摘要:

AbstractA two‐dimensional charged‐disk model is proposed to explain Coulomb‐induced frequencey shifting in Fourier‐transform ion cyclotron resonance (FT‐ICR) mass spectrometry. This model corresponds more closely to the actual FT‐ICR experiment than does the charged‐point model,1which we recently developed. The model consists of a uniformly charged disk of ions of mass m1, whose excited cyclotron motion is perturbed by a second uniformly charged disk of ions of mass m2, whose cyclotron motion is also excited. By looking in a rotating coordinate frame which rotates at the cyclotron frequency of the first disk, it is seen that the second disk creates an average radial force on the first disk which lowers the cyclotron frequency of the first disk. This radial force is numerically evaluated and found to be a function of the cyclotron radius, the ration of the cyclotron radius to the disk radius, and the charges of the two disks. Unlike the charged‐point model, which was flawed by having an infinite average radial Coulomb force, the average radial Coulomb force for the charged‐disk model is finite. This average Coulomb force allows the use of formulae which permit characterization of a given set of model parameters in terms of an ‘apparent Coulomb distance’, for which a model consisting of point charges with a fixed location in a rotating frame would give the same frequency shift. It is argued that the same ‘apparent Coulomb distance’ would apply for a charged cylinder model, which accounts for Coulomb‐induced line broadening in addition to Coulomb‐induced frequency shifting. It is suggested that the treatment in this paper, together with the use of elongated cells equipped with trapping screens, could permit absolute mass

ISSN:0951-4198    

DOI:10.1002/rcm.1290060102

出版商:Heyden&Son Limited    

年代:1992

数据来源: WILEY

摘要:

AbstractMatrix‐assisted laser desorption time‐of flight mass spectrometry has been used to investigate the affinity of aqueous copper ions for a 26‐residue synthetic peptide predicted to have metal‐binding properties. A specific reaction occurred upon the dirct application of aqueous CuSO4to the matrix/peptide sample remaining on the probe tip ater initial mass spectrometric investigation. Results indicated the binding of up to one copper ion per histidine residue and the loss of one proton for each bound copper. Bound copper was not returned to solution upon subsequent cold water washings of the probe tip. These results suggest that covalent interations, between the copper and the peptide, occurred during the probe‐tip application of the metal ion to t

ISSN:0951-4198    

DOI:10.1002/rcm.1290060103

出版商:Heyden&Son Limited    

年代:1992

数据来源: WILEY

摘要:

AbstractElectrospray ionization mass spectra of human hemoglobin chains and of transferrin were acquired on a magnetic sector mass spectrometer. The observed molecular ion for each hemoglobin chain was in good agreement with the theoretical isotopic distribution at a reasonable resolution of 2000. The clear separation of a variant ß‐chain in admixture with the normal counterpart at mass 15867 that differed from it by 14 Da (0.09%) ensured that a smaller mass difference could be detected. The molecular ions for human transferrin were too broad compared with the theoretical shape to determine the molecular mass accurately, probably due to the heterogeneity of the carbohydrate moiety. A decrease in mass by neuraminidase digestion, however, determined the average number of sialic acids in the molecu

ISSN:0951-4198    

DOI:10.1002/rcm.1290060104

出版商:Heyden&Son Limited    

年代:1992

数据来源: WILEY

摘要:

AbstractIonspray mass spectrometry has been used to monitor the purification of saxitoxin, the parent compound in the family of toxins responsible for paralytic shellfish poisoning (PSP), from a strain of the dinoflagellate Alexandrium excavatum. Quantitative results obtained by flow‐injection analysis are compared to those obtained by high‐performance liquid chromatography with post‐column oxidation and fluorescence detection. The coupling of liquid chromatography and capillary electrophoresis with ionspray mass spectrometry is described for the separation of mixtures of PSP toxins and the highly potent pufferfish toxin tetrodotoxin. Tandem mass spectrometry is used to provide the structural information, and the ability to distinguish isomeric PSP toxins both chromatographically and mass spectrometrically is demonst

ISSN:0951-4198    

DOI:10.1002/rcm.1290060105

出版商:Heyden&Son Limited    

年代:1992

数据来源: WILEY

摘要:

AbstractComplexes of the type [crown+M]+were observed following laser desorption ionization of 18‐crown‐6 molecules ‘doped’ with K+, Cs+, and Ba+. Laser desorption ionization of 15‐crown‐5 and 12‐crown‐4 ‘doped’ with the same metals gave [(crown)]2+[M]+type sandwich complexes. Binding energies of crown ethers with different metal ions in all such complexes have been estimated from appearance energies obtained in the collisionally‐activated dissociation of the corresponding last

ISSN:0951-4198    

DOI:10.1002/rcm.1290060106

出版商:Heyden&Son Limited    

年代:1992

数据来源: WILEY

摘要:

AbstractDetoxification of E‐destruxin into E‐diol‐destruxin, conjugated glutathion‐E‐destruxin, cysteinyl‐E‐destruxin, and phosphorylated‐E‐destruxin in vivo inLocusta migratoriais demonstrated using direct negative‐ion fast‐atom bombardment mass spectrometry (FAB‐MS) without the need for prior ext

ISSN:0951-4198    

DOI:10.1002/rcm.1290060107

出版商:Heyden&Son Limited    

年代:1992

数据来源: WILEY

摘要:

AbstractMyoglobins from horse heat muscle, horse skeletal muscle and sperm whale are widely used as calibration standards or test compounds for various mas spectrometric methodologies. In all such cases reproted in the literature, a molecular weight value is used (16950.5 and 17199, respectively) which is based on the assumption that amino acid 122 in this 153 amino‐acid‐long protein is asparagine, overlooking a published suggestion that it is aspartic acid instead. Since the mass assignment accuracy for matrix‐assisted laser desorption mass spectrometry is reproted to be ±0.01% and for electrospray ionization ±0.0025%, and error of one mass unit in ∼ 17000 would be significant. The mass‐to‐charge ration of ions of the tryptic peptide encompassing amino acid 122 derived from commercially available horse heart and horse skeletal myoglobins, the apomyoglobin of the latter, and the tryptic and chymotryptic peptide of sperm whale myoglobin proved that in both proteins amino acid 122 is indeed aspartic acid, rather than asparagine. This finding was further confirmed by the collision‐induced dissociation sectra of the [M+H]+ ions of the tryptic peptides from the horse myoglobins and the chymotriptic peptide from sperm whale myoglobin. Thus, the correct molecular weight of horse myoglobinis 16951.49 and that of the sperm whale prot

ISSN:0951-4198    

DOI:10.1002/rcm.1290060108

出版商:Heyden&Son Limited    

年代:1992

数据来源: WILEY

摘要:

AbstractUnimolecular dissociation of the molecular cations of 1,2‐expoxybutane (1), 1‐methoxypropene (2), 2,3‐epoxybutane (3), ethyl‐vinyl ether (4), 1,2‐epoxy‐2‐methylpropene (5), and 2‐methoxypropene (6)have been investigated. Different behaviour of pairs of [C4H8O]+˙ isomers (1+˙/2+˙), (3+˙/4+˙) and (5+˙/6+˙) have been demonstrated. Isomerization by epoxide ring opening and 1,4‐hydrogen migration is suggested to explain the similar unimolecular chemistry observed for the two partners

ISSN:0951-4198    

DOI:10.1002/rcm.1290060109

出版商:Heyden&Son Limited    

年代:1992

数据来源: WILEY

摘要:

AbstractSubstituted cinnamic acids were dimerized, under fluorescent or UV light, as a glassy coating on a vial then subsequently analysed by GC/MS. Mass Spectrometric analysis of the dimers formed by each acid allowed the assignment of the dimer as a truxillic or truxinic structure since these structures had distinctive fragmentation patterns; the breakdown of the truxillic acids involves a McLafferty rearrangment before fragmentation occurs, whereas the truxinic acids, which have both carboxy groups on one side and both aromatic groups on the other, fragment asymmetrically to give characteristic stilbene and dicarboxylate fragments. It is apparent from the results of the dimerization of the lcinnamic acids that, under the conditions used here, if the monomeric acid had the capacity for hydrogen bonding using the ring substituent as well as the carboxy group, the dimerization products would be overshelmingly truxillic in structure. However, if only the carboxy group could hydrogen bond, the products would be almost exclusively traxinic in structure.

ISSN:0951-4198    

DOI:10.1002/rcm.1290060110

出版商:Heyden&Son Limited    

年代:1992

数据来源: WILEY

摘要:

AbstractImidazole and pyrazole deprotonate preferentially at the 1‐position, and a number of fragmentations are best rationalized as occurring through common ring‐opened intermediate−NHCHCHCN.C‐Methylomidazoles and pyrazoles fragment

ISSN:0951-4198    

DOI:10.1002/rcm.1290060111

出版商:Heyden&Son Limited    

年代:1992

数据来源: WILEY