Search results for "stoichiometry"
showing 10 items of 270 documents
Dual stereocontrolled alkylation of aldehydes with polystyrene-supported nickel complexes derived from α-amino amides
2015
Nickel(II) complexes derived from α-amino amide ligands anchored to gel-type and monolithic polymers act as efficient catalysts for the enantioselective addition of dialkylzinc reagents to aldehydes. Similar to the analogous homogeneous systems, dual stereocontrol in addition products can be achieved by controlling the stoichiometry of the immobilized nickel complex. Aromatic and aliphatic aldehydes were alkylated in good yields with enantioselectivities comparable to those obtained with the homogeneous analogues. These polymer-supported catalysts offer significant advantages as no metal leaching is observed and they can be easily recovered from the reaction mixture by simple filtration and…
Chiral cyclohexane based fluorescent chemosensors for enantiomeric discrimination of aspartate
2008
Some new chiral cyclohexyl based fluorescent anion receptors have been synthesized and their absolute configuration has been determined by using circular dichroism (CD). Complexation experiments have been carried out with several dicarboxylates, and stoichiometries and complexation constants for the corresponding complexes have been determined. The chiral discrimination ability of these ligands for chiral dicarboxylates has been studied and the best results have been obtained with TMA aspartate.
Hyperstoichiometric interaction between silver and mercury at the nanoscale.
2012
Breaking through the stoichiometry barrier: As the diameter of silver particles is decreased below a critical size of 32?nm, the molar ratio of aqueous HgII to Ag0 drastically increases beyond the conventional Hg/Ag ratio of 0.5:1, leading to hyperstoichiometry with a maximum ratio of 1.125:1 (see figure). Therein, around 99?% of the initial silver is retained to rapidly form a solid amalgam with reduced mercury.
Apolar versus polar solvents: a comparison of the strength of some organic acids against different bases in toluene and in water
2010
The constants of ion-pair formation with 3-nitroaniline (3NO(2)A) for eight halogenoacetic acids (HAAs, 3a-h: TFA, TCA, TBA, DFA, DCA, DBA, MCA, and MBA), and five 2,2-dichloroalkanoic acids containing 3-8 carbon atoms (HAs, 5a-e: DCPA, DCBA, DCMBA, DCVA, and DCOA) have been determined in TOL at 298.1 K. The results obtained brought to evidence for HAAs the formation of ion-pairs with two different stoichiometries (base-acid, 1:1 or 1:2), while in contrast the HAs furnish only the 1:1 pairs. The different steric and electronic requirements of HAAs and HAs seem to be responsible for such an unlikely behavior. At the same time, the acid-catalyzed MRH of the (Z)-phenylhydrazone of 5-amino-3-be…
Structural and optical characterization of ZnS ultrathin films prepared by low-temperature ALD from diethylzinc and 1.5-pentanedithiol after various …
2019
The structural and optical evolution of the ZnS thin films prepared by atomic layer deposition (ALD) from the diethylzinc (DEZ) and 1,5-pentanedithiol (PDT) as zinc and sulfur precursors was studied. A deposited ZnS layer (of about 60 nm) is amorphous, with a significant S excess. After annealing, the stoichiometry improved for annealing temperatures &ge
Sustainable Recycling of Insoluble Rust Waste for the Synthesis of Iron-Containing Perovskite-Type Catalysts
2019
Insoluble rust waste from the scraping of rusted iron-containing materials represents a cheap, eco-friendly, and available source of iron. LaFeO3 perovskite-type powders were successfully prepared by solution combustion synthesis using rust waste from an electricity transmission tower manufacturer. Solution combustion synthesis enabled introduction of this insoluble iron precursor directly into the final product, bypassing complex extraction procedures. Catalytic activity in the propylene oxidation of the waste-derived LaFeO3 with stoichiometric Fe/La ratio was almost identical to the commercial iron nitrate-derived LaFeO3 , thus demonstrating the viability of this recycling solution. The a…
Unlocking mixed oxides with unprecedented stoichiometries from heterometallic metalorganic frameworks for the catalytic hydrogenation of CO 2
2021
[EN] Their complex surface chemistry and high oxygen lattice mobilities place mixed-metal oxides among the most important families of materials. Modulation of stoichiometry in mixed-metal oxides has been shown to be a very powerful tool for tuning optical and catalytic properties. However, accessing different stoichiometries is not always synthetically possible. Here, we show that the thermal decomposition of the recently reported metal-organic framework MUV-101(Fe, Ti) results in the formation of carbon-supported titanomaghemite nanoparticles with an unprecedented Fe/Ti ratio close to 2, not achievable by soft-chemistry routes. The resulting titanomaghemite phase displays outstanding catal…
Environmental drivers of lake profundal macroinvertebrate community variation : implications for bioassessment
2011
Phosphorus limitation enhances parasite impact: feedback effects at the population level
2014
Background Nutrient deficiency affects the growth and population dynamics of consumers. Endoparasites can be seen as consumers that drain carbon (C) or energy from their host while simultaneously competing for limiting resources such as phosphorus (P). Depending on the relative demands of the host and the parasite for the limiting nutrient, intensified resource competition under nutrient limitation can either reduce the parasite’s effect on the host or further reduce the fitness of the nutrient-limited host. So far, knowledge of how nutrient limitation affects parasite performance at the host population level and how this affects the host populations is limited. Results We followed the popu…
Does differential iron supply to algae affect Daphnia life history? : An ionome-wide study
2019
The availability of iron (Fe) varies considerably among diet items, as well as ecosystems. Availability of Fe has also changed due to anthropogenic environmental changes in oceanic as well as inland ecosystems. We know little about its role in the nutrition of ecologically important consumers, particularly in inland ecosystems. Physiological studies in several taxa indicate marked effects of dietary Fe on oogenesis. We predicted that differential Fe supply to algae will impact algal Fe concentration with consequences on the life history of the freshwater grazer, Daphnia magna. We found that algal Fe concentration increased with Fe supply, but did not affect algal growth, indicating that the…