445 research outputs found
LightâDriven gemâHydrogenation: An Orthogonal Entry into âSecond Generationâ Ruthenium Carbene Catalysts for Olefin Metathesis
The newly discovered lightâdriven gemâhydrogenation of alkynes opens an unconventional yet efficient entry into fiveâcoordinate Grubbsâtype ruthenium carbene complexes with cisâdisposed chloride ligands. Representatives of this class featuring a chelate substructure formed by an iodoâsubstituted benzylidene unit react with (substituted) 2âisopropoxystyrene to give prototypical âsecond generationâ GrubbsâHoveyda complexes for olefin metathesis. The new approach to this venerable catalyst family is safe and versatile for it uses a triple bond rather than phenyldiazomethane as the ultimate carbene source and does not require any sacrificial phosphines
Light-Driven Alkyne gem-Hydrogenation: An Intramolecular Approach to HoveydaâGrubbs Catalysts
The light-driven gem-hydrogenation of internal alkynes in the presence of [(NHC)(η6-cymene)RuCl2] generates discrete ruthenium carbene complexes. When applied to appropriately designed enyne substrates, the reactive intermediates thus formed will engage the tethered olefin in metathetic ring closure while splitting off a HoveydaâGrubbs-type complex as secondary carbene. This unconventional approach to these classical catalysts for olefin metathesis rivals existing methodology in that it is safe, short, phosphine-free, and uses readily available starting materials
Quasi-analytical formulation for calculation of infiltration and runoff
Prepared for USDA Forest Service, Rocky Mountain Forest and Range Experiment Station.CER81-82-86.December 1981.Bibliography: pages 41-42
Treatment with human growth hormone in patients with Prader-Labhart-Willi syndrome reduces body fat and increases muscle mass and physical performance
Twelve children with documented Prader-Labhart-Willi syndrome were treated with human growth hormone (24 U/m2/week) during 1 year. The children were divided into three groups: group 1: overweight and prepubertal (n = 6, age 3.8-7.0 years); group 2: underweight and prepubertal (n = 3, age 0.6-4.1 years); group 3: pubertal (n = 3, age 9.2-14.6 years). In group 1, height increased from -1.7 SD to -0.6 SD, while weight decreased from 1.1 SD to 0.4 SD, with a dramatic drop in weight for height from 3.8 SD to 1.2 SD. Hand length increased from -1.5 SD to -0.4 SD and foot length from -2.5 SD to -1.4 SD. Body fat, measured by dual X-ray energy absorptiometry, dropped by a third, whereas muscle mass increased by a fourth. Physical capability (Wingate test) improved considerably. The children were reported to be much more active and capable. In group 2, similar changes were seen, but weight for height increased, probably because muscle mass increase exceeded fat mass decrease. Changes in group 3 were similar as in group 1, even though far less distinct. Conclusion: Growth hormone treatment in Prader-Labhart-Willi syndrome led to dramatic changes: distinct increase in growth velocity, height and muscle mass, as well as an improvement in physical performance. Fat mass and weight for height decreased in the initially overweight children, and weight for height increased in underweight childre
Preliminary comparison of magmatic manifestations, calc-alkaline affinity and stephanian-permian age, in the Iberian Chain
[Resumen] En este trabajo se estudian, de forma sintética y actualizada, las manifestaciones (hipovolcånicas y volcanoclåsticas) calco-alcalinas que, con caråcter epizonal, pluriepisódico
y edad Stephaniense-PĂ©rmico, afloran en la Cadena IbĂ©rica. El estudio del magmatismo en la cuenca de Sauquillo de AlcĂĄzar (Soria) permite identificar la geometrĂa y la modalidad de este magmatismo con mayor precisi6n, respecto a lo obtenido en los cuatro afloramientos volcano-clĂĄsticos seleccionados. Los resultados obtenidos facilitan realizar consideraciones sobre el estudio espacio-temporal de este magmatismo..[Abstract] A synthetic and actualized study of several magmatic calc-alkaline manifestations
of Stephanian-Permian age, of the Iberian Chain, is proposed in this papero The Sauquillo de AlcĂĄzar (Soria) outcrop allows a more complete study (with drilling logs and a surface profile) giving improved spacetime information on the geometry and evolution of this magmatism. Four pyroclastic outcrops are integrated in this compariso
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Equilibrium Hydrogen Concentrations of the 800 Series Tanks in Deactivation Mode
Ein neues, unkompliziertes Verfahren zur Bestimmung der Zusammensetzung binĂ€rer FlĂŒssigkeitsgemische
Ein neues Verfahren zur Bestimmung der Zusammensetzung binĂ€rer FlĂŒssigkeitsgemische mit Hilfe solvatochromer Farbstoffe wird beschrieben. Die Analyse erfolgt durch einfache UV/VIS-Absorptionsmessung und ist unter Verwendung einer Zwei-Parameter-Gleichung ein exakter Schnelltest
Nucleocytoplasmic transport: a thermodynamic mechanism
The nuclear pore supports molecular communication between cytoplasm and
nucleus in eukaryotic cells. Selective transport of proteins is mediated by
soluble receptors, whose regulation by the small GTPase Ran leads to cargo
accumulation in, or depletion from the nucleus, i.e., nuclear import or nuclear
export. We consider the operation of this transport system by a combined
analytical and experimental approach. Provocative predictions of a simple model
were tested using cell-free nuclei reconstituted in Xenopus egg extract, a
system well suited to quantitative studies. We found that accumulation capacity
is limited, so that introduction of one import cargo leads to egress of
another. Clearly, the pore per se does not determine transport directionality.
Moreover, different cargo reach a similar ratio of nuclear to cytoplasmic
concentration in steady-state. The model shows that this ratio should in fact
be independent of the receptor-cargo affinity, though kinetics may be strongly
influenced. Numerical conservation of the system components highlights a
conflict between the observations and the popular concept of transport cycles.
We suggest that chemical partitioning provides a framework to understand the
capacity to generate concentration gradients by equilibration of the
receptor-cargo intermediary.Comment: in press at HFSP Journal, vol 3 16 text pages, 1 table, 4 figures,
plus Supplementary Material include
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