We explore the feasibility of conducting electron ionization (EI) in a radio-frequency (rf) ion source trap for mass spectrometry applications. Electrons are radially injected into a compact linear ion trap in the presence of a magnetic field used essentially to lengthen the path of the electrons in the trap. The device can either be used as a stand-alone mass spectrometer or can be coupled to a mass analyzer. The applied parallel magnetic field and the oscillating rf electric field produced by the trap give rise to a set of coupled Mathieu equations of motion. Via numerical simulations, electron trajectories are studied under varying intensities of the magnetic field in order to determine the conditions that enhance ion production. Likewise, the dynamic behavior of the ions are investigated in the proposed EI source trap and the fast Fourier transform FFT formalism is used to obtain the frequency spectrum from the numerical simulations to study the motional frequencies of the ions which include combinations of the low-frequency secular and the high-frequency micromotion with magnetron and cyclotron frequencies. The dependence of these motional frequencies on the trapping conditions is examined and particularly, the limits of applying a radial magnetic field to the EI ion trap are characterized.
Lasso peptides constitute a class of bioactive peptides sharing a knotted structure where the C-terminal tail of the peptide is threaded through and trapped within an N-terminal macrolactam ring. The structural characterization of lasso structures and differentiation from their unthreaded
topoisomers is not trivial and generally requires the use of complementary biochemical and spectroscopic methods. Here we
investigated two antimicrobial peptides belonging to the class II lasso peptide family and their corresponding unthreaded
topoisomers: microcin J25 (MccJ25), which is known to yield two-peptide product ions specific of the lasso structure under
collision-induced dissociation (CID), and capistruin, for which CID does not permit to unambiguously assign the lasso structure.
The two pairs of topoisomers were analyzed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry
(ESI-FTICR MS) upon CID, infrared multiple photon dissociation (IRMPD), and electron capture dissociation (ECD). CID and ECD
spectra clearly permitted to differentiate MccJ25 from its non-lasso topoisomer MccJ25-Icm, while for capistruin, only ECD
was informative and showed different extent of hydrogen migration (formation of c•/z from c/z•) for the threaded and unthreaded topoisomers. The ECD spectra of the triply-charged MccJ25 and MccJ25-lcm showed a series
of radical b-type product ions ( b¢n · ) \left( {b{\prime}_n^{ \bullet }} \right) . We proposed that these ions are specific of cyclic-branched peptides and result from a dual c/z• and y/b dissociation, in
the ring and in the tail, respectively. This work shows the potentiality of ECD for structural characterization of peptide
topoisomers, as well as the effect of conformation on hydrogen migration subsequent to electron capture. 相似文献
Characterization of glycosaminoglycans poses a challenge for current analytical techniques, as they are highly acidic, polydisperse and heterogeneous compounds. The purpose of this study is the separation and analysis of a partially depolymerized heparin-like glycosaminoglycan by on-line ion-pairing reversed-phase high-performance liquid chromatography/electrospray mass spectrometry. The gas-phase behavior of two synthesized glycosaminoglycans has been investigated. Dibutylamine was found to be the best suited ion-pairing reagents for mass spectrometry analysis. The optimized ion-pairing conditions provide reproducible and easily interpretable electrospray mass spectra in both negative and positive ESI modes. The glycosaminoglycans are detected as a non-covalent complex with amines. In fact, the observed ionic species and their gas-phase dissociation under CID conditions revealed the presence of salt bridge interactions in the gas phase. 相似文献
Methylated and partially methylated cyclodextrin homo- and heterodimers linked by diamidosuccinic bridges were synthesised and their inclusion properties were evaluated using NMR and isothermic microcalorimetric measurements ITC. The selective binding of ligands, such as bisadamantyl derivatives, to the cavities of unprotected cyclodextrin dimers showed the equimolar formation of bidendate inclusion complexes (2:2, two ligand guest to two cavities host). 相似文献
Ester‐way to heaven : Unexpected formation of bicyclo[3.1.0]hexene 4 was the main focus of combined experimental and theoretical studies on the Au‐catalyzed cycloisomerization of branched dienyne 1 (see scheme), which provided better understanding of the mechanistic details governing the cyclization of enynes bearing a propargylic ester group.
The study of low molecular weight compounds by matrix-assisted laser desorption/ionization (MALDI) is difficult because of the presence of ions originating from the matrix in the low-m/z range. In order to resolve these problems, new matrix-free approaches were developed based on laser desorption/ionization from the surface of various materials such as graphite and porous silicon. Our work involves the use of 'desorption ionization on porous silicon mass spectrometry' (DIOS-MS) in the negative ion mode to study fatty acid compounds. The potential of the DIOS-MS technique is shown and an insight into the ionization mechanism provided. 相似文献
The unsaturated dicarboxylates (III and IV) form stable (M+N2H7)+ adducts in addition to the (M+NH4)+ adduct. At high ammonia pressure in the ion source, bimolecular reactions between (M+NH4)+ (M+N2H7) adducts and NH3 result in the reduction of olefinic bonds in unsaturated and dicarboxylates. Evidence was obtained from MIKE/CAD data on the possible structure of the product ion. 相似文献
A synthesis of the C29-C51 fragment of spongistatin 1, containing the E and F rings, has been completed. The approach relies on four diastereoselective aldol additions and an asymmetric glycolate alkylation to establish eight of the eleven stereogenic centers. The intact chlorodiene side chain was appended by a Lewis acid catalyzed addition of an allylstannane to an epoxy enol ether. 相似文献
The differential cross section of the 4He(p, d)3He pick-up reaction has been measured at Ep = 770 MeV. The data are analysed in the framework of the DWBA; both one-nucleon and one-N1 transfers are considered. 相似文献
The structure of cinerubine A has been studied by chemical ionisation mass spectrometry. In the NH3/Cl mode, this type of compound with polyfunctional sites undergoes as aminolysis reaction, i.e. hydroxyl and carbonyl groups are substituted by NH3. The protonated molecular ions formed in the ion source fragment to give intense ions which provide useful structural information. Unimolecular fragmentations in the first field-free region permit determination of the reactive sites. Use of ND3 as reagent gas provides information on the number of mobile H atoms and permits the assignment of structure for these ionic species. 相似文献