通过确定初始电离位点预测吲哚类生物碱质谱的特征裂解规律

确定初始电离位点是EI源质谱解析中一个至关重要的环节. 本文提出了一种确定初始电离位点的新方法. 该法通过计算和分析分子离子自旋密度, 进而比较从中性分子到分子离子的电荷变化和键长变化, 从而确定初始电离位点. 对简单吲哚类生物碱质谱的特征裂解机理进行了预测, 结果与标准物质的质谱吻合. 在此基础上, 与传统的根据基团电离能确定电离位点的方法进行了比较. 结果表明, 该法优于电离能方法. 此法不仅可用于预测以α-裂解为主导的吲哚生物碱和其它含氮化合物的质谱裂解规律, 还为揭示其它小分子化合物以及气相多肽离子的裂解机理奠定了基础.

Interpretation of Mass Spectral Characteristic Fragmentation Mechanisms of Indole Alkaloids Through Determining the Initial Ionization Site

Determination of initial ionization site is the most important step in the EI mass spectral interpretation. In this article, a new method for determining the initial ionization site by calculated spin density of molecular radical cation, the changes of charges and the variations of the molecular structures from neutral to ca-tionic form was presented. The characteristic fragmentation mechanisms for the derivatives of indole alkaloids were investigated through determining the initial ionization site. The results predicted by this method can be comparable, even superior to those based on ionization energy method. It will play an important role in predicting the main primary α-cleavage fragmentation not only for indole alkaloids and other compounds which containing N atom, but also for small molecules and gas-phase peptide radical cations.