咖啡酸正离子模式高分辨质谱脱乙烯酮途径解析OA

To elucidate the process and mechanism of the pathway of losing Ketene of the positive ion high-resolution mass spectra of caffeic acid,this study systematically analyzed the fragmentation behavior of the protonated molecule of caffeic acid(m/z 181)by combining quantum chemical calculations and pseudo-MS3 experiments.The results showed that,the deketene pathway of the protonated molecule of caffeic acid(m/z 181)consists of four steps.The precursor ion of the first step is the protonated molecule of caffeic acid with carbonyl α carbon binding proton,and the product is both the ketene molecule and the m/z 139 ion whose structure is 3,4-dihydroxybenzyl alcohol cation.The next step is the loss of CO from the m/z 139 ion to generate m/z 111 ion(catechol cation).The third step is the loss of H2O from the m/z 111 ion to generate m/z 93 ion(2,4-cyclohexadienone cation).The last step is the loss of CO from the m/z 93 ion to generate m/z 65 ion(cyclopentadiene cation).In the first step,the hydroxyl group of the carboxylic acid in the precursor ion is transferred to the β carbon of the carbonyl group,and then the CH2CO molecule is dissociated.The precursor ions of the first step do not have a dominant proportion in the protonated molecular isomers of caffeic acid,so that the product ions of all steps of the pathway of lossing ketene in positive ion mode mass spectrometry of caffeic acid are low-intensity peaks.This study supplemented the mass spectrometry cleavage rules of the positive ion mode of phenolic acids,and provided theoretical support for their high-resolution spectrometry identification.