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Concept

Isomérie cis-trans

En chimie organique, les préfixes cis et trans servent à préciser la configuration géométrique d'une molécule en spécifiant si, par rapport à la chaine principale de la molécule décrite, les principaux groupes fonctionnels sont situés du même côté (cis-, « ensemble » en latin) ou au contraire de part et d'autre (trans-, « à travers » en latin). Les deux configurations cis- et trans- sont donc diastéréoisomères. Pour la détermination cis/trans, la priorité des substituants est définie selon leur encombrement stérique, et non selon la nomenclature Cahn-Ingold-Prelog. Une molécule est dite « trans » si les groupes prioritaires se trouvent de part et d'autre de la double liaison carbone-carbone ; une molécule est dite « cis » par la présence des groupes prioritaires du même côté de la double liaison carbone-carbone ; un exemple d'alcène en présentant l'isomérie cis/trans est le β-butylène (aussi appelé but-2-ène). Cis-2-butene.svg|(''Z'')-butène ou (''Z'')-but-2-ène ou ''cis''-but-2

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CH-112: Organic chemistry

L'objectif de ce cours est de fournir les connaissances et le moyen de comprendre, au niveau moléculaire, le fonctionnement des réactions chimiques organiques. Pendant le cours, l'étudiant réfléchira et résoudra de nouveaux problèmes.

CH-223: Organometallic chemistry

Basic organometallic chemistry will be covered in this course.

Structure and bonding in organometallic compounds.
reactivity of organometallic compounds, stoichiometric reactions, catalyzed reactions and reaction mechanisms.

CH-422: Catalyst design for synthesis

This course on homogeneous catalysis provide a detailed understanding of how these catalysts work at a mechanistic level and give examples of catalyst design for important reactions (hydrogenation, olefin metathesis, cross-coupling).

Mechanistic Insight into Supramolecular Polymerization in Water Tunable by Molecular Geometry

Lukas Pfeifer, Fan Xu

Supramolecular self-assembly in water based on non-covalent bonding is attracting major attention due to the potential of hydrogels and aqueous polymers in biomedical applications. Although supramolecular polymerization in organic solvents is well established, the key design features, the assembly mechanisms in water and achieving control over the aggregate structures remain challenging. Here, we present the assembly and disassembly of geometrical isomers of a stiff-stilbene bis-urea amphiphile (SA) in pure water. A remarkable feature of this system is that the (E)-isomer forms supramolecular polymers in both pure water and organic solvents. Taking advantage of this unique property, the hydrophobic effect was studied by comparing the supramolecular assembly in both systems. The assembly process in water follows an enthalpy-driven nucleation-elongation (cooperative) supramolecular polymerization mechanism with a standard Gibbs free energy (Delta G degrees = -53 kJ mol(-1)) double the value of the one found in toluene. We attributed this distinctive feature to the hydrophobic effect in water. Furthermore, we discovered an isomer-dependent assembly process, which can be used to control aggregation in aqueous media. Due to the substantial geometric difference between (E)-SA and (Z)-SA, we compared their assembly in water to study the influence of different driving forces involved in the process. The supramolecular polymerization of (E)-SA was cooperatively influenced by hydrogen bonding, pi-stacking, and hydrophobic effects, whereas the assembly of (Z)-SA was mainly driven by hydrophobic effects. As a result, the fiber length of (E)-SA in water is much longer than that of (Z)-SA, presenting opportunities for geometrical control of aggregation in aqueous media. [GRAPHICS]

CHINESE CHEMICAL SOC2022

Chargement

Dearomatization of electron poor six-membered N-heterocycles through [3+2] annulation with aminocyclopropanes

Shyamal Chakrabarty, Johannes Preindl, Jérôme Waser

Many abundant and highly bioactive natural alkaloids contain an indolizidine skeleton. A simple, high yielding method to synthesize this scaffold from N-heterocycles was developed. A wide range of pyridines, quinolines and isoquinolines reacted with donor-acceptor (DA)-aminocyclopropanes via an ytterbium(III) catalyzed [3 + 2] annulation reaction to give tetrahydroindolizine derivatives. The products were obtained with high diastereoselectivities (dr > 20 : 1) as anti-isomers. Additionally, the formed aminals could be easily converted into secondary and tertiary amines through iminium formation followed by reduction or nucleophile addition. This transformation constitutes the first example of dearomatization of electron-poor six-membered heterocycles via [3 + 2] annulation with DA cyclopropanes.

2017

Chargement

Generation of photoswitchable peptide ligands by phage display

Silvia Bellotto

Photoswitchable ligands are used to control and study complex biological systems such as folding of proteins and peptides, enzymatic reactions or neuronal signaling. They are typically developed by conjugating photochromic compounds to known ligands so that exposure to light results in the change of the binding affinity of the ligand. Many light-responsive ligands are based on azobenzene, a molecule that undergoes a pronounced change in geometry upon photoisomerization from trans to cis in picoseconds. Currently, photoswitchable ligands are available only to a limited number of targets and their development by rational design is complex. Furthermore, they show low affinity and a relatively small change in binding affinity between the cis and trans conformation. In my PhD work, I aimed at overcoming these shortcomings by establishing an in vitro evolution method to generate light-controlled peptide ligands to targets of choice. Combining the expertise on phage display technology of the Heinis' lab and the knowledge about azobenzene photoswitches of the Wegner's lab, I screened large combinatorial libraries of cyclic peptides containing an azobenzene-based linker for the generation of light controlled ligands. [...]

EPFL2015

Chargement

Chimie

thumb|upright=1.5|Structure chimique de l'ADN. La chimie est une science de la nature qui étudie la matière et ses transformations, et plus précisément les atomes, les molécules, les réactions chimiq

Isomer

In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism refer

Chiralité (chimie)

Le concept de la chiralité existe également dans d'autres domaines. En chimie, un composé est dit chiral (du grec χείρ : la main) s'il n'est pas superposable à son image dans un miroir plan. Il e