MSn Experiments (msn + experiment)

Distribution by Scientific Domains

Selected Abstracts

Reduction of [(C5Me5)2Mo2O5] and [(C5Me5)2Mo2O4] in Methanol/Water/Trifluoroacetate Solutions Investigated by Combined On-Line Electrochemistry/Electrospray-Ionization Mass Spectrometry

Jenny Gun
Abstract Complexes [Cp*2Mo2O5] (Cp* = ,5 -C5Me5) and [Cp*2Mo2O4] were investigated by combined on-line electrochemical (EC) reduction and electrospray-ionization mass spectrometry (ESI-MS) techniques in a trifluoroacetic acid buffered water/methanol solution. The reduction products at the larger negative potentials are identical for both compounds. The studies reveal the existence of a wide range of previously unknown di- and trinuclear MoV, MoIV, MoIII, and mixed-valence complexes that were identified on the basis of their masses and characteristic isotope patterns. The structures of the initial compounds and the product of electroreduction with m/z = 713,729 were supported by in situ MSn experiments that allowed the elucidation of the fragmentation pathway for the collision-induced dissociation. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Mass spectrometric analysis of the marine lipophilic biotoxins pectenotoxin-2 and okadaic acid by four different types of mass spectrometers

Arjen Gerssen
Abstract The performances of four different mass spectrometers [triple-quadrupole (TQ), time-of-flight (ToF), quadrupole ToF (Q-ToF) and ion trap (IT)] for the detection of the marine lipophilic toxins pectenotoxin-2 (PTX2) and okadaic acid (OA) were investigated. The spectral data obtained with the different mass spectrometric analyzers were used to propose fragmentation schemes for PTX2 in the positive electrospray mode and for OA in the negative electrospray mode. TQ data were used to obtain product ions, while ToF and Q-ToF-MS produced accurate mass data of the precursor ion and product ions, respectively. IT data provided a better understanding of the fragmentation pathways using MSn experiments. With respect to analytical performance, all four mass analyzers showed a good linearity (R2 > 0.97) and repeatability (CV < 20%). Detection limits (LoDs) (S/N = 3) were the lowest on triple-quad MS: 12.2 and 2.9 pg on-column for PTX2 and OA, respectively. Copyright 2008 John Wiley & Sons, Ltd. [source]

Negative and positive ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and positive ion nano-electrospray ionization quadrupole ion trap mass spectrometry of peptidoglycan fragments isolated from various Bacillus species

Gerold Bacher
Abstract A general approach for the detailed characterization of sodium borohydride-reduced peptidoglycan fragments (syn. muropeptides), produced by muramidase digestion of the purified sacculus isolated from Bacillus subtilis (vegetative cell form of the wild type and a dacA mutant) and Bacillus megaterium (endospore form), is outlined based on UV matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and nano-electrospray ionization (nESI) quadrupole ion trap (QIT) mass spectrometry (MS). After enzymatic digestion and reduction of the resulting muropeptides, the complex glycopeptide mixture was separated and fractionated by reversed-phase high-performance liquid chromatography. Prior to mass spectrometric analysis, the muropeptide samples were subjected to a desalting step and an aliquot was taken for amino acid analysis. Initial molecular mass determination of these peptidoglycan fragments (ranging from monomeric to tetrameric muropeptides) was performed by positive and negative ion MALDI-MS using the thin-layer technique with the matrix ,-cyano-4-hydroxycinnamic acid. The results demonstrated that for the fast molecular mass determination of large sample numbers in the 0.8,10 pmol range and with a mass accuracy of 0.07%, negative ion MALDI-MS in the linear TOF mode is the method of choice. After this kind of muropeptide screening often a detailed primary structural analysis is required owing to ambiguous data. Structural data could be obtained from peptidoglycan monomers by post-source decay (PSD) fragment ion analysis, but not from dimers or higher oligomers and not with the necessary sensitivity. Multistage collision-induced dissociation (CID) experiments performed on an nESI-QIT instrument were found to be the superior method for structural characterization of not only monomeric but also of dimeric and trimeric muropeptides. Up to MS4 experiments were sometimes necessary to obtain unambiguous structural information. Three examples are presented: (a) CID MSn (n = 2,4) of a peptidoglycan monomer (disaccharide-tripeptide) isolated from B. subtilis (wild type, vegetative cell form), (b) CID MSn (n = 2,4) of a peptidoglycan dimer (bis-disaccharide-tetrapentapeptide) obtained from a B. subtilis mutant (vegetative cell form) and (c) CID MS2 of a peptidoglycan trimer (a linear hexasaccharide with two peptide side chains) isolated from the spore cortex of B. megaterium. All MSn experiments were performed on singly charged precursor ions and the MS2 spectra were dominated by fragments derived from interglycosidic bond cleavages. MS3 and MS4 spectra exhibited mainly peptide moiety fragment ions. In case of the bis-disaccharide-tetrapentapeptide, the peptide branching point could be determined based on MS3 and MS4 spectra. The results demonstrate the utility of nESI-QIT-MS towards the facile determination of the glycan sequence, the peptide linkage and the peptide sequence and branching of purified muropeptides (monomeric up to trimeric forms). The wealth of structural information generated by nESI-QIT-MSn is unsurpassed by any other individual technique. Copyright 2001 John Wiley & Sons, Ltd. [source]

Photocrosslinking of a novel ,,, -unsaturated copolyamide: mass spectrometric study on model compounds with benzophenone as photoinitiator

Marion N'Negue Mintsa
The aim of this work was to understand the reactions involved in the photocrosslinking processes of a ,,, -unsaturated copolyamide foreseen as a new UV-curable powder coating. The crosslinking reaction was photoinitiated with benzophenone. In this paper, the photochemical reaction between benzophenone and several model compounds was investigated. The model compounds contained functional groups which could be present in copolyamide. The products resulting from UV curing were identified using a combination of high-resolution mass spectrometry and MSn experiments. The characterization of the products allowed localization of the hydrogen abstraction by the type II photoinitiator during UV curing and, consequently, the determination of the reactive sites of the unsaturated polyamide chain which were involved in the photochemical reaction. Copyright 2009 John Wiley & Sons, Ltd. [source]

Electrospray tandem mass spectrometry of alkali-cationized BocN-carbo- ,,, - and - ,,, -peptides: differentiation of positional isomers,

P. Nagi Reddy
Dissociation pathways of a series of alkali-cationized hybrid peptides, viz., Boc- ,,, - and - ,,, -carbopeptides, synthesized from C-linked carbo- ,3 -amino acids [Caa (S)] and , -alanine (L-Ala), have been investigated by electrospray ionization tandem mass spectrometry. The positional isomers (six pairs) of the cationized ,,, - and ,,, -peptides can be differentiated by the collision-induced dissociation (CID) spectra of their [M,+,Cat-Boc,+,H]+ ions which give characteristic series of alkali-cationized C- (x, y, z) and N-terminal (a, b, c) ions. Another noteworthy difference is cationized ,,, -peptides eliminate a molecule of ammonia whereas this pathway is absent for ,,, -peptides. This is useful for identifying the presence of a , -amino acid at the N-terminus. The CID spectra of [M,+,Cat-Boc,+,H]+ ions of these peptide acids show abundant rearrangement [bn,+,17,+,Cat]+ (n,=,1 to n,1) ions which is diagnostic for distinguishing between , - and , -amino acid at the C-terminus. MSn experiments of [bn,+,Li,H]+ ions from these hybrid peptides showed the loss of CO and 72 u giving rise to [an,+,Li,H]+ and cationized nitrile product ions which render support to earlier proposals that b or [bn,+,Cat,H]+ ions have protonated or cationized oxazolinone structures, respectively. Copyright 2006 John Wiley & Sons, Ltd. [source]

Characterisation via electrospray ionisation multistage mass spectrometry of three related series of nitrido technetium complexes containing phosphinothiolate and dithiocarbamate ligands

Michela Tubaro
Nine nitrido technetium compounds comprising bis-substituted Tc(N)(PS)2 (1,4) (PS,=,bidentate phosphinothiolate ligands) and Tc(N)(dtc)2 (5, 6) derivatives (dtc,=,bidentate dithiocarbamate), and mixed-ligand Tc(N)(PS)(dtc) (7,9) species, were subjected to electrospray ionisation mass spectrometry and MSn experiments. Bis-substituted phosphinothiolato complexes 1,4 lead to the straightforward formation of dinuclear species reasonably originating from proton bound dimers. These dinuclear species do not show, under collisionally induced fragmentation processes, the formation of monomeric units but cleavages related to the ligand framework, thereby proving the high stability of the [TcH+Tc] bond. Bis-dithiocarbamate compounds 5 and 6 show, instead, abundant [M+H]+, [M+Na]+ and [2M+Na]+ ions, and their collisionally induced fragmentations are highly favoured with cleavages related to the CN and CS bonds. During these processes, the coordination of a water molecule to [MH,L]+ product ions is observed, as proved by the collisionally induced H2O loss detected for this species. Mixed-ligand compounds 7 and 8 show the protonated molecules and Na+ -cationised ions with fragmentation processes related to the dithiocarbamate moiety. This behaviour indicates that coordination of ether- and ester-substituted dithiocarbamates to the [Tc,,N] group is weaker than that of phosphinothiolates. Conversely, diethyldithiocarbamate inserted in mixed complex 9 enhances both CN and TcS bonds, and fragmentation processes suggest that metal-phosphinothiolate and metal-dithiocarbamate show comparable strength. Copyright 2005 John Wiley & Sons, Ltd. [source]

Studies on azaspiracid biotoxins.


In this report, the mass spectral analysis of azaspiracid biotoxins is described. Specifically, the collision-induced dissociation (CID) behavior and differences between CID spectra obtained on a triple-quadrupole, a quadrupole time-of-flight, and an ion-trap mass spectrometer are addressed here. The CID spectra obtained on the triple-quadrupole mass spectrometer allowed the classification of the major product ions of the five investigated compounds (AZA 1,5) into five distinct fragment ion groups, according to the backbone cleavage positions. Although the identification of unknown azaspiracids was difficult based on CID alone, the spectra provided sufficient structural information to allow confirmation of known azaspiracids in marine samples. Furthermore, we were able to detect two new azaspiracid analogs (AZA 1b and 6) in our samples and provide a preliminary structural analysis. The proposed dissociation pathways under tandem mass spectrometry (MS/MS) conditions were confirmed by a comparison with accurate mass data from electrospray quadrupole time-of-flight MS/MS experiments. Regular sequential MSn analysis on an ion-trap mass spectrometer was more restricted in comparison to the triple-quadrupole mass spectrometer, because the azaspiracids underwent multiple [M,+,H,,,nH2O]+ (n,=,1,6) losses from the precursor ion under CID. Thus, the structural information obtained from MSn experiments was somewhat limited. To overcome this limitation, we developed a wide-range excitation technique using a 180-u window that provided results comparable to the triple-quadrupole instrument. To demonstrate the potential of the method, we applied it to the analysis of degraded azaspiracids from mussel tissue extracts. Copyright 2002 John Wiley & Sons, Ltd. [source]

Characterisation and determination of indole alkaloids in frog-skin secretions by electrospray ionisation ion trap mass spectrometry

Stephen McClean
The characterisation of selected indole alkaloids in a quadrupole ion trap mass spectrometer is presented. Fragmentation profiles for tryptamine, 5-hydroxytryptamine (5-HT), N,-methyl 5-hydroxytryptamine (N,-methyl 5-HT), N,,N,-dimethyl 5-hydroxytryptamine (bufotenine), N,,N,,N,-trimethyl 5-hydroxytryptamine (5-HTQ), and N,,N,-dimethyl 5-methoxytryptamine (5-MeODMT) are presented with proposed structures given for each product ion observed. Such MSn experiments can be used to differentiate the isobaric molecular ions of the compounds 5-HTQ (M+) and 5-MeODMT (MH+). The quantitative determination of certain indole alkaloids in the skin secretions of the Australian Golden Bell frog, Litoria aurea, by LC/ESI-ion trap MS is also presented. The concentrations of 5-HT, N,-methyl 5-HT and 5-HTQ were found to be 2.68, 0.26 and 0.54,g per,mg of skin secretion, respectively. Copyright 2002 John Wiley & Sons, Ltd. [source]

Analysis of flavonoid constituents from leaves of Acanthopanax senticosus Harms by electrospray tandem mass spectrometry

Maolian Chen
Three known flavonoids, quercetin, quercitrin (quercetin-3-0-rhamnoside) and rutin (quercetin-3-0-rutinoside), have been identified for the first time in the leaves of Acanthopanax senticosus Harms by using electrospray tandem mass spectrometry techniques (ESI,MSn). The flavonoid hyperin (quercetin-3-0-,-galactoside), already known to be present, was also investigated. The diagnostic fragment ions of the aglycone quercetin were obtained in the ESI,MSn experiments, and a fragmentation mechanism proposed. Copyright 2002 John Wiley & Sons, Ltd. [source]

Determination of the disulfide bond pattern of the endogenous and recombinant angiogenesis inhibitor endostatin by mass spectrometry

Harald John
Endostatin, a C-terminal fragment of collagen XVIII, is a promising protein drug which is in development for cancer therapy due to its anti-angiogenic activity. Although several endogenous molecular forms of human endostatin differing in their N-terminal length and their post-translational modifications (18.5,22,kDa) have been discovered, only one recombinant form of 20,kDa is used in clinical trials. This protein, recombinantly expressed in Pichia pastoris, contains four cysteines forming two disulfide bonds (Cys1-Cys4 and Cys2-Cys3). In contrast, there are conflicting data about the disulfide pattern of endogenous material. This report presents the disulfide analyses of both the endogenous circulating endostatins isolated from human hemofiltrate and the recombinant protein. The determination of the disulfide pattern was performed by Edman degradation, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and electrospray ionization ion trap mass spectrometry (ESI-ITMS) performed in the off-line nanospray mode. All native and recombinant endostatins exhibited a Cys1-Cys4 (Cys162 -Cys302) and Cys2-Cys3 (Cys264 -Cys294) linkage. For a clear discussion of fragmented disulfide-bridged peptide chains obtained from MSn experiments, a modified general nomenclature is proposed. Copyright 2001 John Wiley & Sons, Ltd. [source]