scholarly journals A synthetic chemist's guide to electroanalytical tools for studying reaction mechanisms

2019 ◽  
Vol 10 (26) ◽  
pp. 6404-6422 ◽  
Author(s):  
Christopher Sandford ◽  
Martin A. Edwards ◽  
Kevin J. Klunder ◽  
David P. Hickey ◽  
Min Li ◽  
...  
Keyword(s):  
Reaction Mechanisms ◽  
Redox Reactions ◽  
Synthetic Chemistry

A range of electroanalytical tools can be applied to studying redox reactions, probing key mechanistic questions in synthetic chemistry.

Biopolymer Solution Viscosity Stabilization - Polymer Degradation and Antioxidant Use

1983 ◽  
Vol 23 (06) ◽  
pp. 901-912 ◽  
Author(s):  
Scott L. Wellington
Keyword(s):  
Free Radicals ◽  
Chemical Treatment ◽  
Reaction Mechanisms ◽  
Redox Reactions ◽  
Polymer Degradation ◽  
Mobility Control ◽  
Solution Viscosity ◽  
Degradation Mechanisms ◽  
Literature Study ◽  
Shear Stability

Abstract Dilute solutions of polymers used to provide mobility control for EOR often lose viscosity. especially at higher temperatures. This loss of viscosity with time brings into question the feasibility of using polymers as mobility-control agents. A literature study of the many possible reaction mechanisms indicated that oxidation/reduction (redox) reactions involving free radicals probably caused polymer degradation and concomitant viscosity loss. A preliminary search for antioxidants known to retard free-radical reactions located several types and positive synergistic formulations that significantly retarded biopolymer solution viscosity loss during accelerated tests at high temperature. The most effective type formulation found contained (1) a radical transfer agent; (2) a sacrificial, easily oxidizable alcohol; (3) a compatible oxygen scavenger; and (4) sufficient brine concentration. Samples prepared with this technology have not lost viscosity after 1-year storage at 207 deg. F [97 deg. C]. A high-surface-area effect (so-called "wall effect") known to retard radical propagation, was also found to operate in the presence of sandpacks; this should be beneficial in porous media. The variables and beneficial antioxidant formulations identified in this study allow tentative conclusions and recommendations regarding biopolymer mixing and handling procedures prior to injection. Introduction Two commercially available polymers are currently considered suitable for mobility control. They are (1) the synthetically prepared polyacrylamides, and (2) the biopolymer (xanthan gum) prepared by fermenting the bacterium Xanthomonas campestris and collecting the exude gum. The major advantages of the biopolymer over polyacrylamides are the good shear stability and the good thickening power at high salinity. The major disadvantages of the biopolymer have been the high cost, the difficulty of preparing solutions that do not plug core material, and the prevention of viscosity loss from biochemical or chemical reactions. The requirement of shear stability and tolerance to salts, especially multivalent cations, significantly reduces the number of reservoirs where polyacrylamides can be used. Biopolymer solution-preparation problems have been overcome by development of solution processes including proper mixing equipment, chemical addition-both caustic and enzymes-and filtration techniques. Biopolymer broths, which preclude the need to wet and disperse a dry powder, are also available. Chemical stability of the polymer is the subject of this report. A literature study of the various reaction mechanisms indicates that redox reactions involving free radicals probably cause polymer degradation and concomitant viscosity losses. This is undoubtedly the type of reaction responsible for polyacrylamide decomposition. Removal of oxygen with excess sodium dithionite appears to provide sufficient chemical treatment to prevent autoxidation of polyacrylamide. This straightforward chemical treatment did not prevent biopolymer-solution viscosity loss, and further antioxidant addition was required to stabilize the solution viscosity. Polysaccharide Degradation Mechanisms A literature review of polysaccharide chemistry suggested thermal, biological, mechanical, radiation, and chemical as the most important degradation mechanisms. Thermal- and radiation-induced degradation mechanisms were discounted since biopolymers should not be used if the reservoir is too hot or too radioactive. SPEJ P. 901^

scholarly journals Hydrogen Production by Photoreforming of Renewable Substrates

2012 ◽  
Vol 2012 ◽  
pp. 1-21 ◽  
Author(s):  
Ilenia Rossetti
Keyword(s):  
Hydrogen Production ◽  
Reaction Mechanisms ◽  
Redox Reactions ◽  
Organic Molecules ◽  
Solar Light ◽  
Organic Substrates ◽  
Materials Development ◽  
Key Features

This paper focuses on the application of photocatalysis to hydrogen production from organic substrates. This process, usually called photoreforming, makes use of semiconductors to promote redox reactions, namely, the oxidation of organic molecules and the reduction of H+ to H2. This may be an interesting and fully sustainable way to produce this interesting fuel, provided that materials efficiency becomes sufficient and solar light can be effectively harvested. After a first introduction to the key features of the photoreforming process, the attention will be directed to the needs for materials development correlated to the existing knowledge on reaction mechanisms. Examples are then given on the photoreforming of alcohols, the most studied topic, especially in the case of methanol and carbohydrates. Finally, some examples of more complex but more interesting substrates, such as waste solutions, are proposed.

scholarly journals Noncanonical transnitrosylation network contributes to synapse loss in Alzheimer’s disease

Science ◽  
2020 ◽  
pp. eaaw0843
Author(s):  
Tomohiro Nakamura ◽  
Chang-ki Oh ◽  
Lujian Liao ◽  
Xu Zhang ◽  
Kevin M. Lopez ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Reaction Mechanisms ◽  
Redox Reactions ◽  
Reproductive Period ◽  
Primary Reaction ◽  
Biochemical Pathways ◽  
Synapse Loss ◽  
Guanosine Triphosphatase ◽  
Kinase A

We describe mechanistically-distinct enzymes, i.e., a kinase, a guanosine triphosphatase and a ubiquitin protein hydrolase, which function in disparate biochemical pathways, that can also act in concert to mediate a series of redox reactions. Each enzyme manifests a second, noncanonical function – transnitrosylation – triggering a pathological biochemical cascade in Alzheimer’s disease (AD). The resulting series of transnitrosylation reactions contributes to synapse loss, the major pathological correlate to cognitive decline in AD. We conclude that enzymes with distinct primary reaction mechanisms can form a completely separate network for aberrant transnitrosylation. This network operates in the post-reproductive period, so natural selection against such abnormal activity may be decreased.

Cyclic Voltammetry as an Electroanalytical Tool for Analysing the Reaction Mechanisms of Copper in Chloride Solution Containing Different Azole Compounds

2020 ◽  
Vol 16 (4) ◽  
pp. 465-474 ◽  
Author(s):  
Matjaž Finšgar ◽  
Klodian Xhanari ◽  
Helena O. Ćurković
Keyword(s):  
Cyclic Voltammetry ◽  
Reaction Mechanisms ◽  
Redox Reactions ◽  
Square Root ◽  
Redox Potentials ◽  
Linear Variation ◽  
Peak Potential ◽  
Peak Current ◽  
Diffusion Controlled ◽  
Scan Rate

Background: Cyclic voltammetry is widely employed in electroanalytical studies because it provides fast information about the redox potentials of the electroactive species and the influence of the medium on the redox processes. Azole compounds have been found to be effective corrosion inhibitors for copper in chloride-containing solutions. The aim of this work was to investigate in detail the influence of the addition of various azole compounds on the oxidation mechanism of copper in chloride-containing solutions, using cyclic voltammetry. Methods: The influence of thirteen azole compounds, at three different concentrations on the electrochemical/ chemical reactions of pure copper immersed in 3 wt.% NaCl solution was studied using cyclic voltammetry at different scan rates. The change of the peak current and potential with the scan rate were investigated. The possible linearity was compared with the theoretically derived mechanism. The possible reaction mechanisms were discussed based on the linearity of these parameters (peak current and potential) with the scan rate compared to theoretically derived models. Results: Both the peak current and peak potential of the copper samples immersed in chloridecontaining solutions with additions of the majority of azole compounds showed linearity with the square root of the scan rate, suggesting that copper follows the Müller-Calandra passivation model. The same behavior was also found for copper in chloride-containing solutions without additions of azole compounds. A linear variation of the peak potential with the natural logarithm of the scan rate and linear variation of the peak potential with the square root of the scan rate was observed for the copper samples immersed in chloride-containing solutions with the addition of 10 mM of 2-mercapto-1- methylimidazole, imidazole, or 2-aminobenzimidazole. This suggests that copper follows irreversible redox reactions under a diffusion controlled process. No other linear relations of the peak current and peak potential with the scan rate were found. Conclusion: Copper oxidation in chloride-containing solutions is controlled by passivation (following the Müller-Calandra passivation model) upon the addition of the majority of the selected azoles. In the minority of cases, irreversible redox reactions that follow a diffusion-controlled process were identified. None of the systems followed an adsorption-controlled process. Moreover, none of the tested systems underwent reversible redox reactions that followed a diffusion controlled process.

scholarly journals Li-rich cathodes for rechargeable Li-based batteries: reaction mechanisms and advanced characterization techniques

2020 ◽  
Vol 13 (12) ◽  
pp. 4450-4497 ◽  
Author(s):  
Wenhua Zuo ◽  
Mingzeng Luo ◽  
Xiangsi Liu ◽  
Jue Wu ◽  
Haodong Liu ◽  
...  
Keyword(s):  
Reaction Mechanisms ◽  
Redox Reactions ◽  
Advanced Characterization ◽  
Special Focus ◽  
Characterization Techniques ◽  
Working Mechanisms

This review summarizes the history and critical working mechanisms of Li-rich oxides with a special focus on anionic redox reactions.

Chromium behavior in aquatic environments: a review

2016 ◽  
Vol 24 (4) ◽  
pp. 503-516 ◽  
Author(s):  
Josselin Gorny ◽  
Gabriel Billon ◽  
Catherine Noiriel ◽  
David Dumoulin ◽  
Ludovic Lesven ◽  
...  
Keyword(s):  
Natural Organic Matter ◽  
Reaction Mechanisms ◽  
Redox Reactions ◽  
Surface Sediments ◽  
Bacterial Activity ◽  
Aquatic Environments ◽  
Dissolved Iron ◽  
Diagenetic Processes ◽  
Redox Interconversion

The fate of chromium (Cr) – a redox sensitive metal – in surface sediments is closely linked to early diagenetic processes. This review summarizes the main redox pathways that have been clearly identified over recent decades concerning the behavior of Cr(III,VI) in aquatic environments, and applies them to surface sediments where data for redox speciation remain limited. Overall, abiotic redox reactions that govern the speciation of Cr involve manganese (Mn) (III,IV) (hydr)-oxydes for Cr(III) oxidation, Cr(VI)-reducing species (dissolved iron (Fe) (II) and hydrosulfide (HS)−), and Cr(VI)-reducing phases (ferrous and sulfide minerals, as well as Fe(II)-bearing minerals). Bacterial activity is also responsible for the redox interconversion between Cr(III) and Cr(VI): biotic reduction of Cr(VI) to Cr(III) is observed through either detoxification or dissimilatory reduction. Whereas Mn(II)-oxidizing bacteria are known to promote indirect oxidation of Cr(III) to Cr(VI), the reaction mechanisms are unresolved. Conversely, oxygen (O2), nitrate (NO3−), and nitrite (NO2−) do not appear to play any role in Cr(III) oxidation. Additionally, Mn(II) and ammonium (NH4+) are not known to promote Cr(VI) reduction. Once reduced, the mobility of Cr(III) in sediments is significantly restricted and regulated by precipitation and sorption processes. Finally, even if the role of natural organic matter in sediment has been determined, further research is required to identify the complexation mechanisms.

Sign in / Sign up

Export Citation Format

Share Document