【摘要】 在较高的去簇电压(DP)下,使用三重四极杆质谱仪通过电喷雾胞苷的甲醇-水溶液产生了质子化的胞嘧啶[C+H]+。[C+H]+的碰撞诱导解离过程共有4个相互竞争的解离通道,分别为脱去NH3分子(-17u)形成相对强度较高的碎片离子m/z95;脱去异氢氰酸HNCO(-43u)和H2O(-18u)分别形成m/z69和m/z94;脱去C2NH3(-41u)产生相对强度较低的碎片离子m/z71,随后对这些碎片离子进行了结构确定。通过量化计算对该过程进行了模拟:首先,对9种质子化胞嘧啶的异构体进行了优化,并给出了它们之间异构化过程的势能面曲线;其次,基于质子化胞嘧啶的初始结构对这4个解离通道进行了详细的模拟和推导。模拟结果表明,丢失NH3、HNCO、H2O和C2NH3这4个解离通道的势垒分别为292.2、355.0、586.6和838.6kJ/mol,此结果与质子化胞嘧啶碰撞诱导解离过程中产生的离子m/z95、69、94和71的丰度大小基本一致。更多还原

【Abstract】 Using triple quadrupole mass spectrometry,the gas-phase protonated cytosine could be generated by elctrospraying a water-methanol(50∶50,V/V)solution of cytidine with the higher declustering potential.Collision-induced dissociation(CID)of protonated cytosine has four competing dissociation channels,corresponding to the eliminate NH3(-17u)to form the ion m/z 95,loss of HNCO(-43u)and H2O(-18u)to form the ions m/z69 and m/z94,and loss of C2NH3(-41u)to form the ion m/z71.These primary product ions were further confirmed by their relative fragmentations through CID.Ab initio and density function theory(DFT)calculation were also employed to simulate the whole process.About 9 stable protonated cytosine isomers were optimized and the potential energy surfaces(PESs)for the isomerization processes were explored in detail.With enough energy,isomerization can occur firstly from one structure to the other,and then based on the various isomer structures,the extra energy will drive the dissociation to happen.So the different initial structure will lead to the different dissociation channel to produce different product ions.The four primary and further dissociation channels of protonated cytosine were also theoretically investigated,and the energy barriers for the primary dissociation to eliminate the molecule NH3,HNCO,H2 O and C2NH3 are 292.2,355.0,586.6and 838.6 kJ/mol,respectively,which are consistent with the peak abundant of the energy-resolved CID of protonated cytosine to form the ions m/z95,69,94,71.更多还原