Tropane and related alkaloid skeletons via a radical [3+3]-annulation process.

Tropanes and related bicyclic alkaloids are highly attractive compounds possessing a broad biological activity. Here we report a mild and simple protocol for the synthesis of N-arylated 8-azabicyclo[3.2.1]octane and 9-azabicyclo[3.3.1]nonane derivatives. It provides these valuable bicyclic alkaloid skeletons in good yields and high levels of diastereoselectivity from simple and readily available starting materials using visible-light photoredox catalysis. These bicyclic aniline derivatives are hardly accessible via the classical Robinson tropane synthesis and represent a particularly attractive scaffold for medicinal chemistry. This unprecedented annulation process takes advantage of the unique reactivity of ethyl 2-(acetoxymethyl)acrylate as a 1,3-bis radical acceptor and of cyclic N,N-dialkylanilines as radical 1,3-bis radical donors. The success of this process relies on efficient electron transfer processes and highly selective deprotonation of aminium radical cations leading to the key α-amino radical intermediates

Electron and Proton Transfers Modulate DNA Binding by the Transcription Regulator RsrR

The [Fe2S2]-RsrR gene transcription regulator senses the redox status in bacteria by modulating DNA binding, while its cluster cycles between +1 and +2 states-only the latter binds DNA. We have previously shown that RsrR can undergo remarkable conformational changes involving a 100° rotation of tryptophan 9 between exposed (Out) and buried (In) states. Here, we have used the chemical modification of Trp9, site-directed mutagenesis, and crystallographic and computational chemical studies to show that (i) the Out and In states correspond to oxidized and reduced RsrR, respectively, (ii) His33 is protonated in the In state due to a change in its pKa caused by cluster reduction, and (iii) Trp9 rotation is conditioned by the response of its dipole moment to environmental electrostatic changes. Our findings illustrate a novel function of protonation resulting from electron transfer

Etude par ENDOR de deux centres paramagnetiques |Fe_4S_4|"3"+. Couplages hyperfins des protons et structure electronique et magnetique de ces deux cubanes

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 78367 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Modélisation de l'interaction d'échange par théorie de la fonctionnelle de la densité couplée au formalisme de la symétrie brisée. Application aux dimères de cuivre

La Théorie de la Fonctionnelle de la Densité (DFT) combinée avec la méthode de la Symétrie Brisée (BS) est aujourd'hui très utilisée dans le domaine du magnétisme moléculaire pour le calcul des constantes d'échange. Cette méthode (DFT-BS) reste cependant semi-quantitative et elle souffre de défauts déjà discutés dans la littérature. Dans le but de mieux en comprendre l'origine, nous avons réexaminé les contributions physiques qui participent au mécanisme d'échange. Nous proposons alors plusieurs formules analytiques construites suivant deux approches complémentaires (orbitales moléculaires et liaison de valence). Au cours de notre analyse, nous avons soulevé un problème inédit relatif à l'état de symétrie brisée tel que livré par le calcul DFT. Nos modèles seront appliqués au cas des dimères de cuivre(II) et nous verrons comment quantifier les différents paramètres afin de reconstruire les constantes d'échange. Qui plus est, notre travail permet d'établir une correspondance quantitative originale entre les deux approches pré-citées.Density Functional Theory (DFT) combined with the Broken Symmetry (BS) method is today widely used in the field of molecular magnetism for the computation of exchange coupling constants. But this method (DFT-BS) remains semi-quantitative as it suffers from a series of drawbacks already discussed in the literature. In order to better understand the origin of such problems, we reexamined the physical contributions acting in the exchange phenomenon. We then propose alternative analytical expressions built along two complementary approaches (molecular orbitals and valence bond). During our analysis, we found a new problem linked to the broken symmetry state as it comes out of a DFT calculation. Our models will be applied to copper(II) dimers and we will show how to quantify the different parameters involved in order to reconstruct the coupling constants. Moreover, our work allows for an original quantitative correspondence between the two above-mentioned approaches.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Etude par la Théorie de la Fonctionnelle de la Densité des propriétés électroniques et magnétiques de complexes de fer. Application aux systèmes de types Catalase et Fer-Soufre

Ce travail de thèse s'articule selon deux axes principaux et vise à modéliser, au moyen de la Théorie de la Fonctionnelle de la Densité (DFT), des grandeurs spectroscopiques (Mössbauer, RPE et magnétisme) mesurées pour des systèmes bioinorganiques à base de fer. La première partie de ce travail est relative au calcul théorique de deux quantités caractéristiques issues de la spectroscopie Mössbauer : le déplacement isomérique et de l'éclatement quadripolaire EQ. Dans un premier temps, des corrélations calculs-expérience ont été mises en place pour l'étude de simples complexes de fer. Dans un second temps, nous nous sommes intéressée à l'étude d'un système biologique, la catalase, qui est un composé héminique à base de fer, afin d'en caractériser les différentes formes. La seconde partie de ce travail a été dédiée à la rationalisation des variations conjointes de deux grandeurs spectroscopiques RPE : la valeur moyenne de tenseur , gav (= ( gi)/3), et la constante d'échange effective, Jeff. Nous avons considéré un ensemble d agrégats de type [2Fe-2S] issus de systèmes biologiques (ferrédoxines, protéines Rieske, xanthine oxidases, etc) et nous avons modélisé ces derniers paramètres via un modèle phénoménologique mettant en compétition deux termes antagonistes : le terme B de double-échange traduisant la délocalisation électronique entre les sites de fer et le terme de piégeage E.contribuant à la localisation préférentielle de l électron réducteur sur l un des deux sites de fer. Nous avons pu exprimer analytiquement gav et Jeff en fonction du ratio E/B et expliquer la source des variations observées.This PhD work is divided into two parts and aims at modeling some spectroscopic quantities (Mössbauer, EPR and magnetism) measured in iron containing bioinorganic systems with Density Functional Theory (DFT). The first part of this work deals with the theoretical calculation of two Mössbauer parameters: the isomeric shift and the quadrupole splitting EQ. First, correlations between calculations and experimental data have been established for simple iron complexes. Second, we have been interested in the investigation of a biological system, catalase, an iron containing heme, and we have tried to characterize its various forms. The second part of this work was devoted to rationalizing the variations of two parameters: the EPR g-average value, gav (= ( gi)/3), and the effective exchange coupling constant Jeff. We have considered a set of [2Fe-2S] clusters in biological systems (ferredoxins, Rieske proteins, xanthine oxydases, etc). We have modeled these quantities with a phenomenological model involving the competition between two antagonist terms: the double exchange term B which reflects electronic delocalization between the iron sites and the trapping term E which preferentially localizes the reducing electron on one iron site. We have been able to express analytically gav et Jeff as a function of the ratio E/B allowing us to explain the source of the observed variations.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Mössbauer identification of a protonated ferryl species in catalase from Proteus mirabilis: Density functional calculations on related models

International audienceThe Proteus mirabilis catalase is one of the most efficient heme-containing catalase and forms a relatively stable compound II. Samples of compound II were prepared from PMC enriched in 57Fe. For the first time, two different forms of compound II, namely low pH compound II (LpH II) (43%) and high pH compound II (HpH II) (25%), have been characterized by Mössbauer spectroscopy at pH 8.3. The ratio LpH II/HpH II increases irreversibly with decreasing pH. The large quadrupole splitting value of LpH II (ΔEQ = 2.29 (2) mm/s, with δ/Fe = 0.03 (2) mm/s), compared to that of HpH II (ΔEQ = 1.47 (2) mm/s, with δ/Fe = 0.07 (2) mm/s), reflects the protonation of the ferryl group. Quadrupole splitting values of 1.46 and 2.15 mm/s have been computed by DFT for optimized models of the ferryl compound II (model 1) and the protonated ferryl compound II (model 2), respectively, starting from the FeIVO model initially published by Rovira and Fita [C. Rovira, I. Fita, J. Phys. Chem. B 107 (2003) 5300–5305]. Therefore, we attribute the LpH II compound to a protonated ferryl FeIV–OH complex, whereas the HpH II compound corresponds to the classical ferryl FeIVO complex

Study of Photoinduced N -Hydroxy-arylnitroxide Radicals (ArNO•OH) by Time-Resolved EPR

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The Structural Plasticity of the Proximal [4Fe3S] Cluster is Responsible for the O 2 Tolerance of Membrane-Bound [NiFe] Hydrogenases

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Electronic states of the O2-tolerant [NiFe] hydrogenase proximal cluster

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