1，3-二甲基尿嘧啶二聚体的飞行时间质谱裂解规律研究

采用不同进样方式、不同电子轰击能量和不同反应气压力测定了1,3 二甲基尿嘧啶二聚体(DMUD) 的4个立体异构体A、B、C、D的化学电离(CI)和电子轰击电离(EI)飞行时间质谱.不同方式所测得的CI谱结 果一致,4个异构体出现了强度不同的准分子离子峰(m/z=281),由此推断它们结构之间的相对稳定性次序为: B(trans syn)>D(cis syn)>A(trans anti)>C(cis anti).这一结论被低能量(25eV)电子轰击的EI谱所证实, 并且与合成产物的比例相吻合.EI谱用任何方式测谱均不出现分子离子峰(m/z=280),而出现其单体离子(m/z =140)且为基峰。给出了DMUD的飞行时间质谱裂解途径,同时对CI谱的裂解碎片进行了细致的讨论.

Study on Fragmentation Regularity of 1,3-Dimethyluracil Cyclobutane Dimmer by Time-of-Flight Mass Spectrometry

The CI and EI of time of flight mass spectrometry of four stereo-isomers A, B, C and D of 1,3-dimethyluracil dimer (DMUD) were detected by using different sample introduction, different electronic energy and different pressure of reaction gas. Using the high resolution capabilities of the instrument, exact masses for each fragment were determined. These data were used to infer molecular formulas and elemental compositions from all the four molecular ions and fragments through software interpretation and, by further applying chemical intuition, the majority of ions were fully assigned. The four isomers reached their quasi-molecular ion peaks at m/z=281 with different relative abundances in their spectra, from which the order of relative stability of their structures was deduced as: B(trans-syn)>D(cis-syn)>A(trans-anti)>C(cis-anti). This conclusion was confirmed by both EI (25 eV) mass spectra and the ratio of synthetic products. There is no molecular ion peaks in the EI spectra, detected by using any mode, of all the four isomers, but the monomer ions (m/z=140) of all the isomers appear in the spectra as the base peaks. A few cleavage fragment peaks appear in the EI spectra of the dimmer isomers and the characteristic cleavage fragments include the monomer cation m (m/z=140, 100%), azetine ketone cation a (m/z=83) and aziridinyl cation b (m/z=55). There are three protonated fragments c,d and m+H in CI spectra of DMUD as well as the cations (m,a,b) appear in their EI spectra.