Search results for "cycle"
showing 10 items of 3119 documents
Solid state halogen bonded networks vs. dynamic assemblies in solution: explaining N⋯X interactions of multivalent building blocks
2015
Tetrapyridine functionalized resorcinarene macrocycles were used as multivalent building blocks for the construction of halogen bonded networks with aryl halide linkers. In the solid state, resorcinarene macrocycles and aryl halide linker molecules assembled into interpenetrated, multidimensional halogen bonded networks with porous structure caused by the 3D block scaffold of the resorcinarenes. 19F NMR spectroscopy proved halogen bond formation also in solution, as either upfield or downfield shifts were observed depending on the bivalent or monovalent halogen bond binding mode. The binding mode in solution was explained by density functional theory computations. peerReviewed
5-Substituted 4,5-Dihydro-1,2,4-triazin-3(2H)-ones from the Unprecedented Reaction between α-N-Protected Amino Acid Hydrazides and NaBH4
2006
α-N-Protected amino acid hydrazides (1) readily reacted with NaBH4 to afford 5-substituted 4,5-dihydro-1,2,4-triazin-3(2H)-one derivatives 2 in good yields. Unfortunately, the reaction caused partial racemization at the α-amino acidic carbon atom of the starting hydrazide. A mechanism, supported by experimental evidence, has been proposed in an attempt to explain this to date unprecedented reaction. The structure of compounds 2 was confirmed by X-ray structural analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Electrochemical study on a tricyclic 1,1,1-tricar-bonyl-2,3-1 diazaferrole derivative. II. Activation of carbon monoxide replacement by electron tran…
1986
Etudes, par voltammetrie cyclique, de la reduction electrochimique du complexe de diazaferratricyclodecene, en presence de P(OMe) 3
Enantioselective Protonation of the Lithium Transient Enolate of2-Methyltetralone with 2-Sulfinyl Alcohols
2005
A new catalytic cycle for the enantioselective protonation of cyclic ketone enolates with sulfinyl alcohols has been developed. An enol trifluoroacetate that can be easily obtained from the corresponding ketone is used for the first time as an enolate precursor of a cyclic ketone enolate. In this method, the achiral alcohol plays two roles: it is involved, as is usual in catalytic asymmetric protonation reactions, in the turnover of the chiral proton source and also in the generation of a transient enolate through the reaction of its corresponding alkoxide with the enol trifluoroacetate precursor. Stereoselectivity is highly dependent on the structure of the achiral alcohol. High levels of …
p38 MAPK: A dual role in hepatocyte proliferation through reactive oxygen species
2013
p38 MAPKs are important mediators of signal transduction that respond to a wide range of extracellular stressors such as UV radiation, osmotic shock, hypoxia, pro-inflammatory cytokines, and oxidative stress. The most abundant family member is p38α, which helps to couple cell proliferation and growth in response to certain damaging stimuli. In fact, increased proliferation and impaired differentiation are hallmarks of p38α-deficient cells. It has been reported that reactive oxygen species (ROS) play a critical role in cytokine-induced p38α activation. Under physiological conditions, p38α can function as a mediator of ROS signaling and either activate or suppress cell cycle progression depen…
How Humic Substances Dominate Mercury Geochemistry in Contaminated Floodplain Soils and Sediments
1998
The interaction of mercury (Hg) and humic substances (hs) was studied in floodplain topsoils and surface sediments of the contaminated German river Elbe. An intimate coupling exists between the geochemical cycles of Hg and organic carbon (OC) in this ecosystem. Humic substances exert a dominant influence on several important parallel geochemical pathways of Hg, including binding, transformation, and transport processes. Significant differences exist between the Hg-hs associations in floodplains and sediments. Both humic acids (ha) and fulvic acids (fa) contribute to Hg binding in the sediments. In contrast, ultrafiltration experiments proved that Hg in the floodplain soils is almost exclusi…
Fast and continuous synthesis of nanostructured iron spinel in supercritical water: influence of cations and citrates
2014
International audience; Spinel iron oxide nanoparticles were obtained under supercritical water conditions in a continuous and fast (less than 10s) way by modifying the initial stoichiometric Fe II /Fe III molar ratio from (1/2) to (3/0), without base solution, and using citrates directly with iron precursors. This result opens the way of an economical and environmentally benign approach to synthesize superparamagnetic iron oxide nanoparticles (SPIONs) in important yields.
Regulation of the Urea Cycle during Lactation
1990
We have recently shown that the uptake of amino acids by rat lactating mammary gland is 15 mmoles/day (1). This effect is achieved by an increase in food intake during lactation and probably by changes in amino acid metabolism in other tissues. Rat liver removes 75% of the total amino acids derived from a protein meal (2); therefore plays a key role in the regulation of plasma amino acid concentration.
Biogeochemical evaluation of historical sediment contamination in the Gulf of Palermo (NW Sicily): Analysis of pseudotrace elements and stable isotop…
2012
Abstract Sedimentary biogeochemical data from the Gulf of Palermo, which borders one of the major urban and industrial areas of the central Mediterranean, provide a decennial–centennial-scale record of the effects of human activity on this coastal environment. In this study we report trace elements (TE), C org /N tot ratios, δ 13 C org , and δ 15 N tot from dated ( 210 Pb) sediments collected in two coastal stations variably influenced by urban/fluvial loadings and illegal dumping and we compare them with published data for offshore sediments, in order to investigate at a large spatial scale the influence of on-land activities on sedimentary marine system. TE were generally low except for H…
Effect of earthworms on decomposition processes in raw humus forest soil: A microcosm study
1990
The earthworms Lumbricus rubellus (Hoffmeister) and Dendrobaena octaedra (Savigny) were studied in the laboratory to determine their effects on decomposition and nutrient cycling in coniferous forest soil. CO2 evolution was monitored, and pH, PO 4 3− −P, NH 4 + −N, NO 3 − −N, total N, and total C in the leaching waters were measured. After three destructive samplings, numbers of animals, mass loss, pH, and KCl-extractable nutrients were analysed. The earthworms clearly enhanced the mass loss of the substrate, especially that of litter. L. rubellus stimulated microbial respiration by 15–18%, whereas D. octaedra stimulated it only slightly. The worms significantly raised the pH of the leachin…