Electrocarboxylation of chloroacetonitrile mediated by electrogenerated cobalt(I) phenanthroline

The electrocarboxylation of chloroacetonitrilemediated by [Co(II)(phen)3]2+ has been investigated. Cyclic voltammetry studies of [Co(II)(phen)3]2+ have shown that [Co(I)(phen)3]+, an 18 electron complex, activates chloroacetonitrile by an oxidative addition through the loss of a phenanthroline ligand to give [RCo(III)(phen)2Cl]+. The unstable one-electron-reduced complex underwent Co–C bond cleavage. In carbon dioxide saturated solution, CO2 insertion proceeds after reduction of the alkylcobalt complex. A catalytic current is observed which corresponds to the electrocarboxylation of chloroacetonitrile into cyanoacetic acid. Electrolyses confirmed the process and gave faradic yield of 62% in cyanoacetic acid at potentials that are about 0.3 V less cathodic than the one required for Ni(salen)

Electrocarboxylation of chloroacetonitrile by a Cobalt(I) complex of terpyridine

The electrocarboxylation of chloroacetonitrile (NC–CH2–ClRCl) mediated by [CoIIL2]2+ (L = terpyridine) was investigated by cyclic voltammetry. Electrochemical studies under argon atmosphere showed that the monoelectronic reduction of [CoIIL2]2+ yielded a Cobalt(I) complex which after the loss of a terpyridine ligand reacted with chloroacetonitrile. The oxidative addition of chloroacetonitrile on [CoIL]+ gave an alkylCobalt(III) complex [R–CoIIIL]2+ which was reduced into an alkylCobalt(II) complex, highly unstable and decomposed into an alkyl anion and a Cobalt(II) complex. Under carbon dioxide atmosphere, Cobalt(I) complex was shown to be unreactive towards CO2 but CO2 insertion was observed in the alkylCobalt(III) complex [R–CoIIIL] 2+ giving probably a CO2 adduct [R–CoIIIL(CO2)]2+. This adduct presented a strong adsorption at the carbon electrode and was reduced at potential less cathodic than the one of alkylCobalt(III) complex. After reduction, the carboxylate RCO2− (NC–CH2–CO2−) was released and a catalytic bielectronic carboxylation of chloroacetonitrile took place. Controlled potential electrolyses confirmed the catalytic process and gave for cyanoacetic acid faradic yields up to 60% under low overpotential conditions

X-ray structures of dinuclear copper(I) and polynuclear copper(II) complexes with the 2,4-bis(cyanamido)cyclobutane-1,3-dione dianion

From the 2,4-bis(cyanamido)cyclobutane-1,3-dione dianion (2,4-NCNsq2−), two copper complexes [Cu2(PPh3)4(PhCN)2(μ-2,4-NCNsq)] · PhCN (1) and [Cu(dien)(μ-2,4-NCNsq) · H2O]n (2) have been synthesized and characterized by IR and electronic absorption spectroscopies. Their structures have been determined by X-ray crystallography. Complex 1 is a dinuclear copper(I) compound with a 2,4-NCNsq2− ligand bridging two copper atoms through the nitrile nitrogen atoms. Complex 2 appears as a 3D network constituted of copper(II) atoms bridged by 2,4-NCNsq2− dianions. This complex presents an unexpected coordination mode of the bis(cyanamido) ligands which are both coordinated via the nitrile functions and via the amido nitrogen atoms of the NCN groups

Unexpected effect of copper ions on electrochemical impedance behaviour of self-assembled alkylaminethiol monolayer

Effect of copper ions on the electrochemical behaviour of an alkylaminethiol monolayer has been studied by electrochemical impedance spectrosocpy. RAMAN experiment shows the effective adsorption of receptor onto the gold surfaces. The study of Nyquist plot shows that the gold/monolayer/electrolyte interface can be described by a serial combination of two R, CPE electrical circuits. In the presence of increasing amounts of copper, the Nyquist plots at low frequencies were modified showing an increase of the resistance of the second R, CPE electrical circuit. Moreover, this increase of resistance varies linearly with the amounts of copper ions added in solution from 10−8 mol·L−1 to 10−5 mol·L−1

Characterization of oxidative stress in Leishmaniasis-infected or LPS-stimulated macrophages using electrochemical impedance spectroscopy

The physiological changes caused by external stimuli can be employed as parameters to study pathogen infection in cells and the effect of drugs. Among analytical methods, impedance is potentially useful to give insight into cellular behavior by studying morphological changes, alterations in the physiological state, production of charged or redox species without interfering with in vitro cellular metabolism and labeling. The present work describes the use of electrochemical impedances spectroscopy to simply monitor by modeling impedance plots (Nyquist diagram) in appropriate equivalent circuit, the changes affecting murine macrophage cell line (RAW 264.7) in response to parasite infection by Leishmania amazonensis or to lipopolysaccharide (LPS) treatment. These results demonstrate the ability of electrochemical impedance spectroscopy to discriminate between two opposite cell responses associated to two different stimuli, one caused by the internalization of a parasite, and the other by activation by a bacterium component. Indeed, the study has allowed the characterization, from an electrical point of view, of the extra-cellular NO radical produced endogenously and in great quantities by the inducible form of NO-synthase in the case of LPS-stimulatedmacrophages. This production was not observed in the case of Leishmania-infectedmacrophages for which to survive and multiply, the parasite itself possesses mechanisms which may interfere with NO production. In this latest case, only the intracellular production of ROS was observed. To confirm these interpretations confocal microscopy analysis using the ROS (reactive oxygen species) fluorescent probe 2′,7′-dichlorodihydrofluorescein diacetate and electron paramagnetic resonance experiments using Fe(DETC)2 as NO radical spin trap were carried out

Electrochemical impedance spectroscopy to study physiological changes affecting the red blood cell after invasion by malaria parasites

The malaria parasite, Plasmodium falciparum, invades human erythrocytes and induces dramatic changes in the host cell. The idea of this work was to use RBC modified electrode to perform electrochemical impedance spectroscopy (EIS) with the aim of monitoring physiological changes affecting the erythrocyte after invasion by the malaria parasite. Impedance cell-based devices are potentially useful to give insight into cellular behavior and to detect morphological changes. The modelling of impedance plots (Nyquist diagram) in equivalent circuit taking into account the presence of the cellular layer, allowed us pointing out specific events associated with the development of the parasite such as (i) strong changes in the host cell cytoplasm illustrated by changes in the film capacity, (ii) perturbation of the ionic composition of the host cell illustrated by changes in the film resistance, (iii) releasing of reducer (lactic acid or heme) and an enhanced oxygen consumption characterized by changes in the charge transfer resistance and in the Warburg coefficient characteristic of the redox species diffusion. These results show that the RBC-based device may help to analyze strategic events in the malaria parasite development constituting a new tool in antimalarial research

Correlations between electrochemical behaviors and DNA photooxidative properties of non-steroïdal anti-inflammatory drugs and their photoproducts

Alkali-labile lesion to DNA photosensitized, via an electron transfer mechanism, by three non-steroidalanti-inflammatorydrugs (NSAIDs), ketoprofen, tiaprofenic acid and naproxen and their photoproducts during drug photolysis, was investigated using 32P-end labelled synthetic oligonucleotide. These photooxidative damages were correlated with the photophysical and electrochemicalproperties of drugs, appearing as the photosensitizer PS. Photophysical studies provided the excited state energies of the photosensitizer while their redox potentials and the relative stabilities of the PSradical dot− radical-anions were determined by cyclic voltammetry. On the basis of these data, we have calculated the Gibbs energy of photoinduced electron-transfer and evaluated the exergonicity of the oxidative photodamage. Moreover, kinetic control may be invoked according to the stabilities of PSradical dot−. Applied to this NSAIDs family, the photoxidative damages through electron transfer mechanism were analyzed and a good correlation with photoredox and photobiological properties was established

Aux origines de la linguistique française de Gabriel Bergounious

Dans une collection qui connaît déjà bon nombre de titres, Gabriel Bergounious nous propose un livre qui s’efforce de nous faire remonter aux origines de la linguistique française, c’est-à-dire de nous faire entrer dans une période qui, grosso modo, va de 1810 à 1914. Ces dates sont en fait les deux moments forts qui marquent, l’un la rupture avec la grammaire des Lumières, l’autre l’émergence de la linguistique contemporaine : Bopp et Saussure, chacun à son balcon, honorant et clôturant une ..

Jean-Marie Petit (1941-2020)

En apprenant le décès de Jean-Marie Petit, ma pensée va en premier lieu à son épouse, Odette Camproux, à qui la Revue des langues romanes présente ses condoléances. Elle se retourne aussi, spontanément, vers le passé, et je ressens immédiatement un sentiment de vide profond et comme une sorte d’injustice : de l’équipe d’occitanistes des années quatre-vingts de l’université Paul-Valéry, me voilà désormais seul ; tour à tour Charles Camproux (dont Jean-Marie était le gendre), puis Marcel Barral..