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1.
Xiao Zhou Yali Lu Wenjing Wang Babak Borhan Gavin E. Reid 《Journal of the American Society for Mass Spectrometry》2010,21(8):1339-1351
Protein surface accessible residues play an important role in protein folding, protein-protein interactions and protein-ligand
binding. However, a common problem associated with the use of selective chemical labeling methods for mapping protein solvent
accessible residues is that when a complicated peptide mixture resulting from a large protein or protein complex is analyzed,
the modified peptides may be difficult to identify and characterize amongst the largely unmodified peptide population (i.e.,
the ‘needle in a haystack’ problem). To address this challenge, we describe here the development of a strategy involving the
synthesis and application of a novel ‘fixed charge’ sulfonium ion containing lysine-specific protein modification reagent,
S,S′-dimethylthiobutanoylhydroxysuccinimide ester (DMBNHS), coupled with capillary HPLC-ESI-MS, automated CID-MS/MS, and data-dependant
neutral loss mode MS3 in an ion trap mass spectrometer, to map the surface accessible lysine residues in a small model protein, cellular retinoic
acid binding protein II (CRABP II). After reaction with different reagent:protein ratios and digestion with Glu-C, modified
peptides are selectively identified and the number of modifications within each peptide are determined by CID-MS/MS, via the
exclusive neutral loss(es) of dimethylsulfide, independently of the amino acid composition and precursor ion charge state
(i.e., proton mobility) of the peptide. The observation of these characteristic neutral losses are then used to automatically
‘trigger’ the acquisition of an MS3 spectrum to allow the peptide sequence and the site(s) of modification to be characterized. Using this approach, the experimentally
determined relative solvent accessibilities of the lysine residues were found to show good agreement with the known solution
structure of CRABP II. 相似文献
2.
The application of electrospray ionization (ESI) ion trap mass spectrometry in the characterization of O-glucuronide conjugates of some drugs in urine is described. The conjugated metabolites formed in rabbit and human were separated
by reversed-phase high-performance liquid chromatography (HPLC) and characterized by multi-stage mass spectrometry (MSn) experiments in negative ion mode. The ESI mass spectra showed a deprotonated molecule [M–H]–, which was chosen as precursor ion. Collision-induced dissociation (CID) of [M–H]– in MSn experiments resulted in the appearance of glucuronate ‘fingerprint’ ions at m/z 175 and 113 as well as prominent aglycone
ions which were the same as those produced from authentic specimens. This information can be used to identify this type of
compound directly without the need for derivatization or hydrolysis of enzymes, providing a rapid and specific method for
guiding the isolation and characterization of similar compounds in complex matrices with LC/MS.
Received: 25 January 1999 / Revised: 19 April 1999 / Accepted: 13 May 1999 相似文献
3.
Smith SA Kalcic CL Safran KA Stemmer PM Dantus M Reid GE 《Journal of the American Society for Mass Spectrometry》2010,21(12):2031-2040
To develop an improved understanding of the regulatory role that post-translational modifications (PTMs) involving phosphorylation
play in the maintenance of normal cellular function, tandem mass spectrometry (MS/MS) strategies coupled with ion activation
techniques such as collision-induced dissociation (CID) and electron-transfer dissociation (ETD) are typically employed to
identify the presence and site-specific locations of the phosphate moieties within a given phosphoprotein of interest. However,
the ability of these techniques to obtain sufficient structural information for unambiguous phosphopeptide identification
and characterization is highly dependent on the ion activation method employed and the properties of the precursor ion that
is subjected to dissociation. Herein, we describe the application of a recently developed alternative ion activation technique
for phosphopeptide analysis, termed femtosecond laser-induced ionization/dissociation (fs-LID). In contrast to CID and ETD,
fs-LID is shown to be particularly suited to the analysis of singly protonated phosphopeptide ions, yielding a wide range
of product ions including a, b, c, x, y, and z sequence ions, as well as ions that are potentially diagnostic of the positions of phosphorylation (e.g., ‘a
n+1–98’). Importantly, the lack of phosphate moiety losses or phosphate group ‘scrambling’ provides unambiguous information
for sequence identification and phosphorylation site characterization. Therefore, fs-LID-MS/MS can serve as a complementary
technique to established methodologies for phosphoproteomic analysis. 相似文献
4.
Li Cui Ipek Yapici Babak Borhan Gavin E. Reid 《Journal of the American Society for Mass Spectrometry》2014,25(1):141-148
Abundant neutral losses of 98 Da are often observed upon ion trap CID-MS/MS of protonated phosphopeptide ions. Two competing fragmentation pathways are involved in this process, namely, the direct loss of H3PO4 from the phosphorylated residue and the combined losses of HPO3 and H2O from the phosphorylation site and from an additional site within the peptide, respectively. These competing pathways produce product ions with different structures but the same m/z values, potentially limiting the utility of CID-MS3 for phosphorylation site localization. To quantify the relative contributions of these pathways and to determine the conditions under which each pathway predominates, we have examined the ion trap CID-MS/MS fragmentation of a series of regioselective 18O-phosphate ester labeled phosphopeptides prepared using novel solution-phase amino acid synthesis and solid-phase peptide synthesis methodologies. By comparing the intensity of the –100 Da (–H3PO3 18O) versus –98 Da (–[HPO3 + H2O]) neutral loss product ions formed upon MS/MS, quantification of the two pathways was achieved. Factors that affect the extent of formation of the competing neutral losses were investigated, with the combined loss pathway predominantly occurring under conditions of limited proton mobility, and with increased combined losses observed for phosphothreonine compared with phosphoserine-containing peptides. The combined loss pathway was found to be less dominant under ion activation conditions associated with HCD-MS/MS. Finally, the contribution of carboxylic acid functional groups and backbone amide bonds to the water loss in the combined loss fragmentation pathway was determined via methyl esterification and by examination of a phosphopeptide lacking side-chain hydroxyl groups. Figure
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5.
Eric S. Simon Panagiotis G. Papoulias Philip C. Andrews 《Journal of the American Society for Mass Spectrometry》2010,21(9):1624-1632
The fragmentation characteristics of peptides derivatized at the side-chain ε-amino group of lysyl residues via reductive
amination with benzaldehyde have been examined using collision-induced dissociation (CID) tandem mass spectrometry. The resulting
MS/MS spectra exhibit peaks representing product ions formed from two independent fragmentation pathways. One pathway results
in backbone fragmentation and commonly observed sequence ion peaks. The other pathway corresponds to the unsymmetrical, heterolytic
cleavage of the Cζ-Nε bond that links the benzyl derivative to the side-chain lysyl residue. This results in the elimination of the derivative
as a benzylic or tropylium carbocation and a (n − l)+-charged peptide product (where n is the precursor ion charge state). The frequency of occurrence of the elimination pathway
increases with increasing charge of the precursor ion. For the benzylmodified tryptic peptides analyzed in this study, peaks
representing products from both of these pathways are observed in the MS/MS spectra of doubly-charged precursor ions, but
the carbocation elimination pathway occurs almost exclusively for triply-charged precursor ions. The experimental evidence
presented herein, combined with molecular orbital calculations, suggests that the elimination pathway is a charge-directed
reaction contingent upon protonation of the secondary ε-amino group of the benzyl-derivatized lysyl side chain. If the secondary
ε-amine is protonated, the elimination of the carbocation is observed. If the precursor is not protonated at the secondary
ε-amine, backbone fragmentation persists. The application of appropriately substituted benzyl analogs may allow for selective
control over the relative abundance of product ions generated from the two pathways. 相似文献
6.
Zou X Liu D Zhong L Yang B Lou Y Hu B Yin Y 《Analytical and bioanalytical chemistry》2011,401(4):1251-1261
In this study, we describe a method for highly specific enrichment of phosphopeptides with multifunctional chitosan–glycidyl
methacrylate (GMA)–iminodiacetic acid (IDA)–Fe (III) nanospheres for direct analysis by matrix-assisted laser desorption–ionization
mass spectrometry (MALDI-MS). This is the first time that chitosan has been used to create nanospheres support material for
selective enrichment of phosphopeptides by modification with GMA, derivatization with IDA, and loading with Fe (III) ions.
Chitosan-GMA-IDA-Fe (III) nanospheres with a diameter of 20 to 100 nm have multifunctional chemical moieties which confer
unique properties, good dispersibility in highly acidic binding buffers, as well as good biocompatibility and chemical stability
which improves their specific interaction with phosphopeptides using various types of acid binding buffers. The process of
enrichment is very simple, quick, efficient, and specific. Its high specificity and efficiency for purification of phosphopeptides
is reflected in the very low and substoichiometric amounts of phosphopeptides which can be detected, in quantities as low
as 1:3,000 M ratios. Compared with other state-of the-art technologies such as the use of conventional Fe3+-IMAC and TiO2, these chitosan nanosphere techniques show superior specificity and sensitivity. Moreover, the resultant chitosan-GMA-IDA-Fe3+ nanosphere-absorbed phosphopeptides can be either directly analyzed by MALDI-TOF MS analysis or eluted and further analyzed
by nano-LC-MS/MS. 相似文献
7.
Zhang L Xu J Sun L Ma J Yang K Liang Z Zhang L Zhang Y 《Analytical and bioanalytical chemistry》2011,399(10):3399-3405
In this study, zirconium oxide (ZrO2) aerogel was synthesized via a green sol–gel approach, with zirconium oxychloride, instead of the commonly used alkoxide
with high toxicity, as the precursor. With such material, phosphopeptides from the digests of 4 pmol of β-casein with the
coexistence of 100 times (mol ratio) BSA could be selectively captured, and identified by MALDI-TOF MS. Due to the large surface
area (416.0 m2 g−1) and the mesoporous structure (the average pore size of 10.2 nm) of ZrO2 aerogel, a 20-fold higher loading capacity for phosphopeptide, YKVPQLEIVPN[pS]AEER (MW 1952.12), was obtained compared to
that of commercial ZrO2 microspheres (341.5 vs. 17.87 mg g−1). The metal oxide aerogel was further applied in the enrichment of phosphopeptides from 100 ng nonfat milk, and 17 phosphopeptides
were positively identified, with a 1.5-fold improvement in phosphopeptide detection compared with previously reported results.
These results demonstrate that ZrO2 aerogel can be a powerful enrichment material for phosphoproteome study. 相似文献
8.
Kaddouri A. Gronchi P. Centola P. Del Rosso R. 《Journal of Thermal Analysis and Calorimetry》2000,62(3):609-619
Ni–La/SiO2 catalysts were prepared by using a new metal organic precursor M(OC3H7)n, dissolved in organic solvent, hydrolysed and finally condensed to form inorganic polymers containing M–O–M or M–(μOH)–M
linkages. An optimal distribution of both the active phase ‘Ni’ and the promoter ‘La2O3’ was ensured by addition of their corresponding salts, previously dissolved in propionic acid, to a silica solution prior
to gelation. After drying under vacuum the precursor was submitted to thermal treatment in air at 600°C with a heating rate
of 1°C min–1.
The precursors and the corresponding catalysts were characterised by various techniques (TG-DTA, XRD, FTIR, TEM, BET and porosimetry)
and tested for methane dry reforming.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
Laura Luosujärvi Markus Haapala Mario Thevis Ville Saarela Sami Franssila Raimo A. Ketola Risto Kostiainen Tapio Kotiaho 《Journal of the American Society for Mass Spectrometry》2010,21(2):310-316
A gas chromatography-microchip atmospheric pressure photoionization-mass spectrometric (GC-μAPPI-MS) method was developed and used for the analysis of three 2-quinolinone-derived selective androgen receptor modulators
(SARMs). SARMs were analyzed from spiked urine samples, which were hydrolyzed and derivatized with N-methyl-N-(trimethylsilyl)trifluoroacetamide before analysis. Trimethylsilyl derivatives of SARMs formed both radical cations (M+•) and protonated molecules ([M + H]+) in photoionization. Better signal-to-noise ratios (S/N) were obtained in MS/MS analysis using the M+• ions as precursor ions than using the [M + H]+ ions, and therefore the M+• ions were selected for the precursor ions in selected reaction monitoring (SRM) analysis. Limits of detection (LODs) with
the method ranged from 0.01 to 1 ng/mL, which correspond to instrumental LODs of 0.2–20 pg. Limits of quantitation ranged
from 0.03 to 3 ng/mL. The mass spectrometric response to the analytes was linear (R ≥ 0.995) from the LOQ concentration level
up to 100 ng/mL concentration, and intra-day repeatabilities were 5%–9%. In addition to the GC-μAPPI-MS study, the proof-of-principle of gas chromatography-microchip atmospheric pressure chemical ionization-Orbitrap MS
(GC-μAPCI-Orbitrap MS) was demonstrated. 相似文献
10.
L. R. Gonsalves S. C. Mojumdar V. M. S. Verenkar 《Journal of Thermal Analysis and Calorimetry》2011,104(3):869-873
Cobalt zinc ferrite, Co0.8Zn0.2Fe2O4, nanoparticles have been synthesized via autocatalytic decomposition of the precursor, cobalt zinc ferrous fumarato hydrazinate.
The X-ray powder diffraction of the ‘as prepared’ oxide confirms the formation of single phase nanocrystalline cobalt zinc
ferrite nanoparticles. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric and differential
thermal analysis. The precursor has also been characterized by FTIR, and chemical analysis and its chemical composition has
been determined as Co0.8Zn0.2Fe2(C4H2O4)3·6N2H4. The Curie temperature of the ‘as-prepared oxide’ was determined by AC susceptibility measurements. 相似文献
11.
Tomas Nilsson Eriel Martínez Angeles Manresa Ernst H. Oliw 《Rapid communications in mass spectrometry : RCM》2010,24(6):777-783
Pseudomonas aeruginosa is an opportunistic pathogen, which oxidizes oleic acid to 7(S),10(S)‐dihydroxy‐8(E)‐octadecenoic acid (7,10‐(OH)2‐18:1) of biological and industrial interest. Electrospray tandem mass spectrometric (MS/MS) analysis of hydroxylated fatty acids usually generates characteristic fragments containing the carboxylate anion and formed by α‐cleavage at the oxidized carbon. These fragments indicate the positions of the hydroxyl group. In contrast, liquid chromatography (LC)/MS/MS analysis of 7,10‐(OH)2‐18:1 yielded a series of other ions with structural information. To study the fragmentation mechanism, we prepared 2H‐ and 18O‐labeled isotopomers. We also performed MS3 analysis of the major ions, and for comparison we generated the corresponding 7,10‐dihydroxy metabolites of 16:1n‐7, 18:2n‐6, and 20:1n‐11 with a protein extract of P. aeruginosa. The MS/MS spectra of 7,10‐(OH)2‐18:1 and its isotopomers, 7,10‐(OH)2‐16:1, and 7,10‐(OH)2‐20:1, contained a series of prominent fragments that all hold the omega end. The 8,9‐double bond was not essential for this fragmentation, as 7,10‐(OH)2‐18:0, and its isotopomers, formed essentially the same fragments in the lower mass range. In contrast, 7,10‐dihydroxy‐8(E),12(Z)‐octadecadienoic acid (7,10‐(OH)2‐18:2) fragmented by α‐cleavage at the oxidized carbons with formation of carboxylate anions. Our results demonstrate that C16–C20 fatty acids with a 7,10‐dihydroxy‐8(E) functionality undergo charge‐driven fragmentation after charge migration to the ω‐end, whereas the main ions of 7,10‐(HO)2‐18:2 retain charge at the carboxyl group. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
12.
Peter Max Gehrig Bernd Roschitzki Dorothea Rutishauser Sonja Reiland Ralph Schlapbach 《Rapid communications in mass spectrometry : RCM》2009,23(10):1435-1445
In order to investigate gas‐phase fragmentation reactions of phosphorylated peptide ions, matrix‐assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) tandem mass (MS/MS) spectra were recorded from synthetic phosphopeptides and from phosphopeptides isolated from natural sources. MALDI‐TOF/TOF (TOF: time‐of‐flight) spectra of synthetic arginine‐containing phosphopeptides revealed a significant increase of y ions resulting from bond cleavages on the C‐terminal side of phosphothreonine or phosphoserine. The same effect was found in ESI‐MS/MS spectra recorded from the singly charged but not from the doubly charged ions of these phosphopeptides. ESI‐MS/MS spectra of doubly charged phosphopeptides containing two arginine residues support the following general fragmentation rule: Increased amide bond cleavage on the C‐terminal side of phosphorylated serines or threonines mainly occurs in peptide ions which do not contain mobile protons. In MALDI‐TOF/TOF spectra of phosphopeptides displaying N‐terminal fragment ions, abundant b–H3PO4 ions resulting from the enhanced dissociation of the pSer/pThr–X bond were detected (X denotes amino acids). Cleavages at phosphoamino acids were found to be particularly predominant in spectra of phosphopeptides containing pSer/pThr–Pro bonds. A quantitative evaluation of a larger set of MALDI‐TOF/TOF spectra recorded from phosphopeptides indicated that phosphoserine residues in arginine‐containing peptides increase the signal intensities of the respective y ions by almost a factor of 3. A less pronounced cleavage‐enhancing effect was observed in some lysine‐containing phosphopeptides without arginine. The proposed peptide fragmentation pathways involve a nucleophilic attack by phosphate oxygen on the carbon center of the peptide backbone amide, which eventually leads to cleavage of the amide bond. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
13.
Aaron R. Ledvina Christopher M. Rose Graeme C. McAlister John E. P. Syka Michael S. Westphall Jens Griep-Raming Jae C. Schwartz Joshua J. Coon 《Journal of the American Society for Mass Spectrometry》2013,24(11):1623-1633
We describe the implementation and characterization of activated ion electron transfer dissociation (AI-ETD) on a hybrid QLT-Orbitrap mass spectrometer. AI-ETD was performed using a collision cell that was modified to enable ETD reactions, in addition to normal collisional activation. The instrument manifold was modified to enable irradiation of ions along the axis of this modified cell with IR photons from a CO2 laser. Laser power settings were optimized for both charge (z) and mass to charge (m/z) and the instrument control firmware was updated to allow for automated adjustments to the level of irradiation. This implementation of AI-ETD yielded 1.6-fold more unique identifications than ETD in an nLC-MS/MS analysis of tryptic yeast peptides. Furthermore, we investigated the application of AI-ETD on large scale analysis of phosphopeptides, where laser power aids ETD, but can produce b- and y-type ions because of the phosphoryl moiety’s high IR adsorption. nLC-MS/MS analysis of phosphopeptides derived from human embryonic stem cells using AI-ETD yielded 2.4-fold more unique identifications than ETD alone, demonstrating a promising advance in ETD sequencing of PTM containing peptides. Figure
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14.
Comparative MS/MS studies of singly and doubly charged electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) precursor peptide ions are described. The spectra from these experiments have been evaluated with particular emphasis on the data quality for subsequent data processing and protein/amino acid sequence identification. It is shown that, once peptide ions are formed by ESI or MALDI, their charge state, as well as the collision energy, is the main parameter determining the quality of collision-induced dissociation (CID) MS/MS fragmentation spectra of a given peptide. CID-MS/MS spectra of singly charged peptides obtained on a hybrid quadrupole orthogonal time-of-flight mass spectrometer resemble very closely spectra obtained by matrix-assisted laser desorption/ionization post-source decay time-of-flight mass spectrometry (MALDI-PSD-TOFMS). On the other hand, comparison of CID-MS/MS spectra of either singly or doubly charged ion species shows no dependence on whether ions have been formed by ESI or MALDI. This observation confirms that, at the time of precursor ion selection, further mass analysis is effectively decoupled from the desorption/ionization event. Since MALDI ions are predominantly formed as singly charged species and ESI ions as doubly charged, the associated difference in the spectral quality of MS/MS spectra as described here imposes direct consequences on data processing, database searching using ion fragmentation data, and de novo sequencing when ionization techniques are changed. 相似文献
15.
Ming-Lai Fu Norma L. Rangel Richard D. Adams Jorge M. Seminario 《Journal of Cluster Science》2010,21(4):867-878
Abstract
Thiacalix[4]arenes are a unique family of polydentate ligands that offer a combination of four soft sulfur atoms together with four hard phenol oxygen atoms for binding to metal ions. In this study, the tetranuclear cadmium (II) complex Cd4II(tca)2·1.5CH2Cl2 (tca4− = tetra-anionic p-tert-butylthiacalix[4]arene) (1) was synthesized by reaction of a deprotonated p-tert-butylthiacalix[4]arene and various CdII salts. The structure of 1 was established by single crystal X-ray diffraction analysis. The neutral complex 1 contains a square arrangement of four cadmium (II) ions sandwiched between two tca4− ligands that have a ‘cone’ conformation similar to that of the free ligand. The absorption and emission properties of the free ligand H4tca and complex 1 have been recorded and explained by DFT calculations of the molecular orbitals and electronic transitions between them. 相似文献16.
Vladislav V. Lobodin Joshua J. Savory Nathan K. Kaiser Paul W. Dunk Alan G. Marshall 《Journal of the American Society for Mass Spectrometry》2013,24(2):213-221
We report the first charge reversal experiments performed by tandem-in-time rather than tandem-in-space MS/MS. Precursor odd-electron anions from fullerene C60, and even-electron ions from 2,7-di-tert-butylfluorene-9-carboxylic acid and 3,3′-bicarbazole were converted into positive product ions (–CR+) inside the magnet of a Fourier transform ion cyclotron resonance mass spectrometer. Charge reversal was activated by irradiating precursor ions with high energy electrons or UV photons: the first reported use of those activation methods for charge reversal. We suggest that high energy electrons achieve charge reversal in one step as double electron transfer, whereas UV-activated –CR+ takes place stepwise through two single electron transfers and formally corresponds to a neutralization-reionization (–NR+) experiment. 相似文献
17.
W. B. Liang R. W. Lenz F. E. Karasz 《Journal of polymer science. Part A, Polymer chemistry》1990,28(10):2867-2875
Poly(2-methoxyphenylene vinylene) has been synthesized by a four step reaction sequence beginning with the bromination of 2,5-dimethylanisole and proceeding to the formation of an intermediate sulfonium salt precursor polymer. The infrared and UV-visible spectra of the PPV derivative asymmetrically substituted on the phenyl ring are presented. Films of poly(2-methoxyphenylene vinylene) can be doped with iodine to give a conductivity of 1 S cm?1. Films doped with AsF5 exhibited activated charge transport behavior with room temperature conductivities of about 100 S cm?1. 相似文献
18.
Caroline Barrère Marie Hubert-Roux Carlos Afonso Majed Rejaibi Nasreddine Kebir Nicolas Désilles Laurence Lecamp Fabrice Burel Corinne Loutelier-Bourhis 《Analytica chimica acta》2014
The structural characterization of polyamides (PA) was achieved by tandem mass spectrometry (MS/MS) with a laser induced dissociation (LID) strategy. Because of interferences for precursor ions selection, two chemical modifications of the polymer end groups were proposed as derivatization strategies. The first approach, based on the addition of a trifluoroacetic acid (TFA) molecule, yields principally to complementary bn and yn product ions. This fragmentation types, analogous to those obtained with peptides or other PA, give only poor characterization of polymer end-groups [1]. A second approach, based on the addition of a basic diethylamine (DEA), permits to fix the charge and favorably direct the fragmentation. In this case, bn ions were not observed. The full characterization of ω end group structure was obtained, in addition to the expected yn and consecutive fragment ions. 相似文献
19.
U. B. Gawas V. M. S. Verenkar S. C. Mojumdar 《Journal of Thermal Analysis and Calorimetry》2011,104(3):879-883
Ni0.6Zn0.4Fe2O4 nano-particles have been synthesized by self-propagating auto-combustion of nickel zinc ferrous fumarato-hydrazinate complex.
The precursor complex has been characterized by chemical analysis, IR, AAS, thermal analysis and isothermal mass loss studies.
The precursor on ignition undergoes self-propagating auto combustion to give Ni0.6Zn0.4Fe2O4. The X-ray diffraction studies confirmed the single phase formation of nano-size ‘as synthesized’ Ni0.6Zn0.4Fe2O4. TEM observation showed the average particle size to be 20 nm. Infrared and magnetization studies were also carried out on
the ‘as synthesized’ Ni0.6Zn0.4Fe2O4. The lower value of saturation magnetization and higher Curie temperature of ‘as synthesized’ ferrite also hint at the nano
size nature. 相似文献
20.
Wisut Wichitnithad Terence J. McManus Patrick S. Callery 《Rapid communications in mass spectrometry : RCM》2010,24(17):2547-2553
Isobaric product ions cannot be differentiated by exact mass determinations, although in some cases deuterium labeling can provide useful structural information for identifying isobaric ions. Proposed fragmentation pathways of fentanyl were investigated by electrospray ionization ion trap mass spectrometry coupled with deuterium labeling experiments and spectra of regiospecific deuterium labeled analogs. The major product ion of fentanyl under tandem mass spectrometry (MS/MS) conditions (m/z 188) was accounted for by a neutral loss of N‐phenylpropanamide. 1‐(2‐Phenylethyl)‐1,2,3,6‐tetrahydropyridine (1) was proposed as the structure of the product ion. However, further fragmentation (MS3) of the fentanyl m/z 188 ion gave product ions that were different from the product ion in the MS/MS fragmentation of synthesized 1, suggesting that the m/z 188 product ion from fentanyl includes an isobaric structure different from the structure of 1. MS/MS fragmentation of fentanyl in deuterium oxide moved one of the isobars to 1 Da higher mass, and left the other isobar unchanged in mass. Multistage mass spectral data from deuterium‐labeled proposed isobaric structures provided support for two fragmentation pathways. The results illustrate the utility of multistage mass spectrometry and deuterium labeling in structural assignment of isobaric product ions. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献