여름정기학술대회
2022여름초록
발표자 및 발표 내용
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발표구분 |
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포스터발표 |
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Brief Oral Presentation 발표신청 |
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주저자
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국가 |
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공동저자
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접수자
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The mechanism of base-catalyzed
hydrogen/deuterium exchange (HDX) of the non-labile hydrogens in an aromatic
alkylpyridinium cation has been investigated in the present work. Although HDX reaction
is not expected in non-labile hydrogens in general, non-labile hydrogens at the
α-position of a pyridinium ring can occur in the base condition. Here, we precisely
investigated the detailed kinetics of HDX at the hexadecylpyridinium cation in
the methanol-d (CH3OD) solvent with a base catalyst using electrospray
ionization-mass spectrometry (ESI-MS). The numbers of exchanged hydrogens were
counted by the series of time-dependent mass spectra during the HDX reaction,
and the temperature-dependent reaction rates was determined under various base
concentrations. The HDX reaction become faster as the concentration of the base
catalyst increased, confirming the base-catalyzed mechanisms for HDX reaction. Temperature-dependent
rate constants were used to evaluate the apparent activation energy using
Arrhenius equation, and the dependence of the reaction order on the base
concentration was also examine. Interestingly, the concentration of the base
catalyst show a complicated relationship with the reaction order, deviating from
the single-order relationship. Furthermore, the evaluated activation energy is largely
different from the theoretical prediction which assuming a single-step base
catalyzed HDX mechanism. This suggest that the detailed mechanism of the HDX
reaction is not a simple single-step based catalyzed process, but may include
multiple reaction steps in which surrounding solvents are involved as well.
Further ab initio theoretical calculations are underway to reveal the exact
mechanism in this HDX process.
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