Search results for "ATRA"
showing 10 items of 381 documents
Mesoporous aluminum phosphite
2009
Abstract High surface area pure mesoporous aluminum-phosphorus oxide-based derivatives have been synthesized through an S+I− surfactant-assisted cooperative mechanism by means of a one-pot preparative procedure from aqueous solution and starting from aluminum atrane complexes and phosphoric and/or phosphorous acids. A soft chemical extraction procedure allows opening the pore system of the parent as-prepared materials by exchanging the surfactant without mesostructure collapse. The nature of the pore wall can be modulated from mesoporous aluminum phosphate (ALPO) up to total incorporation of phosphite entities (mesoporous aluminum phosphite), which results in a gradual evolution of the acid…
Mesoporous iron phosphate/phosphonate hybrid materials
2014
Abstract Relatively high surface area pure mesoporous iron-phosphorus oxide-based derivatives have been synthesized through an S + I − surfactant-assisted cooperative mechanism by means of a one-pot preparative procedure from aqueous solution and starting from iron atrane complexes and phosphoric and phosphonic acids. A soft chemical extraction procedure allows opening the pore system of the parent as-prepared materials by exchanging the surfactant without mesostructure collapse. The nature of the pore wall can be modulated from iron phosphate up to hybrids involving approximately 30% of organophosphorus entities (phosphonates or diphosphonates). X-ray powder diffraction, transmission elect…
Generalised syntheses of ordered mesoporous oxides: the atrane route
2000
Abstract A new simple and versatile technique to obtain mesoporous oxides is presented. While implying surfactant-assisted formation of mesostructured intermediates, the original chemical contribution of this approach lies in the use of atrane complexes as precursors. Without prejudice to their inherent unstability in aqueous solution, the atranes show a marked inertness towards hydrolysis. Bringing kinetic factors into play, it becomes possible to control the processes involved in the formation of the surfactant–inorganic phase composite micelles, which constitute the elemental building blocks of the mesostructures. Independent of the starting compositional complexity, both the mesostructu…
Expanding the atrane route: Generalized surfactant-free synthesis of mesoporous nanoparticulated xerogels
2008
Abstract A diversity of silica-based and non-silica nanoparticulated mesoporous xerogels have been synthesized from aqueous solution using a surfactant-free strategy, and starting from molecular atrane complexes as precursors. This approach constitutes an extension of the “atrane route” previously described for the surfactant-assisted synthesis of mesoporous materials, and allows us to unify the multiplicity of protocols described for the preparation of conventional xerogels. In fact, we have used exactly the same preparative conditions for obtaining all the compositions reported here. The xerogels synthesized in this way include pure silica (UVM-11), aluminosilicates and titanosilicates (M…
Phosphine-diène and Salicylamidines ligands : coordination chemistry, catalysis and therapy
2017
The subject of this thesis concerns the development of new ligands, their coordination chemistry, and the synthesis of the corresponding metal complexes for catalysis and therapy.The first part of this work relates to the synthesis of diene-phosphine ligands, their saturated analogs, and the corresponding arene-ruthenium complexes. Arene decoordination allows the formation of a cationic bimetallic complex where the ligand is diène-η4/κ-P coordinated to the ruthenium. These complexes have been applied to atom transfer radical addition (ATRA) of CCl4 to styrene. When harsh reaction conditions are used, the superiority of the “diene” complexes is highlighted comparing to saturated analogs.The …
Cytotoxic activity of several ent-kaurane derivatives of atractyligenin. Synthesis of unreported diterpenic skeleton by chemical rearrangement
2022
Atractyloside, carboxyatractyloside, their aglycon atractyligenin, and several synthetic derivatives were tested and found to be active against a panel of human tumor cell lines. Atractyligenin was subjected to oxidation, bromination, and elimination reactions, obtaining several compounds. A singular skeleton was synthesized by chemical rearrangement starting from 3 beta-bromo-2,15-diketoatractyligenin methyl ester. The synthesized compounds resulted active against all cell lines tested. In particular, 15-ketoatractyligenin methyl ester and 3 beta bromo-2,15-diketoatractyligenin methyl ester resulted the most active with IC50 values of 0.427 and 0.723 mu M against A375 melanoma cell line. E…
Triterpenes and fatty acids from the rhyzomes of Atractylis gummifera L
1999
It is reported the investigation of the light petroleum ether extract of the rhizomes of Atractylis gummifera L. GC-MS analysis and medium pressure chromatographies afforded the presence of seven fatty acids and of the following triterpenes: lupenyl acetate, α-amyrin acetate, β-amyrin acetate, taraxasterol acetate, α-amyrin, lupeol, β-amyrin, taraxasterol, campesterol, β-sitosterol, stigmasterol, betulin, erythrodiol, uvaol, ursolic acid, oleanolic acid and betulinic acid.
Sociāli vājākās grupas (atraitnes, bāreņi, sveštautieši, vergi) Senās Izraēlas sabiedrībā 1207-1010.g.p.m.ē.
2017
Darba tēma ir “Sociāli vājākās grupas (atraitnes, bāreņi, sveštautieši, vergi) Senās Izraēlas sabiedrībā 1207. – 1010. g.p.m.ē.” Šī tēma tika izvēlēta, jo sociālā vēsture Senajā Izraēlā ir nepietiekami izpētīta tēma, kurai pēdējās desmitgadēs pavērušās jaunas pētījumu iespējas un metodes. Tika pētīts, kā veidojās un funkcionēja Izraēlas sabiedrība laikā pirms monarhijas un kādā stāvoklī atradās tās sociāli vājākās grupas, kuras kā tādas apraksta Vecā Derība – atraitnes, bāreņi, sveštautieši un vergi. Tika secināts, ka šīs grupas nonāk sociāli marginalizētā stāvoklī, zaudējot klana aizsardzību – nomirstot ģimenes galvam, nabadzības dēļ vai indivīdiem pametot kalnu kopīgi apdzīvotās teritorij…
Environmentally-conditioned human rights: a good idea?
2021
The emergence of the rights of nature is a clear response to the current environmental crisis. But such trend is not to walk alone: it is to be espoused to the many still remaining human rights issues, otherwise the power and credibility of both are at danger. This chapter focuses on one of the many possible points of encounter between the rights of nature and human rights. It explores how they may be combined within biocultural rights—the basket of rights of indigenous peoples and local communities necessary to maintain their role as ecosystem stewards—and tries to understand what the consequences of combining nature and human interests as their foundations may be. In particula…
Out of Asia: Mitochondrial DNA Evidence for an Oriental Origin of Tiger Frogs, Genus Hoplobatrachus
2001
Most examples of intercontinental dispersal events after the Miocene contact between Africa and Asia involve mammal lineages. Among amphibians, a number of probably related groups are known from both continents, but their phylogenies are so far largely unresolved. To test the hypothesis of Miocene dispersal against a Mesozoic vicariance scenario in the context of Gondwana fragmentation, we analyzed fragments of the mitochondrial 16S rRNA gene (572 bp) in 40 specimens of 34 species of the anuran family Ranidae. Results corroborated the monophyly of tiger frogs (genus Hoplobatrachus), a genus with representatives in Africa and Asia. The African H. occipitalis was the sister group of the Asian…