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The Mechanism of a Retro-Diels–Alder Fragmentation of Luteolin: Theoretical Studies Supported by Electrospray Ionization Tandem Mass Spectrometry Results

1
Department of Organic Chemistry, Faculty of Chemistry, Gdańsk University of Technology, Narutowicza 11/12, 80-233 Gdańsk, Poland
2
Laboratory of Quantum Chemistry, Faculty of Chemistry, University of Gdańsk, Wita Stwosza 63, 80-308 Gdańsk, Poland
*
Author to whom correspondence should be addressed.
Academic Editor: Israel Fernández
Molecules 2022, 27(3), 1032; https://doi.org/10.3390/molecules27031032
Received: 14 December 2021 / Revised: 27 January 2022 / Accepted: 1 February 2022 / Published: 3 February 2022
(This article belongs to the Section Computational and Theoretical Chemistry)
The mechanisms of retro-Diels–Alder fragmentation of luteolin are studied theoretically using the Density Functional Theory method (B3LYP hybrid functional) together with the 6-311++G(d,p) basis set and supported by electrospray ionization tandem mass spectrometry (ESI-MS) results. The reaction paths leading to the formation of 1,3A and 1,3B fragment ions observed as the main spectral features in the ESI-MS spectrum are described and discussed, including the structures of the transition states and intermediate products. The heights of the activation energy barriers which have to be overcome along the reaction paths corresponding to 1,3-retrocyclization cleavage of the ionized luteolin are predicted to span the 69–94 kcal/mol range (depending on the initial isomeric structure) for the concerted retrocyclization mechanism and the 60–89 kcal/mol (first barrier) and 24–52 kcal/mol (second barrier) barriers for the stepwise mechanism (also depending on the initial isomeric structure). It is also demonstrated that the final fragmentation products (1,3A and 1,3B) are in fact represented by various isomeric systems which are not experimentally distinguishable. In addition, the absence of the spectral feature corresponding to the [M-B] fragment ion formed by the rupture of the C-C bond connecting luteolin’s B and C rings (which does not occur during the ESI-MS experiment) is explained by much larger energy barriers predicted for such a process. View Full-Text
Keywords: flavonoids; luteolin; fragmentation mechanism; retrocyclization; liquid chromatography mass spectrometry flavonoids; luteolin; fragmentation mechanism; retrocyclization; liquid chromatography mass spectrometry
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MDPI and ACS Style

Śliwka-Kaszyńska, M.; Anusiewicz, I.; Skurski, P. The Mechanism of a Retro-Diels–Alder Fragmentation of Luteolin: Theoretical Studies Supported by Electrospray Ionization Tandem Mass Spectrometry Results. Molecules 2022, 27, 1032. https://doi.org/10.3390/molecules27031032

AMA Style

Śliwka-Kaszyńska M, Anusiewicz I, Skurski P. The Mechanism of a Retro-Diels–Alder Fragmentation of Luteolin: Theoretical Studies Supported by Electrospray Ionization Tandem Mass Spectrometry Results. Molecules. 2022; 27(3):1032. https://doi.org/10.3390/molecules27031032

Chicago/Turabian Style

Śliwka-Kaszyńska, Magdalena, Iwona Anusiewicz, and Piotr Skurski. 2022. "The Mechanism of a Retro-Diels–Alder Fragmentation of Luteolin: Theoretical Studies Supported by Electrospray Ionization Tandem Mass Spectrometry Results" Molecules 27, no. 3: 1032. https://doi.org/10.3390/molecules27031032

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