Effet inductif

Résumé

Au sein d'un composé chimique, l'effet inductif consiste en la propagation d'une polarisation électronique au fil des liaisons chimiques, due à la différence d'électronégativité des différents éléments liés entre eux. Électronégativité Définition L'électronégativité est la capacité d'un élément à attirer les électrons, donc leur charge électrique, lorsqu'il est lié à un autre atome. L'électronégativité est relative : un élément A est électronégatif par rapport à un autre élément B si A attire de façon plus forte les électrons, B sera alors dit électropositif par rapport à A. L'électronégativité est généralement notée χ. Échelle d'électronégativité Il existe plusieurs échelles d'électronégativité. La plus utilisée est l'échelle de Pauling. La comparaison des valeurs d'électronégativités de différents éléments chimiques dans l'échelle de Pauling permet d'estimer quel est l'atome d'une liaison qui attirera le plus les électrons à lui. Liaison A-

Source officielle

https://fr.wikipedia.org/wiki/Effet_inductif

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Publications associées (30)

Publications associées

Chargement

Personnes associées

Chargement

Unités associées

Chargement

Concepts associés (9)

Concepts associés

Chargement

Cours associés (13)

Cours associés

Chargement

Séances de cours associées (34)

Afficher plus

Séances de cours associées

Chargement

Arginine-Based Biodegradable Ether–Ester Polymers with Low Cytotoxicity as Potential Gene Carriers

Lucia Baldi Unser, Sagar Shashidhar Manoli, Tamar Memanishvili, Christine Wandrey, Nino Zavradashvili

The success of gene therapy depends on safe and effective gene carriers. Despite being widely used, synthetic vectors based on poly(ethylenimine) (PEI), poly(l-lysine) (PLL), or poly(l-arginine) (poly-Arg) are not yet fully satisfactory. Thus, both improvement of established carriers and creation of new synthetic vectors are necessary. A series of biodegradable arginine-based ether–ester polycations was developed, which consists of three main classes: amides, urethanes, and ureas. Compared to that of PEI, PLL, and poly-Arg, much lower cytotoxicity was achieved for the new cationic arginine-based ether–ester polymers. Even at polycation concentrations up to 2 mg/mL, no significant negative effect on cell viability was observed upon exposure of several cell lines (murine mammary carcinoma, human cervical adenocarcinoma, murine melanoma, and mouse fibroblast) to the new polymers. Interaction with plasmid DNA yielded compact and stable complexes. The results demonstrate the potential of arginine-based ether–ester polycations as nonviral carriers for gene therapy applications.

Amer Chemical Soc2014

Chargement

The world population being increasing, a good energy production management is therefore necessary. Biomass production through short forest rotation by using fast-growing trees appears as a sensible way to limit fossil fuel uses. In Mediterranean regions of south-east Spain, soils present weakened ecosystem with low organic matter and nutrients content which are prone to irremediable degradation processes. The very low fertility of those soils usually makes them unfit to food production and so tree plantation with amendment addition seems to be a possible solution in order to use those soil and improve their qualities. In this study, a low fertility soil was exposed to the addition of two types of amendment (a compost of “Alperujo” and one of biosolid) and to the plantation of two different fast-growing trees (poplars and eucalyptus) during a time period of four months. The soil quality was determined by measuring different selected biochemical (β-glucosidase, phosphatase, dehydrogenase and urease activities), chemical (pH, electrical conductivity, organic matter, phosphate, potassium, water-soluble carbon, N-Kjeldahl, permanganate oxidizable carbon and metal extractible with CaCl2) and plants (nutrients, and trace elements) parameters. No significant differences between the different conditions were found. This was due to the very short time period, the too small doses of compost additions and the very high spatial variability due to the field conditions. It seems however that the composts had a positive effect on the chemical and biochemical parameters in the plots planted with poplars as the results presented systematically higher values for the amended plots than for the control plots (without amendment addition). This was attributed to the fact that all poplars were dead at the time of the study and so the soil was not confronted to any interference by the rhizosphere. Most of the parameters (chemical as well as biochemical) of the soil were improved in the eucalyptus plots compared to the poplar ones. This suggests the stimulation of the nutrient cycles by the tree roots, which improved the conditions for the microorganisms, increasing therefore their metabolic activities. The effect of composts in the eucalyptus plots were therefore clearly less obvious, probably due to the fact that the rhizosphere have had more time (tree planted in July 2011) to influence the soil properties than the compost (added in November 2011). Although both composts contained a non negligible quantity of micronutrients and trace elements, the extractible by CaCl2 0.01M quantities in soil (representing the available quantity for plants) did not present values too high to be toxic for plants and were all in normal ranges. The biomass development of the trees seems to have been improved by the compost of “Alperujo”, but presented a very high spatial variability. The compost of biosolids for its part did not show any difference as compared to the control. Next studies should reveal more significant differences between the plots, the soil having more time to react to the new conditions. It is however recommended to increase the addition doses of composts (double or more) in order to show better their effects

2012

Chargement

Supported ruthenium nanoparticles for supercritical water gasification - synthesis, activity and stability

Christopher Marc Hunston

Supercritical water gasification (SCWG) is a promising and versatile technology for the conversion of a variety of wet biomass streams into renewable natural gas. In this work, the focus was set on methane production with the help of an active and stable methanation catalyst. The supercritical water (SCW) environment can lead to rapid catalyst deactivation through different mechanisms, namely poisoning, coking, sintering or leaching. Although addressed, it remains challenging to disentangle them in SCWG. The goal of this thesis is to get a better understanding of the aforementioned deactivations pathways by trying to study them individually, in order to tailor an active and robust SCWG catalyst.The intrinsic gasification activity of carbon supports exhibiting different properties was assessed by feeding glycerol at 400°C and 30MPa. The negative effect of micropores was shown by significant coke deposition and surface area loss around 90%, compared to mesoporous carbons that only lost 20%. Carbon nanofibers (CNF) proved to be an interesting support showing very good stability and inertness. The synthesis of 5%Ru catalysts on selected supports confirmed these trends. Highly microporous Ru/C catalysts were less stable than the ones supported on carbon frameworks of more open pore structure. Ru/CNF seemed to be a promising SCWG catalyst, with an enhanced resistance towards coke formation. The completely open pore structure of CNF was found to be a crucial parameter.Ruthenium loss was investigated by measuring the its content in the process waters with ICP-MS. Ru was successfully quantified at levels close to thermodynamic models for Ru/AC and Ru/CNF of different loadings (0.01-0.2 µg L-1). Furthermore, the process parameters had no effect on the quantified Ru, showing that the steady-state loss represents a thermodynamically-driven leaching. Fluctuations in feed rate and pressure damaged the catalyst through friction and led higher Ru losses, mainly through the release of carbon domains containing Ru. Metal oxides were compared to AC by synthesising 2%Ru catalysts on alpha-Al2O3, ZrO2 and TiO2. They yielded 20-40 times higher Ru loss rates than for 2%Ru/AC and a significantly lower activity, confirming once again the superiority of Ru/C as SCWG catalyst. Ru losses were similar on larger rigs during glycerol and sewage sludge gasification, with values around 0.14-0.29 µg gRu-1 h-1.With Ru/CNF proving to be an interesting SCWG catalyst, more in-depth studies were performed on this system. Catalysts of different loadings (1-30%) were successfullysynthesised yielding very small Ru NPs (0.9-2.2 nm) with an easy synthesis method. Ru/CNF catalysts exhibited high gasification activities and improved stability compared to Ru/AC. The initial activity correlated with the Ru dispersion. However, 1%Ru/CNF catalysts underwent rapid deactivation compared to 5%Ru/CNF, showing the importance of site density to avoid rapid deactivation. The effect of surface Ru atom density was shown with a optimum in turnover frequency in the range 0.4-0.7 atomRu,sfc nm-2. For the first time, a particle size effect and more importantly a surface atom density effect was shown during SCWG of glycerol. Coke deposition was also investigated and observed at very high space velocities. The coke deposits could partially be removed by extraction in a mix of solvents, opening a potential new route for the regeneration of Ru/C catalysts.

EPFL2021

Chargement

2012

Supported ruthenium nanoparticles for supercritical water gasification - synthesis, activity and stability

Christopher Marc Hunston

EPFL2021