Quantum Chemistry Study On ESI-ITMS~n Cleavage Regularity Of Flavonol Compounds

Objective This paper aimed to study on the cleavage regularity of flavonol compounds in electrospray ion trap mass spectrometry(ESI-ITMS) by combining quantum chemistry with mass spectrometry, and calculated theoretically. In order to provide a theoretical basis and reference data for the explanation of fragmentation mechanism of such substances in the soft ionization mass spectrometry and lay the foundation for other substances under the same ionization way.Methods In the electrospray ion trap mass spectrometry negative ion mode, we obtained the two and multistage spectrum of 9 flavonol compounds(3-hydroxyflavone, Kaempferol, Morin, Quercetin, Myricetin, Isorhamnetin, Fisetin, Kaempferide, Galangin) by using automatic and manual extraction ion ways, and sought the lowest energy of each molecular conformation with Density Functional Theory B3LYP/6-31+g(2d, 2p) method. Then, the obtained conformations were optimized respectively to obtain the preferred conformation and molecular parameters of each molecule. On the basis of the preferred conformations, the possible quasi-molecular ion configurations of each molecule were also optimized by using the same method, and calculated the energy at the level RB3LYP/6-31+g(2d,2p). Through a comparative analysis of energy, we confirmed the quasi-molecular ion optimal configuration for each compound. Finally, we resolved the cleavage behavior of nine flavonol compounds in the ESI-ITMS with combining mass spectral data and quantum chemical calculations.Results(1) Molecular preferred conformation. In addition to Morin, which was the B ring and A, C plane had a certain twist angle, the preferred conformations of other 8 flavonol compounds were all the plane conjugated system, they were respectively coplanar including A, C and B ring.(2) Optimal configurations of quasi-molecular ions. The quasi- molecular ion of 3-hydroxyflavone was the configuration of 3-OH deprotonated. When the molecule exists 4’-OH and 7-OH, referring to Kaempferol, Morin, Quercetin, Myricetin, Isorhamnetin, Fisetin, the 4’-OH are more prone to the formation of protonated molecular ions, when 4’-OH was absent, but 7-OH was in the presence, referring to Galangin and Kaempferide, the 7-OH easily deprotonated to form molecular ions.(3) In the electrospray ion trap mass spectrometry negative ion mode, the nine flavonol compounds mainly took place the cracking process as follows: dehydrogenation, lost CO, lost CO2 or C2H2 O, cross-ring cracking of C rings, as well as the loss of the B ring and so on, and 4(C=O) was the active center of the cleavage reactions.Conclusions In this study, we obtained the molecular preferred conformations and optimal quasi-molecular ion configurations of 9 flavonol compounds successfully, and made a reasonable explanation for the spectrometric behavior of such substances in the soft ionization mode. The result also laid a good foundation for mass spectrometry analysis of other substances.