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Fragmentation Mechanisms (fragmentation + mechanism)

Distribution by Scientific Domains

Chemistry	88%

Selected Abstracts

Fragmentation Mechanism of Trans -,-Aryl-,-enamino Esters

CHINESE JOURNAL OF CHEMISTRY, Issue 8 2002
Nan Jiang
Abstract Electron impact-induced fragmentation mechanisms of trans-, -aryl- , -enamino esters were investigated using mass-analyzed ion kinetic energy (MIKE) spectrometry and high resolution accurate mass data. It was found that the main characteristic fragmentations of compounds studied were: an odd electron ion M+ - EtOH was formed by losing a neutral molecule of ethanol; and the skeletal rearrangements took place; and the ring opening reaction happened after losing a carbon monoxide; and the typical McLafferty rearrangement underwent in ester group. The cyclization reaction caused by losing neutral molecule of TsNH2 due to the ortho -effects of substituted group of aromatic ring was also observed. [source]

Electron ionization mass spectrometric study of monomeric models of O -polysaccharides of Vibrio cholerae O:1, serotypes Ogawa and Inaba

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2003
Vladimír Ková
Abstract Fragmentation mechanisms of electron ionization (EI) mass spectrometry of the title compounds have been elucidated by high-resolution (HR) mass spectrometric measurements of the elemental composition and measurements of the metastable transitions (B2/E, CID). The experimental results were interpreted with the help of Mass Frontier 3.0 software, which aided the elucidation of fragmentation mechanisms and helped to deduce structures of the ions formed. Characteristic under the conditions of EI-MS measurement was the production of protonated adducts. Three distinct pathways observed include the formation of oxonium type ions, the conjugated transfer of electrons in the pyranose ring, and cleavage of the acylamide side chains. By applying the results obtained, the molecular mass, as well as the structures of both the saccharide and acylamide side chain involved in related substances, can be determined. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Matrix-assisted laser desorption/ionization collision-induced dissociation of linear single oligomers of nylon-6

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2001
Renata Murgasova
Abstract Matrix-assisted laser desorption/ionization, collision induced-dissociation (MALDI-CID) has been used to obtain structural information for linear single oligomers of nylon-6. The effects of matrix and cationization agent in MALDI-CID analysis have been investigated. Fragmentation mechanisms are proposed for the series of ions that are observed in the MALDI-CID spectra of the hexamer, octamer and dodecamer. Fragmentation processes observed in the MALDI-CID spectra include cleavage of the end groups followed by dissociation of the m/z 113 unit. Cleavage of the oligamide chain occurs at the amide linkage, as well as at adjacent bonds. For the four matrices and three cationization agents investigated, 2,5-dihydroxybenzoic acid and sodium chloride showed the best performance for MALDI-CID analysis of the dodecamer. In addition, yields of the fragment ions in MALDI-CID spectra were found to be dependent on the chain length distribution. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Unimolecular dissociation of protonated trans -1,4-diphenyl-2-butene-1,4-dione in the gas phase: rearrangement versus simple cleavage

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 17 2006
Lianming Wu
Fragmentation mechanisms of trans -1,4-diphenyl-2-butene-1,4-dione were studied using a variety of mass spectrometric techniques. The major fragmentation pathways occur by various rearrangements by loss of H2O, CO, H2O and CO, and CO2. The other fragmentation pathways via simple alpha cleavages were also observed but accounted for the minor dissociation channels in both a two-dimensional (2-D) linear ion trap and a quadrupole time-of-flight (Q-TOF) mass spectrometer. The elimination of CO2 (rather than CH3CHO or C3H8), which was confirmed by an exact mass measurement using the Q-TOF instrument, represented a major fragmentation pathway in the 2-D linear ion trap mass spectrometer. However, the elimination of H2O and CO becomes more competitive in the beam-type Q-TOF instrument. The loss of CO is observed in both the MS2 experiment of m/z 237 and the MS3 experiment of m/z 219 but via the different transition states. The data suggest that the olefinic double bond in protonated trans -1,4-diphenyl-2-butene-1,4-dione plays a key role in stabilizing the rearrangement transition states and increasing the bond dissociation (cleavage) energy to give favorable rearrangement fragmentation pathways. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Energy Balance of Low Hydrated Starches Transition Under Shear

JOURNAL OF FOOD SCIENCE, Issue 4 2002
C. Barron
ABSTRACT Moistened (25% to 30% total basis) starches were processed on a pre-shearing rheometer under controlled conditions of temperature, residence time, and shear rate. The specific mechanical energy (30 to 1000 J.g -1) was measured and starch transformations assessed. The conversion of compacted native starch into a suspension of granule fragments in a melt was modeled by a simplified energy balance of the shearing zone. A theoretical fragmentation mechanism was proposed with a critical fracture energy of 125 J.m -2. The computed mechanical energy and time necessary for achieving this transition varied in agreement with experimental results, for different operating conditions and starch botanical origins. Interparticle friction influenced granule fragmentation, whereas crystal melting was associated with viscous dissipation. [source]

End-functionalized copolymers prepared by the addition,fragmentation chain-transfer method: Vinyl acetate/methacrylonitrile system

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2001
W. Ken Busfield
Abstract Copolymers of vinyl acetate and methacrylonitrile were prepared by free-radical polymerization in the presence of the chain-transfer agent (CTA) ethyl-,- (t -butanethiomethyl)acrylate. Molecular weight measurements showed that the chain-transfer constants increased with the vinyl acetate content of the comonomer mixture, ranging from 0.42 for methacrylonitrile to 6.3 for the copolymerization of a vinyl acetate-rich monomer mix (89/11). The bulk copolymer composition was not appreciably affected by the amount of CTA used in the copolymerization. The efficiency of the addition,fragmentation mechanism in producing specifically end-functionalized copolymers was investigated with 1H NMR spectroscopy. Spectral peaks consistent with all the expected end groups were observed for all comonomer feeds. Peaks consistent with other end groups were also observed, and these were particularly prominent for copolymers made with lower CTA concentrations. At the highest concentrations used, quantitative measurements of end-group concentrations indicated that 70,80% of the end groups were those expected on the basis of the addition,fragmentation chain-transfer mechanism. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2911,2919, 2001 [source]

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

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 4 2002
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]

Influence of differently ionized species on fragmentation pathways and energetics of a potential adenosine receptor antagonist using a triple quadrupole and a multistage LTQ-OrbitrapÔ FTMS instrument

JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2009
Wendy Zhong
A systematic study was conducted to investigate the influence of differently ionized species on the fragmentation pathways and energetics of a piperazine-containing adenosine by using different cations or anions. Very different fragmentation mechanisms were observed in protonated- versus sodiated-molecules, which indicated that the proton is mobilized to promote the charge-direct fragmentation, whereas Na+ cation was fixed at the heterotricyclic ring structure provoking charge-remote fragment ions. This finding was also supported by the results observed in the fragmentation behaviors in the deprotonated-molecule. The energetics of these fragment ions were also explored by using the breakdown curves obtained from the triple quadrupole and LTQ-OrbitrapÔ instrument. The data indicated that the lowest energy pathways in the protonated-molecule [M+H]+ involve breaking a CN bond connecting an ethylene bridge and heterotricyclic ring structure. The lowest energy pathway is the cleavage of a CO bond connecting the methoxy ethyl group and phenolic oxygen to form a distonic radical ion for a sodiated-molecule [M+Na+]and a deprotonated-molecule [M-H],. The data suggest that by choosing the differently ionized species, one can probe different fragmentation channels that can provide additional structure information for an unknown impurity and possibly degradation product identification. In addition, by comparing the data obtained from triple quadrupole and LTQ-Orbitrap instruments, one can develop further understanding of the differences in the fragmentation behaviors due to the variations in the collision activation-dissociation process. From the side-by-side comparison with the breakdown curves obtained for both instruments, the difference in fragmentation behaviors caused by the difference in dissociation processes that occur in these two types of instruments can be probed. J. Heterocyclic Chem., (2009). [source]

Electron ionization mass spectrometric study of monomeric models of O -polysaccharides of Vibrio cholerae O:1, serotypes Ogawa and Inaba

Electrospray mass spectrometry of stable iminyl nitroxide and nitronyl nitroxide free radicals

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2002
Craig D. Smith
Abstract Electrospray ionization (ESI) mass spectra have been recorded for a range of substituted nitronyl nitroxide and iminyl nitroxide monoradicals and biradicals. Secondary species formed in the ESI source were observed as the dominant ions in both the iminyl nitroxide and nitronyl nitroxide spectra. Daughter ion spectrometry was used to establish fragmentation mechanisms for the nitronyl nitroxide and iminyl nitroxide moieties as well as the secondary species under ESI conditions. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Elucidation of fragmentation mechanisms involving transfer of three hydrogen atoms using a quadrupole time-of-flight mass spectrometer

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 5 2001
Cornelis E. C. A. Hop
[source]

Fission processes following core level excitation in closo -1,2-orthocarborane

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2009
E. Rühl
Abstract Time-of-flight mass analysis with multi-stop coincidence detection was used to study the multi-cation ionic fragmentation of the closo carborane cage molecule closo -1,2-orthocarborane (C2B10H12) following inner-shell excitation in or above the B 1s regime. Electron ion coincidence spectra reveal the cationic products which are formed after core level excitation. Distinct changes in fragmentation pattern are observed as a function of excitation energy. Photoelectron,photoion,photoion coincidence (PEPIPICO) spectroscopy was used to study the dominant fission routes in the core level excitation regime. Series of ion pairs are identified, where asymmetric fission dominates, leading to ion pairs of different mass. Suitable fission and fragmentation mechanisms are discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

New features on the fragmentation patterns of homoisoflavonoids in Ophiopogon japonicus by high-performance liquid chromatography/diode-array detection/electrospray ionization with multi-stage tandem mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 15 2010
Jin Qi
Homoisoflavonoids, a special class of flavonoids, are mainly distributed in the Liliaceae family and have various biological activities. Previously, very little research has been reported on the gas-phase fragmentation patterns of homoisoflavonoids by electrospray ionization mass spectrometry. In this paper, we report the use of high-performance liquid chromatography with a diode-array detector (HPLC-DAD) and electrospray ionization multi-stage tandem mass spectrometry (ESI-MSn) to study the fragmentation behavior of 11 homoisoflavonoid standards and to analyze homoisoflavonoids in Ophiopogon japonicus. In total, 28 homoisoflavonoids (including seven novel constituents) were characterized. The deprotonated [MH], molecules of the homoisoflavonoids containing a saturated C2C3 bond afforded the A or B product ion (base peak) according to whether the B-ring was substituted with a hydroxyl group. For the homoisoflavonoids containing a C-2C-3 double bond, the product ions (A or C ion) were created from the precursor [MH], ion as the base peak when the B-ring was substituted with a hydroxyl group. The homoisoflavonoids carrying a formyl group in the A-ring readily eliminated one molecule of CO to form the product ion [M,+,HCO], (base peak) irrespective whether the C-2C-3 bond was saturated or not. This product ion afforded the [MHCOB-ringCH2,+,H], ion by cleavage of the C3C9 bond. This latter product ion always appeared in tandem mass (MS/MS) spectra of type I homoisoflavonoids. The common features of flavonoids observed during the gas-phase fragmentation mechanisms were the loss of the following groups: 15,Da (CH3), 18,Da (H2O), 28,Da (CO), 44,Da (CO2) and 46,Da (CH2O2). A retro-Diels-Alder (RDA)-like cleavage was also observed for the homoisoflavonoids. The different gas-phase fragmentation routes were characterized for the deprotonated molecules obtained from the various homoisoflavonoids and collision-induced dissociation (CID) fragmentation differences were noted for the different locations of the various substituents. In conclusion, we can say that this study allowed us to structurally elucidate and identify homoisoflavonoids distributed in related plants and their complex prescriptions. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Electrospray ionization tandem mass spectrometry fragmentation of protonated flavone and flavonol aglycones: a re-examination

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 2 2009
Gonçalo C. Justino
Flavonoids are important phytochemicals which have been intensively studied in the last decades in view of their antioxidant activity, which is of particular importance in the case of flavones and flavonols, that differ in a single 3-OH group. Mass spectrometry has been used to elucidate the structures of many types of flavonoids and their metabolites. The work we present here is focused on the electrospray ionization tandem mass spectrometry (ESI-MS/MS) analysis of flavone and flavonols aglycones. Their fragmentation mechanisms in the positive ion mode are described and compared with previously reported mechanisms. We analyzed flavonoid derivatives produced by reaction of the flavonoids with chemically synthesized hypohalous acids (HOCl, HOBr and HOI) and peroxynitrite, reactive species involved in the inflammatory response. All the proposed pathways have been analyzed using computational chemistry methods in order to seek for possible variations and establish the most plausible ones. We observed that the losses of one and two CO molecules can be useful in terms of antioxidant activity prediction. Losses of one and two C2H2O groups are also informative in terms of structure and activity predictions. The retro-Diels-Alder fragmentations, and subsequent neutral losses, were reviewed and, according to our calculations, the most plausible structures for the product ions were established. These fingerprints will be of great value for differentiating flavonoids from other compounds in complex biological mixtures and for a thorough structural identification of flavonoid aglycones and their invivo metabolites. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Mass spectrometric characterization of 4-oxopentanoic acid and gas-phase ion fragmentation mechanisms studied using a triple quadrupole and time-of-flight analyzer hybrid system and density functional theory

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2008
Basem Kanawati
4-Oxopentanoic acid was characterized experimentally by electrospray ionization using a triple quadrupole and time-of-flight analyzer hybrid system. This compound was chosen as a model substance for small organic compounds bearing an acetyl and a carboxyl group. Collision-induced dissociation experiments at different activation energies were performed to elucidate possible fragmentation pathways. These pathways were also studied on the theoretical level using density functional theory (DFT) B3LYP/6-311++G(3df,3pd)//B3LYP/6-31+G(d)+ZPVE calculations. CO2 ejection from the [M,H], anion of 4-oxopentanoic acid was observed and the fragmentation pathway studied by DFT reveals a new concerted mechanism for CO2 elimination accompanied by an intramolecular proton transfer within a pentagonal transition state structure. Successive elimination of water and CO from the [M,H], anion of 4-oxopentanoic acid was also observed. A rearrangement in the primary deprotonated ketene anion produced after water elimination was found on the theoretical level and leads to CO elimination from the primary product anion [M,H,H2O],. Energy diagrams along the reaction coordinates of the fragmentation pathways are presented and discussed in detail. Mulliken charge distributions of some important structures are presented. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Electrospray ionization tandem mass spectrometric characteristics and fragmentation mechanisms of distamycin analogues

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2002
Feili Tang
The electrospray ionization tandem mass spectrometric (ESI-MS/MS) characteristics and fragmentation mechanisms of eight distamycin analogues containing N -methylpyrrole and N -methylimidazole were investigated. The members of two isomeric groups of distamycin analogues with the same elemental composition can be distinguished by MS/MS spectra of protonated molecules and of significant fragment ions. Copyright © 2002 John Wiley & Sons, Ltd. [source]