摘要:

AbstractMass spectral data are reported for an extended series of synthesized acylcarnitines. Direct mass spectrometry was performed using ionization by fast atom bombardment in combination with high‐energy collisional activation andB/Elinked scanning. The data show that it is possible to distinguish between isomeric compounds using this technique. Gas chromatographic/mass spectrometric analysis data for acylcarnitines, as their acyloxylactone derivatives, are reported. Both electron impact and chemical ionization modes were used, permitting the unequivocal characterization and identification of the various compounds. In view of the recent marked increase in acylcarnitine profiling activities, the comprehensively reported mass spectrometric and gas chromatographic data may be useful for reference purpose

ISSN:1076-5174    

DOI:10.1002/jms.1190300112

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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 ofm/z93. 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 hy

ISSN:1076-5174    

DOI:10.1002/jms.1190300113

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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 degradatio

ISSN:1076-5174    

DOI:10.1002/jms.1190300114

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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 all12C 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‐attache

ISSN:1076-5174    

DOI:10.1002/jms.1190300115

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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

ISSN:1076-5174    

DOI:10.1002/jms.1190300116

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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 m

ISSN:1076-5174    

DOI:10.1002/jms.1190300117

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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 the13C‐isotope distribution within an individual charge state. Instead, acetone is used here to append a C3H4group 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 t

ISSN:1076-5174    

DOI:10.1002/jms.1190300118

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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)ncapabilities by allowing the selective accumulation of any dissociation product in any step along a given dissoci

ISSN:1076-5174    

DOI:10.1002/jms.1190300119

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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

ISSN:1076-5174    

DOI:10.1002/jms.1190300120

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

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 instrumen

ISSN:1076-5174    

DOI:10.1002/jms.1190300121

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY