Bernard Fahys

Electrochemical Oxidation of Ethylenediamine: New Way to Make Polyethyleneimine‐Like Coatings on Metallic or Semiconducting Materials

A mechanism is proposed for the anodic polymerization of ethylenediamine (EDA). Initially, there occurs the formation of the radical cation NH 2 CH 2 CH 2 NH +. 2 , followed by the breaking of the C-N bond, the expulsion of NH . 2 , and concomitant formation of the primary carbocation NH 2 CH 2 CH + 2 or the aziridinium cation. This cation reacts with an NH 2 group of an EDA molecule, yielding a new amine which can be further oxidized. The product on the anode is a polyethyleneimine-like polymer. A similar product was found for diethylenetriamine, whose oxidation was studied too. Other pure ω-amines can also polymerize if they are primary amines and have vicinal alkyl groups which are secondary, i.e., have the formula NH 2 CH 2 RCH 2 NH 2 .

Miniaturized pH biosensors based on electrochemically modified electrodes with biocompatible polymers.

Potentiometric pH sensors based on linear polyethylenimine (L-PEI) and linear polypropylenimine(L-PPI), two synthetic enzymes and biocompatible polymers, films were prepared by electropolymerization of three different monomers: ethylenediamine (EDA), 1,3-diaminopropane (1,3-DAP) and diethylenetriamine (DETA) in order to be used in clinical, dermatological and biological applications, such as in vivo analysis. In a first step a biosensor was tested which consisted in a platinum wire protruded from glass sheath. The polymer film coated on these platinum electrodes showed good linear potentiometric responses to pH changes from pH 3 to 10. Resulting electrodes present both good reversibility and good stability versus time. The effect of the different polymer film thicknesses to potentiometric responses was also studied. This study allowed us to develop a miniaturized pH biosensor in the second step. This sensor was fabricated using photo-lithography, followed by sputtering and lift-off processes, and it included an electronic detection system. We have also successfully studied the potentiometric responses to pH changes of this device over a period of 1 month, and so we propose this new pH micro-biosensor as an alternative to classical pH sensors currently used in dermatology.

The use of polyethyleneimine for fabrication of potentiometric cholinesterase biosensors.

Potentiometric biosensors based on butyrylcholinesterase are developed by co-reticulation of the enzyme with glutaraldehyde on an electropolymerized polyethyleneimine film at the electrode surface. The BuChE-electrode was tested as biochemical sensor for detection of an organophosphorus pesticide, trichlorfon in liquid, the detection being based on the enzyme inhibition. The enzyme electrode showed a detection limit for trichlorfon below 10(-7) M.

How does the European common lizard, Lacerta vivipara, survive the cold of winter?

Although the European common lizard, Lacerta vivipara, is among the most common Eurasian reptile species, we know little about how these lizards cope with very low temperatures. In this study we examined microenvironmental conditions, body temperature, behavior, and cold strategies to see whether strategies of freezing and supercooling, while normally considered to be mutually exclusive, may in fact be adopted simultaneously by the common lizard. Following up on an earlier study of a lowland population, this time we used a mountain population (850 m) to discover differences in overwintering strategies between the two populations. Differential scanning calorimetry conducted during the hibernation period (vs. the activity period) showed that the blood of highland lizards had an increased ability to resist ice formation, confirming an ecophysiological effect most likely mediated by physical properties of the blood. Mean blood glucose level of unfrozen L. vivipara in the field increased significantly (about fourfold) from 8.5+/-0.7 mmol l(-1) in September to 33.2+/-5.6 mmol l(-1) in March. The blood glucose level then experienced a significant decline as it fell to 6. 2+/-0.8 mmol l(-1) after hibernation in April. Glucose, in conclusion, seems to play a role of cryoprotectant rather than antifreeze.

pH Sensing at Pt Electrode Surfaces Coated with Linear Polyethylenimine from Anodic Polymerization of Ethylenediamine

A novel pH sensor using a smooth Pt electrode coated with an electrically insulating polymer is addressed in this study. We present a new electrochemically modified Pt electrode. Its modification results from the anodic oxidation of pure ethylenediamine, charged with lithium trifluoromethanesulfonate, which leads to the formation of a polymer coating in one step. The assembly of the electrode surface coated with electropolymerized ethylenediamine acts as a transducer of the electrode potential vs. the pH value in aqueous solutions. It has been shown that the anodic oxidation of pure ethylenediamine yields polyethylenimine which is a high impedance polymer containing amino groups sensitive to H + concentration. Since the reproducibility of polymer-based pH sensors is a controversial subject, we examined both the effect of the electrode-bias time, which can be linked to the polymer thickness, and the aging of the polymer on the potentiometric response of the sensor. The pH sensor we propose here has a quasi-Nernstian behavior. It is reliable for some weeks in the pH range from 3 to 11 in aqueous media.

Ab initio study of the polymerization mechanism of poly(p-phenylenediamine)

The electrochemical oxidation of paraphenylenediamine (1,4-diaminobenzene, PPD) leads to the passivation of the electrode surface by a thin film as shown by using Cyclic Voltammetry technique. This film can be identified by InfraRed-Attenuated Total Reflectance as a polymeric film of poly(p-phenylenediamine), polyPPD. To establish the mechanism leading from PPD to polyPPD, we performed computations of energy and thermochemical values with the quantum-chemical Self-Consistent Field method at the Hartree–Fock level of theory. Then we compared this mechanism to the ones, previously established with similar ab initio calculations, leading to polyethyleneimine and polypropyleneimine in an attempt to generalize the mechanism of electropolymerization of diamines.

Surface modification of p-Si by a polyethylenimine coating: influence of the surface pre-treatment. Application to a potentiometric transducer as pH sensor

p-Si electrodes coated with linear polyethylenimine (L-PEI) allow the fabrication of a pH sensitive film for potentiometric transducers. The coating is realized in one step through the anodic oxidation of pure ethylenediamine (EDA) charged with 0.1 M LiCF3SO3 (Lithium Triflate). Such an electrochemical procedure leads to the thickness control of the coating. The best silicon surface pre-treatment before any coating is obtained with potassium dichromate in sulfuric acid, which leads to OH-terminated p-Si. This pre-treatment allows a uniform thin coating. In this work, the thickness is 2.6 nm. The pH response is high and close to 50 mV per pH unit.

New handy relationship between the conductivity of concentrated nonaqueous electrolyte solutions and the dielectric constant and viscosity of the solvents

Abstract For nonaqueous electrolyte solutions, we correlated the equivalent conductance Λ 0 at infinite dilution and the conductivity maximum κ MAX with only two intrinsic parameters of the pure solvents: the dielectric constant and the viscosity. On the basis of two new handy empirical formulas, predictions of Λ 0 and κ MAX can now be made for a given salt in any solvent on the basis of only one Λ 0 or κ MAX measurement in only one solvent.

Ab initio study of the electrochemical polymerization mechanism of ω–diamines

The anodic oxidation of liquid ω–diamine based-electrolyte leads to the passivation of the electrode surface by an insulating film as shown by using an electrochemical quartz crystal microbalance (EQCM) coupled with cyclic voltammetry (CV) technique. These films were identified by infrared-attenuated total reflectance (IR-ATR) as polymeric films: linear polyethylenimine (L-PEI) film for EDA based-electrolyte and linear propylenimine (L-PPI) for 1,3 DAP. We also performed computations of energy and thermochemical values with the quantum-chemical Onsager self-consistent reaction field (SCRF) method at the Hartree–Fock level for modeling the reaction mechanisms leading to the polymeric films.

Spectroscopic and ab initio study of polymeric films used as chemical sensors

Electrochemical oxidation of ethylenediamine leads to the coating of different electrode surfaces by a thin polymeric film. This film was characterized as a polyethylenimine one using both spectroscopic methods such as infrared-attenuated total reflection or infrared absorption spectroscopy and ab initio calculations. More, since the polymeric coating changes the electrochemical behavior of different surfaces, this film can be used successfully to make new chemical sensors.