Search results for "Step"
showing 10 items of 509 documents
Electrochemical and DFT studies of the oxidative decomposition of the trihydride complexes Cp*M(dppe)H3 (M = Mo, W) in acetonitrile
2006
International audience; A detailed electrochemical study of the oxidative decomposition of the trihydride complexes Cp*M(dppe)H3 (M = Mo, W) in acetonitrile is presented. For the Mo complex, the decomposition occurs by four different pathways involving classical and non-classical tautomers, whereas only the classical form is accessible for the W derivative. Each of the decomposition pathways has been quantitatively assessed by analyses of the linear sweep voltammograms. In addition to the previously established (B. Pleune, D. Morales, R. Meunier-Prest, P. Richard, E. Collange, J. C. Fettinger and R. Poli, J. Am. Chem. Soc., 1999, 121, 2209–2225) deprotonation, disproportionation, and H2 red…
Two- and one-step cooperative spin transitions in Hofmann-like clathrates with enhanced loading capacity
2014
Structural, magnetic, calorimetric and Mo¨ssbauer studies of the cooperative spin crossover naphthalene and nitrobenzene clathrates of the novel FeII Hofmann-like porous metal–organic framework {Fe(bpb)[Pt(CN)4]}2Guest are described (bpb = bis(4-pyridyl)butadiyne).
A theoretical study of carbon-carbon bond formation by a Michael-type addition.
2012
A theoretical study of the Michael-type addition of 1,3-dicarbonyl compounds to α,β-unsaturated carbonyl compounds has been performed in the gas phase by means of the AM1 semiempirical method and by density functional theory (DFT) calculations within the B3LYP and M06-2X hybrid functionals. A molecular model has been selected to mimic the role of a base, which is traditionally used as a catalyst in Michael reactions, an acetate moiety to modulate its basicity, and point charges to imitate the stabilization of the negative charge developed in the substrate during the reaction when taking place in enzymatic environments. Results of the study of six different reactions obtained at the three di…
Fast synthesis of single-phased 110 K bismuth superconductor by freeze-drying of acetic precursors. Kinetic role of calcium and copper oxides
1993
Abstract Although the usefulness of solution procedures to improve the synthesis of bismuth HTSC has been argued, an adequate control of the procedural variables has allowed us to isolate the 110 K phase as the only superconducting phase after such a short sintering time as 22 h. The precursors used have been freeze-dried powders resulting from acetic solutions containing excess Ca and Cu. TGA-DTA and XRD experiments have been performed to follow the subsequent solid-state reaction processes. The initial formation of a mixed bismuth-lead oxoacetate, as intermediate to (Bi 1− y Pb y ) 2 CuO 4 , and the presence of an excess of Ca 2 CuO 3 in the last reaction step are two of the main factors …
Grasslands and Shrublands of Kazakhstan and Middle Asia
2020
Kazakhstan and Middle Asia comprise 4 million km2 of plains, uplands and tall mountain ranges in the core of the Eurasian continent. The region’s semi-arid climate, grazing pressure by wild and domestic ungulates, and long pastoral tradition, have given rise to a variety of open habitat types and a distinct flora and fauna. Grasslands and shrublands are a natural and dominant vegetation type in the forest-steppe and steppe zone of northern and central Kazakhstan, as part of the Eurasian grassland biome. In Middle Asia, grasslands and shrublands are widespread habitat types in the Tian Shan, Pamir-Alai and Pamir—mountain systems that have been recently acknowledged as a global biodiversity h…
Distribution of graminoids in open habitats in Tajikistan and Kyrgyzstan
2022
Aims: Landscapes of Middle Asia are exposed to human influence due to long-lasting pastoral tradition, and now are largely dominated by non-forest vegetation. Graminoids perform key ecosystem functions, and constitute an important feed source for livestock. We studied the distribution patterns of graminoids cover under climatic and grazing pressure gradients in different open vegetation types. Study area: Tajikistan, Kyrgyzstan. Methods: 1,525 vegetation plots representing five open vegetation types (mires, salt marshes, tall-forb communities, pseudosteppes and steppes) were extracted from the Vegetation of Middle Asia Database. We assessed the relative cover of graminoid species in each ve…
The Di-Tert-Butyl Oxymethylphosphonate Route to the Antiviral Drug Tenofovir
2020
<div>The present manuscript describes a simple, two step synthesis of tenofovir from HPA through phosphonomethalation with a novel doubly protected oxymethylphosphonate electrophile. The crystalline electrophile can be prepared in a simple reaction sequence and can be deblocked more easily than its ditehyl analogue involved in the current commercial process for making the drug.</div><div>The approach is general and can also be used for the preparation of related antivirals and the synthesis of adefovir is described as well.<br></div>
La scoperta, sistemazione e conservazione della grande Iscrizione di Gortina, nell'isola di Creta (1884-1921): la protezione delle testimonianze e le…
2013
La scoperta e la conservazione della Grande Iscrizione di Gortina a Creta, da parte degli studiosi italiani, fra la fine del XIX sec. e i primi decenni del XX sec., rappresentò un grande riconoscimento scientifico-culturale per la giovane nazione italiana. Nel passato, l’isola di Creta era stata legata alla Repubblica di Venezia e anche questo rapporto favorì l’invio a Creta del giovane epigrafista F. Halbherr, il quale fra notevoli peripezie rinvenne, assieme all’epigrafista tedesco E. Fabricius, la famosa l’iscrizione nell’antica città di Gortina. L’iscrizione, fra le più antiche e complete finora conosciute in tutta Europa, conteneva le norme sulla famiglia, l’eredità e in generale i dir…
The Two‐Step Spin Conversion in a Supramolecular Triple Helicate Dinuclear Iron(II) Complex Studied by Mössbauer Spectroscopy
2006
The triple helicate dinuclear iron(II) complex, [Fe-2(L)(3)](ClO4)(4)center dot 2H(2)O (1), previously reported by Tuna et al. (Chem. Eur. J. 2004, 10, 5737), was prepared and characterised by detailed SQUID and Fe-57 Mbssbauer measurements. Compound 1 exhibits a thermochromic two-step spin conversion at T-SC((1)) ca. 240 K and T-SC((2)) ca. 120 K, but does not switch its spin state further below 20 K as proven by Mossbauer spectroscopy. The sharp variation of the susceptibility below 20 K is due to zero-field splitting of the remaining iron(II) high-spin species. Applied field Fe-57 Mossbauer spectroscopy experiments at 4.2 K indicate that the gradual thermal spin conversion from [HS-HS] p…
Nanocrystalline ZnCO3—A novel sorbent for low-temperature removal of H2S
2013
Abstract The reactivity of a nanocrystalline ZnCO 3 toward H 2 S (0.2 vol% in N 2 /H 2 mixture) at 140–180 °C was characterized by thermal gravimetric analysis and by breakthrough curves measurements. We have found that under used conditions transformation of ZnCO 3 into ZnS is complete and the rate determining step of the sulfidation is the surface reaction. Such behavior is in strike contrast with that of ZnO whose sulfidation is severely limited by diffusion. The higher reactivity of ZnCO 3 in comparison with ZnO is attributed to the different microstructure of ZnS layer formed in these materials after a partial sulfidation. As in ZnO–ZnS transformation the molar volume increases (from 1…