Hydrogen (H-) transfer reactions in solution can serve as models for understanding the mechanism of those reactions in enzymatic systems. Currently, the studies of many enzymatic reactions have produced results that cannot be explained by classical or semi-classical transition state theories. Newer H-tunneling models have been employed, which utilize H’s non-classical wave properties, to explain how transferring (1°) isotopes have unique wave properties that, in turn, influence secondary C-H bond vibrations and 2° kinetic isotope effects (KIEs). A new theory based on the Marcus-like tunneling model can explain the observation of deflated D-transfer 2° KIEs through the concept that D-tunneling reactions require a shorter donor-acceptor distance (DAD) for transfer than H-tunneling reactions and, thus, have a more crowded reaction site. The greater steric crowding limits the 2° C-H vibrations and deflates the 2° KIE. Our group hypothesis states that H- and D-tunneling reactions have different tunneling ready state (TRS) structures which arise from their difference in DAD, and this difference is evident in the 1° isotopic dependence of 2° KIEs that should be more pronounced in more sterically hindered systems. Previously, our group designed several hydride transfer reaction systems in solution to test the steric effect on both near (α- and β-) and remote (ε-) 2° KIEs, and the results supported the isotopically different TRS concept. However, interesting results from ε-2° KIE systems prompted the development of new instrumental methods to test this hypothesis under a competitive reaction system and confirm the observations. This work studies the investigation of Mass Spectrometry (MS) and Nuclear Magnetic Resonance (NMR) Spectroscopy as potential instrumental techniques to be used to determine competitive 2° KIEs. The results are consistent with the previous observations in support of the isotopically different TRS concept, and modifications and improvements for the method are still underway.
|Commitee:||Tucker, Kevin, Wei, Chin-Chuan|
|School:||Southern Illinois University at Edwardsville|
|School Location:||United States -- Illinois|
|Source:||MAI 81/3(E), Masters Abstracts International|
|Subjects:||Physical chemistry, Organic chemistry, Chemistry|
|Keywords:||Hydrogen transfer reactions, Enzymatic systems, Kinetic isotope effects|
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