Meiyu He

Mass spectrometric study of γ‐aryl‐α,­γ‐diethoxy‐α, β‐butenolides

Electron impact mass spectra of eight of the title compounds are reported. Abundant fragment ions were produced under electron impact (EI) conditions and, with one exception, the ( O) ions were the base peaks. The EI fragmentation mechanisms of two representative compounds were studied with the aid of high-resolution and mass-analyzed ion kinetic energy spectrometry (MIKES) data. The M+ ions fragment to give both an odd-electron ion and an even-electron fragment ion. Two H-atom rearrangements proceeding via four-membered ring intermediates and three losses of CO through i- and α-fragmentations were observed under EI. On comparing fragmentations under EI conditions with those under FAB conditions for two of the compounds, the fragmentation mechanisms were reasonably similar, with additional fragmentations rationalized in terms of the ionization proton being located on the oxygen atom of the β-ethoxy group. Copyright

Characterization of mesogen-jacketed liquid crystalline polymers by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

For synthetic polymers, a proper sample preparation method is essential for successful characterization by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. In this work, six synthetic mesogen-jacketed liquid crystalline polymers (MJLCPs) with different main-chain, spacer and mesogenic units were investigated by MALDI-TOF mass spectrometry. Several factors that affect the analysis of these polymers were examined. These factors include matrices used, cationization salts used, the concentration of polymers, and the ratio of sample to matrix. After testing different conditions, we found a suitable sample preparation method for these six polymers. The number average molecular weight (M(n)), weight average molecular weight (M(w)) and polydispersity (PD) were calculated using data obtained in the linear mode. The end groups of the polymers were proposed using data obtained in reflectron mode. Copyright 2000 John Wiley & Sons, Ltd.

Positive-ion Electrospray–Fourier Transform Ion Cyclotron Resonance Mass Spectra of Polypeptides and Proteins

We have determined the mass spectra of three polypeptides which have been designed as an effective reagent to be used in the diagnosis of a Chinese strain of Hepatitis E Virus (HEV). The spectra were determined by electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometer. These are peptide 30, peptide 33 and peptide 42, where the guanidine amino group of arginine in each polypeptide was protected. The molecular weights were respectively measured as 3575, 4094 and 5390 Dalton, against the molecular weights of bovine serum albumin (66430 Da) and bovine insulin (5732.77 Da).

Sequence analysis of peptides with biological activities using electrospray-Fourier trans form ion cyclotron resonance mass spectrometry

The mass spectra of five peptides with biological activities are reported. All mass spectra were recorded using a 4.7-T Fourier transform ion cyclotron resonance mass spectrometer equipped with an external electrospray source. The accurate molecular weights for the five peptides prepared by solid phase synthesis were measured as 1765.9013, 1063.5420, 1092.5254, 820.3804 and 1078.5193, respectively. All the data were obtained with the external calibration. Differences between observed and theoretical monoisotopic molecular weights were in the 0.2–1.0)×10−6 range. The complete primary sequence for the five polypeptides were determined using the method of insource electrospray ionization/collision induced dissociation (ESI/CID). All the intact y series ions and b series ions were obtained from various peptides respectively, thus determining the sequences of the five polypeptides. We found that the measured accurate molecular mass of sample 4 was not in agreement with that expected from the planned synthetic peptide. The sequences of sample 4 were determined through analysis. The corresponding accurate masses of b series ions and y series ions were gained, which proved that it was correct to redetermine the sequences.

Electron impact fragmentation mechanisms of some cyclic esters with helical structures

The electron impact mass spectra of several cyclic esters with helical structures have been studied. Their fragmentation pathways were proposed and confirmed by mass-analyzed ion kinetic energy (MIKE) and high-resolution data. In general, the dominant fragmentation pathways in the spectra of these compounds originate from a alpha-cleavage with loss of a hydrogen or methyl group. The difference between hydrogen and methyl group loss greatly affects the subsequent fragmentations. Although, due to their helicity, these cyclic esters are optically active no stereo-related fragmentation pathway was observed. Copyright 2000 John Wiley & Sons, Ltd.

Mass spectrometric study of six cyclic esters

A series of cyclic esters, which are optically active as a consequence of their helical structures, were synthesized to investigate the relationships between their structures and their optical activities. This paper reports the electron impact fragmentation mechanisms of these six cyclic esters. Accurate mass measurements and mass analyzed ion kinetic energy spectrometry confirmed fragmentation patterns. The stability of the fragment ions has a great influence on the fragmentation pathways, but no correlation with the optical activity was found.

Mass spectrometric study of gamma-aryl-alpha,-gamma-diethoxy-alpha, beta-butenolides.

Electron impact mass spectra of eight of the title compounds are reported. Abundant fragment ions were produced under electron impact (EI) conditions and, with one exception, the ( O) ions were the base peaks. The EI fragmentation mechanisms of two representative compounds were studied with the aid of high-resolution and mass-analyzed ion kinetic energy spectrometry (MIKES) data. The M+ ions fragment to give both an odd-electron ion and an even-electron fragment ion. Two H-atom rearrangements proceeding via four-membered ring intermediates and three losses of CO through i- and α-fragmentations were observed under EI. On comparing fragmentations under EI conditions with those under FAB conditions for two of the compounds, the fragmentation mechanisms were reasonably similar, with additional fragmentations rationalized in terms of the ionization proton being located on the oxygen atom of the β-ethoxy group. Copyright

Mass spectrometric study of ?-aryl-?,?-diethoxy-?, ?-butenolides

Electron impact mass spectra of eight of the title compounds are reported. Abundant fragment ions were produced under electron impact (EI) conditions and, with one exception, the ( O) ions were the base peaks. The EI fragmentation mechanisms of two representative compounds were studied with the aid of high-resolution and mass-analyzed ion kinetic energy spectrometry (MIKES) data. The M+ ions fragment to give both an odd-electron ion and an even-electron fragment ion. Two H-atom rearrangements proceeding via four-membered ring intermediates and three losses of CO through i- and α-fragmentations were observed under EI. On comparing fragmentations under EI conditions with those under FAB conditions for two of the compounds, the fragmentation mechanisms were reasonably similar, with additional fragmentations rationalized in terms of the ionization proton being located on the oxygen atom of the β-ethoxy group. Copyright

Electron impact mass spectral characteristics and fragmentation pathways of isomeric tetradecadien‐1‐ols

Characteristics of mass spectra of isomeric tetradecadien-1-ols were investigated by electron impact mass spectrometry, and mass spectral fragmentation pathways were proposed based on collision-induced dissociation experiments and mass-analyzed ion kinetic energy spectrometry. Copyright 1999 John Wiley & Sons, Ltd.

Mass spectrometric study on methyl 5-methyl-2-oxo-3-[2-(4-R-phenyl)-1-ethyl]cyclopentanecarboxylates and methyl 2-oxo-5-(4-R-phenyl)-3-propylcyclopentanecarboxylates

The mechanisms of mass spectrometric fragmentation of eight new compounds, including methyl 5-methyl-2-oxo-3-[2-(4-R-phenyl)-1-ethyl]cyclopentanecarboxylates (Group I, R = substituent) and methyl 2-oxo-5-(4-R-phenyl)-3-propylcyclopentanecarboxylates (Group II, R = substituent), were studied using mass analyzed ion kinetic energy spectrometry. The chemical compositions of these compounds and some of their important fragment ions were verified by high-resolution MS data. There were two types of H-rearrangement as regards the route of fission. In one type, the γ-H migration was influenced by both the electron effect and the steric hindrance of substituents, whereas on the other α-H migration losing methanol was due to the α-position active hydrogen located between two carbonyls, and this was verified by the method of deuterium labelling.