槲皮素与桑色素ESI-MS裂解行为的比较分析

运用量子化学方法辅助解析并比较槲皮素与桑色素在电喷雾离子阱质谱(ESI-MS)负离子模式下的裂解行为。依据密度泛函理论(Density functional theory,DFT),在B3LYP/6-31G(d)水平,对槲皮素与桑色素的分子空间构型进行优化,确定稳定的几何构型与去质子化位点,在RB3LYP/6-31+G(2d,2p)水平,计算相对碎裂电压下的二级质谱中碎片离子处于稳定状态时的能量,通过比较准分子离子稳定构型并结合基组重叠误差(Basis set superposition error,BSSE)校正后的键解离能(Bond dissociation energy,BDE),推导了质谱碎裂过程。结果显示:槲皮素的稳定构型为A,B,C环处于同一平面,桑色素上的2'-OH使得B环与AC环之间翻转一定角度,二面角D(1,2,1',6')为-134.662 4°。槲皮素与桑色素的质谱裂解过程主要通过C环跨环裂解产生,且具有多种开裂方式,开裂先后顺序为:1,2开裂、0,2开裂、1,3开裂、1,4开裂与0,4开裂,分别生成碎片离子1,2A-,0,2A-,1,3A-,1,4A-与0,4A-,并逐步进行后续裂解,而2'-OH的存在促进了桑色素的裂解。该研究为进一步揭示黄酮醇类化合物的质谱裂解规律提供了理论依据。

Analysis and Comparison on Fragmentation Behavior of Quercetin and Morin by ESI-MS

The fragmentation behaviors of quercetin and morin were analyzed and compared by the quantum chemistry method with electrospray ionization mass spectrometry (ESI-MS) in negative ion mode.Based on the density functional theory(DFT),at the level of B3LYP/6-31 G(d),quantum chemistry calculation was carried out to optimize the molecular spatial configurations of quercetin and morin,in order to confirm the stable geometric configurations and deprotonation locations of quasimolecular ions.The energy of fragment ions on the stable state under the relative framentation voltage in the second order mass spectrometry,was calculated at the level of RB3LYP/6-31 + G(2d,2p).The fragmentation pathway was deduced by comparing the stable configurations of quasi-molecular ions and combined with basis set superposition error (BSSE)-corrected bond dissociation energy (BDE).The results indicated that the stable configuration of quercetin was that the A,B,C rings stayed in the same plane,but morin was not like this because of the 2'-OH,and the dihedral angle between B ring and AC rings was-134.662 4°.The fragmentation processes of quercetin and morin occurred mainly through the cross-ring cleavages of C ring with various of cleavage ways.The precedence order was:1,2 cleavage,0,2 cleavage,1,3 cleavage,1,4 cleavage and 0,4 cleavage,the fragment ions of 1,2A-,0,2A-,1,3A-,1,4A-and 0,4A-were generated,respectively.The difference between them was that the existence of 2'-OH on morin facilitated the cross-ring cleavages.Subsequently,the rest of fragment ions were produced step by step.This study provided a theoretical basis for further revealing the fragmentation pathway of flavonol compounds.