2,2-二羟甲基丙二酸二乙酯的化学电离质谱分析

化学电离(chem ical ionization,CI)是由Munson和Field[1]于1966年提出的一种质谱电离技术,其原理实际上是分子-离子反应[2,3]。在化学电离条件下,常常可以得到丰度很强的准分子离子峰,没有或很少碎片离子,能准确提供相对分子质量信息,但缺乏结构信息。我们在实验中发现,采用适     

Comparative study of ion kinetic energy,chemical ionisation and field desorption spectra

A comparison of the fragmentation processes operating in the first field free region was made with the fragmentation in the ion source under electron ionisation, chemical ionisation and field desorption conditions for some selected compounds which undergo retro-DielsI-Alder fragmentation in the ion source under electron ionisationconditions. The fragmentation processes which com-ete with retro-Diels-Alder fragmentation under chemical ionisation and field desorption conditions are discussed. The complementary nature of these techniques are illustrated.     

Fragmentation of poly(amidoamine) dendrimers in matrix-assisted laser desorption

Fragmentation of different generations of poly(amidoamine) dendrimers was explored in five common MALDI matrices: 2,5-dihydroxybenzoic acid (DHB), 4-hydroxy-3-methoxycinnamic acid (FER), α-cyano-4-hydroxycinnamic acid (ACH), 2,4,6-trihydroxyacetophenone (THAP), and 3-hydroxypicolinic acid (HPA). Of these, DHB was the softest matrix and ACH produced significant fragment intensity already at MALDI threshold, FER and THAP being in between. HPA was not a convenient matrix for dendrimers and produced a specific fragmentation pattern. Fragmentation analysis was mainly concentrated on generation G1, which contains already all essential structural elements. Dendrimers showed complicated fragmentation behavior with multiple fragmentation channels in our MALDI experiments. The relative intensities of these channels depended selectively on choice of the matrix and showed dissimilar dependence on the laser pulse energy. This was attributed to different fragmentation mechanisms, due to different protonation pathways, occurring in the same MALDI plume. The fragmentation pathways were proposed for all observed fragmentation channels. All fragmentation sites of protonated ions were found to be directly attached to the protonation sites and the fragmentation was surplus charge driven in this sense. No charge remote fragmentation channels were detected. Cationized dendrimers showed higher stability than the protonated ions.     

Mass spectrometry of thio analogues of pyrimidine bases: 4-alkoxycarbonyl-alkylthiouracils

The mass spectral fragmentation of twelve new 4-alkoxycarbonylakyithio substituted derivatives of uracils is discussed and fragmentation pathways. Elucidation of which assisted by accurate mass measurements and metastable transitions, are proposed. The comparison between the mass fragmentation of 2- and 4-alkoxycarbonylakylthiouracils have shown that the position of uracil ring thiation may be deduced on the basis of mass special fragmentation patterns.     

Identification of fragmentation channels of dinucleotides using deuterium labeling

The fragmentation of the totally deuterated dinucleotide dAT⁻ in labile positions (heteroatom-bound hydrogens) was compared for different MS/MS methods: CID, IRMPD, and EID. These experiments allowed us to affirm the coexistence of several fragmentation channels. They can be classified according to the involvement of nonlabile or labile protons in the fragmentation process. Moreover, double resonance experiments were performed in IRMPD and EID. They demonstrated the existence of consecutive fragmentation processes. The probability with which each channel is taken depends on the fragmentation technique used, i. e., the energy and the time scale of the method. The fragmentation channels that involve labile protons requiring peculiar three-dimensional structures are entropically unfavorable and enthalpically favorable. They are more observed in IRMPD and EID. The involvement of labile and, therefore, exchangeable protons in the fragmentation mechanism casts doubt on the use of tandem mass spectrometry to localize incorporated deuteriums in oligonucleotides.     

Five-membered ring formation in unimolecular reactions of peptides: a key structural element controlling low-energy collision-induced dissociation of peptides

Unimolecular fragmentation reactions of peptides in low-energy collision-induced dissociation are reviewed in the mechanistic context of five-membered ring formation. This structure of intermediates or of fragment ions is recognized as a key element that governs unimolecular peptide fragmentation within the structural framework determined by the peptide backbone and its side-chains. A collection of collision-induced dissociation reactions is presented covering (i) b-ion formation, (ii) the fragmentation of N-terminally acylated peptides, (iii) neutral loss of the C-terminal amino acid in alkali or silver cationized peptides, (iv) the fragmentation of isoAsp-containing peptides and (v) the fragmentation of negatively charged Asp- or Glu-containing peptides. It appears that for all possible nucleophile-electrophile interactions leading to a five-membered ring structure an associated unimolecular peptide fragmentation reaction can be observed.     

Further investigation of the mass fragmentation of dinucleotide analogues containing the 6-azauracil moiety

The mass fragmentation of four dinucleotide analogues in which uracil and 6-azauracil derivatives are connected by a trimethylene bridge is discussed. The fragmentation pathways have been proposed on the basis of high resolution data and metastable transitions. The distinct influence of alkyl substituents in the 5-position of the uracil moiety on the fragmentation pathway has been observed and a novel fragmentation of 6-azapyrimidine ring noted.     

Statistical versus non-statistical photo-fragmentation of protonated GWG tri-peptide induced by UV excitation

A new experimental method is described in which photo-induced fragmentation of protonated molecules in an electric field is investigated by the detection in coincidence of the ion and neutral fragments. This technique allows measuring fragmentation times, in the tens of nanosecond range, for each fragmentation channel independently. As an example, the method has been used to study the photo-fragmentation of the protonated tri-peptide GWG. It is shown that the various fragmentation channels have different fragmentation times. This is a clear signature of non-ergodic mechanisms occurring during fragmentation of such a large molecule.     

The charge ratio between O and N on amide bonds: a new approach to the mobile proton model

The influence of charge distribution on the cleavage of the peptides was investigated by fragmentation efficiency curves and quantum chemical calculations in order to clarify the fragmentation mechanism in this paper. The peptide Arg-Gly-Asp-Cys (RGDC) was oxidized to change the charge distribution, but its main sequence was retained. Under this study, it was illustrated that the fragmentation of the peptide RGDC became easier with each addition of an O atom to the Cys hydrosulfide group and the relative charge ratios between O and N (QO/QN) in the amide bonds had much to do with the cleavage of the peptide RGDC. For each amide bond, the situations coincided with overall conclusion: the increase of the QO/QN values results in a higher fragmentation efficiency and vice versa. The methods which combined fragmentation efficiency curves with the charge distribution of peptides provided a way to refine the mobile proton model for peptide fragmentation and to probe the discrepant fragmentation of peptides in peptide/protein identification.     

Understanding the fragmentation of glucose in mass spectrometry

The fragmentation mechanism of D-glucose was investigated in detail by two different fragmentation techniques, namely, collision-induced dissociation (CID) and infrared multiphoton dissociation (IRMPD) using all six ¹³C-labeled isotopomers and ²H-labeled isotopomers. For both CID and IRMPD energy-resolved measurements were carried out. Individual fragmentation pathways were studied at MS² and MS³ levels. Additionally, we have developed an HPLC-tandem MS method to separate the anomers of D-glucose using a HILIC column and investigated their fragmentation patterns individually. We propose a complete fragmentation landscape of D-glucose, demonstrating that a rather simple multifunctional molecule displays extreme complexity in gas phase dissociation, following multiple parallel fragmentation routes yielding a total of 23 distinct fragment ions. The results allowed a detailed formulation of the complex fragmentation mechanism of D-glucose. The results have immediate consequences for the full structure analysis of complex carbohydrates.     

流化床条件下煤的一次爆裂特性的实验研究

流化床锅炉中煤的爆裂特性对锅炉运行的炉内传热、碳转化率和细微颗粒的排放等许多方面有重要影响。本文在一台小型常压流化床反应器中研究了了种烟煤的一次爆裂烟煤的。对此烟煤不同宏观煤岩类型（亮煤和暗煤）的一次爆裂特性进行了比较研究。实验发现颗粒的一次爆裂率和爆裂程度很大程度上取决于颗粒粒径以及煤颗粒的组成,亮煤具有与暗煤不同的一次爆裂特性,同一粒径的煤颗粒爆裂后形成具有一定特点的粒径分布。针对不同煤岩类型     

Desorption and fragmentation studies of organic molecules by laser-induced mass spectrometry

Desorption, fragmentation, and cationization of a variety of organic molecules using a laser mass spectrometer are described. At low laser power densities, desorption of organic molecules takes place. With progressively higher laser power densities, fragmentation characteristic of molecular structure occurs and at very high laser power densities, indiscriminate fragmentation occurs. It is also possible to observe parent peaks from mixtures of organic molecules without any fragmentation.     

The investigation of substituent effects on the fragmentation pathways of pentacoordinated phenoxyspirophosphoranes by ESI‐MSn

The fragmentation pathways of pentacoordinated phenoxyspirophosphoranes were investigated in the positive mode by electrospray ionization multistage mass spectrometry. The results demonstrate that the sodium adducts of the title compounds undergo two competitive fragmentation pathways, and the fragmentation patterns are heavily dependent on the various substituent patterns at the phenolic group. An electron‐withdrawing substituent at the ortho‐position always results in the removal of a corresponding phenol analogue, while cleavage by spiroring opening becomes the predominant fragmentation pathway if an electron‐donating substituent is at the phenolic group. The substituent effects on the competitive fragmentation pathways were further elucidated by theoretical calculations, single crystal structure analysis, and high‐resolution mass spectrometry. The results contribute to the understanding of the gas‐phase fragmentation reactions and the structure identification of spirophosphorane analogues by electrospray ionization multistage mass spectrometry.     

New fragmentation pathways in the electron impact mass spectrometry of derivatized pyrano-1,3-diphenylprop-2-enones

The fragmentation patterns of closely related chalcones, cinnamoylchromans and cinnamoylchromenes, are reported to be strikingly different. The mass spectra of the first group show peaks typical of the fragmentation of simple chalcones balanced by additional fragmentation routes competing effectively with the typical chalcone fragmentation. For the other group with the introduced double bond the fragmentation is considerably changed. Initial loss of a methyl group gives rise to formation of the base peak in three of four examples. The [M – CH₃]⁺ ion decomposes further, eliminating a styrene yielding the m/z 187 ion. This process may be rationalized as a retro-Diels–Alder fragmentation of a flavanone formed on intramolecular rearrangement of the molecular ion.     

Spectres de masse des composés organiques. 5e communication. Perte de méthane et d'éthylène à partir des ions butyle

The loss of methane and ethylene in the mass-spectrometric fragmentation of different isomeric butyl ions which originate from butyl halides has been studied. The different carbon atoms in n-butyl are already equivalent after 10^?7 s, whereas the statistical distribution of the hydrogen atoms within the molecule can only be observed for the metastable peaks. A protonated cyclobutane structure is proposed as an intermediate product in the fragmentation of the n-butyl ion. The fragmentation of this model has been simulated by a computer. This allows prediction as to the time-scale of fragmentation. The comparison of this model fragmentation with that of isomeric butyl ions shows that, even in the decay of the tertiary butyl ion, the formation of the proposed rearranged cyclic structure competes favorably with the direct fragmentation.     

Interpretation of alkyl diselenide and selenosulfenate mass spectra

The mass spectral fragmentation of aliphatic diselenides and selenosulfenates is analyzed to gain a better understanding of the behavior of these species. The main fragmentation pathways of these species include the fragmentation along the Se-C bond, fragmentation along the Se-Se or Se-S bonds and intra-molecular rearrangements. In general, negative ionization favors the fragmentation along the Se-Se or Se-S bonds while positive ionization leads to stable molecular ions. Density functional theory calculations of bond dissociation energies and molecular orbital analysis was undertaken to explain the observed trends in molecular fragmentation. Besides the analysis of molecular fragmentation, a phenomenon of molecular association in negative electron impact and positive chemical ionization conditions was observed and investigated using a high resolution time-of-flight mass spectrometer. Molecular association that occurs during the ionization of species includes the formation of symmetrical diselenides from asymmetrical selenosulfenates and formation of alkylseleno adducts from the corresponding diselenides. For species which is hard to resolve by mass analysis, such as isobars of CHSe, CH₂Se, and CH₃Se, the isotope pattern superimposition procedure was applied to define the overlapping clusters.     

龙岩煤不同宏观煤岩组分的热破碎性质研究

用筛分和浮选法对龙岩煤进行分选, 得到不同粒径、不同宏观煤岩的龙岩煤颗粒。在热天平上进行热解破碎研究,并在自制的小型流化床上进行燃烧破碎试验。结果表明,亮煤与灰煤均发生一次破碎, 破碎后生成许多细小颗粒, 其中粒径0.8mm以下的细颗粒占多数;暗煤则不发生一次破碎。随着升温速率和颗粒粒径的增大, 一次破碎变得较为剧烈;颗粒性质、颗粒粒径、炉床温度和燃烧时间等因素对龙岩煤在流化床燃烧中的破碎均有重要影响。亮煤与灰煤因结构致密, 颗粒中大孔隙少, 显微硬度大, 灰分少等原因使得它们在燃烧中发生严重破碎;而暗煤颗粒则因相反的原因不发生破碎或仅发生轻微破碎。粒径越大, 炉床温度越高, 燃烧时间越长, 破碎越剧烈;亮煤与灰煤在燃烧中均发生了二次破碎, 其中亮煤的二次破碎更剧烈;燃烧后期, 亮煤的颗粒破碎比灰煤更快;由于破碎, 入炉煤颗粒平均粒径在燃烧早期迅速减小, 而后随着燃烧的进行而逐步趋于一个稳定值;亮煤在流化床燃烧中服从等密度燃烧模式, 暗煤服从等直径燃烧模式, 而灰煤则服从混合燃烧模式。     

Ultraviolet photodissociation of protonated pharmaceuticals in a pressurized linear quadrupole ion trap

Ultraviolet photodissociation (UVPD) was evaluated as a technique for generating ion fragmentation information that is alternative and/or complementary to the information obtained by collision‐induced dissociation (CID). Ions trapped in a pressurized linear ion trap were dissociated using a 355 nm or a 266 nm pulsed laser. Comparisons of UVPD and CID spectra using a set of aromatic chromophore‐containing compounds (desmethyl bosentan, haloperidol, nelfinavir) demonstrated distinct characteristic fragmentation patterns resulting from photodissociation. The wavelength of light and the pressure of the buffer gas in the UVPD cell are important parameters that control fragmentation pathways. The wavelength effect is related to the absorption cross section, location of the chromophore and the energy carried by one photon. Thus, UV irradiation wavelength affects fragmentation pathways as well as the fragmentation rate. The pressure effect can be explained by collisional quenching of ‘slow’ fragmentation pathways. We observed that higher pressure of the buffer gas during UVPD experiments highlights unique fragment ions by suppressing slow fragmentation pathways responsible for CID‐like fragmentation patterns. Copyright © 2010 John Wiley & Sons, Ltd.     

Electron impact induced alkyl-group fragmentation on the acridine nucleus

The fragmentation of simple alkyl acridines closely resembles that of the analogous quinoline derivatives. Interaction between the heteroatom and a 4-alkyl substituent dramatically influences the fragmentation pattern with resultant γ-cleavage or rearrangement to the heteroatom and corresponding elimination of an alkene fragment. The fragmentation of the 9-chloroalkylacridines closely resembles that of the acridines with the loss of the clorine atom superposed on the alkylacridine fragmentation. Redistribution of the centre of apparent charge localization occurs for the acridones with a tendency for interaction with the 9-position.     

Fragmentation-based QM/MM simulations: length dependence of chain dynamics and hydrogen bonding of polyethylene oxide and polyethylene in aqueous solutions

Molecular fragmentation quantum mechanics (QM) calculations have been combined with molecular mechanics (MM) to construct the fragmentation QM/MM method for simulations of dilute solutions of macromolecules. We adopt the electrostatics embedding QM/MM model, where the low-cost generalized energy-based fragmentation calculations are employed for the QM part. Conformation energy calculations, geometry optimizations, and Born-Oppenheimer molecular dynamics simulations of poly(ethylene oxide), PEO(n) (n = 6-20), and polyethylene, PE(n) ( n = 9-30), in aqueous solution have been performed within the framework of both fragmentation and conventional QM/MM methods. The intermolecular hydrogen bonding and chain configurations obtained from the fragmentation QM/MM simulations are consistent with the conventional QM/MM method. The length dependence of chain conformations and dynamics of PEO and PE oligomers in aqueous solutions is also investigated through the fragmentation QM/MM molecular dynamics simulations.