• Login
    View Item 
    •   Home
    • UA Graduate and Undergraduate Research
    • UA Theses and Dissertations
    • Dissertations
    • View Item
    •   Home
    • UA Graduate and Undergraduate Research
    • UA Theses and Dissertations
    • Dissertations
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Browse

    All of UA Campus RepositoryCommunitiesTitleAuthorsIssue DateSubmit DateSubjectsPublisherJournalThis CollectionTitleAuthorsIssue DateSubmit DateSubjectsPublisherJournal

    My Account

    LoginRegister

    About

    AboutUA Faculty PublicationsUA DissertationsUA Master's ThesesUA Honors ThesesUA PressUA YearbooksUA CatalogsUA Libraries

    Statistics

    Most Popular ItemsStatistics by CountryMost Popular Authors

    The Electrochemical Reduction of Superoxide in Acetonitrile: A Concerted Proton-Coupled Electron Transfer (PCET) Reaction.

    • CSV
    • RefMan
    • EndNote
    • BibTex
    • RefWorks
    Thumbnail
    Name:
    azu_etd_1377_sip1_m.pdf
    Size:
    2.433Mb
    Format:
    PDF
    Description:
    azu_etd_1377_sip1_m.pdf
    Download
    Author
    Singh, Pradyumna Shaakuntal
    Issue Date
    2005
    Keywords
    electrochemical reduction of superoxide
    superoxide
    proton-coupled electron transfer
    PCET
    concerted proton and electron transfer (CPET)
    non-adiabatic electron transfer
    Advisor
    Evans, Dennis H.
    Committee Chair
    Evans, Dennis H.
    
    Metadata
    Show full item record
    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Abstract
    Superoxide, the product of the one-electron reduction of dioxygen, is a molecule of enormous importance. It participates in a variety of critical physiological processes and is also an important component of fuel cells where it is an intermediate in the cathodic reaction. However, the electrochemical behavior of superoxide, mainly its reduction, is not well understood. Here, the electrochemical behavior of superoxide has been investigated in acetonitrile on glassy carbon electrodes, through cyclic voltammetry experiments. By stabilizing the electrogenerated superoxide, aprotic solvents afford an opportunity to study its electrochemical reactions further. Superoxide was generated electrochemically from dioxygen at the first voltammetric peak. In the presence of hydrogen-bond donors (water, methanol, 2-propanol), the superoxide forms a complex with the donor resulting in a positive shift in the formal potential which can be analyzed to obtain formation constants for these complexes. Stronger acids (2,2,2- trifluoroethanol, 4-tert-butylphenol) result in protonation of superoxide followed by reduction to produce HO₂-. On scanning to more negative potentials a second peak is observed which is irreversible and extremely drawn out along the potential axis indicating a small value of the transfer coefficient α. Addition of hydrogenbond donors, HA, brings about a positive shift in this peak, without a noticeable change in shape. The reaction occurring at the second peak is a concerted proton-coupled electron transfer (PCET) in which the electron is transferred to superoxide and a proton is transferred from HA to superoxide forming HO₂- and A- in a concerted process. We estimate the standard potential for this reaction for the case of water as the donor. This value suggests that the reaction at the second peak occurs at very high driving forces. Kinetic simulations using both Butler-Volmer and Marcusian schemes were performed to estimate the kinetic parameters. The unusually low rate constants obtained suggest high nonadiabaticity for this PCET reaction. The reaction was also found to proceed with an unusually large reorganization energy. Consistent with a PCET, a kinetic isotope effect, HA vs. DA, was detected for the three hydrogen-bond donors.
    Type
    text
    Electronic Dissertation
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Chemistry
    Graduate College
    Degree Grantor
    University of Arizona
    Collections
    Dissertations

    entitlement

     
    The University of Arizona Libraries | 1510 E. University Blvd. | Tucson, AZ 85721-0055
    Tel 520-621-6442 | repository@u.library.arizona.edu
    DSpace software copyright © 2002-2017  DuraSpace
    Quick Guide | Contact Us | Send Feedback
    Open Repository is a service operated by 
    Atmire NV
     

    Export search results

    The export option will allow you to export the current search results of the entered query to a file. Different formats are available for download. To export the items, click on the button corresponding with the preferred download format.

    By default, clicking on the export buttons will result in a download of the allowed maximum amount of items.

    To select a subset of the search results, click "Selective Export" button and make a selection of the items you want to export. The amount of items that can be exported at once is similarly restricted as the full export.

    After making a selection, click one of the export format buttons. The amount of items that will be exported is indicated in the bubble next to export format.