Hybrid catalysis for enantioselective Baeyer-Villiger oxidation and stereoselective epoxidation: a Cp*Ir complex to fuel FMN and FAD reduction for flavoprotein monooxygenase modules

Taking advantage of the unique properties of two-component flavo-monooxygenases and the ability of [Cp*Ir(bpy-OMe)H]+ to transfer hydrides to reduce flavins, we extended the scope of the pH- and oxygen-robust iridium(iii)-complex to drive the enzymatic reaction of a FMN-dependent Baeyer-Villiger monooxygenase and a FAD-dependent styrene monooxygenase (respectively FPMO Group C and E), using formic acid as H-donor for NADH recycling

Analyse par Résonnance Magnétique Nucléaire à l'Angle Magique de transformation chimiques dans des systèmes hétérogènes

LILLE2-BU Santé-Recherche (593502101) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Kinetics, Dynamics, Photochemistry, and Excited States UV Photochemistry of Acetylacetaldehyde Trapped in Cryogenic Matrices

International audienceThe broad band UV photochemistry of acetylacetaldehyde, the hybrid form between malonaldehyde and acetylacetone (the two other most simple molecules exhibiting an intramolecular proton transfer), trapped in four cryogenic matrices, neon, nitrogen, argon, and xenon, has been studied by IRTF spectroscopy. These experimental results have been supported by B3LYP/6-311G++(2d,2p) calculations in order to get S0 minima together with their harmonic frequencies. On those minima, we have also calculated their vibrationally resolved UV absorption spectra at the time-dependent DFT ωB97XD/6-311++G(2d,2p) level. After deposition, only the two chelated forms are observed while they isomerize upon UV irradiation toward nonchelated species. From UV irradiation effects we have identified several nonchelated isomers, capable, in turn, of isomerizing and fragmenting, even if this last phenomenon seems to be most unlikely due to cryogenic cages confinement. On the basis of these findings, we have attempted a first approach to the reaction path of electronic relaxation. It appeared that, as with acetylacetone, the path of electronic relaxation seems to involve triplet states

Investigation of dirigent like domains from bacterial genomes

International audienceDIRs are mysterious protein that have the ability to scavenge free radicals, which, are highly reactive with molecules in their vicinity. What is even more fascinating is that they carry out from these highly unstable species, a selective reaction (i.e., stereoenantioselective) from a well-defined substrate to give a very precise product. Unfortunately, to date, only three products have been demonstrated following studies on DIRs from the plant world, which until now was the kingdom where these proteins had been demonstrated. Within this kingdom, each DIR protein has its own type of substrate. The products identified to date, have on the other hand, a strong economic impact: in agriculture for example, the biosynthesis of (+)-gossypol could be highlighted (a repellent antifood produced by the cotton plant) by the DIRs of cotton. In forsythia plant species, it is the biosynthesis of (−)-pinoresinol, an intermediate leading to the synthesis of podophyllotoxine (a powerful anicancerous agent) which has been revealed. Recently, a clear path of study, potentially with strong impact, appeared by the hypothesis of the potential existence of protein DIR within the genomes of prokaryotes. The possibility of working with this type of organism is an undeniable advantage: since many sequenced genomes are available and the molecular tools are already developed. Even easier to implement and working on microbes, of less complex composition, offers many opportunities for laboratory studies. On the other hand, the diversity of their environment (e.g., soil, aquatic environments, extreme environmental conditions (pH, temperature, pressure) make them very diverse and varied subjects of study. Identifying new DIR proteins from bacteria means identifying new substrate or product molecules from these organisms. It is the promise of going further in understanding the mechanism of action of these proteins and this will most likely have a strong impact in the fields of agricultural, pharmaceutical and/or food chemistry. Results Our goal is to obtain as much information as possible about these proteins to unlock the secrets of their exceptional functioning. Analyzes of structural and functional genomic data led to the identification of the Pfam PF03018 domain as characteristic of DIR proteins. This domain has been further identified in the sequence of bacterial proteins therefore named as DIR-like (DIRL). We have chosen a multidisciplinary bioinformatic approach centered on bacterial genome identification, gene expression and regulation signals, protein structures, and their molecular information content. The objective of this study was to perform a thorough bioinformatic analysis on these DIRLs to highlight any information leading to the selection of candidate bacteria for further cloning, purification, and characterization of bacterial DIRs. Conclusions From studies of DIRL genes identification, primary structures, predictions of their secondary and tertiary structures, prediction of DIRL signals sequences, analysis of their gene organization and potential regulation, a list of primary bacterial candidates is proposed

Controlling the polymerization of coniferyl alcohol with cyclodextrins

International audienceThe mono-electronic oxidation of coniferyl alcohol leads to phenoxy radicals and ultimately to the synthesis of dimericlignans. Coniferyl alcohol and lignans are all potential guests for cyclodextrins (CDs) to form noncovalent host-guestinclusion complexes. Here, the influence of CDs with different cavity volumes (i.e. α, β or γCD) on the laccase-drivenoxidation of coniferyl alcohol is studied. We are clearly showing that βCD interacts with the lignan products and selectivelyprevent their further oxidation by the enzyme. Moreover, amongst the three lignans generated the system made of alaccase and βCD allows a selective enrichment of pinoresinol, a behaviour somehow mimicking that of plant dirigentproteins

Clicked Bifunctional Dendrimeric and Cyclopeptidic Addressable Redox Scaffolds for the Functionalization of Carbon Nanotubes with Redox Molecules and Enzymes

International audienceCarbon nanotube electrodes were modified with ferrocene and laccase using two different click reactions strategies and taking advantage of bifunctional dendrimers and cyclopeptides. Using diazonium functionalization and the efficiency of oxime ligation, the combination of both multiwalled carbon nanotube surfaces and modified dendrimers or cyclopeptides allows the access to a high surface coverage of ferrocene in the order of 50 nmol cm–2, a 50-fold increase compared to a classic click reaction without oxime ligation of these highly branched macromolecules. Furthermore, this original immobilization strategy allows the immobilization of mono- and bi-functionalized active multicopper enzymes, laccases, via copper(I)-catalyzed azide–alkyne cycloaddition. Electrochemical studies underline the high efficiency of the oxime-ligated dendrimers or cyclopeptides for the immobilization of redox entities on surfaces while being detrimental to electron tunneling with enzyme active sites despite controlled orientation

Pyrene Adsorption on a Ag(111) Surface

International audienceThis work describes the adsorption of pyrene molecules on a Ag(111) surface. We first demonstrate that despite its high vapor pressure, pyrene molecules can form ordered films under ultrahigh vacuum conditions, presenting a well-contrasted diffraction pattern. Studies using high-resolution electron energy loss spectroscopy and ultraviolet photoelectron spectroscopy provide compelling evidence of a physisorbed system where the molecules only weakly interact with the substrate underneath. Comparisons with theoretical calculations, as well as with data obtained from optical spectroscopies, clearly demonstrate that the vibrational and electronic properties of the adsorbed molecules are similar to the expected ones for pristine pyrene. Finally, we used temperature-programmed X-rays photoelectron spectroscopy to study the desorption process of pyrene on the Ag(111) surface and estimate its activation energy to desorption

Modulation of laccase catalysed oxidations at the surface of magnetic nanoparticles

International audienceWe explored the coupling of laccases to magnetic nanoparticles (MNPs) with different surface chemical coating. Two laccase variants offering two opposite and precise orientations of the substrate oxidation site were immobilised onto core-shell MNPs presenting either aliphatic aldehyde, aromatic aldehyde or azide functional groups at the particles surface. Oxidation capabilities of the six-resulting laccase-MNP hybrids were compared on ABTS and coniferyl alcohol. Herein, we show that the original interfaces created differ substantially in their reactivities with an amplitude from 1 to > 4 folds depending on the nature of the substrate. Taking enzyme orientation into account in the design of surface modification represents a way to introduce selectivity in laccase catalysed reactions