Frédéric Reymond

Electrochemistry at liquid/liquid interfaces: methodology and potential applications

Electrochemistry at the interface between two immiscible electrolyte solutions (ITIES) gains more and more interest due to its wide range of applications. The present review encompasses the various domains of charge transfer reactions in biphasic systems, with some emphasis on certain studies that marked the advances of electrochemistry at ITIES and that, in a noticeable manner, have been presented in large majority at the ISE meetings during the last two decades. These studies, as well as some subjects in which our recent research interest is concerned, are used here to describe the fundamental aspects of charge transfer reactions at liquid:liquid interfaces and to outline their various applications. This overview presents the methodologies offered by the ITIES in the fields of amperometric sensors, solvent extraction, pharmacokinetics, thermo-electricity and solar energy conversion, and the accent is put on the perspectives of their potential development in the coming years.

Polymer microfluidic chips for electrochemical and biochemical analyses.

Our recent developments concerning the fabrication of polymer microchips and their applications for biochemical analyses are reviewed. We first describe two methods of fabrication of polymer microfluidic chips, namely UV‐laser photoablation and plasma etching that are well suited for the prototyping and mass fabrication of microchannel networks with integrated microelectrodes. These microanalytical systems can be coupled with various detection means including mass spectrometry, and their applications in capillary electrophoresis are presented here. We also present how UV laser photoablation can be used for the patterning of biomolecules on polymer surfaces for generating two‐dimensional arrays of microspots to carry out affinity assays. Finally, the use of the microchips for the development of fast affinity and immunological assays with electrochemical detection is presented, demonstrating the potential of these polymer microchips for medical diagnostics and drug discovery.

Protein purification by Off-Gel electrophoresis

A novel free‐flow protein purification technique based on isoelectric electrophoresis is presented, where the proteins are purified in solution without the need of carrier ampholytes. The gist of the method is to flow protein solutions under an immobilised pH gradient gel (IPG) through which an electric field is applied perpendicular to the direction of the flow. Due to the buffering capacity of the IPG gel, proteins with an isoelectric point (pI) close to pH of the gel in contact with the flow chamber stay in solution because they are neutral and therefore not extracted by the electric field. Other proteins will be charged when approaching the IPG gel and are extracted into the gel by the electric field. Both a demonstration experiment with pI markers and a simulation of the electric field distribution are presented to highlight the principle of the system. In addition, an isoelectric fractionation of an Escherichia coli extract is shown to illustrate the possible applications.

Facilitated ion transfer reactions across oil|water interfaces : Part II. Use of the convoluted current for the calculation of the association constants and for an amperometric determination of the stoichiometry of MLjz+ complexes

Cyclic voltammetric experiments for reversible ion transfers across the aqueous/organic interface facilitated by a neutral macrocyclic ligand are presented for complexation reactions of 1:1 to 1:4 ion-to-ligand stoichiometries. The convoluted current is taken into account to derive general theoretical equations relating the half-wave potential to the initial concentrations of both the metal Mz+ and the ligand L. Analytical relationships are obtained for both limiting cases of ligand and, respectively, metal excess and for any type of reaction mechanisms. Likewise, considerations on the convoluted current provide a condition on the transition point between the diffusion regimes where either the metal or the ligand limits the transfer, which constitutes an amperometric determination of the complex stoichiometry. It is shown that the half-wave potential depends on the various over-all association constants, on the partition coefficient of the ligand and on the initial concentrations of both Mz+ and L. This dependence is the same for the TIC, TOC and TID mechanisms, but differs in the case of the ACT mechanism. The theoretical predictions are corroborated by the results deduced from various calculated voltammograms and are verified experimentally for the transfer of Pb2+ assisted by the thioether ligand 1,4,7,10-tetrathiacyclododecane at the water/1,2-DCE interface. Thanks to the simulation, it is shown that the experimental current waves are due to 1:1 and 1:2 complex formation and that the first association constant in the organic phase is log K-1(0) approximate-to 5

Polymer microchips bonded by O2-plasma activation

This paper presents a fabrication of polymer microchips with homogeneous material technique due to surface treatment by plasma before sealing. UV laser photoablation was used for fast prototyping of microstructures, and oxygen plasma was used as a surface treatment for both the microfabricated substrate and the polymer cover. It was found that with an oxidative plasma treatment, successful bonding could be achieved without adhesive material between polymer sheets substantially below the glass transition temperature of the polymer. Homogeneous polyethylene terephthalate (PET) microstructures were characterized by scanning electron microscopy (SEM) and analyzed by X‐ray photoelectron spectroscopy (XPS) surface analyses after different surface treatments. The electroosmotic flow characteristics including the velocity and the stability over 20 days have been tested and compared to composite channels, in which the cover presents a polyethylene (PE) adhesive layer. Capillary zone electrophoresis in both homogeneous and composite microanalytical devices were then performed and compared in order to evaluate the separation efficiency. In preliminary experiments, a plate height of 0.6 νm has been obtained with homogenous microchannels. The surface analysis pointed out that the surface chemistry is of prime importance for the performance of microfluidic separation.

MICROCHANNEL NETWORKS FOR ELECTROPHORETIC SEPARATIONS

UV excimer laser photoablation was used to micro‐machine polymer substrates not only to drill microchannel structures but also to change the surface physical properties of the substrates. We first describe how UV laser photoablation can be used for the patterning of biomolecules on a polymer and discuss parameters such as surface coverage of active antibodies and equilibration time. Secondly, we show how to design a single‐use capillary electrophoresis system comprising an on‐chip injector, column and electrochemical detector. The potential of this disposable plastic device is discussed and briefly compared to classical systems. Finally, preliminary results on protein separation by isoelectric focusing on a disposable microchip are presented.

Microfabricated polymer injector for direct mass spectrometry coupling

This paper demonstrates the coupling of a plasma etched polymer microfluidic system with an electrospray mass spectrometer by generation of a nanospray. Taking advantage of the microtechnology processes and polymer properties, high volume production with good reproducibility of hydrophobic interfaces could be obtained. The nanospray was directly produced from the outlet of the plastic microfabricated chip positioned in front of the capillary entrance of the mass spectrometer. No chemical background due to the polymer has been observed under standard nanospray conditions. The performances of the spray as well as its efficiency have been demonstrated by flow measurements, stability establishment and tandem mass spectrometry experiment on angiotensin II. The spray was actuated without additional flow in methanol: water:acetic acid (50:49:1%) solution. A 40 fmol/νL detection limit could be reached.

Structure-Lipophilicity Relationships of Neutral and Protonated β-Blockers, Part I, Intra- and Intermolecular Effects in Isotropic Solvent Systems

The objectives of this study were to validate new experimental techniques used to measure the log P of protonated drugs, and to investigate the inter- and intramolecular forces influencing the partitioning behavior of β-blockers in isotropic biphasic solvent systems. The lipophilicity parameters of a number of β-blockers were measured by two-phase titration, centrifugal partition chromatography (CPC), and cyclic voltammetry (CV) in one or more of the following solvent systems: octanol/water, 1,2-dichloroethane/water, and dibutyl ether/water. CV proved to be a promising technique for measuring the lipophilicity of protonated β-blockers. Derived parameters such as Δlog P (difference between log P in two different solvent systems, a parameter valid for a given solute in a given electrical form) and diff (difference between log P of two different electrical forms of a given solute, in the same system) yielded insights into inter- and intramolecular interactions characteristic of β-blockers. The relevance of these parameters in structure-permeation relationships is explored.

Facilitated ion transfer reactions across oil|water interfaces. Part I. Algebraic development and calculation of cyclic voltammetry experiments for successive complex formation

Reference LEPA-ARTICLE-1998-015doi:10.1016/S0022-0728(97)00430-0View record in Web of Science Record created on 2005-11-07, modified on 2017-05-12

Combined Molecular Lipophilicity Descriptors and their Role in Understanding Intramolecular Effects

Traditional lipophilicity parameters (log P and log D) are well-known physico-chemical descriptors largely used in QSAR studies. Besides their numerical value, log P data contain a variety of information about inter- and intramolecular forces affecting partitioning and its related biological phenomena. The deconvolution of information from log P can be accessed only by adequate interpretative tools, such as new lipophilic-combined descriptors, of which features and some applications are presented in this review.