Ligand (chimie) | EPFL Graph Search

Un ligand est un atome, un ion ou une molécule portant des groupes fonctionnels lui permettant de se lier à un ou plusieurs atomes ou ions centraux. Le terme de ligand est le plus souvent utilisé en chimie de coordination et en chimie organométallique (branches de la chimie inorganique). L'interaction métal/ligand est du type acide de Lewis/base de Lewis. La liaison ainsi formée est nommée « liaison covalente de coordination ». Dans ce cadre, l'association d'un ou de plusieurs cation(s) (ou atome) métallique(s) central(aux) avec un/des ligands(s) est un édifice qui se nomme « complexe de coordination » (ou « complexe organométallique » s'il contient au moins une liaison métal-carbone). Le mot français désignant un ligand est « coordinat ». En effet, ligand est un mot anglais, bien que très employé en chimie française. Différents types de ligands - Denticité Denticité Les ligands sont de nature très variée. Parmi les plus courants, on trouve des molécules porteuses de do

Copper(I) Based Photoredox Chemistry

Murat Alkan

Photoredox catalysis has become a powerful tool for chemists. However, the reliance on expensive Ir and Ru based photoredox catalysts (PC) motivates research for more sustainable options. Copper complexes based on favorable photophysical properties, high abundance and comparatively low prices offer a more sustainable alternative which is outlined in Chapter 1. This dissertation is dedicated to the development of new Cu(I) complexes and their investigation as PCs. Chapter 2 describes the synthesis of a new 2,2'-bipyridine (bpy) based ligand and the heteroleptic [Cu(N^N)(P^P)][PF6] complexes in combination with 4,5-Bis(diphenyl- phosphino)-9,9-dimethylxanthene (Xantphos, 1) and Bis[(2-diphenylphosphino)phenyl] ether (POP, 2). The complexes were thoroughly characterized and employed as PCs for the chlorotrifluoromethylation of activated alkenes with CF3SO2Cl. Complex 1 shows high activity with high yields and wide functional group tolerance in the chlorotrifluoromethylation of styrenes as well as alkenes adjacent to electron-withdrawing groups. The reaction with unactivated alkenes proved to be inefficient. Consequently, the design, synthesis and application of a new Cu(I) based photoredox catalyst is described. Chapter 3 details the use of complex 1 as PC for the chlorosulfonation of alkenes and alkynes with sulfonyl chlorides. The reactions occur under mild conditions and exhibit high functional group tolerance with broad scope in terms of both alkene and sulfonyl chloride. Notably, the reaction occurs with alkynes albeit in moderate to low yields to give exclusively the (E)âproduct. Chapter 4 reports the synthesis of new bpy based ligands and their heteroleptic [Cu(N^N)(xantphos)][PF6] complexes to investigate possible structure-activity relationships. The synthesized Cu(I) complexes are characterized and their activities as photoredox catalysts compared to different Cu(I) based complexes are investigated. Consequently, it is shown that PC 1 is the most active catalyst in the chlorosulfonation of styrenes based on a variety of substrates due its long excited state lifetime in combination with a relatively high photoluminescence quantum yield and photo-stability.

EPFL2020

Electron Beam Induced Copper Deposition from Carboxylate Precursors and the Study of Underlying Growth Mechanisms

Luisa Berger

The fabrication of defined and high-quality metal nanostructures is an ongoing topic of research. Direct-write deposition of copper nanostructures is of great value for many fields of research and industrial applications. Focused electron beam induced deposition (FEBID) is an additive fabrication technique with extremely high resolution and versatility. Physisorbed, gaseous precursor molecules are locally dissociated by a finely focused electron beam resulting in volatile fragments which desorb and non-volatile fragments forming the deposit. When applying suitable deposition parameters, these deposits can be as small as the beam diameter and have ideally little to no contamination. For electron beam induced metal deposition, metal-organic compounds are chosen as precursors. However, organic ligand material is often co-deposited, which is detrimental to the depositâs properties. This work addresses the study of the perfluorinated copper carboxylate [Cu2(ÎŒ-O2CC2F5)4] (Cu2(pfp)4) and its aminated derivatives Cu2(EtNH2)2(pfp)4 and Cu2(tBuNH2)2(pfp)4 as viable FEBID precursors. 25 at.% of copper was achieved with the amine free compound, and 15 at.% with each of the two aminated complexes. Based on the chemical analysis of the deposits, electron-induced dissociation paths were proposed for the adsorbed species, demonstrating the influence of the ligand chemistry and fragmentation on the deposit composition. In parallel, the perfluorinated silver carboxylate Ag2(pfp)2 was reported and compared directly to its copper equivalent. The silver complex yielded up to 74 at.% metal content and exhibited strong susceptibility to varying electron beam densities throughout the deposit. Cu2(pfp)4 did not manifest the same electron sensitivity. Theoretical models, combining analytical solutions with Monte Carlo simulations of primary and backscattered electrons were successfully fitted to the cross sections of deposits from both carboxylates, determining the growth regimes within a single spot deposit. Additionally, two previously reported Î²-diketonates, Cu(hfac)2 and Cu(tbaoac)2, were directly compared to the other Cu(II) precursors with the aim to determine any dependence of the ligand size, electron density or dwell time on the deposit purity. The investigations concluded that the metal content rather depends on the chemistry of the metal-ligand bond than on the ligand size. This applies to both, the variation of ligands and the variation of the metal center. vii Furthermore, two copper complexes, Cu(hfac)2 and Cu2(pfp)4, were investigated in situ with a dedicated, custom-made setup. The âeQCMâ combines a low energy electron source (10- 100 eV) with a quartz crystal microbalance and serves to study fundamental processes occurring during FEBI deposition. First results yielded the total dissociation cross section for each precursor at varying electron energies. Finally, alternative approaches for the electron induced copper deposition from Cu2(pfp)4 were investigated. A two-step post-purification recipe of as-deposited material was reported to yield pure copper crystals (> 97 at.%). Additionally, direct electron beam lithography in a layer of condensed precursor was explored. This room temperature deposition approach yielded in lower metal contents but could potentially produce high resolution deposition.

EPFL2020

Electrophysiology and fluorescence microscopy of ligand-gated ion channels

Christoph Schreiter

The thesis presented here describes studies of ligand binding, function, and arrangement of ligand-gated ion channels in cell membranes. Fluorescence microscopy and the patch clamp technique are used to investigate the nicotinic acetylcholine receptor and the serotonergic 5-HT3 receptor. Charge effects on ligand binding were investigated on the 5-HT3 receptor by site directed mutagenesis of strongly conserved charged amino acids close to the ligand-binding site. It turns out that steric effects have a higher impact on ligand binding than charges but that charged amino acids change the local environment strongly. This was exploited using a fluorescently labelled ligand to determine the distance of the bound ligand to the mutated amino acid. Ligand binding to the acetylcholine receptor was studied with a novel fluorescent ligand based on a toxin from the venom of marine snails (α-conotoxin GI).The fluorescent toxin acts as antagonist and can be bind completely reversible and with excellent specificity to muscle type acetylcholine receptors. Repetitive cycles of binding and unbinding were performed to obtain binding kinetics on single cells.The developed fluorescence microscope experiment enables the detection of only very low amount of fluorescent ligand from around 103 down to single molecules. The reversible binding was exploited to label single acetylcholine receptor and to monitor their diffusion in cell membranes. HEK293 cells served as a model system where co-expression of the anchoring protein rapsyn strongly influences receptor diffusion. Data were compared to diffusion in muscle cell lines during differentiation into myotubes. To obtain new information on ligand binding and channel gating, an experiment has been developed to simultaneously measure fluorescence and ion channel activity. The fluorescently labelled α-conotoxin GI was used to demonstrate the capability of this system. In addition, to increase the yield of electrophysiological measurements, a technique to perform patch clamp on a chip was further developed towards automation.

EPFL2005

Copper(I) Based Photoredox Chemistry

Murat Alkan

EPFL2020

Electrophysiology and fluorescence microscopy of ligand-gated ion channels

Christoph Schreiter

EPFL2005

Electron Beam Induced Copper Deposition from Carboxylate Precursors and the Study of Underlying Growth Mechanisms

Luisa Berger

EPFL2020