Search

The detection of Rhamnolipid virulence factor produced by Pseudomonas aeruginosa involved in nosocomial infections is reported by using the redox liposome single impact electrochemistry. Redox liposomes based on 1,2-dimyristoyl-sn-glycero-3-phosphocholine as a pure phospholipid and potassium ferrocyanide as an encapsulated redox content are designed for using the interaction of the target toxin with the lipid membrane as a sensing strategy. The electrochemical sensing principle is based on the weakening of the liposomes lipid membrane upon interaction with Rhamnolipid toxin which leads upon impact at an ultramicroelectrode to the breakdown of the liposomes and the release/electrolysis of its encapsulated redox probe. We present as a proof of concept the sensitive and fast sensing of a submicromolar concentration of Rhamnolipid which is detected after less than 30 minutes of incubation with the liposomes, by the appearing of current spikes in the chronoamperometry measurement.

In vitro and in vivo experimental models, mainly based on cell cultures, animals, healthy humans and clinical trials, are useful approaches for identifying the main metabolic pathways. However, time, cost, and matrix complexity often hinder the success of these methods. In this study, we propose an alternative non-enzymatic method, using electrochemistry (EC) coupled to liquid chromatography (LC) – high resolution mass spectrometry (HRMS) – DFT theoretical calculations (EC/LC-MS/DFT) for the mimicry/simulation of the environmental degradation of phenylurea herbicides, and for the mechanism elucidation of this class of herbicides. Fenuron, monuron, isoproturon, linuron, monolinuron, metoxuron and chlortoluron were selected as relevant model compounds. The intended compounds are oxidized by EC, separated by LC and detected using electrospray ionization HRMS. The main oxidation products were hydroxylated compounds obtained by substitution and addition reactions. Unstable quinone imines/methines, rarely observed by conventional methods, have been identified during the oxidative degradation of phenylurea herbicides for the first time in this study. Some were directly observed and the others were trapped by glutathione GSH. Reactions such as hydrolytic substitutions (−Cl/+OH and −C3H7/+OH and −CH3/+OH and −OCH3/+OH), aromatic hydroxylation, alkyl carbon hydroxylation, dehydrochlorination/dehydromethylation/dehydromethoxylation and conjugation have been successfully mimicked. The obtained results, supported by theoretical calculations, are useful for simulating/understanding and predicting the oxidative degradation pathways of pesticides in the environment.

This work aims to design a high sensitivity and selectivity biosensor based on the electrochemistry of single impacts onto ultramicroelectrode (UME) to detect and identify various bacterial strains. The main objective is to establish a unique electrochemical signature for each bacterial cell through the individual impact event signal on the surface of the UME [1, 2]. First, we focus on the detection of well-known electroactive Gram-negative bacteria such as Shewanella oneidensis in order to be able to selectively detect these different single cells. In this case, the strategy currently used is to record a chronoamperometric curve in an aqueous potassium phosphate buffer (pH = 7.4) solution containing a redox probe at an UME polarized at the oxidation or reduction potential of the electrochemical active aqueous species and to observe a “current step” when one bacterium impacts the UME, corresponding to a “blocking effect” [3] (Figure A). The response signal expected from single bacterium collision may also be a “current spike” corresponding to either the own electrochemical activity of the bacterium toward the redox probe and the UME applied potential or a “bouncing effect” of the bacterium which does not stick onto UME surface (Figure B). In order to be able to identify the type of bacterial cell striking the UME surface, an adapted functionalization (covalent grafting via reduction of diazonium aryl salts) with appropriate affinity (bio)chemical species such as antibodies or aptamers could be performed. This strategy could confer to the UME surface a selectivity of the signal generated during single impacts. For example, the electro-grafting of diazo-pyridinium cations for microbial fuel cell electrodes showed to promote and improve the development of bacterial electroactive films [4]. [1] E. Lebègue, N. L. Costa, R. O. Louro, F. Barrière, J. Electrochem. Soc. 16 (2020) 105501 [2] A. T. Ronspees, S. N.Thorgaard, Electrochimica Acta. 278 (2018) 412-420 [3] G. Guanyue, W. Dengchao, B. Ricardo, Z. Jinfang, M. Michael V. Anal. Chem. 90 (2018) 12123−12130 [4] H. Smida, E. Lebègue, J-F. Bergamini, F. Barrière, C. Lagrost, Bioelectrochemistry. 120 (2018) 157-165 Figure 1

The single-entity impact method is a very sensitive and powerful electroanalytical tool for biological and environmental purposes such as electrochemical detection of pathogens.[1] The versatility of ultramicroelectrodes (UMEs) gives unique and essential properties for electroanalytical sensing owing to their small size, high sensitivity, fast steady-state response, low double-layer charging current and minimal ohmic loss. The observation of these stochastic events can provide information on various single nanoparticles contrary to ensemble (bulk) measurements. The main advantage of studying collisions of single entities is the low limit of detection (in principle, one single species) inherent to this electroanalytical method and the ability to study single entities (cells, viruses, nanoparticles...) in real time (dynamic measurement).[2–4] Electrochemistry of single redox liposome impacts at an UME consists in detecting the electrolysis of a redox probe encapsulated inside a liposome when it is released at the UME after impact (or collision). The UME is polarized at the oxidation or reduction potential of the encapsulated redox probe and a concentration of several pico-molar of redox liposomes added to the aqueous buffer electrolyte is enough to detect “current spikes” in the chronoamperometry (i-t) curve corresponding to discrete collision events.[3,4] The electron transfer does not readily occur across a lipid bilayer, thus the electrolysis of the liposome redox active content after collision and membrane rupture or opening at the UME surface led to many studies dealing with the membrane permeation mechanism.[3,4] Here, our work is based on the previous results where no current spike was observed in the chronoamperometry curve because the redox DMPC liposomes did not break during impact (or collision) onto the UME surface.[3,4] Hence, the electrochemical sensing principle is based on the weakening of the liposomes lipid membrane upon interaction with a destructive bacterial virulence factor which leads upon impact at an UME to the breakdown of the liposomes and the release/electrolysis of its encapsulated redox probe, as previously reported.[5] In the presence of RL toxin in solution (acting like a surfactant in the lipid membrane), current spikes corresponding to the electrolysis of the encapsulated redox probe released from weakened liposomes are detected (see Figure). Thanks to the redox liposome single impact electrochemistry, the highest detection limit of RL toxin (500 nM) has been reached in comparison to several micromoles per liter previously reported.[5] [1] Lebègue, E.; Costa, N.L.; Louro, R.O.; Barrière, F. Communication—Electrochemical Single Nano-Impacts of Electroactive Shewanella Oneidensis Bacteria onto Carbon Ultramicroelectrode. J. Electrochem. Soc. 2020, 167, 105501, doi:10.1149/1945-7111/ab9e39. [2] Dick, J.E.; Lebègue, E.; Strawsine, L.M.; Bard, A.J. Millisecond Coulometry via Zeptoliter Droplet Collisions on an Ultramicroelectrode. Electroanalysis 2016, 28, 2320–2326, doi:10.1002/elan.201600182. [3] Lebègue, E.; Anderson, C.M.; Dick, J.E.; Webb, L.J.; Bard, A.J. Electrochemical Detection of Single Phospholipid Vesicle Collisions at a Pt Ultramicroelectrode. Langmuir 2015, 31, 11734–11739, doi:10.1021/acs.langmuir.5b03123. [4] Lebègue, E.; Barrière, F.; Bard, A.J. Lipid Membrane Permeability of Synthetic Redox DMPC Liposomes Investigated by Single Electrochemical Collisions. Anal. Chem. 2020, 92, 2401–2408, doi:10.1021/acs.analchem.9b02809. [5] Luy, J.; Ameline, D.; Thobie-Gautier, C.; Boujtita, M.; Lebègue, E. Detection of Bacterial Rhamnolipid Toxin by Redox Liposome Single Impact Electrochemistry. Angew. Chem. Int. Ed. 2021, accepted , doi: 10.1002/anie.202111416. Figure 1

International audience; Currently, there is a growing interest in the study of environmental degradation pathways of organic contaminants such as pesticides, with the objective to better understand their potential risk for environmental systems and living organisms. In this context, DFT (conceptual density functional theory) and predictive methods may systematically be used to simplify and accelerate the elucidation of environmental degradation. We report herein the electrochemical behavior/degradation of the carbendazim (CBZ) fungicide widely used to treat cereal and fruit crops. Oxidative degradation of CBZ was studied using an electrochemical flow-through cell directly coupled to a mass spectrometer for rapid identification of CBZ degradation products. The structural elucidation of CBZ oxidation products was based on retention time, accurate mass, isotopic distribution and fragmentation pattern by using LC-HRMS an LC-HRMS2. The most important chemical reactions found to occur in the transformation of CBZ were hydrolysis and hydroxylation. EC-LC-MS and EC-MS analysis has made it possible to highlight the identification of degradation products of CBZ. In addition to previously known transformation products common to those observed during environmental degradation (monocarbomethoxyguanidine, benzimidazole-isocyanate, 2-aminobenzimidazole, hydroxy-2-aminobenzimidazole, hydroxycarbendazim, CBZ-CBZ dimer), two new degradation products were identified in this work: a quinone imine and a nitrenium ion. Electrochemistry mass spectrometry hyphenated techniques represent an accessible, rapid and reliable tool to elucidate the oxidative degradation of CBZ, including reactive degradation products and conjugates.

Three new copper(I) complexes [Cu(LX)2]+(PF6-) (where LX stands for 2,9-dihalo-1,10-phenanthroline and X = Cl, Br, and I) have been synthesized in order to study the impact of halogen substituents tethered in the α position of the chelating nitrogen atoms on their physical properties. The photophysical properties of these new complexes (hereafter named Cu-X) were characterized in both their ground and excited states. Femtosecond ultrafast spectroscopy revealed that early photoinduced processes are faster for Cu-I than for Cu-Cl or Cu-Br, both showing similar behaviors. Their electronic absorption and electrochemical properties are comparable to benchmark [Cu(dmp)2]+ (where dmp stands for 2,9-dimethyl-1,10-phenanthroline); furthermore, their optical features were fully reproduced by time-dependent density functional theory and ab initio molecular dynamics calculations. All three complexes are luminescent at room temperature, showing that halogen atoms bound to positions 2 and 9 of phenanthroline are sufficiently bulky to prevent strong interactions between the excited Cu complexes and solvent molecules in the coordination sphere. Their behavior in the excited state, more specifically the extent of the photoluminescence efficiency and its dependence on the temperature, is, however, strongly dependent on the nature of the halogen. A combination of ultrafast transient absorption spectroscopy, temperature-dependent steady-state fluorescence spectroscopy, and computational chemistry allows one to gain a deeper understanding of the behavior of all three complexes in their excited state.

International audience; The development of new bio-orthogonal ligation methods for the conjugation of native proteins is of particular importance in the field of chemical biology and biotherapies. In this work, we developed a traceless electrochemical method for protein bioconjugation. The electrochemically promoted tyrosine-click (e-Y-CLICK) allowed the chemoselective Y-modification of peptides and proteins with labeled urazoles. A low potential is applied in an electrochemical cell to activate urazole anchors in situ and on demand, without affecting the electroactive amino acids from the protein. The versatility of the electrosynthetic approach was shown on biologically relevant peptides and proteins such as oxytocin, angiotensin 2, serum bovine albumin, and epratuzumab. The fully conserved enzymatic activity of a glucose oxidase observed after e-Y-CLICK further highlights the softness of the method. The e-Y-CLICK protocols were successfully performed in pure aqueous buffers, without the need for co-solvents, scavenger or oxidizing chemicals, and should therefore significantly broaden the scope of bioconjugation.

The use of electrochemistry (EC) coupled to mass spectrometry (MS) has been widely reported in the past two decades as a tool for simulating drug metabolism. EC-MS is now used to generate metabolites in a simple matrix with easy implementation for high-throughput analysis. Another interesting use of EC in drug-metabolism investigation is simulation of the formation of reactive drug metabolites. Electrochemical reactions tend to be limited to the simulation of single-electron transfers initiated by cytochrome P450 reactions, hence the need for new analytical developments. This review aims to describe current knowledge of the use of EC-MS for the generation and the identification of reactive drug metabolites. We detail the electrochemical formation of electrophilic aryl, nitroso, aromatics and nitrogen-oxide species in the first part. We give future perspectives related to the surface-modified electrode coupled with MS for inhibition.

International audience; Transparent C, Au and Pt films with thickness in the 5-10 nm range have been deposited by a DC magnetron sputtering system on commercial ITO (indium tin oxide) coated glass substrate for evaluation as electrode of spectro-electrochemical transducer. The transmission, over the investigated spectral range, is superior to 55% with the best transmission values obtained for C films (higher than 80%). The deposited films have been characterized by AFM, XPS and electrochemical methods. Results showed a low roughness, improved in comparison with uncoated electrodes. Electrochemical properties of the Au and Pt films evidenced a metallic behavior, which allowed qualifying them as conductive optically transparent electrodes for spectro-electrochemical devices.

The cross-coupling reactions of 3,6-dihalopyridazines with triaryl- or triheteroarylbismuth compounds were performed under palladium catalysis. The reaction was highly chemoselective, affording functionalized aryl- or heteroarylpyridazinyl chlorides in moderate to good yields.

A simple and versatile novel method for the preparation of triaryl- and trihetero-arylbismuths bearing electron withdrawing or electron donating groups was accomplished by the reaction of organozinc reagents with BiCl 3 . Scope and limits of the process are investigated.

Polarography at dropping mercury electrode and infrared spectroscopy were used to confirm the reaction of copper(II) ions with humic acid in solution. Polarography allowed observing the reaction to follow the concentration of the Cu(II) in solution while infrared permitted one to follow the humic acid complexation. Cyclic voltammetry experiments, at stationary carbon paste electrode, showed original properties of humic acid which adsorbs at the surface of carbon paste electrode that becomes appropriate for the preconcentration and identification of Cu(II) species. Although very promising the use of adsorption showed the disadvantage of not being reproducible therefore we developed a new preparation method for the carbon paste electrodes modified with humic acid that allow highly repeatable measurements. Humic acid was dissolved in base solution before mixing it with carbon graphite powder and freeze-drying to lead to a fine powder that allows reproducible batches of electrodes. The modification of carbon paste electrode with two different humic acids revealed that the electrochemical behavior of Cu(II) solutions depends on the nature of the humic material. The effects on the electrochemical behavior of Cu(II) of the solutions pH and the ratio of humic acid in the bulk of the electrode were also examined. Such carbon paste electrodes modified with humic acid extracted from a peat area in the Mogi GuaAu River at Sao Paulo State in Brazil showed high reproducibility and particular stability in solution (pH range of 3.0 to 5.5) entitling them to be very good candidates for analytical purposes.

The electrochemical method for the synthesis of 3-amino-6-arylpyridazines is complementary to the classic Suzuki-, Stille- or Nigishi-cross-coupling reactions and provides the products with higher yields.

3-Amino-6-aryl- and 3-amino-6-heteroarylpyridazines have been obtained in generally good yield using a nickel-catalyzed electrochemical cross-coupling between 3-amino-6-chloropyridazines and aryl or heteroaryl halides at room temperature. Comparative experiments involving classical palladium-catalyzed reactions, such as Suzuki, Stille, or Negishi cross-couplings, reveal that the electrochemical method can constitute a reliable alternative tool for biaryl formation. A possible reaction mechanism is proposed on the basis of electrochemical analyses.

Novel methods are developed for the preparation of the synthetically important bismuth agents.

The presence of an N-benzoyl group is necessary to facilitate the sulfonamide cleavage and prevent β-fragmentation and epimerization.

The electrochemical reduction of sensitive sulfonamides is described. The addition of a benzoyl group on the nitrogen atom facilitates the reductive cleavage of sulfonamides preventing β-fragmentation and epimerization. This strategy was successfully applied to the cyclopropylamine and to α-amino stannanes.

International audience

A new thiophene derivative containing a tetrathiafulvalene (TTF) moiety covalently attached to the thiophene ring via a linear oxadecyl spacer has been synthesized. Although in acetonitrile the voltammogram of this compound exhibits the cyclic voltammetric features of TTF and 3-alkalthiophenes, all attempts of electropolymerization remained unsuccessful, presumably because of the scavenging of the thiophene cation radicals by TTF. In contrast, electropolymerization can be achieved by application of repetitive potential scans in nitrobenzene solutions. This result suggests, in agreement with UV-visible absorption spectra, that the formation of a donor-acceptor complex between nitrobenzene and the TTF moiety decreases its reactivity toward thiophene cation radicals

International audience; Synthesis of alternating pyridine-pyrrole molecular strands composed of two electron-rich pyrrole units (donors) sandwiched between three pyridinic cores (acceptors) is described. The envisioned strategy was a smooth electrosynthesis process involving ring contraction of corresponding tripyridyl-dipyridazine precursors. 2,6-Bis[6-(pyridazin-3-yl)]pyridine ligands 2a-c bearing pyridine residues at the terminal positions were prepared in suitable quantities by a Negishi metal cross-coupling procedure. The yields of heterocyclic coupling between 2-pyridyl zinc bromide reagents 12a-c and 2,6-bis(6-trifluoromethanesulfonylpyridazin-3-yl)pyridine increased from 68 to 95% following introduction of electron-donating methyl groups on the metallated halogenopyridine units. Favorable conditions for preparative electrochemical reduction of tripyridyl-dipyridazines 2b,c were established in THF/acetate buffer (pH 4.6)/acetonitrile to give the targeted 2,6-bis[5-(pyridin-2-yl)pyrrol-2-yl]pyridines 1b and 1c in good yields. The absorption behavior of the donor-acceptor tripyridyl-dipyrrole ligands was evaluated and compared to theoretical calculations. Highly fluorescent properties of these chromophores were found (ν(em)≈2 × 10(4) cm(-1) in MeOH and CH(2)Cl(2)), and both pyrrolic ligands exhibit a remarkable quantum yield in CH(2)Cl(2) (φ(f)=0.10). Structural studies in the solid state established the preferred cis conformation of the dipyrrolic ligands, which adopting a planar arrangement with an embedded molecule of water having a complexation energy exceeding 10 kcal mol(-1). The ability of the tripyridyl-dipyrrole to complex two copper(II) ions in a pentacoordinate square was investigated.

International audience; An electrochemical transducer based on vertically aligned carbon nanotubes (CNT) was prepared as a platform for biosensor development. Prior to enzyme immobilization, the CNT were treated using a microwave plasma system (CO2 and N2/H2) in order to functionalize the CNT surface with oxygenated and aminated groups. The morphological aspect of the electrode surface was examined by SEM and its chemical structure was also elucidated by XPS analysis. It was found out that microwave plasma system (CO2 and N2/H2) not only functionalizes the CNT but also permits to avoid the collapse phenomena retaining thus the alignment structure of the electrode surface. The electrochemical properties of the resulting new material based on CNT were carried out by cyclic voltammetry and were found suitable to develop high sensitive enzyme (HRP) biosensors operating on direct electron transfer process.

The nickel-2,2'-bipyridine catalyzed electrochemical cross-coupling reaction between an aryl halide and a chloropyridazine was investigated by an electrochemical study The electrochemical behavior of the divalent nickel complex is affected by the presence of pyridazine rings which act as co-ligands of nickel Cyclic voltammetry indicates that the cross-coupling reaction involves first a rapid oxidative addition of the chloropyridazine on the electrogenerated zerovalent nickel complex. The coupling product is then obtained by reaction with the aryl halide. (C) 2010 Elsevier Ltd. All rights reserved.

International audience; Radiofrequency argon plasma was used for screen-printed carbon electrodes (SPCE) surface treatment. The cyclic voltammetry of ferri/ferrocyanide as redox couple showed a remarkable improvement of the electrochemical reactivity of the SPCE after the plasma treatment. The effect of the plasma growth conditions on the efficiency of the treatment procedure was evaluated in term of electrochemical reactivity of the SPCE surface. The electrochemical study showed that the electrochemical reactivity of the treated electrodes was strongly dependant on radiofrequency power, treatment time and argon gas pressure. Xray photoelectron spectroscopy (XPS) analysis showed a considerable evolution on the surface chemistry of the treated electrodes. Our results clearly showed that the argon plasma treatment induces a significant increase in the C-SP2/C-SP3 ratio. The scanning electron micrograph (SEM) also showed a drastic change on the surface morphology of the treated SPCEs.

The electrochemical reduction of N-phenylsulfonyl N-substituted amines in a protic medium under constant cathodic potential was found to be a mild desulfonylation method, which is able to challenge the chemical ones. The influence of the nature of the N-substituents was considered in order to clarify the mechanistic aspects and to evaluate the scope of the method.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The electrochemical reduction of N-phenylsulfonyl N-substituted amines in a protic medium under constant cathodic potential was found to be a mild desulfonylation method, which is able to challenge the chemical ones. The influence of the nature of the N-substituents was considered in order to clarify the mechanistic aspects and to evaluate the scope of the method.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The preparation of a humic acid modified carbon paste electrode (HA-MCPE) as well as the behavior of its surface as complexing agent toward Cu2+ cations are described. Electrochemical studies of the reduction of the complexed cations and of the anodic stripping oxidation of the resulting copper are outlined. The anodic stripping current was correlated to the Cu2+ concentrations. A well-defined method for the preparation of reproducible electrodes is described. The effects on the current response obtained by cyclic voltammetry of the humic acid ratio, the pH, the accumulation time, and the speed scan rate were studied. Calibration graphs were linear over the range 3 x 10(-8)-10(-5) mol L(-1) Cu2+ and the relative standard deviation (R.S.D.) was 1.2% (n=5) for [Cu2+] = 1.6 x 10(-5) mol L(-1). 5 min accumulation time for [Cu2+]10(-7) mol L(-1) and 10 min for [Cu2+]10(-7) mol L(-1) were sufficient to permit sensitive and reproducible measurements. The electrode was successfully used to measure Cu2+ in real samples and the results were compared to those obtained by the standard method with differential pulse anodic stripping voltammetry.

Despite t remendous research effort invested in the development of functional poly(thiophenes) (PTs) [1], the control of the long-range order and dimensionality of these materials has received less attention. In addition to a possible control of the bandgap [2], the development of PTs of higher dimensionality may open interesting perspectives in the field of modified electrodes or of molecular electronics [3]. In a first at tempt in this direction, we report here the electro-oxidation of a tetrahedral precursor 1 in which four terthienyl moities (3T) are linked to a silicon atom. Preliminary electrochemical and optical investigations show that although electrodeposition leads to a cation radical salt, subsequent electroreticulation by coupling of the 3T units leads to an electroactive material with electrochemical and optical properties consistent with a 3D structure.

A hydrophilic conjugated polymer with a bandgap of 1.2 eV has been obtained by electropolymerization of 4,4-ethylenedioxy-4H-cyclopenta[2,1-b;3,4-b′]dithiophene.

Rigidified tetrathiafulvalene–bithiophene hybrid systems with multi-step oxidation and reduction stages and bandgaps

A new synthetic approach for the reduction of the bandgap of molecular and polymeric conjugated systems is presented.

Rigidification of E-1,2(2,2′-dithienylethylene) by bridging the thiophene rings with the central double bond leads to a ca. 0.40 eV decrease of the bandgap of the resulting conducting polymer.

0022-3263; International audience; A general efficient electrochemical method for the preparation of aryl- and heteroarylpyridazines in a nickel-catalyzed cross-coupling reaction of 3-chloro-6-methoxypyridazine and 3-chloro-6-methylpyridazine with a range of functionalized aryl or heteroaryl halides is reported.