Guillaume Herlem

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.

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.

Nanovectorization of TRAIL with single wall carbon nanotubes enhances tumor cell killing

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL or Apo2L) is a member of the tumor necrosis factor (TNF) superfamily. This type II transmembrane protein is able to bound specifically to cancer cell receptors (i.e., TRAIL-R1 (or DR4) and TRAIL-R2 (or DR5)) and to induce apoptosis without being toxic for healthy cells. Because membrane-bound TRAIL induces stronger receptor aggregation and apoptosis than soluble TRAIL, we proposed here to vectorize TRAIL using single-walled carbon nanotubes (SWCNTs) to mimic membrane TRAIL. Owing to their exceptional and revolutional properties, carbon nanotubes, especially SWCNTs, are used in a wide range of physical or, now, medical applications. Indeed due to their high mechanical resistance, their high flexibility and their hydrophobicity, SWCNTs are known to rapidly diffuse in an aqueous medium such as blood, opening the way of development of new drug nanovectors (or nanocarriers). Our TRAIL-based SWCNTs nanovectors proved to be more efficient than TRAIL alone death receptors in triggering cancer cell killing. These NPTs increased TRAIL pro-apoptotic potential by nearly 20-fold in different Human tumor cell lines including colorectal, nonsmall cell lung cancer, or hepatocarcinomas. We provide thus a proof-of-concept that TRAIL nanovector derivatives based on SWCNT may be useful to future nanomedicine therapies.

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.

N-glycosylation of mouse TRAIL-R and human TRAIL-R1 enhances TRAIL-induced death.

APO2L/TRAIL (TNF-related apoptosis-inducing ligand) induces death of tumor cells through two agonist receptors, TRAIL-R1 and TRAIL-R2. We demonstrate here that N-linked glycosylation (N-glyc) plays also an important regulatory role for TRAIL-R1-mediated and mouse TRAIL receptor (mTRAIL-R)-mediated apoptosis, but not for TRAIL-R2, which is devoid of N-glycans. Cells expressing N-glyc-defective mutants of TRAIL-R1 and mouse TRAIL-R were less sensitive to TRAIL than their wild-type counterparts. Defective apoptotic signaling by N-glyc-deficient TRAIL receptors was associated with lower TRAIL receptor aggregation and reduced DISC formation, but not with reduced TRAIL-binding affinity. Our results also indicate that TRAIL receptor N-glyc impacts immune evasion strategies. The cytomegalovirus (CMV) UL141 protein, which restricts cell-surface expression of human TRAIL death receptors, binds with significant higher affinity TRAIL-R1 lacking N-glyc, suggesting that this sugar modification may have evolved as a counterstrategy to prevent receptor inhibition by UL141. Altogether our findings demonstrate that N-glyc of TRAIL-R1 promotes TRAIL signaling and restricts virus-mediated inhibition.

Ab initio study of the electronic and structural properties of the crystalline polyethyleneimine polymer

Polyethyleneimine is a very interesting polymer, not only for its extensive use in biological applications, but also for its crystal structure as a double-stranded helix in the anhydrous state. In order to elucidate the electronic bulk properties of the crystalline (or linear) polyethyleneimine built from ethylenediamine molecules in anhydrous conditions, we performed ab initio density functional theory calculations on water-free molecular crystal structures. The resulting polymer is a semiconductor with a small band gap: Eg = 0.40 eV.

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.