Ojeda  M Dorée 《Science (New York, N.Y.)》1990,247(4940):327-329

The product of the yeast cell cycle control gene cdc2, and its homologs in higher eukaryotes (p34cdc2), all contain a perfectly conserved sequence of 16 amino acids that has not been found in any other protein sequence. Microinjection of this peptide triggers a specific increase in the concentration of intracellular free Ca2+ that originates from intracellular stores in both starfish and Xenopus oocytes. Thus, p34cdc2 might interact through its conserved peptide domain with some component of the Ca2(+)-regulatory system.  相似文献   

Wireless power transfer via strongly coupled magnetic resonances   总被引：4，自引：0，他引：4  

Kurs A  Karalis A  Moffatt R  Joannopoulos JD  Fisher P  Soljacic M 《Science (New York, N.Y.)》2007,317(5834):83-86

Using self-resonant coils in a strongly coupled regime, we experimentally demonstrated efficient nonradiative power transfer over distances up to 8 times the radius of the coils. We were able to transfer 60 watts with approximately 40% efficiency over distances in excess of 2 meters. We present a quantitative model describing the power transfer, which matches the experimental results to within 5%. We discuss the practical applicability of this system and suggest directions for further study.  相似文献