James J. Noël

Protein Oxidative Modifications During Electrospray Ionization: Solution Phase Electrochemistry or Corona Discharge-Induced Radical Attack?

The exposure of solution-phase proteins to reactive oxygen species (ROS) causes oxidative modifications, giving rise to the formation of covalent +16 Da adducts. Electrospray ionization (ESI) mass spectrometry (MS) is the most widely used method for monitoring the extent of these modifications. Unfortunately, protein oxidation can also take place as an experimental artifact during ESI, such that it may be difficult to assess the actual level of oxidation in bulk solution. Previous work has demonstrated that ESI-induced oxidation is highly prevalent when operating at strongly elevated capillary voltage V(0) (e.g., +8 kV) and with oxygen nebulizer gas in the presence of a clearly visible corona discharge. Protein oxidation under these conditions is commonly attributed to OH radicals generated in the plasma of the discharge. On the other hand, charge balancing oxidation reactions are known to take place at the metal/liquid interface of the emitter. Previous studies have not systematically explored whether such electrochemical processes could be responsible for the formation of oxidative +16 Da adducts instead of (or in combination with) plasma-generated ROS. Using hemoglobin as a model system, this work illustrates the occurrence of extensive protein oxidation even under typical operating conditions (e.g., V(0) = 3.5 kV, N(2) nebulizer gas). Surprisingly, measurements of the current flowing in the ESI circuit demonstrate that a weak corona discharge persists for these relatively gentle settings. On the basis of comparative experiments with nebulizer gases of different dielectric strength, it is concluded that ROS generated under discharge conditions are solely responsible for ESI-induced protein oxidation. This result is corroborated through off-line electrolysis experiments designed to mimic the electrochemical processes taking place during ESI. Our findings highlight the necessity of using easily oxidizable internal standards in biophysical or biomedical ESI-MS studies where knowledge of protein oxidation in bulk solution is desired. Strategies for eliminating ESI-induced oxidation artifacts are discussed.

Effects of Temperature and Potential on the Passive Corrosion Properties of Alloys C22 and C276

Potentiostatic polarization experiments were performed as a function of potential (200 to 700 mV Ag/AgCl ) and temperature (25-85°C) on the Ni-Cr-Mo alloys C22 and C276. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF SIMS) were used to determine the chemical composition and thickness of the films formed. The currents recorded as a function of applied potential were due to dissolution, with only minor increases in film thicknesses observed. Measured currents for C22 were lower than for C276 and decayed over the entire period of measurement at each temperature. Those on C276 more closely approached steady state. The temperature dependence of the currents on C22 was significantly lower than that on C276. Surface analyses, performed on specimens anodically treated at one potential but after a sequence of temperatures up to 85°C, confirmed that the passive films on both alloys consisted of a Mo, Cr, and Ni oxide, with Cr present as Cr 3 + and Mo present in several oxidation states. The passive films on C22 showed a distinct layered structure, consisting of an inner layer rich in Cr and Ni, and an outer layer enhanced in Mo. By contrast, the oxide films on C276 did not show such a clear separation into layers, and the relative Cr content was much lower. The increase in oxide thickness with increasing anodic potential and the low temperature dependence of the passive current observed for C22 are consistent with an oxide dissolution rate which is low compared to the rate of creation of oxygen vacancies leading to film growth. The absence of a dependence of film thickness on potential and the higher temperature dependence of the passive currents on C276 are consistent with control of the overall anodic process by ion-transfer at the oxide/solution interface.

Temperature Dependence of Crevice Corrosion Initiation on Titanium Grade-2

The temperature dependence of crevice corrosion initiation on titanium grade-2 has been investigated using a galvanic coupling technique. The film breakdown/repassivation transients indicate a temperature threshold, around 65°C, for the initiation of crevice corrosion. The number, size, frequency, and background current of these events increased when the temperature was increased from 65 to 80°C. Analysis of single transients suggests that the temperature also has an effect on the repassivation mechanism. Image analysis of corroded coupons reveals that crevice initiation and deeper penetration occur around the edge of the creviced area. Surface studies using electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy show oxide film flaws accompanied by water incorporation at temperatures above the 65°C threshold. Under creviced conditions, the occurrence of film flaws is the key process leading to the development of acidity and the initiation of crevice corrosion.

Effects of Iron Content on Microstructure and Crevice Corrosion of Grade-2 Titanium

Abstract The effects of iron content on the microstructure and crevice corrosion of Grade-2 titanium (Ti-2) were studied using a galvanic coupling technique combined with optical microscopy and sec...

An Electrochemical Investigation of the Dissolution of Magnetite in Acidic Electrolytes

The electrochemical behavior of magnetite was investigated in perchloric acid and ethylenediaminetetra-acetic acid (EDTA). The potential dependence of the total dissolution flux is similar for both acids; the form of this dependence indicates that ion-transfer reactions are rate determining. In EDTA-containing electrolytes, equilibrium is established by electron-transfer between the magnetite and the Fe 2+ /Fe 3+ species liberated by dissolution. This process defines the open-circuit potential of magnetite (E oc ) in this electrolyte. A similar process does not determine E oc in perchloric acid; the nature of the processes defining this potential in perchloric acid remains uncertain

Effect of gamma irradiation on gas-ionic liquid and water-ionic liquid interfacial stability

The effect of γ-radiation on gas-ionic liquid (IL) and water-IL interfacial stability was investigated. Three phosphonium-based ILs, which vary considerably in their viscosity, conductivity and miscibility with water, were examined. The gas phase above the IL samples (headspace gas) was analyzed using gas chromatography with a mass spectrometer detector while the changes in the IL and aqueous phases were followed by conductivity measurements and Raman spectroscopy. For the gas-IL systems, the headspace samples showed trace amounts of the radiolytic decomposition products of the ILs that were small and volatile enough to become airborne. The type of cover gas, air or Ar, had no effect on the gas speciation. Negligible changes in the conductivity and the Raman spectra of the IL phase due to irradiation indicate that γ-irradiation induces negligible chemical changes in the IL phase when it is in contact with a gas phase. For the water-IL systems, the initially immiscible layers slowly developed an interfacial emulsion layer, even in the absence of radiation. This layer started at the water-IL interface and then grew downwards, eventually converting the entire IL phase to an emulsion. Gamma-irradiation accelerated the conversion of the IL phase to an emulsion. The development of the emulsion layer was accompanied by changes in the conductivity and the Raman spectra of both the IL and water phases. Based on these results, a mechanism involving the formation of micelles at, or near, the water-IL interface has been proposed to explain the development of an emulsion layer. We also suggest that radiolytic decomposition of ILs produces surfactants that can accumulate at the interface and, even at low concentrations, accelerate the emulsification process.

Glassy Metals as Electrocatalysts for Hydrogen Evolution and Oxidation Part I : Electrocatalytic Properties of Amorphous Pt‐Si Alloy

The adsoption of hydrogen and the kinetics of the hydrogen evolution reaction (HER) on the vitreous Pt 77 Si 23 alloy have been investigated. Five differently treated samples of the alloy have been studied and their electrocatalytic activities have been compared with those of pure polycrystalline Pt

Temperature Effects on Oxide Film Properties of Grade-7 Titanium

Abstract The passive corrosion properties of Grade-7 titanium (Ti-7) have been studied at elevated temperatures up to 150°C and as a function of time at a constant temperature of 150°C in 0.27 mol/L sodium chloride (NaCl) solution using a combination of open-circuit potential and electrochemical impedance spectroscopy (EIS) measurements. It was found that the influence of temperature on the passive behavior of Ti-7 depended on the manner in which the temperature was changed. If the temperature was raised slowly in 10°C steps, passivity was maintained up to 150°C, but metastable breakdown events commenced once the temperature was increased to ≥70°C. These events could be associated with the active dissolution of Fe-stabilized β-phase and/or TixFe particles in grain boundaries. Impedance analyses showed that the changes in film resistance and capacitance were observable but minor. If the temperature was raised very rapidly to 150°C, an observable film breakdown occurred, leading to a drop of >150 mV in corr...

Galvanic corrosion of copper-coated carbon steel for used nuclear fuel containers

ABSTRACT Canada is currently considering Cu-coated carbon steel containers for the long-term storage of used nuclear fuel in a deep geological repository. The Cu coating provides a corrosion-resistant barrier, protecting the underlying steel from coming into contact with groundwater. However, galvanically accelerated corrosion of steel is possible if there is a defect through the Cu coating. To investigate this scenario, the progression of steel corrosion at the base of a simulated though-coating defect was imaged using synchrotron X-ray micro-computed tomography. Results show that coatings produced using different methods (cold spray, annealed cold spray, electrodeposition) lead to different corrosion propagation geometries. These findings can be used for modelling steel corrosion at a though-coating defect under deep geological repository conditions. This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.

The active/passive conditions for copper corrosion under nuclear waste repository environment

ABSTRACT The focus of this research is to determine the conditions under which passivity of Cu is (with the possibility of pitting) or is not possible, in anticipated bentonite pore water compositions expected to contact a Cu-coated container in a deep geological repository. Cyclic voltammetry has been used to deduce the active/passive maps that define the environmental conditions (in terms of [Cl−], [], [], pH, and temperature) under which the Cu surface could be active or passive. A range of temperatures (up to 80°C), pH values (neutral to alkaline), and electrolyte compositions have been investigated. Such a database of maps shows that active/passive conditions change with the pH, temperature, and the type and concentration of anions. These maps will provide a basis for container corrosion models, as well as guidelines regarding the water compositions used when compacting the bentonite, the repository saturation time, and the optimum container spacing. This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.