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1.
Williams BJ Barlow CK Kmiec KL Russell WK Russell DH 《Journal of the American Society for Mass Spectrometry》2011,22(9):1622-1630
We present here a study of the collision induced dissociation (CID) of deprotonated cysteic acid containing peptides produced
by MALDI. The effect of cysteic acid (Cox) position is interrogated by considering the positional isomers, CoxLVINVLSQG, LVINVLSQGCox, and LVINVCoxLSQG. Although considerable variation between the CID spectra is observed, the mechanistic picture that emerges involves charge
retention at the deprotonated cysteic acid side chain. Fragmentation occurs in the proximity of the cysteic acid group by
charge directed mechanisms as well as remote from this group to form ions, which may be rationalized by charge remote mechanisms.
Additionally, the formation of the SO3–• ion is observed in all cases. Fragmentation of CoxLVINVLSQCox provides both N- and C-terminal, y and b ions, respectively indicating that the negative charge may be retained at either
of the cysteic acids; however, there is some evidence that charge retention at the C-terminal cysteic acid may be preferred.
Fragmentation of tryptic type peptides containing a C-terminal arginine or lysine residue is considered through comparison
of three peptides CoxLVINKLSQG, CoxLVINVLSQK, and CoxLVINVLSQR. Lastly, we rationalize the formation of b
n–1 + H2O and a
n–1 ions through a mechanism involving rearrangement of the C-terminal residue to form a mixed anhydride intermediate. 相似文献
2.
Zhaoxiang Wu Francisco A. Fernandez-Lima David H. Russell 《Journal of the American Society for Mass Spectrometry》2010,21(4):522-533
Matrix assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) and theoretical calculations
[density functional theory (DFT)] were utilized to investigate the influence of cysteine side chain on Cu+ binding to peptides and how Cu+ ions competitively interact with cysteine (−SH/SO3H) versus arginine. Results from theoretical and experimental (fragmentation reactions) studies on [M+Cu]+ and [M+2Cu−H]+ ions suggest that cysteine side chains (−SH) and cysteic acid (−SO3H) are important Cu+ ligands. For example, we show that Cu+ ions are competitively coordinated to the −SH or SO3H groups; however, we also present evidence that the proton of the SH/SO3H group is mobile and can be transferred to the arginine guanidine group. For [M+2Cu−H]+ ions, deprotonation of the −SH/SO3H group is energetically more favorable than that of the carboxyl group, and the resulting thiolate/sulfonate group plays
an important role in the coordination structure of [M+2Cu−H]+ ions, as well as the fragmentation patterns. 相似文献
3.
Zhaoxiang Wu Francisco A. Fernandez-Lima Lisa M. Perez David H. Russell 《Journal of the American Society for Mass Spectrometry》2009,20(7):1263-1271
The dinuclear copper complex (α-cyano-4-hydroxycinnamic acid (CHCA) copper salt (CHCA)4Cu2), synthesized by reacting CHCA with copper oxide (CuO), yields increased abundances of [M + xCu − (x−1)H]+ (x = 1–6) ions when used as a matrix for matrix-assisted laser desorption ionization (355 nm Nd:YAG laser). The yield of
[M + xCu − (x−1)H]+ (x = 1∼6) ion is much greater than that obtained by mixing peptides with copper salts or directly depositing peptides onto
oxidized copper surfaces. The increased ion yields for [M + xCu − (x−1)H]+ facilitate studies of biologically important copper binding peptides. For example, using this matrix we have investigated
site-specific copper binding of several peptides using fragmentation chemistry of [M + Cu]+ and [M + 2Cu − H]+ ions. The fragmentation studies reveal interesting insight on Cu binding preferences for basic amino acids. Most notable
is the fact that the binding of a single Cu+ ion and two Cu+ ions are quite different, and these differences are explained in terms of intramolecular interactions of the peptide-Cu ionic
complex. 相似文献
4.
The use of 5-formylsalicylic acid (5-FSA) and 5-nitrosalicylic acid (5-NSA) as novel matrices for in-source decay (ISD) of
peptides in matrix-assisted laser desorption/ionization (MALDI) is described. The use of 5-FSA and 5-NSA generated a- and x-series ions accompanied by oxidized peptides [M – 2 H + H]+. The preferential formation of a- and x-series ions was found to be dependent on the hydrogen-accepting ability of matrix. The hydrogen-accepting ability estimated
from the ratio of signal intensity of oxidized product [M – 2 H + H]+ to that of non-oxidized protonated molecule [M + H]+ of peptide was of the order 5-NSA > 5-FSA > 5-aminosalicylic acid (5-ASA) ≒ 2,5-dihydroxyl benzoic acid (2,5-DHB) ≒ 0. The
results suggest that the hydrogen transfer reaction from peptide to 5-FSA and 5-NSA occurs during the MALDI-ISD processes.
The hydrogen abstraction from peptides results in the formation of oxidized peptides containing a radical site on the amide
nitrogen with subsequent radical-induced cleavage at the
\textCa - \textC {{\text{C}}_{\alpha }} - {\text{C}} bond, leading to the formation of a- and x-series ions. The most significant feature of MALDI-ISD with 5-FSA and 5-NSA is the specific cleavage of the
\textCa - \textC {{\text{C}}_{\alpha }} - {\text{C}} bond of the peptide backbone without degradation of side-chain and post-translational modifications (PTM). The matrix provides
a useful complementary method to conventional MALDI-ISD for amino acid sequencing and site localization of PTMs in peptides. 相似文献
5.
Yizhak Marcus 《Journal of solution chemistry》2009,38(5):513-516
In concentrated salt solutions the average distances between the ions, d
av=1.1844⋅(∑ν
i
c
i
)−1/3 nm, are commensurate with the sizes of the solvated ions, so that no ‘bulk solvent’ remains. This is illustrated with two
saturated aqueous solutions, where 16.67 mol⋅dm−3 CsF at 75 °C has d
av(Cs–F)=0.368 nm and 14.54 mol⋅dm−3 LiI at 80 °C has d
av(Li–I)=0.385 nm. The minimal distance required for the bare ions (sum of their radii) are 0.303 nm for CsF and 0.289 nm for
LiI. Hence no water molecule, diameter 0.276 nm, can be fitted between the ions to form linear or slightly bent hydrogen bonds.
Some recent work ignoring such constraints, even in 3–6 mol⋅dm−3 solutions, is criticized on this account. 相似文献
6.
Motoshi Sakakura Mitsuo Takayama 《Journal of the American Society for Mass Spectrometry》2010,21(6):979-988
The use of 5-aminosalicylic acid (5-ASA) as a new matrix for in-source decay (ISD) of peptides including mono- and di-phosphorylated
peptides in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is described. The use of 5-ASA in MALDI-ISD
has been evaluated from several standpoints: hydrogen-donating ability, the outstanding sharpness of molecular and fragment
ion peaks, and the presence of interference peaks such as metastable peaks and multiply charged ions. The hydrogen-donating
ability of several matrices such as α-cyano-4-hydroxycinnamic acid (CHCA), 2,5-dihydroxybenzoic acid (2,5-DHB), 1,5-diaminonaphthalene
(1,5-DAN), sinapinic acid (SA), and 5-ASA was evaluated by using the peak abundance of a reduction product [M + 2H + H]+ to that of non-reduced protonated molecule [M + H]+ of the cyclic peptide vasopressin which contains a disulfide bond (S-S). The order of hydrogendonating ability was 1,5-DAN
> 5-ASA > 2,5-DHB > SA = CHCA. The chemicals 1,5-DAN and 5-ASA in particular can be classified as reductive matrices. 5-ASA
gave peaks with higher sharpness for protonated molecules and fragment ions than other matrices and did not give any interference
peaks such as multiply-protonated ions and metastable ions in the ISD mass spectra of the peptides used. Particularly, 1,5-DAN
and 5-ASA gave very little metastable peaks. This indicates that 1,5-DAN and 5-ASA are more “cool” than other matrices. The
1,5-DAN and 5-ASA can therefore be termed “reductive cool” matrix. Further, it was confirmed that ISD phenomena such as N-Cα
bond cleavage and reduction of S-S bond is a single event in the ion source. The characteristic fragmentations, which form
a− and (a + 2)-series ions, [M + H − 15]+, [M + H − 28]+, and [M + H − 44]+ ions in the MALDI-ISD are described. 相似文献
7.
V. K. Mavrodiev I. I. Furlei Sh. Sultanov Yu. S. Nekrasov Yu. A. Belousov 《Russian Chemical Bulletin》1997,46(6):1113-1115
Negative ion mass spectra of cyclopentadienyltricarbonylmanganese and-rhenium derivatives RC5H4M(CO)3 (R=H, CN, COOH, COMe, COOMe, CH2OH, CHO; M=Mn, Re) were studied. The subsequent detachment of carbonyl groups is the main process of the fragmentation of
these compounds under the conditions of the resonance capture of electrons. On going fron the rhenium complexes to manganese
derivatives, the maxima of the yields of the ions [M-nCO]− (n=1–3) shift to the lower energy region indicating that the stability of the Re−CO bond is higher than that of Mn−CO. The average
lifetimes of the molecular negative ions relative to the autodetachment of an electron (τa) and to dissociation (τd) were measured. It was found that electron-accepting substituents increase the τa value and decrease τd.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1161–1164, June, 1997. 相似文献
8.
V. V. Burdin V. D. Maiorov G. I. Voloshenko O. Yu. Antonova N. B. Librovich 《Russian Chemical Bulletin》1998,47(12):2415-2418
Ion-molecular interactions in the HCl−BuiOH system with different compositions (from neat isobutyl alcohol to 37 mol.% HCl) were studied by Multiple Attenuated Total
Reflectance (MATR) IR spectroscopy at 30 °C. Proton disolvates (Bui(H)O…H…O(H)Bui)+ with strong symmetrical H bonds are formed upon the addition of HCl to BuiOH. At high concentrations of HCl (C
0
HCl>33 mol.%), (Cl…H…Cl)− ions are formed along with (BuiOH)2H+. The spectra of positively and negatively charged proton disolvates were compared to those of similar ions in the HCl−PriOH and HCl−MeOH systems.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2496–2500, December, 1998. 相似文献
9.
V. V. Senuta S. N. Bendrysheva M. A. Proskurnin 《Journal of Analytical Chemistry》2009,64(11):1174-1184
Thermal lens spectrometry was used for the differential kinetic determination of aniline (over the concentration range of
8 × 10−4–3.2 × 10−3 M) and 4-nitroaniline (2 × 10−4–1.6 × 10−3 M) present in combination in a single sample based on the oxidation reaction with periodate ions in an acidic medium (this
determination is not possible with the spectrophotometric monitoring of the rate of reaction). The thermal lens procedure
(λe = 488.0 nm; 80 mW) was characterized by good performance characteristics in the determination of aniline (c
min = 3 × 10−4 M; c
d = 8 × 10−4 M) and 4-nitroaniline (c
min = 7 × 10−5 M; c
d = 2 × 10−4 M), simplicity, and rapidity. 相似文献
10.
Negative-ion low-energy collisionally activated dissociation (CAD) tandem mass spectrometry of electrospray-produced ions permits structural characterization of phosphatidylglycerol (PG). The major ions that identify the structures arise from neutral loss of free fatty acid substituents ([M − H − R x CO2H]−) and neutral loss of the fatty acids as ketenes ([M − H − R′ x CH = C = O]−), followed by consecutive loss of the glycerol head group. The abundances of the ions arising from neutral loss of the sn-2 substutient as a free fatty acid ([M − H − R2CO2H]−) or as a ketene ([M − H − R′2CH = C = O]−) are greater than those of the product ions from the analogous losses at sn-1. Nucleophilic attack of the anionic phosphate site on the C-1 or the C-2 of the glycerol to which the carboxylates attached expels the sn-1 (R1CO2−) or the sn-2 (R2CO2−) carboxylate anion, resulting in a greater abundance of R2COO− than R1COO−. These features permit assignments of fatty acid substituents and their position in the glycerol backbone. The results are also consistent with our earlier findings that pathways leading to those losses at sn-2 are sterically more favorable than those at sn-1. Fragment ions at m/z 227, 209 and 171 reflect the glycerol polar head group and identify the various PG molecules. Both charge-remote fragmentation (CRF) and charge-drive fragmentation (CDF) processes are the major pathways for the formation of [M − H − R x COOH]− ions. The CRF process involves participation of the hydrogen atoms on the glycerol backbone, whereas the CDF process involves participation of the exchangeable hydrogen atoms of the glycerol head group. The proposed fragmentation pathways are supported by CAD tandem mass spectrometry of the analogous precursor ions arising from the H-D exchange experiment, and further confirmed by source CAD in combination with tandem mass spectrometry. 相似文献
11.
Scott G. Summerfield Kathleen A. Cox Simon J. Gaskell 《Journal of the American Society for Mass Spectrometry》1997,8(1):25-31
Low energy collisionally activated dissociations (CAD) of doubly protonated peptides incorporating cysteic acid and arginine residues have been studied. Deuterium labeling experiments have established that loss of the elements of H2SO3 occurs with cleavage of one CH bond and transfer of the hydrogen to a neutral fragment. Prominent d-type ions were observed corresponding to cleavage at the cysteic acid residue. The analysis of structural analogs suggested that the unexpectedly low energy requirement for this process is attributable to a charge-proximal process promoted by intra-ionic interaction of the arginine and cysteic acid side chains. CAD (in the collision hexapole of a tandem quadrupole instrument) of electrospray source-formed fragment ions established that the d-type ions can form via b-type ions; there was no evidence of formation via (a n + 1) or (b n — H2SO3) ions. The equivalent d-ion was observed, albeit with lesser abundance, when the cysteic acid residue was replaced by aspartic acid, but not by glutamic acid. 相似文献
12.
Chen X Chan WY Wong PS Yeung HS Chan TW 《Journal of the American Society for Mass Spectrometry》2011,22(2):233-244
Peptides adducted with different divalent Group IIB metal ions (Zn2+, Cd2+, and Hg2+) were found to give very different ECD mass spectra. ECD of Zn2+ adducted peptides gave series of c-/z-type fragment ions with and without metal ions. ECD of Cd2+ and Hg2+ adducted model peptides gave mostly a-type fragment ions with M+• and fragment ions corresponding to losses of neutral side chain from M+•. No detectable a-ions could be observed in ECD spectra of Zn2+ adducted peptides. We rationalized the present findings by invoking both proton-electron recombination and metal-ion reduction
processes. As previously postulated, divalent metal-ions adducted peptides could adopt several forms, including (a) [M + Cat]2+, (b) [(M + Cat – H) + H]2+, and (c) [(M + Cat – 2H) + 2H]2+. The relative population of these precursor ions depends largely on the acidity of the metal–ion peptide complexes. Peptides
adducted with divalent metal-ions of small ionic radii (i.e., Zn2+) would form predominantly species (b) and (c); whereas peptides adducted with metal ions of larger ionic radii (i.e., Hg2+) would adopt predominantly species (a). Species (b) and (c) are believed to be essential for proton-electron recombination
process to give c-/z-type fragments via the labile ketylamino radical intermediates. Species (c) is particularly important for the formation of
non-metalated c-/z-type fragments. Without any mobile protons, species (a) are believed to undergo metal ion reduction and subsequently induce
spontaneous electron transfer from the peptide moiety to the charge-reduced metal ions. Depending on the exothermicity of
the electron transfer reaction, the peptide radical cations might be formed with substantial internal energy and might undergo
further dissociation to give structural related fragment ions. 相似文献
13.
Jinmao You Yanyan Fu Zhiwei Sun Yourui Suo 《Analytical and bioanalytical chemistry》2010,396(7):2657-2666
2-(5-Benzoacridine)ethyl-p-toluenesulfonate (BAETS), a dual-sensitive probe, was reacted with bile acids in the presence of K2CO3 catalyst in dimethyl sulfoxide (DMSO) solvent to give BAETS–bile acid derivatives. Derivatives exhibited intense fluorescence
(FL) with an excitation maximum at λ
ex 270 nm and an emission maximum at λ
em 510 nm. MS analysis using APCI-MS indicated that derivatives had excellent APCI-MS ionizability with percentage ionization
δ values changing from 0 to 88.83% in aqueous acetonitrile and from 0 to 89.15% in aqueous methanol. The collision induced
dissociation spectra of m/z [M + H]+ contained specific fragment ions at m/z [M + H−H2O]+, [M + H−2H2O]+, [M + H−3H2O]+, 347.3, and 290.1. Repeatability was good for LC separation of BAETS–bile acid derivatives with aqueous acetonitrile as mobile
phase. The relative standard deviations (RSDs) of retention time and peak area at 6.6 nmol mL−1 levels with fluorescence detection (FL) were from 0.045 to 0.072% and from 2.16 to 2.73%, respectively. Excellent linear
responses were observed, with regression coefficients >0.9995. The FL detection limits (S/N = 3) were in the range of 18.0–36.1 fmol. The online APCI-MS detection limits are in the range of 500–790 fmol (at a signal-to-noise
ratio of 3). 相似文献
14.
O. P. Charkin 《Russian Journal of Inorganic Chemistry》2011,56(11):1775-1781
The equilibrium geometric parameters and energetic and spectroscopic characteristics of low-lying conformers for several series
of model cage-substituted (mixed) borane, alane, and gallane closo-dianions M
i
M′12 − i
H122−(M, M′ = B, Al, Ga), as well as of “bare” gallium-aluminum anions Ga
i
Al12−i
− with i = 0–12, were calculated within the B3LYP approximation of the density functional theory using 6–31G* and 6–311+G** basis
sets. Differences in structure and stability between alanoborane clusters of similar composition are revealed. In clusters
where the M and M’ heteroatoms are close in size and electronegativity (in gallonoalanes and gallium-aluminum anions), successive
substitutions of M′ for M are accompanied by small energy changes and occur quasi-stochastically in different positions of
the cage. When the substituents are significantly different (in alanoboranes), mixed clusters are unstable against disproportionation
into homonuclear “predecessors” M12H122− and M′12H122−, and the most favorable M
i
M′12 − i
H122− structures among them are those in which M
i
M′12 − i
the cages are subdivided into homonuclear “subclusters” M
i
and M′t′12−i
with a maximal number of homonuclear bonds (M-M and M′-M′) and a minimal number of heteronuclear bonds (M-M′). 相似文献
15.
The dissociation behavior of phosphorylated and sulfonated peptide anions was explored using metastable atom-activated dissociation
mass spectrometry (MAD-MS) and collision-induced dissociation (CID). A beam of high kinetic energy helium (He) metastable
atoms was exposed to isolated phosphorylated and sulfonated peptides in the 3– and 2– charge states. Unlike CID, where phosphate
losses are dominant, the major dissociation channels observed using MAD were Cα – C peptide backbone cleavages and neutral losses of CO2, H2O, and [CO2 + H2O] from the charge reduced (oxidized) product ion, consistent with an electron detachment dissociation (EDD) mechanism such
as Penning ionization. Regardless of charge state or modification, MAD provides ample backbone cleavages with little modification
loss, which allows for unambiguous PTM site determination. The relative abundance of certain fragment ions in MAD is also
demonstrated to be somewhat sensitive to the number and location of deprotonation sites, with backbone cleavage somewhat favored
adjacent to deprotonated sites like aspartic acid residues. MAD provides a complementary dissociation technique to CID, ECD,
ETD, and EDD for peptide sequencing and modification identification. MAD offers the unique ability to analyze highly acidic
peptides that contain few to no basic amino acids in either negative or positive ion mode. 相似文献
16.
ESI multiple-stage linear ion-trap (LIT) mass spectrometric approaches for a near-complete structural characterization of
cardiolipins (CLs), including identification of the fatty acyl substituents, assignment of the fatty acid substituents on
the glycerol backbone, and location of the double-bond(s) or cyclopropyl group along the fatty acid chain are described. Upon
collisionally activated dissociation (CAD) on the [M − 2H + 3Li]+ ions of CL in an ion-trap (MS2), two sets of fragment ions (designated as (a + 136) and (b + 136) ions) analogous to those previously reported for the [M − 2H + 3Na]+ ions were observed, leading to assignment of the phosphatidyl moieties attached to 1′- or 3′-position of the central glycerol.
Further dissociation of the (a + 136) (or (b + 136)) ions (MS3) gives rise to the (a + 136 − R1(or 2)CO2Li) (or b + 136 − R1(or 2)CO2Li) ion pairs that identify the fatty acid moieties and their position on the glycerol backbone. This is followed by MS4 on the (a + 136 − R1(or 2)CO2Li) (or b + 136 − R1(or 2)CO2Li) ion to eliminate a tricylic glycerophosphate ester residue (136 Da) to yield the (a − R1(or 2)CO2Li) ion, which is then subjected to MS5. The MS5 spectrum contains the structural information that locates the double-bond(s) or cyclopropyl group of the fatty acid
substituents. Finally, the subsequent MS6 on the dilithiated fatty acid ions generated from MS5 also yields feature ions that confirm the assignment. 相似文献
17.
Ester Marotta Cristina Paradisi 《Journal of the American Society for Mass Spectrometry》2009,20(4):697-707
The positive APCI-mass spectra in air of linear (n-pentane, n-hexane, n-heptane, n-octane), branched [2,4-dimethylpentane, 2,2-dimethylpentane and 2,2,4-trimethylpentane (i-octane)], and cyclic (cyclohexane) alkanes were analyzed at different mixing ratios and temperatures. The effect of air humidity
was also investigated. Complex ion chemistry is observed as a result of the interplay of several different reagent ions, including
atmospheric ions O2+•, NO+, H3O+, and their hydrates, but also alkyl fragment ions derived from the alkanes. Some of these reactions are known from previous
selected ion/molecule reaction studies; others are so far unreported. The major ion formed from most alkanes (M) is the species
[M − H]+, which is accompanied by M+• only in the case of n-octane. Ionic fragments of C
n
H2n
+1/+ composition are also observed, particularly with branched alkanes: the relative abundance of such fragments with respect
to that of [M − H]+ decreases with increasing concentration of M, thus suggesting that they react with M via hydride abstraction. The branched
C7 and C8 alkanes react with NO+ to form a C4H10NO+ ion product, which upon collisional activation dissociates via HNO elimination. The structure of t-Bu+(HNO) is proposed for such species, which is reasonably formed from the original NO+(M) ion/molecule complex via hydride transfer and olefin elimination. Finally, linear alkanes C5–C8 give a product ion corresponding to C4H7+(M), which we suggest is attributed to addition of [M − H]+ to C4H8 olefin formed in the charge-transfer-induced fragmentation of M. The results are relevant to applications of nonthermal plasma
processes in the fields of air depuration and combustion enhancement. 相似文献
18.
K. A. Venkatesan K. V. Shyamala M. P. Antony T. G. Srinivasan P. R. Vasudeva Rao 《Journal of Radioanalytical and Nuclear Chemistry》2008,275(3):563-570
Batch and dynamic extractions of uranium(VI) in 10−3–10−2M concentrations in 3–4M nitric acid medium have been investigated using a commercially available phosphinic acid resin (Tulsion
CH-96). The extraction of uranium(VI) has been studied as a function of time, batch factor (V/m), concentrations of nitric acid and uranium(VI) ion. Dual extraction mechanism unique to phosphinic acid resin has been established
for the extraction of uranium(VI). Distribution coefficient (K
d
) of uranium(VI) initially decreases with increasing concentration of nitric acid, reaches a minimum value at 1.3M, followed
by increases in K
d
. A maximum K
d
value of ∼2000 ml/g was obtained at 5.0M nitric acid. Batch extraction data has been fitted into the linearized Langmuir
adsorption isotherm. The performance of the resin under dynamic extraction conditions was assessed by following the breakthrough
behavior of the system. Effect of flow rate, concentrations of nitric acid and uranium ion in the feed on the breakthrough
behavior of the system was studied and the data was fitted using Thomas model. 相似文献
19.
Brunet C Antoine R Dugourd P Canon F Giuliani A Nahon L 《Journal of the American Society for Mass Spectrometry》2012,23(2):274-281
We have studied the photodissociation of gas-phase deprotonated caerulein anions by vacuum ultraviolet (VUV) photons in the
4.5 to 20 eV range, as provided by the DESIRS beamline at the synchrotron radiation facility SOLEIL (France). Caerulein is
a sulphated peptide with three aromatic residues and nine amide bonds. Electron loss is found to be the major relaxation channel
at every photon energy. However, an increase in the fragmentation efficiency (neutral losses and peptide backbone cleavages)
as a function of the energy is also observed. The oxidized ions, generated by electron photodetachment were further isolated
and activated by collision (CID) in a MS3 scheme. The branching ratios of the different fragments observed by CID as a function of the initial VUV photon energy are
found to be independent of the initial photon energy. Thus, there is no memory effect of the initial excitation energy on
the fragmentation channels of the oxidized species on the time scale of our tandem MS experiment. We also report photofragment
yields as a function of photon energy for doubly deprotonated caerulein ions, for both closed-shell ([M–2H]2–) non-radical ions and open-shell ([M–3H]2–•) radical ions. These latter ions are generated by electron photodetachment from [M–3H]3– precursor ions. The detachment yield increases monotonically with the energy with the appearance of several absorption bands.
Spectra for radical and non-radical ions are quite similar in terms of observed bands; however, the VUV fragmentation yield
is enhanced by the presence of a radical in caerulein peptides. 相似文献
20.
A method for the identification and quantification of underivatised steryl sulphates in invertebrates by liquid chromatography
(LC) coupled with tandem mass spectrometry (MS) involving a single cleanup step has been developed. Negative electrospray
ionisation and positive and negative atmospheric-pressure chemical ionisation (APCI) spectra of steryl sulphate showed pseudomolecular
ions ([M+H–H2SO4]+or [M–H]−). Collision-induced dissociation (CID) was efficient only in positive APCI. LC-MS in negative APCI was least susceptible
to interference and possible differences in response factors. The detection limits (signal-to-noise ratio of 3) based on cholest-5-enyl-3-sulphate
in positive and negative APCI modes are 3.66 and 0.73 pmol μL−1, respectively. Calibration plots and response factors for cholest-5-enyl-3-sulphate relative to the internal standard, cholecalciferyl-3-sulphate,
in both positive and negative polarities, were linear in the concentration range from 1.22 to 16.4 pmol μL−1 with good coefficients of determination (R
2>0.98). It is suggested that the structure elucidation of steryl sulphates is best achieved in CID positive APCI mode, whereas
their quantification should be carried out using negative APCI. 相似文献