bluuebunny/crossref_metadata_2025_split huggingface dataset:
Methionine specific sequence ions formed by the dissociation of protonated peptides at high collision energies
Authors: Downard Kevin M. , Biemann Klaus 
Published: May 2005

AbstractTwo methionine‐specific sequence ions are described that are formed upon the dissociation of protonated methionine‐containing peptides at high (keV) collision energies. These ions, hiherto unassigned, are denoted an + 1 − CH3S⋅ and zn + 1 − CH3S⋅. Precursor ion scans reveal that these species originate from the an + 1 and zn + 1 ions, respectively, where methionine resides at position n‐1 relative to the N‐ or C‐terminus. A comparison of the collision‐induced dissociation (CID) spectra for several related peptides demonstrates that methionine residues are involved in the genesis of these species and mechanisms for their formation are proposed. Several structural features of a peptide that are important to the formation of these species are described. The importance of identifying these ions in order to correctly sequence a methionine‐containing peptide based on its CID spectrum is illustrated.
Identification of the neutral products from the unimolecular dissociation of singly and multiply charged C60 fullerene ions
Authors: McHale Kevin J. , Polce Michael J. , Wesdemiotis Chrys 
Published: May 2005

AbstractThe neutral products eliminated upon the collisionally activated dissociation (CAD) of C ions (z = 1–4) are post‐ionized to cations or anions and collected in neutral fragment‐reionization (+NfR+,−) mass spectra. These spectra provide conclusive evidence that the decompositions C → C + C2n (where x >30 and 2n < 30) proceed by cleavage of whole C2n clusters, not consecutive losses of nC2. As teh charge of the fullerene precursor ion increases, the largest detectable neutral loss decreases, from C28 for z = 1 to C12 for z = 4. Post‐ionization of C2n to cations preferentially produces odd‐carbon cluster ions (e.g., C5+, C7+, C11+, C+15) whereas post‐ionization to anions yields abundant even‐carbon cluster ions (C6−, C8−).
High‐resolution tandem mass spectra of 37‐67 kDa proteins
Authors: Speir J. Paul , Senko Michael W. , Little Daniel P. , Loo Joseph. A. , McLafferty Fred W. 
Published: May 2005

AbstractBy dissociating noncovalent adducts with infrared radiation and minimizing ion charge density during measurement, Fourier‐transform mass spectrometry with electrospray ionization yields 160 000 resolving power for porcine albumin. Its molecular weight calculated from the published sequence is 66 740, but values found for two different samples are MW = 66 736 and 66 886. The spectrum of their mixture confirms this mass difference. Similar measurements of two Protein A (45 kDa) samples also give molecular weights in substantial disagreement with literature sequences. Tandem mass spectrometry gives partial sequence information that demonstrates errors in some of the reported sequences.
Ion–neutral complex formation and hydrogen‐shifts in the alkene loss from ionized alkyl phenyl thioethers in the gas phase
Authors: Van Amsterdam Margot W. , Ingemann Steen , Nibbering Nico M. M. 
Published: May 2005

AbstractThe mechanistic aspects of alkene loss from ionized ethyl‐and n‐propyl phenyl thioethers have been studied by use of deuterium labelling and tandem mass spectrometry. Loss of ethene from the molecular ion of ethyl phenyl thioether proceeds predominantly by a specific H‐shift from the β‐position of the ethyl group to the remaining part of the ion. In contrast, deuterium labelling reveals that elimination of propene from the molecular ions of the n‐propyl phenyl and n‐propyl 2,6‐dimethylphenyl thioethers involves three competing reactions: (i) a 1,2‐hydride shift assisted cleavage of the bond between the propyl group and the sulfur atom yielding an ion–neutral complex of a thiophenyoxy radical and a secondary propyl carbenium ion, which reacts further by proton transfer prior to dissociation; (ii) a partially reversible 1,5‐H shift from the β‐position to the 2‐ or 6‐position of the ring; and (iii) a 1,3‐H shift from the β‐position to the sulfur atom. The preference for transfer of a hydrogen atom from the β‐position is particularly pronounce for the reactions of the metastable molecular ions of the n‐propyl phenyl and n‐propyl 2,6‐dimethylphenyl thioethers. This indicates that the critical energies of the processes involving H‐shifts are lower than the critical energy for propene loss with intermediate formation of an ion–neutral complex. In addition to ethene elimination, ionized ethyl phenyl thioether expels a HS+· radical. This reaction is preceded by an interchange between the hydrogen atoms at the α‐methylene group and the hydrogen atoms at the 2‐ and 6‐positions of the ring as observed also for ionized methyl phenyl thioether.
Collision‐induced photon emissions from 8 ke V O and CO ion beams
Authors: Holmes J. L. , Mayer P. M. 
Published: May 2005

AbstractThe optical emission spectra between 190 and 680 nm of 8 keV O and CO collisions with He and N2 target gases were obtained and analyzed on a modified commercial VG ZAB‐2F mass spectrometer. Emissions observed were from O, O+, He, N (B2∑+u → X2∑+g) and N2 (C3∏u → B3∏g) in the case of O projectiles and C, CO (B2∑+u, A 2∏u → X 2∏g), CO+· (B2∑+ → X2∑+), N (B2 ∑+g → X2∑g) and N2 (C3∏u → B 3∏g) in the case of CO projectiles. The results are discussed in relation to previous reports on N–target collisions and the collision–induced dissociation mass spectral characteristics of O and CO.
Studies on the formation of reactive intermediates from the antineoplastic agent N,N′Bis(2‐chloroethyl)‐N‐nitrosourea (BCNU) in vitro and in Vivo. Characterization of novel glutathione adducts by ionspray tandem mass spectrometry
Authors: Davis Margaret R. , Baillie Thomas A. 
Published: May 2005

AbstractIn a study designed to examine the nature of short‐lived, electrophilic intermediates liberated during decomposition of N,N′‐bis(2‐chloroethyl)‐N‐nitrosourea (BCNU) in vitro and also on administration of BCNU (140 μmol i.p.) to rats in vivo, both on‐line and off‐line LC/MS/MS techniques were employed to detect and characterize the corresponding glutathione (GSH) adducts present in incubation media and excreted into bile, respectively. In vitro, four GSH conjugates were formed and these were identified, on the basis of their product ion spectra, as products of S‐and N‐carbamoylation and alkylation reactions. Although the relative proportions of these in vitro adducts were found to depend on the molar ratios of GSH and BCNU, the major adduct under all conditions studied proved to be S‐(2‐chloroethylcarbamoyl)glutathione (SCG). Analysis of untreated bile samples by means of on‐line LC/MS/MS with constant neutral loss (129 u) and precursor ion (m/z 179) scanning techniques again led to the detection of four GSH conjugates, although only one of these (SCG) was common to the group of adducts identified in vitro. All of the GSH conjugates detected in bile represented products of S‐carbamoylation, indicating that the alkylating moiety released from BCNU undergoes reactions in vivo with nucleophiles other than GSH.
Gas‐phase reactions of the 4‐dehydroanilinium ion and its isomers
Authors: Chyall Leonard J. , Kenttämaa Hilkka I. 
Published: May 2005

AbstractCollisional activation of protonated 2‐, 3‐ and 4‐iodoanilines in a dual‐cell Fourier transform ion cyclotron resonance spectrometer results in the loss of an iodine atom to yield product ions of m/z 93. Ion–molecule reactions and energy‐resolved collision‐activated dissociation experiments demonstrate that these three ions are structurally distinct, and that they are distonic ions. The ions were identified as the 2‐, 3‐ and 4‐dehydroanilinium ions, the high‐energy distonic isomers of ionized aniline. The reactivity of these charged phenyl radicals is largely analogous to that of the phenyl radical. For example, the 4‐dehydroanilinium ion abstracts an iodine atom from isopropyl iodide, a thiomethyl group from dimethyl disulfide, and adds to cyclohexene. Comparison of the collision‐activated dissociation product abundances of the ion formed upon CH3S abstraction to that of a reference ion suggests that bond formation occurs at the formal radical site upon CH3S abstraction. Hence, the reaction probably occurs via a simple radical abstraction mechanism similar to that of the phenyl radical. However, some neutral reagents react with the charge site of the 4‐dehydroanilinium ion, and yet others undergo a two‐step reaction sequence involving the charge site in addition to the radical site. For example, certain basic molecules induce isomerization of the 4‐dehydroanilinium ion to the significantly more stable ionized aniline by deprotonating the charge site and then donating a hydrogen atom to the radical site.
Tandem mass specatrometry of carbonic anhydrase (29 kDa)
Authors: O'Connor Peter B. , Speir J. Paul , Senko Michael W. , Little Daniel P. , McLafferty Fred W. 
Published: May 2005

AbstractUsing electrospray ionization with a Fourier‐transform mass spectrometer, MS/MS of molecular ions and seven fragment ions of carbonic anhydrase (259 amino acids) yields 74 identifiable fragment ions, including 23 amino acid spacings. Such sensitive and specific direct characterization of proteins appears to be complementary to conventional techniques including LC/MS/MS sequencing of oligopeptides from protein degradation.
Peptide amino acid sequence analysis using matrix‐assisted laser desorption/ionization and fourier transform mass spectrometry
Authors: Castoro John A. , Wilkins Charles L. , Woods Amina S. , Cotter Robert J. 
Published: May 2005

AbstractHigh‐performance matrix‐assisted laser desorption/ionization (MALDI) using 7 T Fourier transform mass spectrometry (FTMS) was investigated for peptide amino acid sequence analysis. Two synthetic peptides representative of the type which would be displayed by major histocompatibility complex molecules from tumor cells were investigated by MALDI/FTMS. Molecular ions of the two 9‐amino acids peptides were detected with resolving power of 8000–17 900 and mass measurement accuracy between 8 and 81 ppm for the all 12C isotope ions. An ultra‐high resolution spectrum (RP 300 000) for the molecular ion of one of the two peptides was obtained. Structurally useful sequence information was obtained by use of surface‐induced dissociation (SID) of the molecular ion species. Interestingly, SID of a sodium‐attached peptide molecular ion resulted in the production of numerous sodium‐attached sequence ions.
Direct mass spectrometric sequencing of low‐picomole amounts of oligodeoxynucleotides with up to 21 bases by matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Nordhoff E. , Karas M. , Cramer R. , Hahner S. , Hillenkamp F. , Kirpekar F. , Lezius A. , Muth J. , Meier C. , Engels J. W. 
Published: May 2005

AbstractUV and IR matrix‐assisted laser desorption/ionization mass spectrometry (UV‐ and IR‐MALDI) have demonstrated their potential for the accurate and sensitive mass determination of oligonucleotides. Metastable molecule ion fragmentation was found to be the main limitation in both desorption schemes for the analysis of larger nucleic acid sequences. Fragment ions from additional prompt decays, observed only in IR‐MALDI, offer structural data, which allow sequence information to be derived for low‐picomole amounts of oligodeoxynucleotides with up to 21 bases from a single mass spectrum. Two examples demonstrating the feasibility of this new sequencing technique are given. A model is introduced and discussed, which proposes a reaction scheme for the observed fragment ion patterns of nucleic acids and differentiates prompt and metastable fragmentation mechanisms. The role of fragmentation in direct mass spectrometric sequencing schemes and as a limitation for the accessible mass range in nucleic acid MALDI mass spectrometry is discussed.
Cation‐exchange resins for removal of alkali metal cations from oligonucleotide samples for fast atom bombardment mass spectrometry
Authors: Vollmer David L. , Gross Michael L. 
Published: May 2005

AbstractCation‐exchange resins are useful matrix additives for the positive and negative ion FAB‐MS determination of nucleotides. Several factors including the amount and type of matrix, the amount and type of the resin, the molecular weight of the nucleotide, and the salt content of the nucleotide sample are investigated. For positive ions, the most abundant [M + H]+ ions are obtained with 1 μL of DTT/DTE with 75–100 resin beads in the H+ form is used. For negative ions, the most abundant [M − H]− ions are produced from 1 μL TEA and 75–100 resin beads in the NH4+ form. In several cases, the use of cation‐exchange resins give superiors results compared to those obtained with other matrix additives.
Charge state assignment from schiff‐base adducts in low resolution electrospray mass spectra of protein mixtures and dissociation products
Authors: Guan Ziqiang , Campbell Victoria L. , Laude David A. 
Published: May 2005

AbstractSchiff‐bases formed by reaction between ketones and free amine sites in proteins yield mass‐shifted ions that are useful in assigning charge states in low resolution electrospray ionization mass spectra of mixtures and dissociation products. The technique is attractive for those mass analyzers incapable of achieving sufficient resolving power to distinguish the 13C‐isotope distribution within an individual charge state. Instead, acetone is used here to append a C3H4 group to the protein and achieve a forty‐fold reduction in the necessary mass resolution for charge state determination. The utility of Schiff‐base adducts for assigning charge states among a mixture of proteins is demonstrated; here, the molecular weights for horse myoglobin (MW 16 950) and cytochrome c (MW 12 360) in a two component mixture are unambiguously determined from a mass spectrum with a mass resolution of only 800. The CN bond formed by the Schiff base is sufficiently strong to survive ion dissociation processes and permit assignment of charge state to fragment ions in tandem mass spectrometry experiments. For example, adducted sequence ions are observed in high yield when a melittin/acetone solution is subjected to nozzle‐skimmer dissociation conditions in the electrospray process. Other advantages of Schiff‐base reaction include site‐specificity and minimal alteration to the charge state. This site‐specific binding feature appears to be promising method for locating the lysine groups in structural characterization by tandem mass spectrometry.
Selected ion accumulation of noncovalent complexes in a fourier transform ion cyclotron resonance mass spectrometer
Authors: Bruce James E. , Van Orden Steven L. , Anderson Gordon A. , Hofstadler Steven A. , Sherman Michael G. , Rockwood Alan L. , Smith Richard D. 
Published: May 2005

AbstractAn electrospray ionization–Fourier transform ion cyclotron resonance (ESI–FTICR) mass spectrometer has been used in conjunction with the technique of selected‐ion accumulation (SIA) to investigate its utility for the study of the gas phase behavior of noncovalent complexes from solution. SIA is demonstrated to provide the selective accumulation of weakly bound species, providing a significant enhancement in the attainable signal‐to‐noise ratio and dynamic range. The frequency response of quadrupole excitation was first determined by selectively accumulating single charge states of large, highly adducted, highly charged molecules such as bovine albumin and bovine albumin dimer. Under the conditions employed, the response (selective accumulation) was found to be as narrow as 500 Hz. Additionally the SIA was found to be sufficiently gentle to allow accumulation of both specific and nonspecific weak noncovalent complexes, such as the myoglobin–heme complex observed in basic solutions and complexes of myoglobin and single amino acids, such as tryptophan. This result is probably due to the continual application of quadrupole excitation during the high pressure accumulation event, preventing any significant growth of magnetron motion, and subsequently, allowing interconversion to form only small cyclotron radii. We also demonstrate the simultaneous application of SIA with dipolar sustained off‐resonance irradiation (SORI) during the ion accumulation period so as to allow selective accumulation of dissociation products. The SIA/SORI combination promises to greatly extend (MS)n capabilities by allowing the selective accumulation of any dissociation product in any step along a given dissociation pathway.
Tunable degree of fragmentation of volatile organic compounds with a low‐pressure penning ion source
Authors: Kohler M. , Schlunegger U. P. 
Published: May 2005

AbstractThe properties of a low‐pressure ion source based on the principle of the Penning cell (Penning ion source) were investigated. At low discharge currents, spectra similar to standard electron impact ionization (EI at 70 eV) spectra were obtained (positive‐ion‐mode). However, at high discharge currents, it was found by experiments carried out partly with labelled compounds that molecules are decomposed to small fragments and even single atoms. Species such H2+, C+, CH+, CH2+, CH3+, O+, OH+, H2O+, C2 +, C2H+, C2H2+, C2H3+, O2+, Cl+ and Cl2+ have been obtained from various organic compounds. The degree of fragmentation of the molecular ion has been found to be directly dependent on the discharge current. These observation demonstrate that the Penning ion source allows one to tune the degree of framentation. In the negative‐ion mode, halogenated organic compounds yielded spectra dominated by the signals of the halogen atoms they contain. High abundances of F−, Cl−, Br−, and Br2− were observed, next to weak signals for O−, C−, C2−, C2H−, C2−, and C4−, orginating from the CHO skeleton of the sample molecule. In contrast to the results found in the positive‐ion mode, intense fragmentation, even at low discharge currents, was found.
Massive cluster impact ionization on a four sector tandem mass spectrometer
Authors: Fabris D. , Wu Z. , Fenselau C. C. 
Published: May 2005

AbstractHigh energy gycerol cluster ions from an electrohydrodynamic ion gun have been used as a primary ion beam to generate secondary ions of proteins with molecular weights up to 29 kDa and oligonucleotides. The technique not only demonstrated good performance in the picomole/nanomole range for the desorbtion of highly polar and fragile molecules such as proteins and deoxyoligonucleotides, but it also allowed the observation of a non‐covalent complex in the form of a deoxyoligonucleotide duplex. We have also shown that it is feasible to carry out structural analysis of oligonucleotides by collisional activation in a four sector tandem instrument.
Differentiation of olefin isomers by survivor‐ion mass spectrometry
Authors: Tureček František , Gu Ming 
Published: May 2005

AbstractSurvivor‐ion mass spectrometry is a method that relies on the selective monitoring of non‐dissociating ions that underwent collisional neutralization and reionization. These charge‐permutation processes are found to modulate the relative intensities of precursor ions, both molecular ions and fragments, formed by electron impact from C6H10, C6H12, C6H12O, and xylene isomers. The relative intensities of highly‐unsaturated ions, such as C5H5+, C4H, C3H3+, and C2H, and enol ions are enhanced in the survivor‐ion spectra in dependence on the neutralization gas. Isomer differentiation through survivor‐ion spectra is achieved for conjugated hexadienes, 1,4‐hexadiene and cyclohexene, but not for hexenols and xylenes.
Effect of metal cationization on the collision‐induced decomposition of 2,3‐diphenylpropenoic acid derivatives
Authors: Madhusudanan K. P. 
Published: May 2005

AbstractThe effect of metal cationization on the collision‐induced decomposition of 2,3‐diphenylpropenoic acid derivatives was studied with the help of linked scan (B/E = constant) spectra of their [M + H]+, [M − H]−, [M + Met]+, [M + 2Met − H]+ and [M + Met − H]+ ions using metal ions such as Li+, Na+, K+, Cs+, Ag+ and Ba2+. Decarboxylation is triggered by metal cationization.
Fragmentation of (η5‐cyclopentadienyl)dicarbonyl‐acyliron complexes under electron impact
Authors: Baranowska ElżBieta , Danikiewicz Witold , Pakulski Zbigniew , Zamojski Aleksander 
Published: May 2005

AbstractFragmentation patterns under electron impact of selected (η5‐cyclopentadienyl)dicarbonylacyliron complexes were studied. Fragmentation pathways were confirmed using accurate mass measurements and B/E = constant and mass‐analysed ion kinetic energy fragment ion spectra.
Beam‐induced dehalogenation in LSIMS: Effect of halogen type and matrix chemistry
Authors: Théberge R. , Bertrand M. J. 
Published: May 2005

AbstractThe LSIMS beam‐induced dehalogenation of several 4‐halo‐phenylalanine methyl esters (I, Br, Cl, F) was investigated and compared to that of atrazine using 12 different matrix compounds including diethyl phthalate for which the empirical electron affinity was known. The extent of dehalogenation, induced by a one‐electron reduction process, is in agreement with the leaving group ability of the corresponding halogens (I >Br >Cl >F) and the dehalogenation inhibiting efficiency of the matrices. The latter is rationalized in terms of electron scavenging capacity and matrix structural features relating to that capacity. The extent of dehalogenation observed for 4‐I‐phenylalanine methyl ester is similar to that of atrazine, a chlorinated compound, which indicates that the halogen effect is not overwhelming in determining the extent of dehalogenation. The bracketing of matrix reduction potential was attempted based on the propensity of the matrices to induce M+· formation from analytes of known oxidation potentials. The ability of matrices to induce M+· formation parallels their dehalogenation and reduction inhibiting efficiencies. The last observation underlines the importance of matrix redox properties in effecting or inhibiting beam‐induced processes, be they reductive or oxidative.
Formation and fragmentations of organometallic complexes involving aliphatic α‐amino acids and transition metal cations—a plasma desorption mass spectrometry study
Authors: Bouchonnet Stéphane , Hoppilliard Yannik , Ohanessian Gilles 
Published: May 2005

AbstractAmino acid/transition metal chloride mixtures were studied by plasma desorption mass spectrometry. The six aliphatic α‐amino acids were considered: glycine (Gly), alanine (Ala), valine (Val), leucine (Leu), isoleucine (Ile) and proline (Pro), together with four transition metal chloride salts: CoCl2, NiCl2, CuCl2 and FeCl2. Mixtures spectra show that MCat+ complexes are formed where M = amino acid and Cat = Co, Ni, Cu or FeCl. Fragmentations of MCat+ ions lead to both organometallic and organic ions. Isotopic labelling has allowed to demonstrate some fragmentation mechanisms.
Observation of large subunit protein complexes by electrospray ionization mass spectrometry
Authors: Loo Joseph A. 
Published: May 2005

AbstractMass spectrometry with electrospray ionization and a magnetic sector instrument was used to detect multiply charged molecules for the non‐covalently bound dimeric subunit protein complexes of horse liver alcohol dehydrogenase (Mr ∼ 80 000) and the tetrameric complexes of yeast alcohol dehydrogenase (Mr ∼ 147 000) and rabbit muscle pyruvate kinase (Mr ∼ 232 000). Ions for the pyruvate kinase complex represent one of the largest intact protein complexes resolved by mass spectrometry. Solvation of the large gas phase complexes is indicated by the mass spectrometric results.