ISSN:0951-4198    

DOI:10.1002/rcm.1290081202

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe base sequence of synthetic peptide nucleic acids (PNAs), novel antisense agents, was analyzed by positive‐ion fast‐atom bombardment tandem mass spectrometry (FAB‐MS/MS). Upon high‐energy collisional activation decomposition, PNA oligomers provided apparent MS/MS product ions resulting from specific cleavage along the PNA b

ISSN:0951-4198    

DOI:10.1002/rcm.1290081203

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractA strong research effort has been devoted in recent years to the mammalian lignans enterolactone and enterodiol because of their claimed protective effects against breast and colon cancer. Some plant lignans appear to be precursors of these molecules. This paper reports a novel identification procedure for one of these precursors, the secoisolariciresinol diglucoside, in the extracts of defatted flax‐seed meal. The procedure is based on high‐performance liquid chromatography coupled with either ionspray or continuous‐flow fast‐atom bombardment mass spectrometry. The application of these techniques allowed the identification in flax seed of two isomeric forms of this precursor for the first time. The isomers are reasonably the two diastereoisomers, due to the two equivalent stereogenic centers present in the m

ISSN:0951-4198    

DOI:10.1002/rcm.1290081204

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractElectrospray ionization tandem quadrupole mass spectrometry has been applied to a series of lysine‐substituted octaalanines and some naturally occurring peptides containing more than two basic amino acid residues. Unusually high fragmentation efficiency along with site‐specific cleavages at the outer side of and remote from basic residues were observed for collisionally activated dissociation spectra of multiply charged peptides (MCP) with basic residues in close proximity. It was suggested that Coulomb energy (CE) rather than Coulomb repulsion (CR) was responsible for promoting fragmentation of the MCP studied. A possible fragmentation mechanism of MCP is proposed, in which the conversion of CE into internal vibrational energy was brought about by intramolecular proton migration in the presence of CR between charged si

ISSN:0951-4198    

DOI:10.1002/rcm.1290081205

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe exact determination of electrostatic potential is vital in specifying the resolution in ion‐beam focusing devices such as quadrupole mass spectrometers (QMS). Current numerical routines are marked by poor convergence on boundaries and become unwieldy when the number of electrodes, 2n, is greater than four, or when the structure is modified. Using a conformal transformation we have succeeded in finding theexactelectrostatic potential distribution everywhere within a QMS which contains four cylindrical electrodes. All the coefficients in the multipole expansion of the potential are readily calculated. The boundary value problem is solved by matching coefficients on the electrode surface, which is a circle embedded in the transformed coordinate frame. We have proven that for every allowed position of the electrode centre,R, there exists a corresponding electrode radius,r, for which the dodecapole term in the potential expansion vanishes. Our analytically obtained relationship between the above‐mentioned parameters differs slightly from that in current use. As these parameters are based on an exact solution, their practical use in mass determination may be considera

ISSN:0951-4198    

DOI:10.1002/rcm.1290081206

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractResolution in Fourier spectra can be significantly enhanced by displaying magnitudes of the complex peak derivatives with respect to frequency. These derivatives are computed by the judicious application of a new kind of windows, which reduce peak widths. When thus sharpened peaks are purely Lorentzian, then simple linear or parabolic regressions allow one to compute their parameters. A Fourier‐transform ion cyclotron resonance mass spectrometric example of such an improvement is presente

ISSN:0951-4198    

DOI:10.1002/rcm.1290081207

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe ability of liquid chromatography combined with positive‐ion low‐collision‐energy tandem mass spectrometry for screening and characterization of atrazine metabolites in aqueous solutions is examined. The strategy used was defined after investigations on the structure and origin of the main daughter ions through experiments done by desorption chemical ionization with NH3or ND3as reagent gas. Following this, a three‐step procedure was proposed which included parent‐ion spectra based on [XCNC(NH)NH2]+(with X  Cl or OH) ions apparently formed via ion‐dipole complexes and found to be highly diagnostic for chlorotriazines and hydroxytri

ISSN:0951-4198    

DOI:10.1002/rcm.1290081208

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThis study demonstrates the influence of cooling time, applied prior to (and after) resonance excitation, on the internal energy carried by ions subjected to tickle excitation. Competitive fragmentations of ionized butylbenzene have been used to estimate the internal energy average transferred during collision processes. Two competitive effects have been observed by using a delay time before tickle: kinetic energy relaxation (up to 15 ms) related to an internal energy decrease effect and, at higher cooling time values, collisional excitation with helium buffer gas allows one to increase the internal energy of precursor ions.

ISSN:0951-4198    

DOI:10.1002/rcm.1290081209

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractA cyclodepsipeptide‐glutathionyl conjugate has been analysed for the first time using negative‐ion fast‐atom bombardment linked‐scan mass spectroscopy. Fragment anions produced by collision‐induced dissociation are

ISSN:0951-4198    

DOI:10.1002/rcm.1290081210

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractA new strategy, based on sequential product‐ion spectra (MS2and MS3) and reaction‐intermediate scanning (MS3), provides a rapid and unambiguous sequence determination of E‐destruxin, a cyclodepsipeptidic toxin fromMetarrhizium anisopliaef

ISSN:0951-4198    

DOI:10.1002/rcm.1290081211

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY