质量分析器新理论初探

本文主要介绍带电粒子的恒动量加速方法,以及应用恒动量加速方法形成的多种质量分析器,在质谱分析检测方面有多种应用。带电粒子恒动量加速可以提高某些质量分析器的性能,也可以创造出新类型的质量分析器。本文介绍了6种应用方法:高分辨飞行时间质量分析器、扇形电场方向聚焦质量分析器、静电场偏转质量分析器、脉冲电场偏转质量分析器、扇形磁场能量聚焦质量分析器,环柱形电场质量分析器,并从这些质量分析器中总结出一些带电粒子在电场或磁场中的运动规律。

Dissociation Pathway Analysis of Thymine under Low Energy VUV Photon Excitation

Photon-induced dissociation pathways of thymine are investigated with vacuum ultraviolet photoionization mass spectrometry and theoretical calculations. The photoionization mass spectra of thymine at different photon energy are measured and presented. By selecting suitable photon energy, exclusively molecular ion m/z=126 is obtained. At photon energy of 12.0 eV, the major ionic fragments at m/z=98, 97, 84, 83, 70, and 55 are obtained, which are assigned to C4H6N2O＋, C4H5N2O＋, C3H4N2O＋ （or C4H6NO＋）, C4H5NO＋, C2NO2＋, and C3H5N＋, respectively. With help of theoretical calculations, the detailed dissociation pathways of thymine at low energy are well established.

Investigation on Non-covalent Complexes of Cyclodextrins with Li＋ in Gas Phase by Mass Spectrometry

To investigate the non-covalent interaction between cyclodextrins （CD） and lithium ion, a stoichiometry of α-CD, β-CD, heptakis（2,6-di-O-methyl）-β-CD （DM-β-CD）, or heptakis（2,3,6-tri-O-methyl）-β-CD （TM-β-CD） was mixed with lithium salt, respectively, and then incubated at room temperature for 10 min to reach the equilibrium. In posi- tive mode, the electrospray ionization mass spectrometry （ESI-MS） results demonstrated that lithium ion can conjugate to α-, β-, DM-β- or TM-β-CD and form 1：1 stoichiometric non-covalent complexes. The binding of the complexes was further confirmed by collision- induced dissociation. The dissociation constants Kdl of four complexes （Li＋α-CD, Li＋β- CD, Li＋DM-β-CD, and Li＋TM-β-CD） were determined by mass spectrometric titration. The results showed Kdl were 18.7, 26.7, 33.6, 30.5 μmol/L for the complexes of Li＋ with α-CD, β-CD, DM-β-CD, and TM-β-CD, respectively. Kdl for the Li＋ complexes of/3-CD is smaller than that of DM-β-CD due to its steric effect of the partial substituted -CH3. The Kdl for the Li＋ complexes of DM-β-CD is nearly in agreement with that of TM-β-CD, indicating Li＋ is more likely to locate in the small rim of DM-β-CD＇s hydrophobic cavity. The DFT results showed through electrostatic interaction, one Li＋ can strongly conjugate to four neighboring oxygen atoms. For the （α-CD＋Li）＋ complex, one Li＋ may also situate the small rim of α-CD＇s hydrophobic cavity to form a non-specific host-guest complex.

基于UPLC-Triple-TOF-MS/MS结合SWATH技术对不同泌乳期人乳脂质变化分析

为深入了解婴儿时期人乳中复杂的脂质含量的动态变化,采用超高效液相色谱-三重四极杆串联飞行时间质谱及具有高采集命中率的顺序窗口采集所有理论质谱模式(sequential window acquisition of all theoretical mass spectra,SWATH)对不同泌乳阶段人乳中的脂质进行鉴定及相对定量分析。结果显示,在3个泌乳阶段的人乳中共检测到229种脂质。根据“脂质代谢途径研究计划”中的分类,共检测到五大类物质:甘油酯类(glycerolipid,GL)主要包括24种甘油二酯和28种甘油三酯;甘油磷脂类(glycerophospholipid,GP)主要包括33种磷脂酰乙醇胺、21种磷脂酰胆碱、8种磷脂酰丝氨酸、13种磷脂酰甘油、10种磷脂酸和7种磷脂酰肌醇;鞘脂类(sphingolipid,SP)化合物共22种;甾醇脂类(sterol lipid,ST)化合物共10种;脂肪酸类及其衍生物(fatty acids,FAs)共4种。随着泌乳期的延长,GL、SP的相对含量逐渐增加,而GP、ST、FAs的相对含量逐渐下降。本研究实现了人乳中脂质的全面定性与相对定量分析,方法灵敏度高、精密度及稳定性良好,同时搭配SWATH采集模式,为科学模拟各阶段人乳及开发不同段龄婴幼儿奶粉的研发提供一定参考依据。

CO Oxidation by Neutral Gold-Vanadium Oxide Clusters

Oxidation of CO by gas-phase atomic clusters is being actively studied to understand the molecular-level mechanisms of heterogeneous CO oxidation over related catalytic surfaces. However, it is experimentally challenging to study CO oxidation by neutral heteronuclear metal oxide clusters because of the difficulty of cluster ionization and detection without fragmentation. Herein, the neutral AuVO2-4 clusters were experimentally generated and their reactions with CO and O2 were studied. The experimental results showed that CO adsorption is the dominant channel on the interactions of AuVO4 and AuVO3 with CO, and AuVO2 can pick up an O2 molecule to generate AuVO4. Theoretical studies indicated that the oxidation of the trapped CO in AuVO3,4CO into CO2 is exothermic while the reaction barriers have to be overcome at the elevated temperatures. A catalytic cycle for CO oxidation by AuVO2-4 is proposed.

Exploring the Interactions of Atomic Oxygen on Silver Clusters with Hydrogen

The interactions between AgnO- （n=1-8） and H2 （or D2） were explored by combination of the mass spectroscopy experiments and density function theory （DFT） calculations. The experiments found that all oxygen atoms in AgnO- （n--1-8） are inert in the interactions with H2 or D2 at the low temperature of 150 K, which is in contrast to their high reactivity with CO under the same condition. These observations are parallel with the preferential oxidation （PROX） of CO in excess hydrogen catalyzed by dispersed silver species in the condensed phase. Possible reaction paths between AgnO- （n=1-8） and H2 were explored using DFT calculations. The results indicated that adsorption of H2 on any site of AgnO- （n=1-8） is extremely weak, and oxidation of H2 by any kind of oxygen in AgnO- （n=1-8） has an apparent barrier strongly dependent on the adsorption style of the ＂O＂. These experiments and theoretical results about cluster reactions provided molecule-level insights into the activity of atomic oxygen on real silver catalysts.

Experimental and Theoretical Study on Pyrolysis of Isopsoralen

The pyrolysis of isopsoralen was studied by synchrotron vacuum ultraviolet photoionization mass spectrometry at low pressure. The pyrolysis products were detected at different photon energies, the ratios of products to precursor were measured at various pyrolysis temperatures. The experimental results demonstrate that the main pyrolysis products are primary CO and sequential CO elimination products （C10H602 and C9H60）. The decomposition channels of isopsoralen were also studied by the density functional theory, then rate constants for competing pathways were calculated by the transition state theory. The dominant decom- position channels of isopsoralen and the molecular structures for corresponding products were identified by combined experimental and theoretical studies.

Hydrogen-Assisted C-C Coupling on Reaction of CuC3H-Cluster Anion with CO

A fundamental study on C-C coupling,that is the crucial step in the Fischer-Tropsch synthesis(FTS)process to obtain multi-carbon products,is of great importance to tailor catalysts and then guide a more promising pathway.It has been demonstrated that the coupling of CO with the metal carbide can represent the early stage in the FTS process,while the related mechanism is elusive.Herein,the reactions of the CuC3H-and CuC3-cluster anions with CO have been studied by using mass spectrometry and theoretical calculations.The experimental results showed that the coupling of CO with the C3H-moiety of CuC3H can generate the exclusive ion product COC3H-.The reactivity and selectivity of this reaction of CuC3H-with CO are greatly higher than that of the reaction of CuC3-with CO,and this H-assisted C-C coupling process was rationalized by theoretical calculations.

H2 Dissociation by Au1-Doped Closed-Shell Titanium Oxide Cluster Anions

Dissociation of molecular hydrogen （H2） is extensively studied to understand the mechanism of hydrogenation reactions. In this study, H2 dissociation by Aul-doped closed-shell titanium oxide cluster anions AuTi3O7 and AuTi3O8 has been identified by mass spectrometry and quantum chemistry calculations. The clusters were generated by laser ablation and mass- selected to react with H2 in art ion trap reactor. In the reaction of AuTi3O8 with H2, the ion pair Au＋-O22 rather than Au＋-O2 is the active site to promote H2 dissociation. This finding is in contrast with the previous result that the lattice oxygen is usually the reactive oxygen species in H2 dissociation. The higher reactivity of the peroxide species is further supported by frontier molecular orbital analysis. This study provides new insights into gold catalysis involving H2 activation and dissociation.

基于UPLC-Q TOF MS/MS技术结合SWATH采集法同时定性定量分析地胆草中的化学成分

目的:基于超高效液相色谱串联四极杆飞行时间质谱联用(UPLC-Q TOF MS/MS)技术,系统表征地胆草中化学成分并同时测定其中13个化学成分(新绿原酸、绿原酸、隐绿原酸、木犀草素-7-O-葡萄糖醛酸苷、木犀草苷、异绿原酸B、异绿原酸A、芹菜素-7-O-β-D-葡萄糖醛酸苷、异绿原酸C、去氧地胆草素、异去氧地胆草素、异地胆草种内酯、地胆草种内酯)的含量。方法:采用UPLC-Q TOF MS/MS技术,结合顺序窗口采集所有理论质谱模式(SWATH),采集不同批次地胆草样品的数据。使用Waters HSS T3 C_(18)(100 mm×2.1 mm,1.8μm)色谱柱,以乙腈(A)-0.1%甲酸水溶液(B)为流动相,梯度洗脱,流速0.4 mL·min^(-1),柱温35℃,进样量2μL。采用电喷雾离子源(ESI),正、负离子模式下采集数据。结合对照品信息,参考相关文献完成对地胆草中化学成分的结构鉴定。同时建立地胆草中13个化学成分的含量测定方法并进行方法学考察。结果:地胆草中初步鉴定出36个化学成分,其中包括有机酸类20个,黄酮类7个,倍半萜内酯类6个,香豆素类1个及其他成分2个;含量测定的13个成分在测定浓度范围内线性关系良好,相关系数≥0.9990,精密度、稳定性、重复性等均符合要求,平均加样回收率为94.9%~103.5%,RSD≤3.8%。不同批次地胆草所含化学成分基本相似,但13个成分的含量存在一定差异。结论:本研究建立的UPLC-Q TOF MS/MS方法,可同时对地胆草进行定性定量分析,方法灵敏准确,稳定性和重复性良好,可以为地胆草的质量控制及开发提供方法参考及数据支撑。

Theoretical studies of structures and spectroscopic properties of [(tpy)(bpy)RuC≡CC_6H_4R]^+(tpy = 2,2′:6′,2″-terpyridine, bpy = 2,2′-bipyridine; R = F, Cl, H, Me and OMe)

A series of polypyridine ruthenium （II） acetylide complexes, [（tpy）（bpy）RuC≡CC6H4R]^＋ （tpy = 2,2＇：6＇,2＂-terpyridine, bpy = 2,2＇-bipyridine; R = F （1）, C1 （2）, H （3）, Me （4） and OMe （5）） are investigated theoretically to explore their electronic structures and spectroscopic properties. Their ground/excited state geometries, electronic structures and spectroscopic properties are first calculated using density functional theory （DFT） and time-dependent DFT （TDDFT）. The absorption and emission spectra of the complexes in acetonitrile solution are also obtained by using TDDFT （B3LYP） method associated with the CPCM model. The calculations show that the energy levels of HOMOs for 1-5 are sensitive to the substituent on phenylacetylide ligand and increase with the same order of the electron-donating ability of the substituents; however, those of polypyridine-based LUMOs vary slightly. The lowest-energy absorptions and emissions for 1-5 are progressively red-shifted in the order of 1 ~ 2 〈 3 〈 4 〈 5 when the electron-donating groups are introduced into the phenylacetylide [igand. The phosphorescence of 1 are attributed to {[dxz（Ru） ＋π（C≡C）]→[π^＊（tpy）]} （3MLCT/3LLCT） transition, whereas those of 2-5 are originated from { [dxz/dxy（Ru）＋ π（C ≡C）＋g（C6H4R）] → [＊（tpy/bpy）] } （3MLCT/3LLCT） transitions.