摘要:

AbstractElectrospray ionization mass spectrometry is an accurate and sensitive analytical method to characterize the purity of oligodeoxynucleotides being tested for pharmacological studies. We report the preparation procedure (‘desalting’) of natural and modified oligodeoxynucleotides (ODNs) and their analysis by negative‐ion electrospray mass spectrometry. We evaluate the sensitivity and the accuracy of the method for two antisense ODN sequences. Mass analysis of the 25‐mer phosphorothioate can be performed to within 0.001% accuracy (standard error of 0.05 Da) for a sample concentration of 12 pmol/μL. In addition, the adduct ion and the failure sequence can be identified to characterize the antis

ISSN:0951-4198    

DOI:10.1002/rcm.1290090102

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe gas‐phase behaviour of organophosphorus compounds such as diethylmethylphosphonate towards electron impact (EI) ionization occurring in a quadrupole ion‐trap instrument is investigated. If all ions observed in conventional EI mass spectra are detected, ion/molecule reactions are seen to occur leading to formation of protonated molecules and adduct ions such as 2M+·and [2M + H]+. The keto‐to‐enol‐like isomerization of the molecular M+·ion seems to favour proton transfer to neutral M species and a “self chemical ionization” ion is observed with correspondin

ISSN:0951-4198    

DOI:10.1002/rcm.1290090103

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractSeveral studies have investigated stereochemical effects observed in the electron ionization and low‐energy collision‐induced dissociation (CID) mass spectra of molecular ions from synthetic and natural alkaloids. More recently, it has been shown that low‐collision‐energy CID spectra of protonated epimeric alkaloids can yield additional information. For instance, three epimeric tetracyclic alkaloids studied in the present work are characterized by different cis/trans ring junction geometries and by different configurations of the ethyl group linked to the C‐ring. Low‐energy collisional spectra of the epimeric MH+ions show large differences depending both on the ring junction geometry and the stereochemistry of the side chain. Interpretation of certain specific processes invokes ion‐dipole formation, allowing internal electron transfer. Consecutive decompositions have also bee

ISSN:0951-4198    

DOI:10.1002/rcm.1290090104

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe behaviour of 3′,4′‐dihydroxybenzyl fatty acid ester towards the NH3/NH 2−system has been investigated under negative‐ion chemical ionization (NICI) conditions. Under NICI, proton abstraction takes place regioselectively at one phenol site rather than from the enolizable position. Analysis of specific fragmentations of the isotopically labelled phenoxide species prepared in the gas phase by ND3indicates that isomerization into an ion‐dipole intermediate (via charge‐promoted cleavage) takes place prior to fragmentation. Its dissociation provides fatty acid carboxylate ions (the charge is stabilized by coiling of the side chain). The acidity of the phenol group must be enhanced by the presence of a second group at the positionorthoto the first. This explains why the previous ion‐dipole complex isomerizes by proton transfer into a second isomeric form which decomposes yielding the phenoxide species, as shown by labelling experiments. Stabilization of the negative charge by hydrogen bonding (ArO−…︁H+…︁O−Ar) from the phenoxide form is possible. A similar situation characterizes 3′,4′‐dihydroxybenzyl phenyl ethyl ester and 3′,4′‐dihydroxybenzyl benzyl ester. Their behaviour was also studied to find the influence of the side chain structure on the pathway of ion‐dipole dis

ISSN:0951-4198    

DOI:10.1002/rcm.1290090105

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe aim of the present work is to study the oxidation reactions between an aromatic hydrocarbon, toluene and oxygen. Experiments have been performed in a low‐pressure plasma tubular reactor supplied by an RF 13.56 MHz generator. On‐line mass spectrometry and off‐line gas chromatography were used for a qualitative and quantitative analysis of the effluents. The reaction can lead to the formation of products in the solid (deposited on the wall of the reactor), liquid or gas state. Hydrocarbons (benzene, ethylbenzene, diphenylethane), as well as oxygenated species resulting from competition between the oxidation of the aromatic ring (phenol, cresols) and the oxidation of the alkyl side chain (benzyl alcohol, benzaldehyde), can be obtained. The power and the amount of added oxygen were studied by comparing the mass spectrometry and gas chromatography results. Reaction mechanisms are disc

ISSN:0951-4198    

DOI:10.1002/rcm.1290090106

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractTandem mass spectrometry in negative‐ion mode using ammonia as reagent gas has contributed to the differentiation of polyhydroxysteroids and to the study of stereochemical effects. The present study provides additional examples of sterochemical effects. A first observation of intramolecular OH−catalysis yielding stereospecific H2O elimination is propo

ISSN:0951-4198    

DOI:10.1002/rcm.1290090107

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe decomposition of carbon tetrafluoride (CF4) in two types of plasma reactor has been investigated by using mass spectrometry. The optimization of the plasma process requires the establishment of an adequate chemical balance between major components and also traces in the reactor effluent, in order to minimize toxic emissions by control of the proper reactor parameters. On‐line mass spectrometric characterization of the effluent has been used to optimize the CF4decomposition yield. A GC/MS protocol has been developed to quantify both major and minor components of the effluent in order to evaluate its toxicit

ISSN:0951-4198    

DOI:10.1002/rcm.1290090108

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractMatrix‐assisted laser desorption ionization (MALDI) time‐of‐flight mass spectrometry has been used to characterize the reaction products of the 18‐mer deoxyribonucleotide d(AACGGTTAACCGTTAATT) with [Pt(NH3)3(H2O)]2+andcis‐[Pt(NH3)2(H2O)2]2+. Characteristic peaks corresponding to different monofunctional adducts {18‐mer+n[Pt(NH3)3]} (n=1, 2, 3 and 4) have been observed with the triamino–monoaqua complex. With the diamino‐diaquacis‐Pt complex, formation of a chelate {18‐mer+[Pt(NH3)2]} involving two adjacent guanines has been demonstrated. A good correlation between MALDI and polyacrylamide gel electrophoresis

ISSN:0951-4198    

DOI:10.1002/rcm.1290090109

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractLithium cationized hydrophobic peptides in the molecular weight range 1900–2650 Da have been studied by liquid secondary‐ion mass spectrometry. The mass spectra exhibit characteristic lithiated sequence ions. N‐terminal [an+LiH]+and [dn+LiH]+ions together with limited C‐terminal [ypro+Li+H]+ions lead to an easy sequencing of the peptides studied, without the need for tandem mass s

ISSN:0951-4198    

DOI:10.1002/rcm.1290090110

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractGlycosylation sites in bovine α1‐acid glycoprotein (AGP) have been identified, and the inherent heterogeneity evaluated, by capillary electrophoretic and reversed‐phase liquid chromatography/electrospray‐mass spectrometric analyses of proteolytic digests of this glycoprotein. The success of these methods in locating glycopeptides relied on significant heterogeneity within each glycosylation site. In order to rapidly locate sites in glycoproteins of any degree of heterogeneity, a novel mass spectrometric method was applied to selectively identify the glycopeptides in a proteolytic digest of bovine α1‐AGP. The glycopeptides were selectively located by the generation and detection of characteristic oxonium ions from the carbohydrate moieties by collision‐induced dissociation (CID) during liquid chromatography/electrospray‐tandem mass spectrometry, and liquid chromatography/CID mass spectrometry, in which fragmentation was induced in the supersonic expansion region of the electr

ISSN:0951-4198    

DOI:10.1002/rcm.1290090111

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY