Azote solide

L'azote solide est la forme solide de l'élément azote. Il s'obtient par refroidissement du diazote en dessous d'environ , sous une atmosphère. Production L'azote solide a été produit pour la première fois en 1884, par liquéfaction de l'hydrogène à l'aide de l'évaporation d'azote liquide et ensuite en utilisant l'hydrogène liquide pour geler l'azote. De nos jours, il s'obtient industriellement en diminuant la pression de l'azote liquide bouillant (en équilibre avec sa vapeur saturante) par un pompage par le vide. Il sert principalement à former le mélange azote liquide-solide afin d'obtenir un fluide refroidissant plus efficace que l'azote liquide bouillant. Occurrence naturelle vignette|droite|Une grande partie de la surface de Triton est couverte par la forme hexagonale de l'azote solide (la phase β), qui apparaît comme une bande vert-bleuâtre autour de l'équateur sur ce photomontage. Il s'agit d'un composant de surface important de Pluton et de certaines lune

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Isolation and characterization of diazoolefins

Zhaowen Dong, Farzaneh Fadaei Tirani, Rosario Scopelliti, Kay Severin, Paul Varava

Diazoolefins tend to be highly reactive compounds that rapidly lose dinitrogen. So far, most experimental evidence for diazoolefins is indirect, via trapping experiments. Here we show that diazoolefins are observed to form in reactions of N-heterocyclic olefins with nitrous oxide. The products benefit from resonance stabilization, which enables isolation on a preparative scale, and comprehensive characterization, which includes crystallographic analyses. N-heterocyclic diazoolefins show a strong ylidic character, with a high charge density at the carbon atom next to the diazo group. Despite the presence of terminal N2 groups, N-heterocyclic diazoolefins display a good thermal stability, which surpasses that observed for most diazoalkanes. N-heterocyclic diazoolefins can bind transition and main group metal complexes without the liberation of dinitrogen, and spectroscopic data show that they are strong electron donors. They can also undergo reactions that involve the N2 group, as evidenced by cycloaddition reactions.

2021

Chargement

When neighbours become competitors - Autotrophic assimilation rates of individual symbionts depend on local density when Stylophora pistillata is regularly fed

Maoz Fine, Thomas Krüger, Anders Meibom

The symbiosis between dinoflagellate microalgae and their cnidarian host represents the fundamental mechanism that allows zooxanthellate corals to access the inorganic nutrient pool of the surrounding seawater and conserve and recycle nutrients within their tissues. Experiments have shown that colony symbiont density is strongly affected by ambient nitrogen levels and the nitrogen status of the host. Under oligotrophic conditions, the symbiont population is N- and potentially DIC-limited. Here, we investigated how a feeding-induced increase in colony symbiont density modulates the phototrophic assimilation of individual symbionts. Using stable isotopes in combination with NanoSIMS-imaging of fixed coral coenosarc tissue, we quantified in hospite C and N assimilation of individual symbionts and related these values to the local tissue density. Stylophora pistillata displayed a general negative correlation between colony symbiont density and symbiont carbohydrate and protein content, independent of feeding state. Under unfed conditions, cell-specific assimilation rates for C and N were not affected by local symbiont density. However, when the colony symbiont density was increased by regular feeding, we observed a significant negative effect: Individual autotrophic assimilation of C and N declined on average by 26% for a local density range from one to ten Symbiodinium cells. Thus, the increase in global symbiont density created conditions where symbionts in some microhabitats might be subject to competition, governed by individual performance, local host supply or light microenvironment.

2017

Chargement

Synthesis of Four-Membered BN3 Heterocycles by the Borylation of Triazenes

Rosario Scopelliti, Kay Severin, Abdusalom Suleymanov

Borylated triazenes were synthesized by the dehydrocoupling of triazenes with 9-borabicyclo(3.3.1)nonane, by the condensation of triazenes with BEt3, or by the reaction of sodium triazenides with dialkyl- or diarylboron halides. The structures of the products were found to depend on the size of the substituents. Sterically demanding mesityl groups at boron or nitrogen gave rise to open-chain structures, whereas smaller substituents led to the formation of novel BN3 heterocycles.

2022

Chargement

ChE-204: Introduction to transport phenomena

This course aims at understanding the basic equations behind macroscopic and microscopic transport phenomena (mass, heat and momentum).

CH-160(en): Advanced general chemistry (english)

This course aims to teach essential notions of the structure of matter, chemical equilibria and reactivity. Classes and exercises provide the means to analyze and solve, by reasoning and calculation, novel problems of geeneral chemistry.

EE-582: Lessons learned from the space exploration

The objective of the course is to present with different viewpoints, the lessons learned which lead to the decisions in the space exploration and their consequences today and for the decades to come. A semester continuous evaluation is done through a project (see below).

Azote

L'azote est l'élément chimique de numéro atomique 7, de symbole N (du latin nitrogenium). C'est la tête de file du groupe des pnictogènes. Dans le langage courant, l'azote désigne le corps simple N

New Horizons

New Horizons (« Nouveaux Horizons » en français) est une sonde de l'agence spatiale américaine (NASA) dont l'objectif principal est l'étude de la planète naine Pluton et ses satellites, ce qui a été r

Ceinture de Kuiper

La ceinture de Kuiper (parfois appelée ceinture d'Edgeworth-Kuiper, prononcé en néerlandais : ) est une zone du Système solaire s'étendant au-delà de l'orbite de Neptune, entre 30 et (au). Cette zo