Search results for "Synthesis"
showing 10 items of 2844 documents
Structural Characterization of Zirconia Nanoparticles Prepared by Microwave-Hydrothermal Synthesis
2009
Nanocrystalline zirconia powders have been prepared by microwave-hydrothermal synthesis starting from aqueous solution of ZrOCl2·8H2O. Results of investigations on the aqueous suspension stability of the washed zirconia nanopowders by dynamic light scattering showed that the suspension, constituted by superaggregates of nanoparticles (131 ± 10 nm), was stable up to 15 days. Nanopowders were investigated by means of transmission electron microscopy and small angle x-ray scattering measurements which proved that the zirconia nanopowder is constituted by small primary nanoparticles of ca. 8 nm that agglomerate forming bigger aggregates of 50 ± 1 nm.
Effect of temperature on the growth of alfa-PbO2 nanostructures
2010
Abstract Ordered arrays of α-PbO 2 nanostructures were grown by galvanostatic anodic deposition into the channels of alumina templates. Electrodepositions were performed in an aqueous solution containing lead acetate and sodium acetate at pH 5.4. Bath temperature and electrodeposition time were varied to check their effect on the growth of nanostructures. It has been found that filling of alumina pores is independent of the time and electrodeposition temperature, whilst height and growth kinetics of nanostructures vary with both parameters. Temperature greatly influences morphology: wires grown at room temperature consisted of clusters of particles, leading to poorly compact structures, whi…
Aminosäureester als chirale Hilfsgruppen bei Barbier-Reaktionen in wäßriger Lösung
1991
Amino Acid Esters as Chiral Auxiliaries in Barbier-Type Reactions in Aqueous Solution Valine and proline benzyl ester are converted into the aliphatic and aromatic α-oxo amides 5 by activation of the respective α-oxo acid by means of N,N′-diisopropylcarbodiimide. The α-oxo amides 5 undergo Barbier-type reactions with differently substituted allyl halides in the presence of zinc and pyridinium toluenesulfonate in water/THF (2:1, v/v) at 4°C. Thereby, the α-hydroxy amides 8/9 are formed in high yields and, in the case of the proline ester amides, with diastereomer ratios of 4–6:1. In the absence of any allyl halide, or if the addition of the allyl moiety to the carbonyl groups is only slow, t…
Photocatalytic green synthesis of piperonal in aqueous TiO2 suspension
2014
Abstract Piperonal (heliotropine or 3,4-methylenedioxybenzaldehyde) has been synthesized by oxidizing piperonyl alcohol in aqueous UV-irradiated TiO2 suspensions. This compound was identified by GC–MS chromatography, 1H NMR and melting point determination. The other products of the photoprocess were 1,3-bis(3,4-(methylenedioxy)benzyl) ether (found in traces) and CO2, derived from the parallel pathway of photo-mineralization. Commercial and home-prepared TiO2 samples have been tested and the best selectivity (ca. 35%) was obtained by using the home-prepared ones. The reported green process allows to obtain an added value product (piperonal), upon partial oxidation of a cheap reagent.
Temporal aspects of copper homeostasis and its crosstalk with hormones
2015
To cope with the dual nature of copper as being essential and toxic for cells, plants temporarily adapt the expression of copper homeostasis components to assure its delivery to cuproproteins while avoiding the interference of potential oxidative damage derived from both copper uptake and photosynthetic reactions during light hours. The circadian clock participates in the temporal organization of coordination of plant nutrition adapting metabolic responses to the daily oscillations. This timely control improves plant fitness and reproduction and holds biotechnological potential to drive increased crop yields. Hormonal pathways, including those of abscisic acid, gibberellins, ethylene, auxin…
Study of oligogalacturonides-triggered Nitric Oxide (NO) production provokes new questioning about the origin of NO biosynthesis in plants
2014
Addendum to: Rasul S, Dubreuil-Maurizi C, Lamotte O, Koen E, Poinssot B, Alcaraz G, et al. Nitric oxide production mediates oligogalacturonide-triggered immunity and resistance to Botrytis cinerea in Arabidopsis thaliana. Plant Cell Environ 2012; PMID:22394204; http://dx.doi. org/10.1111/j.1365-3040.2012.02505.x.; International audience; We investigated the production and function of nitric oxide (NO) in Arabidopsis thaliana leaf discs as well as whole plants elicited by oligogalacturonides (OGs). Using genetic, biochemical and pharmacological approaches, we provided evidence that OGs induced a Nitrate Reductase (NR)-dependent NO production together with an increased NR activity and NR tran…
Arachnid oenocytes: ecdysone synthesis in the legs of harvestmen (Opilionidae).
1981
Cells measuring up to 130 microns have been found in the proximal segments of the femora of all four pairs of walking legs in various species of harvestmen (Phalangium opilio, Leiobonum limbatum, Opilio parietinus, and Opilio ravennae). These cells exhibit all the fine-structural characteristics of insect oenocytes, in particular the conspicuous agranular endoplasmic reticulum. Radioimmunoassay after in vitro incubation of these cells has demonstrated the synthesis of alpha- and beta-ecdysone. These ecdysteroids have been found in the ovaries and tergites of the opisthosoma as well as in the oenocytes.
The influence of smoke volatiles on sexual maturation and juvenile hormone biosynthesis in the black army cutworm, Actebia fennica (Lepidoptera: Noct…
2000
0965-1748 (Print) Journal Article Research Support, Non-U.S. Gov't; Outbreaks of the black army cutworm, Actebia fennica, are associated with recently burned sites, where larvae feed on early successional plants. In the present paper we show that smoke volatiles stimulate juvenile hormone biosynthesis in virgin females, resulting in a more rapid rate of oocyte maturation and a significant advance in the age of first calling (the release of the sex pheromone) compared to control females. The ecological implications of this physiological effect are discussed.
Total Synthesis and Biological Investigation of (−)‐Artemisinin: The Antimalarial Activity of Artemisinin Is not Stereospecific
2018
Here, we describe an efficient and diversity-oriented entry to both (-)-artemisinin (1) and its natural antipode (+)-artemisinin, starting from commercially and readily available S-(+)- and R-(-)-citronellene, respectively. Subsequently, we answered the still open question regarding the specificity of artemisinins action. By using a drug-sensitive Plasmodium falciparum NF54 strain, we showed that the antimalarial activity of artemisinin is not stereospecific. Our straightforward and biomimetic approach to this natural endoperoxide enables the synthesis of artemisinin derivatives that are not accessible through applying current methods and may help to address the problem of emerging resistan…
An active form of sphingosine kinase-1 is released in the extracellular medium as component of membrane vesicles shed by two human tumor cell line.
2010
Expression of sphingosine kinase-1 (SphK-1) correlates with a poor survival rate of tumor patients. This effect is probably due to the ability of SphK-1 to be released into the extracellular medium where it catalyzes the biosynthesis of sphingosine-1-phosphate (S1P), a signaling molecule endowed with profound proangiogenic effects. SphK-1 is a leaderless protein which is secreted by an unconventional mechanism. In this paper, we will show that in human hepatocarcinoma Sk-Hep1 cells, extracellular signaling is followed by targeting the enzyme to the cell surface and parallels targeting of FGF-2 to the budding vesicles. We will also show that SphK-1 is present in a catalitycally active form i…