Jesús Iniesta

Influence of chloride ion on electrochemical degradation of phenol in alkaline medium using bismuth doped and pure PbO2 anodes

Electrochemical method at laboratory scale for the treatment of biorefractory solutions with high phenol content--1000 ppm is described. Total degradation of phenol was obtained at alkaline pH when NaCl was present using Bi-doped and pure lead dioxide electrodes. A filter press cell of 63 cm2 geometric area was used for this purpose. Measurements of chemical oxygen demand (COD), phenol, carbon monoxide, carbon dioxide, and volatile organic compounds (VOCs) have been used to characterise the electrochemical process for phenol elimination. It is worth noting that in the absence of NaCl, the charge efficiency of COD removal was independent of the current density in the range studied (50-100 mA cm(-2)) Moreover, when NaCl was present, the current efficiency for COD and phenol removal increase as the chloride concentration increases. Chloroform was the only halocompound detected at the end of reaction. For both electrodes, Bi-doped and pure lead dioxide, the chloroform concentration at the end of the electrolysis decreases, working at low current densities and for low chloride concentrations.

Electrochemical lactate biosensor based upon chitosan/carbon nanotubes modified screen-printed graphite electrodes for the determination of lactate in embryonic cell cultures

l-lactate is an essential metabolite present in embryonic cell culture. Changes of this important metabolite during the growth of human embryo reflect the quality and viability of the embryo. In this study, we report a sensitive, stable, and easily manufactured electrochemical biosensor for the detection of lactate within embryonic cell cultures media. Screen-printed disposable electrodes are used as electrochemical sensing platforms for the miniaturization of the lactate biosensor. Chitosan/multi walled carbon nanotubes composite have been employed for the enzymatic immobilization of the lactate oxidase enzyme. This novel electrochemical lactate biosensor analytical efficacy is explored towards the sensing of lactate in model (buffer) solutions and is found to exhibit a linear response towards lactate over the concentration range of 30.4 and 243.9 µM in phosphate buffer solution, with a corresponding limit of detection (based on 3-sigma) of 22.6 µM and exhibits a sensitivity of 3417 ± 131 µAM(-1) according to the reproducibility study. These novel electrochemical lactate biosensors exhibit a high reproducibility, with a relative standard deviation of less than 3.8% and an enzymatic response over 82% after 5 months stored at 4 °C. Furthermore, high performance liquid chromatography technique has been utilized to independently validate the electrochemical lactate biosensor for the determination of lactate in a commercial embryonic cell culture medium providing excellent agreement between the two analytical protocols.

Freestanding three-dimensional graphene foam gives rise to beneficial electrochemical signatures within non-aqueous media

Freestanding three-dimensional (3D) graphene foam has been fabricated via a Chemical Vapour Deposition (CVD) methodology which has a macroscopic structure with microscopic (graphene) features. The 3D graphene macrostructure is characterised with SEM, EDX, XPS and Raman spectroscopy and is found to comprise pristine graphene (O/C of 0.05) which is in the range of mono- to few-layered graphene sheets and is thus termed quasi-graphene. This unique 3D graphene foam is electrochemically explored in both aqueous and non-aqueous solutions and compared to a freestanding 3D reticulated vitreous carbon (RVC) foam alternative. In aqueous solutions, the 3D graphene foam exhibits poor voltammetric responses. Contact angle measurements reveal the 3D graphene to exhibit a value of 120° representing quasi-super-hydrophobicity. Consequently the freestanding 3D graphene foam is found to give rise to significantly improved voltammetric signatures in non-aqueous media (ionic liquids) over that of a freestanding 3D RVC alternative. The 3D graphene foam provides a promising and beneficial architecture over 2D pristine graphene due to its ease of use and macroscopic/microscopic structure, which will have wide implementation in the field of electrochemistry.

Electrochemical Treatment of Industrial Wastewater Containing Phenols

The use of phenolic resins for manufacturing different textile products in a company, our case example, generates wastewater with high phenol concentration (30-400 ppm) and chemical oxygen demand (COD) between 3,000 and 15,000 ppm. Moreover, the effluent also contains high chloride concentrations ranging between 4000 and 7000 ppm, Ca 2+ ions with a concentration of ca. 2000 ppm, and suspended solids. A study at the laboratory scale of the anodic electrochemical treatment of this industrial effluent has been carried out. The influence of variables such as current density, pH, and charge passed on phenol degradation and COD reduction was studied. As anodes, PbO 2 /Ti or Bi-PhO 2 /Pt/Ti or Pt/Ti were used. As the separator, a 117 Nafion cation exchange membrane was employed. The results showed that the final COD value was lower than 1000 ppm. After electrochemical treatment the final concentration of phenol was lower than 1 ppm, and the COD decrease was 70-80%. Unidentified aliphatic carboxylic acids and alcohols were the main products of oxidation. For electrolyses carried out at alkaline pH, the only halocompound detected in the anolyte, gas, and aqueous phases, was chloroform regardless the electric charge passed, the current density employed, and the anode used.

Electron capture dissociation mass spectrometry of tyrosine nitrated peptides.

In vivo protein nitration is associated with many disease conditions that involve oxidative stress and inflammatory response. The modification involves addition of a nitro group at the position ortho to the phenol group of tyrosine to give 3-nitrotyrosine. To understand the mechanisms and consequences of protein nitration, it is necessary to develop methods for identification of nitrotyrosine-containing proteins and localization of the sites of modification. Here, we have investigated the electron capture dissociation (ECD) and collision-induced dissociation (CID) behavior of 3-nitrotyrosine-containing peptides. The presence of nitration did not affect the CID behavior of the peptides. For the doubly-charged peptides, addition of nitration severely inhibited the production of ECD sequence fragments. However, ECD of the triply-charged nitrated peptides resulted in some singly-charged sequence fragments. ECD of the nitrated peptides is characterized by multiple losses of small neutral species including hydroxyl radicals, water and ammonia. The origin of the neutral losses has been investigated by use of activated ion (AI) ECD. Loss of ammonia appears to be the result of non-covalent interactions between the nitro group and protonated lysine side-chains.

Top-Down Mass Analysis of Protein Tyrosine Nitration: Comparison of Electron Capture Dissociation with “Slow-Heating” Tandem Mass Spectrometry Methods

Tyrosine nitration in proteins is an important post-translational modification (PTM) linked to various pathological conditions. When multiple potential sites of nitration exist, tandem mass spectrometry (MS/MS) methods provide unique tools to locate the nitro-tyrosine(s) precisely. Electron capture dissociation (ECD) is a powerful MS/MS method, different in its mechanisms to the “slow-heating” threshold fragmentation methods, such as collision-induced dissociation (CID) and infrared multiphoton dissociation (IRMPD). Generally, ECD provides more homogeneous cleavage of the protein backbone and preserves labile PTMs. However recent studies in our laboratory demonstrated that ECD of doubly charged nitrated peptides is inhibited by the large electron affinity of the nitro group, while CID efficiency remains unaffected by nitration. Here, we have investigated the efficiency of ECD versus CID and IRMPD for top-down MS/MS analysis of multiply charged intact nitrated protein ions of myoglobin, lysozyme, and cytochrome c in a commercial Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. CID and IRMPD produced more cleavages in the vicinity of the sites of nitration than ECD. However the total number of ECD fragments was greater than those from CID or IRMPD, and many ECD fragments contained the site(s) of nitration. We conclude that ECD can be used in the top-down analysis of nitrated proteins, but precise localization of the sites of nitration may require either of the “slow-heating” methods.

Effects of ultrasound on the electrodeposition of lead dioxide on glassy carbon electrodes

The electrodeposition of lead dioxide from lead(II) nitrate in an acid medium has been used as a test reaction to study the effects of an ultrasound field. The different behaviours found between platinum and glassy carbon electrodes have been compared by means of cyclic voltammetry and simple potential steps. The current–time response for a platinum electrode is not affected by the presence or absence of ultrasound; in contrast, significant changes have been observed in the characteristic regions of these curves (induction time t0) with the glassy carbon electrode. Scanning electron microscopy (SEM) has been employed to follow changes in the surface topography after the electrodes had been exposed to ultrasound. Results indicate that neither pits nor structural modifications that may increase the electrode surface occur with the device used. It is concluded that the activation of glassy carbon electrodes by the action of an ultrasound field for electrodeposition of lead dioxide is associated with the surface functionalization caused by the reaction of OH radicals (derived from aqueous sonolysis) with the carbon surface.

Sonoelectrochemical effects in electro-organic systems.

This paper describes recent studies in organic sonoelectrochemistry at Coventry University, including the oxidation of thiophene monoxides, degradation of dye pollutants, formation of conducting polymers and electrosynthetic modification of proteins.

Early stages of lead dioxide electrodeposition on rough titanium

The electrodeposition of lead dioxide onto rough titanium surfaces has been studied using both voltammetric and chronoamperometric techniques. The behaviour of the system is a function of the upper potential limit and also of the surface topography, and can be explained bearing in mind the competence between the (inactivation) of the support and the electrodeposition process. The influence of an ultrasonic field in the process has also been analyzed.

Kinetics of Electrocrystallization of PbO2 on Glassy Carbon Electrodes Partial Inhibition of the Progressive Three‐Dimensional Nucleation and Growth

Conselleria de Cultura, Educacion y Ciencia de la Generalidad Valenciana (project GV-2231-94) and D.G.I.C.Y.T. (project QUI97-1086).