Tristhiolato Pseudopeptides Bind Arsenic(III) in an AsS 3 Coordination Environment Imitating Metalloid Binding Sites in Proteins

The AsIII binding of two NTA-based tripodal pseudopeptides, possessing three cysteine (ligand L1) or D- penicillamine residues (ligand L2) as potential coordinating groups for soft semimetals or metal ions, was studied by experimental (UV, CD, NMR, and ESI-MS) and theoretical (DFT) methods. All of the experimental data, obtained with the variation of the AsIII:ligand concentration ratios or pH values in some instances, evidence the exclusive formation of species with an AsS3-type coordination mode. The UV-monitored titration of the ligands with arsenous acid at pH = 7.0 provided an absorbance data set that allowed for the determination of apparent stability constants of the forming species. The obtained stabilities (logK ' = 5.26 (AsL1) and logK ' = 3.04 (AsL2)) reflect high affinities, especially for the sterically less restricted cysteine derivative. DFT calculated structures correlate well with the spectroscopic results and, in line with the 1H NMR data, indicate a preference for the all-endo conformers resembling the AsIII environment at the semimetal binding sites in various metalloproteins

Inspections ab initio des hystereses magnetiques et redox

Les systèmes bistables connaissent un intérêt croissant motivé, entre autres, par la perspective d'applications en électronique moléculaire. Parmi ces systèmes certains possèdent la capacité d'exister sous deux états électroniques dans les mêmes conditions, Le. présentant une hystérèse. Deux propriétés sont couramment associées à l'hystérèse, le magnétisme et l'activité rédox. Si ces phénomènes sont connus de longues dates, des zones d'ombre demeurent dans leur mécanisme. Par l'application de calculs ab initio basés sur la fonction d'onde, l'objet de ce travail est de dégager les phénomènes physiques sous-jacents à l'ouverture de boucle d'hystérésis dans les composés à transition de spin (bistabilité magnétique) et dans des complexes de porphyrine (bistabilité rédox). Les ingrédients microscopiques ainsi récoltés sont utilisés pour remonter au comportement macroscopique des matériaux par le biais de modèles thermodynamiques ou de hamiltoniens modèles.Bistable systems are more and more present; part of the reason is to be found in the possible applications in molecular electronics. Sorne of those systems can exist under two different electronic states under the same conditions. As a consequence its present an hysteresis. Two properties are commonly associated with the hysteresis response, magnetism and redox activity. Even though these phenomena are not new, parts of the mechanisms remains unknown. Thanks to wavefunction-based ab initio calculations, this work aims at shedding sorne light on the physics behind the hysteretic behavior in spin-crossover compounds (magnetic bistability) and porphyrin-based complexes (redox bistability). These previous microscopie elements are then collect into thermodynamic models or model Hamiltonian in order to retrieve the macroscopic behaviour of the materials.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Nouvelles chiroporphyrines bridées : synthèse et études de la flexibilité conformationnelle

New chiral porphyrins were designed and synthesized in order to obtain systems where a redox bistability is connected with a conformational switch. The synthesis was inspired by biocartol derived chiral porphyrins already studied in the laboratory: cyclohexyl or cyclopentyl meso-substituted porphyrins with bridles linking two adjacent meso substituents were examined. Thanks to an enzymatic procedure, a kinetic resolution of racemic compound was achieved and led to new chiral porphyrins in both their enantiomeric forms. First, simple systems were studied in order to give an idea of the energies implied in conformational changes. Then, bridled chiroporphyrins with variable bridle length were examined. ln this last case, the influence of bridle length and metallation of the porphyrin on the conformational equilibriums were studied by spectroscopic techniques: nuclear magnetic resonance and circular dichroism.De nouvelles porphyrines chirales ont été conçues et synthétisées dans le but d'accéder à des systèmes où une bistabilité redox pourrait être reliée à une bistabilité conformationnelle. La synthèse de porphyrines portant en méso des substituants cyclohexyl ou cyclopentyl liés deux à deux de façon chirale a été étudiée, en s'inspirant de la structure des porphyrines dérivées du biocartol, étudiées précédemment au laboratoire. La synthèse des nouvelles molécules chirales a pu être menée à bien grâce à la mise en œuvre d'une résolution cinétique du racémique par voie enzymatique. Ainsi, ces porphyrines chirales ont pu être synthétisées dans leurs deux formes énantiomériques. Dans un premier temps des systèmes de porphyrines simples ont été étudiés dans le but de connaitre les énergies de changements conformationnels de ces porphyrines. Dans un second temps nous avons caractérisé les chiroporphyrines bridées, de longueur de bride variable (de 5 à 10 groupements méthylènes). Pour ce cas, l'influence de la longueur de bride et de la métallation sur les équilibres conformationnels a été étudiée par des techniques spectroscopiques: résonance magnétique nucléaire et dichroïsme circulaire.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

DFT analysis of the electronic structure of Fe(IV) species active in nitrene transfer catalysis: influence of the coordination sphere.

International audienceNitrene transfer reactions to various hydrocarbon molecules can be efficiently catalyzed by Fe complexes through a mechanism reminiscent of the oxygen transfer function of oxygenase enzymes. Such enzymes exhibit a high-valent iron oxo Fe(IV) = O as the active species, and it has also been proposed that an analogous species, i.e., Fe(IV) = NR (NR being the nitrene group) is responsible for the nitrene transfer activity. We describe here the influence of the Fe(IV) coordination sphere on some key parameters for nitrene transfer efficacy, such as the spin state of the Fe(IV) cation, the electronic affinity, and the bond dissociation energy of the NHR moiety. We explore here the electronic properties of Fe(IV) = NTs (NTs = tolylsulfonylimido group) mononuclear complexes with ligands involving phenolate and nitrogen donor groups, as catalytic properties with such ligands have been found to be quite promising. Six tetradentate ligands were studied, which derive from three different scaffolds: 2-methylenepyridine-N,N-bis(2-methylene-4,6-dichlorophenol) and 2-methylenepyridine-N,N-bis(2-methylene-4,6-dimethylphenol), N,N-dimethyl-N’,N’-bis(2-methylene-4,6-dichlorophenol) ethylenediamine, and N,N-dimethyl-N’,N’- bis(2-methylene-4,6-dimethylphenol) ethylenediamine, N,N’-bis(2-methylene-4,6-dichlorophenol)-N,N’-dimethyl-1,2-diaminoethane and N,N’-bis(2-methylene-4,6-dimethylphenol)-N,N’-dimethyl-1,2-diaminoethane. Thanks to thorough DFT computations, we present some rationalization of the electronic properties of the resulting Fe(IV) = NTs complexes in relation to their coordination sphere and compare them to other Fe(IV) nitrene active species. We show in particular the important role of the anionic character and strong π-donation of the phenolate groups

DFT modeling of the relative affinity of nitrogen ligands for trivalent f elements: an energetic point of view

In many theoretical studies dealing with the selective complexation of trivalent actinides with respect to trivalent lanthanides, the method of calculation is assessed by comparing computed geometries with crystal structures that are often available. Yet, the selectivity is better rationalized through thermodynamic data, as enthalpy and entropy terms. In this article, we have theoretically modeled competing complexation reactions of [Ce(terpy)₃]³⁺, [U(terpy)₃]³⁺, [Ce(MeBTP)₃]³⁺ and [U(MeBTP)₃]³⁺ systems (terpy = 2,2′:6′2″-terpyridine; MeBTP = methyl-2,6-di(1,2,4-triazin-3-yl)pyridine) within the framework of the Density Functional Theory. Our calculations manage to qualitatively account for the experimental relative stabilities of terpy and MeBTP complexes, and in particular for the better coordinating strength of MeBTP for trivalent uranium. We also show by comparing the MeBTP ligand with its non-alkylated form (HBTP) that model systems often used in quantum chemistry must be carefully chosen when energetic comparisons are undertaken