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Mass Spectrometric Study of Electrochemical and Organic Reaction Mechanisms

Lu, Mei
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1437474195

Abstract Details

2015, Doctor of Philosophy (PhD), Ohio University, Chemistry and Biochemistry (Arts and Sciences).
This dissertation research focuses on the monitoring of electrochemistry (EC) redox reactions and the elucidation of organic reaction mechanisms by mass spectrometry (MS). First, the online coupling of EC with MS using desorption electrospray ionization (DESI) was developed for elucidating the redox reaction mechanisms of several biologically relevant reduction and oxidation reactions and exploring their analytical applications. The complete electrochemical reduction of complicated disulfides in peptides greatly enhanced the sequence coverage from tandem MS analysis, which helps sequence the peptides. The stepwise nitro-reduction mechanism was also confirmed for several nitroaromatic drug compounds. The transient one-electron transfer product chlorpromazine radical cation was also captured successfully by MS for the first time. Electrochemical reactions taking place in water are rarely studied using online MS techniques. The second project presents EC/DESI-MS applications in some aqueous phase redox reactions with biological significance. The MS evidence that nitrosothiol reduction leads to free thiol species by loss of NO was obtained. The characteristic mass decrease of 29 Da and the reduced intensity of the precursor peptide ions provide a quick way to identify nitrosylated species. In addition, it was also found that saccharides undergo electrooxidation to produce the corresponding carboxylic acid in alkaline aqueous solution, but not at neutral and acidic pHs. Upon electrochemical oxidation, carbamazepine was found to undergo ring contraction and amide bond cleavage, which parallels the oxidative metabolism observed for this drug in leucocytes. MS is also of great importance for fundamental gas phase ion chemistry study. In the third project, the MS instrument was successfully modified to perform ion/molecule reactions. The reactivity and structure investigation of oxidized metal thiolate compounds by MS in conjunction with ion/molecule reactions was conducted. The addition reactions of isolated intermediate ions with alkenes and methyl ketones in the gas phase were confirmed. More importantly, the thiyl radical nature (i.e., the distonic ion nature) of the oxidized metal thiolate ions was verified by the gas-phase reaction with dimethyl disulfide (CH3SSCH3). Last, MS was also applied for silver- and gold-catalyzed organometallic reaction monitoring. A surprisingly ligand effect was uncovered in the silver-catalyzed alkyne activation: the proper ligand to silver ratio is crucial for maintaining the activity of the catalyst. MS also provided strong evidence for the reaction mechanism elucidation of the ligand-assisted gold-catalyzed cross-coupling of terminal alkynes with aryldiazonium salts.
Hao Chen (Advisor)
Chemistry
Mass spectrometry

Recommended Citations

Citations

  • Lu, M. (2015). Mass Spectrometric Study of Electrochemical and Organic Reaction Mechanisms [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1437474195

    APA Style (7th edition)

  • Lu, Mei. Mass Spectrometric Study of Electrochemical and Organic Reaction Mechanisms. 2015. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1437474195.

    MLA Style (8th edition)

  • Lu, Mei. "Mass Spectrometric Study of Electrochemical and Organic Reaction Mechanisms." Doctoral dissertation, Ohio University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1437474195

    Chicago Manual of Style (17th edition)

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This open access ETD is published by Ohio University and OhioLINK.