Electrochemical Real‐Time Mass Spectrometry (EC‐RTMS): Monitoring Electrochemical Reaction Products in Real Time

Methods that provide real‐time information are essential to resolve transients occurring at dynamic interfaces. Now a powerful method is presented that enables the time‐ and potential‐resolved characterization of liquid and gaseous products of electrochemical reactions shortly after their formation. To demonstrate its extraordinary potential, the electrochemical real time mass spectrometry (EC‐RTMS) approach is used to determine the products of the CO₂ reduction reaction (CO₂RR) during potential step or sweep experiments on pristine and in situ anodized copper. The enhanced formation of several C₂₊ products over C₁ products is tracked directly after copper anodization, with unprecedented temporal resolution. This new technique creates exciting new opportunities for resolving processes that occur at short timescales and eventually for guiding the design of new, robust catalysts for selective electrosynthesis under dynamic operation.     

Electrochemical and Spectroscopic Behaviour of Bis(2‐mercaptopyridine‐N‐oxide)oxovanadium(IV)

The complex [VO(MPO)₂] (MPO = deprotonated 2‐mercaptopyridine N‐oxide) was synthesized and characterized by IR spectroscopy. Its electrochemical behaviour was investigated by cyclic voltammetry in different organic solvents. The V^IV/V^V and V^IV/V^III couples could be identified. The nature of the electroactive species is strongly dependent on the solvent. The results are discussed in terms of a reaction mechanism describing the characteristics of the electron transfer processes and the involved chemical reactions, and the stability of the complex in each solvent was also determined. The electronic spectra of the investigated solutions gave additional support to the proposed mechanisms.     

Electrochemical Study of Tryptophan‐containing Peptides‐Cu(II) Complexes

This article presents rotating ring‐disc electrode investigations of (A = alanine, F = phenylalanine, G = glycine, L = leucine, W = tryptophan) W, GW, WGG, GWG, GGW, GWGG, and GGWA. In addition, the analyses of the copper complexes of the same peptides plus GF, FGG, GFG, FGG, GGFL, GGGG, AAAA, and GGGGGG have been carried out. The results suggest that an influential step in the reaction mechanism of the copper complexes of the tryptophan‐containing peptides (W‐peptides) is the alteration of the peptide structure after the one‐electron oxidation of tryptophan. This change in structure leads to a positive shift in redox potential for the Cu(III)/Cu(II) couple. The analytical implications for the electrochemical detection of W‐peptides as their copper complexes are applied for detection of W‐containing bioactive peptides. Application of the optimized detection conditions of peptides as their Cu(II) complexes are as follows: (1) If sensitivity is paramount, detect the copper complexes at a relatively high potential, around 0.7 V vs. Ag/AgCl. (2) If selectivity is paramount, use a dual electrode detector, oxidize at an upstream anode at 0.4 V, and detect at the downstream cathode at 0–0.1 V.     

Electrochemical synthesis of poly(3‐methylthiophene): A kinetic study

Poly(3‐methylthiophene) (P3MT) films were electrogenerated on both platinum and carbon‐felt working electrodes. The kinetic equation was determined by the monomer and electrolyte concentrations being changed for different reaction times. For each sample, the weight of the polymer obtained was measured along with the polymerization charge, the oxidation charge, the ratio (R) between the two magnitudes, the charge storage efficiency (SE), and the doping level. The results obtained from the kinetic study indicate significant electrolyte participation in the electropolymerization process. The SE and the doping level decreased inversely proportionately to both the reaction time and the concentrations of the monomer and electrolyte. The ratio R increased with reaction time as well as with monomer or electrolyte concentrations for all P3MTs generated on the carbon‐felt electrodes, whereas for those films generated on platinum electrodes, the highest values were obtained for the lowest monomer and electrolyte concentrations. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1258–1266, 2000     

Metal Enhanced Electrochemical Cyclooxygenase‐2 (COX‐2) Sensor for Biological Applications

Pain measurement is commonly required in biomedical and other emergency situations, yet there has been no pain biosensor reported in literature. Conventional approaches for pain measurement relies on Wong‐Baker face diagrams, which are grossly inadequate for situations involving children or unconscious people. We report a label‐free immunosensor for monitoring the pain biomarker cylooxygenase‐2 (COX‐2) in blood. The sensor is based on the concept of metal‐enhanced detection (MED). MED relies on the idea that the immobilization of underpotential deposition (upd) metallic films deposited either as a monolayer or electrostatically held onto a solid gold substrate could significantly amplify bimolecular recognition such as involving antigen‐antibody (Ab‐Ag) interactions. The surface bound Ab‐Ag complex insulates the electrode; causing a decrease in concentration‐dependent redox signals. A linear detection range of (3.64–3640.00)×10^?4 ng/mL was recorded with a detection limit of 0.25×10^?4 ng/mL, which was 4 orders of magnitude lower than that reported for ELISA for the same biomarker. The immunosensor exhibited selectivity of less than 6 % for potential interferents.     

Stretchable Electrochemical Sensor for Real‐Time Monitoring of Cells and Tissues

Stretchable electrochemical sensors are conceivably a powerful technique that provides important chemical information to unravel elastic and curvilinear living body. However, no breakthrough was made in stretchable electrochemical device for biological detection. Herein, we synthesized Au nanotubes (NTs) with large aspect ratio to construct an effective stretchable electrochemical sensor. Interlacing network of Au NTs endows the sensor with desirable stability against mechanical deformation, and Au nanostructure provides excellent electrochemical performance and biocompatibility. This allows for the first time, real‐time electrochemical monitoring of mechanically sensitive cells on the sensor both in their stretching‐free and stretching states as well as sensing of the inner lining of blood vessels. The results demonstrate the great potential of this sensor in electrochemical detection of living body, opening a new window for stretchable electrochemical sensor in biological exploration.     

Electroconductive Hydrogels: Electrical and Electrochemical Properties of Polypyrrole‐Poly(HEMA) Composites

Composites of inherently conductive polypyrrole (PPy) within highly hydrophilic poly(2‐hydroxyethyl methacrylate)‐based hydrogels (p(HEMA)) have been fabricated and their electrochemical properties investigated. The electrochemical characteristics observed by cyclic voltammetry suggest less facile reduction of PPy within the composite hydrogel compared to electropolymerized PPy, as shown by the shift in the reduction peak potential from ?472 mV for electropolymerized polypyrrole to ?636 mV for the electroconductive composite gel. The network impedance magnitude for the electroconductive hydrogel remains quite low, ca. 100 Ω, even upon approach to DC, over all frequencies and at all offset potentials suggesting retained electronic (bipolaronic) conductivity within the composite. In contrast, sustained application of +0.7 V (vs. Ag/AgCl, 3 M Cl^?) for typically 100 min. (conditioning) to reduce the background amperometric current to <1.0 μA, resulted in complete loss of electroactivity. Nyquist plots suggest that sustained application of such a modest potential to the composite hydrogel results in impedance characteristics that resembles p(HEMA) without evidence of the conducting polymer component. PPy composite gels supported a larger ferrocene monocarboxylate diffusivity (D_appt=7.97×10^?5 cm² s^?1) compared to electropolymerized PPy (D_appt=5.56×10^?5 cm² s^?1), however a marked reduction in diffusivity (D_appt=1.01×10^?5 cm² s^?1) was observed with the conditioned hydrogel composite. Cyclic voltammograms in buffer containing H₂O₂ showed an absence of redox peaks for electrodes coated with PPy‐containing membranes, suggesting possible chemical oxidation of polypyrrole by the oxidant     

Electrochemical Reduction of 1,2-Di（p-tolylimino）ethane and 1,2-Di（2,4-dimethylphenylimino）ethane in Dimethylformamide

1,2-Di（p-tolylimino）ethane （Ⅰ） and 1,2-Di（2,4-dimethylphenylimino）ethane （Ⅱ） were synthesized and their electrochemical behavior investigated in dimethylformamide using classical voltammetry, differential pulse voltammetry, cyclic voltammetry, chronoamperometry, controlled potential electrolysis and coulometry. Both bis-Schiff base ligands examined show a cathodic irreversible peak which corresponds to one-electron reduction of the substrate to form anion radical. According to the fact obtained from cyclic voltammetry, that the current function （ip/v^1/2） is a decreasing function of the scan rate, it can be concluded that there is a following coupling chemical reaction （EC mechanism）. Thus, the most probable mechanism of electroreduction of both ligands is the coupling of two radicals to form a dimer.     

Electrochemical Detection of Thioether‐Based Fluorosurfactants in Aqueous Film‐Forming Foam (AFFF)

Using cyclic voltammetry (CV) and impedance (IMP), we report a simple approach to detect new fluorosurfactant ingredient formulated in aqueous film‐forming foam (AFFF), specifically the thioether‐based one. First, we employ ion chromatography (IC) to identify all possible elements with the help of chemical oxidation and infrared spectrum (IR) to identify all possible functional groups. We thus propose a possible thioether‐based molecular structure of fluorosurfactant formulated in AFFF. By studying the self‐assembled monolayer (SAM) formed on gold (Au) surface via thio‐Au bond, we establish a relationship between the SAM density and the amount of the thioether‐based fluorosurfactant for the AFFF detection. Solid phase extraction (SPE) and nanoporous Au electrode are employed to enhance the sensitivity. Consequently, a detection limit of 10 ppb (v/v) has been achieved for AFFF‐spiked tap water sample.     

Tetrathiafulvalene–Oligo(para‐phenyleneethynylene) Conjugates: Formation of Multiple Mixed‐Valence Complexes upon Electrochemical Oxidation

Short monodisperse oligo‐ (para‐phenyleneethynylene) (pOPE) units bearing laterally attached tetrathio‐substituted tetrathiofulvalene (TTF) units have been synthesised from functionalised aromatic building blocks by using the Sonogashira cross‐coupling methodology. The unusual redox properties of these TTF–pOPE conjugates were observed by employing electrochemical methods, such as cyclic voltammetry and exhaustive electrolysis. We found that formally one half of the TTF units in the pOPE monomer 1 , dimer 2 , and trimer 3 (with 2, 4, and 6 TTF units, respectively) are electrochemically silent during the first‐step oxidation at 0.49 V. We propose the formation of persistent mixed‐valence complexes from the TTF and TTF^+. units present in an equal ratio. Such mixed‐valence dyads (single or multiple in the partially oxidised 1 – 3 ) exhibit an unusual stability towards oxidation until the potential of the second oxidation at 0.84 V is achieved. This finding suggests that below this potential the oxidation of the respective mix‐valence complexes is extremely slow.     

Influence of Dopant Loading on the Photo‐ and Electrochemical Properties of (N,O)‐Co‐doped Graphene.

A series of (N, O)‐co‐doped graphenes with different N and O loadings are prepared by the pyrolysis of natural chitosan. When the percentage of dopant increases, the conduction‐band potential and charge‐separation quantum yield increase, whereas the charge‐separation lifetime decreases.