Céline Fosse

Coupled Sensitizer-Catalyst Dyads: Electron-Transfer Reactions in a Perylene-Polyoxometalate Conjugate

Ultrafast discharge of a single-electron capacitor: A variety of intramolecular electron-transfer reactions are apparent for polyoxometalates functionalized with covalently attached perylene monoimide chromophores, but these are restricted to single-electron events. (et=electron transfer, cr=charge recombination, csr=charge-shift reaction, PER=perylene, POM=polyoxometalate).A new strategy is introduced that permits covalent attachment of an organic chromophore to a polyoxometalate (POM) cluster. Two examples are reported that differ according to the nature of the anchoring group and the flexibility of the linker. Both POMs are functionalized with perylene monoimide units, which function as photon collectors and form a relatively long-lived charge-transfer state under illumination. They are reduced to a stable pi-radical anion by electrolysis or to a protonated dianion under photolysis in the presence of aqueous triethanolamine. The presence of the POM opens up an intramolecular electron-transfer route by which the charge-transfer state reduces the POM. The rate of this process depends on the molecular conformation and appears to involve through-space interactions. Prior reduction of the POM leads to efficient fluorescence quenching, again due to intramolecular electron transfer. In most cases, it is difficult to resolve the electron-transfer products because of relatively fast reverse charge shift that occurs within a closed conformer. Although the POM can store multiple electrons, it has not proved possible to use these systems as molecular-scale capacitors because of efficient electron transfer from the one-electron-reduced POM to the excited singlet state of the perylene monoimide.

(η6-Arene) ruthenium(II) complexes and metallo-papain hybrid as Lewis acid catalysts of Diels–Alder reaction in water

Covalent embedding of a (eta(6)-arene) ruthenium(II) complex into the protein papain gives rise to a metalloenzyme displaying a catalytic efficiency for a Lewis acid-mediated catalysed Diels-Alder reaction enhanced by two orders of magnitude in water.

Cysteine‐Specific, Covalent Anchoring of Transition Organometallic Complexes to the Protein Papain from Carica papaya

Site‐directed and covalent introduction of various transition metal–organic entities to the active site of the cysteine endoproteinase, papain, was achieved by treatment of this enzyme with a series of organometallic maleimide derivatives specially designed for the purpose. Kinetic studies made it clear that time‐dependent irreversible inactivation of papain occurred in the presence of these organometallic maleimides as a result of Michael addition of the sulfhydryl of Cys25. The rate and mechanism of inactivation were highly dependent on the structure of the organometallic entity attached to the maleimide group. Combined ESI‐MS and IR analysis indicated that all the resulting papain adducts contained one organometallic moiety per protein molecule. This confirmed that chemospecific introduction of the metal complexes was indeed achieved. Thus, three novel reagents for heavy‐atom derivatization of protein crystals, which include ruthenium, rhenium and tungsten, are now available for the introduction of electron‐dense scatterers for phasing of X‐ray crystallographic data.

Braunicetals: acetals from condensation of macrocyclic aldehydes and terpene diols in Botryococcus braunii.

Two series of braunicetals were isolated from the green microalga Botryococcus braunii. Based on spectroscopic and chemical evidence, their structures were determined to be acetals formed by the condensation of C32 and C34 macrocyclic aldehydes with C33 and C34 methylated squalene diols (series I), or a C40 lycopaene diol (series II).

Facile synthesis and electrochemical properties of two trinuclear ruthenium complexes based on star-shaped terpyridine derivatives

Two trinuclear ruthenium complexes [{TolylTerpyRu}3(L3A)]·(PF6)9 and [{TolylTerpyRu}3(L3B)]·(PF6)9 containing the star-shaped ligands 1,3,5-tris{[4′-(2,2′:6′,2″-terpyridinyl)-1-pyridiniumyl]methylphenyl}benzene (L3A) and 2,4,6-tris{[4′-(2,2′:6′,2″-terpyridinyl)-1-pyridiniumyl]methyl}mesitylene (L3B), respectively, have been synthesized and characterized using electrospray ionization mass spectrometry, UV-Vis spectroscopy, 1H and 13C NMR spectroscopy. These cationic ligands have been synthesized using a 1,3,5-triphenylbenzene or a mesitylene core and the N-alkylation of the 4′-pyridyl group of 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine (terpy,py). The electrochemical properties of the two trinuclear ruthenium complexes have been compared to analogous dinuclear and mononuclear ruthenium complexes.

A biosynthetic microbial ability applied for the oxidative ring cleavage of non-natural heterocyclic quinones

Abstract The regiospecific oxidative ring cleavage of naphthothiazole and naphthooxazole quinonic derivatives was performed by a microbial methodology using a Streptomyces strain. The subsequent CC bond cleaved products were new 2-substituted-5-(2-hydroxybenzoyl)thiazole or oxazole-4-carboxylic acid derivatives obtained in one step with 30–65% yields.