Laurent Thouin
École Normale Supérieure
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Featured researches published by Laurent Thouin.
Journal of Electroanalytical Chemistry | 2001
Christian Amatore; Sabine Szunerits; Laurent Thouin; Jean-Stéphane Warkocz
A model accounting for the role of convection in macroscopically immobile solutions (viz., not submitted to any macroscopic flow or any density gradient) is developed to predict the resulting alterations on electrochemical experiments performed at long time durations. The model is based on a seminal idea introduced by Levich, and shows that in macroscopically still solutions microscopic chaotic motion has the same effect as an apparent diffusion coefficient that depends on the distance from the electrode, x. When the electrochemical perturbation affects only the viscous sub-layer adjacent to the electrode, this apparent diffusion coefficient varies as x4. The model remarkably predicts the experimental distortions of chronoamperometric currents from their ideal Cottrellian behavior. The model is thoroughly tested with success by comparing its predictions to experimental results (current and concentration profiles) obtained for the oxidation of Fe(CN)64− in aqueous KCl.
Analytical Chemistry | 2008
Christian Amatore; Nicolas Da Mota; Célia Lemmer; Cécile Pebay; Catherine Sella; Laurent Thouin
The development of any particular analytical or preparative applications using electrochemical techniques in microfluidic devices requires integration of microelectrodes. This involves detailed predictions for optimizing the design of devices and selecting the best hydrodynamic conditions. For this purpose, we undertook a series of works aimed at a precise investigation of mass transport near electrodes with focus on analytical measurements. Part I of this series (Anal. Chem. 2007, 79, 8502-8510) evaluated the common case of a single microband electrode embedded within a microchannel under laminar flow. The present work (Part 2) investigated the case of a pair of microband electrodes operating either in generator-generator or generator-collector modes. The influence of the confining effect and flow velocity on the amperometric responses was examined on the basis of numerical simulations under steady-state regime. Several situations were identified, each of them corresponding to specific interactions taking place between the electrodes. Related conditions were extracted to establish a zone diagram describing all the situations. These predictions were systematically validated by experimental measurements. The results show that amperometric detections within microchannels can be performed at dual electrodes with higher analytical performances than at single ones.
Analytical Chemistry | 2010
Christian Amatore; Cécile Pebay; Laurent Thouin; Aifang Wang; Jean-Stéphane Warkocz
Natural convection in macroscopically immobile solutions may still alter electrochemical experiments performed with electrodes of micrometric dimensions. A model accounting for the influence of natural convection allowed delineating conditions under which it interferes with mass transport. Several electrochemical behaviors may be observed according to the time scale of the experiment, electrode dimensions, and intensity of natural convection. The range of parameters in which ultramicroelectrodes behave under a true diffusional steady state was identified. Mapping of concentration profiles was performed experimentally by scanning electrochemical microscopy in the vicinity of microelectrodes of various radii. The results validated remarkably the predictions of the model, evidencing in particular the alteration of the diffusional steady state by natural convection.
Journal of Electroanalytical Chemistry | 2000
Christian Amatore; Frédéric Bonhomme; Jean-Luc Bruneel; Laurent Servant; Laurent Thouin
Abstract Confocal Raman microspectroscopy is a very efficient means for probing the molecular composition of micrometric-sized samples. Its coupling with Raman resonance spectroscopy allows the specific tracking of very dilute species by considerably enhancing its Raman bands. Thus, spatially resolved information on the chemical composition of diffusion layers, which build up spontaneously near an active surface placed in a solution, can be obtained with a micrometric resolution. In this work, the applicability of the method for imaging diffusional transport towards ultramicroelectrodes with a micrometric resolution is examined. The efficiency and versatility of confocal resonance Raman microspectroscopy have been tested by probing the composition of the two different diffusion layers which build up in the vicinity of an ultramicroelectrode during the reduction of tetracyanoquinodimethane (TCNQ) on its first or second electrochemical wave. Besides the establishment of the method, this work affords the first direct experimental evidence of the existence and role of conproportionation reactions, which take place on the second reduction wave of EE electrochemical systems. In both cases, the concentration profiles of the radical anion TCNQ − agree extremely well with the theoretical predictions.
Electrochemistry Communications | 2000
Christian Amatore; Sabine Szunerits; Laurent Thouin; Jean-Stéphane Warkocz
Abstract A platinum-disk ultramicroelectrode is used to monitor amperometrically the concentrations of the electroactive substrate and of its electrogenerated product(s) inside the diffusion layer created by a larger working electrode. This allows a direct monitoring of the target species concentration profiles without any assumption even when diffusion coefficients differ significantly. The validity of the method is established experimentally through the study of the one-electron reversible oxidation of the Fe(CN) 6 3− /Fe(CN) 6 4− couple in aqueous KCl, under steady-state or under transient diffusion conditions. Under steady-state conditions, the results compare excellently with those we obtained by means of the potentiometric method reported in Part II of this series. Under transient diffusion conditions, the measured concentration profiles match perfectly those predicted for planar diffusion, which demonstrates the interest of the method for the analysis of dynamic diffusion-kinetic problems. The validity of the method in a complex diffusional situation is established as previously (Part II) by the investigation of the effect of a conproportionation reaction taking place during the second reduction of tetracyanoquinodimethane (TCNQ) in DMF.
Electrochemistry Communications | 2000
Christian Amatore; Frédéric Bonhomme; Jean-Luc Bruneel; Laurent Servant; Laurent Thouin
Abstract Confocal microspectroscopy is known to be a very efficient means for probing composition of spatially resolved micrometric volumes inside a macroscopic sample. In this paper, the applicability of confocal Raman microspectroscopy for imaging molecular diffusion at microelectrodes with a micrometric resolution is established. The efficiency and versatility of the method have been tested by probing the composition of the two different diffusion layers which build up in the vicinity of an ultramicroelectrode during reduction of tetracyanoquinodimethane (TCNQ) on its first or second electrochemical wave. This is performed by mapping the concentration profiles of the TCNQ − anion radical under each condition using its resonance Raman spectrum. As a correlation, this provides the first direct experimental proof of a conproportionation reaction taking place when the electrode potential is poised on the second wave of a two-wave EE electrochemical system. In both cases, the concentration profiles of the radical anion TCNQ − agree extremely well with theoretical predictions.
Electrochemistry Communications | 2000
Christian Amatore; Sabine Szunerits; Laurent Thouin
A platinum-disk ultramicroelectrode is used to monitor electrochemical potential variations inside the steady-state diffusion layer created by a larger electrode. The experimental potential variations result from combination of a pure electrochemical component (viz., as given by the Nernst law) with a smaller ohmic drop contribution, which varies linearly with the distance from the working electrode surface so that it can be readily eliminated. From the ensuing corrected potential variations, the concentration profiles of the electroactive species present within the diffusion layer can be reconstructed by application of the Nernst law. The validity and great interest of the method are demonstrated experimentally by the study of the one-electron reversible oxidation of the Fe(CN)63−/Fe(CN)64− couple in aqueous KCl solutions. As a correlation, this demonstrates also for the first time the validity of the Nernst layer approximation. The method is then applied to examine the specific structure of the diffusion layers, which result from the involvement of a conproportionation reaction during the second reduction of tetracyanoquinodimethane (TCNQ) in DMF.
Analytical Chemistry | 2008
Christian Amatore; Nicolas Da Mota; Catherine Sella; Laurent Thouin
In this work, we established theoretically that amperometric detector arrays consisting of a series of parallel band microelectrodes placed on the wall of a microchannel may offer excellent analytical detection performances when implemented onto microfluidic (bio)analytical devices after the separative stages. In combination with the concentration imprinting strategies reported in a previous work, these exceptional performances may be extended to nonelectroactive or poorly diffusing analytes. Using an array of electrodes instead of a large single band allows the whole core of the channel to be probed though keeping an excellent time resolution. Thus, analytes with close retention times may be characterized individually with a resolution which eventually outpaces that of spectroscopic detections. Such important advantages may be obtained only through a complete understanding of the complex coupling between diffusional and convective transport of molecules in microfluidic solutions near an electrochemical detector. As a consequence, the conditions underlying the theoretical data presented in this work have been selected after optimizing procedures rooted on previous theoretical analyses. They will be fully disclosed in a series of further works that will also establish the experimental performances of such amperometric detectors and validate the present concept.
Chemistry: A European Journal | 2001
Christian Amatore; Cécile Pebay; Onofrio Scialdone; Sabine Szunerits; Laurent Thouin
Lipid-modified proteins play decisive roles in important biological processes such as signal transduction, organization of the cytoskeleton, and vesicular transport. Lipidated peptides embodying the characteristic partial structures of their parent lipidated proteins and semisynthetic proteins synthesized from such peptides are valuable tools for the study of these biological phenomena. We have developed an efficient synthesis strategy that allows for the synthesis of long multiply lipidated peptides embodying various side chain functional groups. The strategy was successfully applied in the synthesis of the N-terminal undetrigintapeptide of endothelial NO-synthase and related lipopeptides. Key elements of the synthesis strategy are the combined use of the enzyme-labile para-phenylacetoxybenzyloxycarbonyl (PhAcOZ) urethane as N-terminal blocking group, the Pd0-sensitive allyl ester as C-terminal protecting function and acid-labile side chain protecting groups for solution-phase synthesis of labile S-palmitoylated building blocks under the mildest conditions with solid-phase techniques and solution-phase fragment condensations. The successful synthesis of the triply lipidated 29-mer eNOS peptide convincingly demonstrates the full capacity of the protecting group methods.
Electroanalysis | 2001
Christian Amatore; Sabine Szunerits; Laurent Thouin; Jean-Stéphane Warkocz
Using an ultramicroelectrode placed inside the diffusion layer of a larger working electrode we demonstrated to which extent amperometric and potentiometric detections allow spatially resolved information at the micrometric scale, so that the composition of a diffusion layer created in the vicinity of a millimetric working electrode can be examined with adequate precision. The validity of both methods was established experimentally in steady state conditions through the investigation of a simple redox reaction as well as for more complex mechanistic situations. The amperometric detection is also used to probe a time-expanding diffusion layer, thus showing the transition from perfect Cottrellian behavior to steady state imposed by spontaneous convection.