摘要:

AbstractThe study of host–guest chemistry in the gas phase has been pursued systematically only in the last 5 years, after sporadic interest in the 1980s, despite extensive investigation of this chemistry in the condensed phase and the success encountered in several fields of application. Most gas‐phase studies have been performed under the controlled conditions that can be achieved inside a mass spectrometer, where solvent effects are not present. At this point, the first evaluation of the achievements and knowledge emerging from these mass spectrometric investigations can be attempted. At the same time, it is possible to evaluate the most promising subjects for future research. This review undertakes these tasks, by presenting (i) applications where mass spectrometry was used to investigate condensed phase equilibria and, more extensively, (ii) experiments where host–guest complexes were formed directly in the gas phase. The latter processes are discussed in detail in relation to the structural and electronic effects, the energetic requirements and the dependence on size, rigidity, spatial geometry and functional groups of both hosts and guests. All these effects combined are likely to contribute to the strength and multiplicity of the non‐covalent bonds that allow the complex to be formed. The macro(poly)cyclic hosts considered include crown ethers, cryptands, cyclodextrins, calixarenes, cryptophanes, cavitands, carcerands and macrolides. The guests are either metal cations or organic molecules a

ISSN:1076-5174    

DOI:10.1002/jms.1190300702

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractAn analytical protocol suggested previously for the mass spectrometric sequence analysis of cyclosporins was extended by addition of methods for discrimination among isobaric amino acids differing either in the nature of the side‐chain orN‐substitution. The former goal was achieved by comparison ofB/Elinked‐scan mass spectra of corresponding collisionally activated immonium ions with those of standard amino acids and the latter by comparison ofB/Efragment ion spectra of [M + H]+and [Md+2H]+ions. The use of the improved protocol is illustrated by the structure elucidation of a novel natural cyclosporin, [Le

ISSN:1076-5174    

DOI:10.1002/jms.1190300703

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe protonated and sodium cationized pseudomolecular ions of a series of reducing and non‐reducing oligosaccharides possessing aldopentopyranosyl, 6‐deoxyaldohexopyranosyl, ketohexofuranosyl, 4‐O‐methyl glucuronopyranosyl methyl ester andN‐acetyl 2‐deoxyglucopyranosylamine units were studied using collision‐induced dissociation (CID) fast atom bombardment (FAB) mass spectrometry. The CID spectra of the [M + H]+ions provide information about the sequence of the monosaccharide units, while dissociation of the [M + Na]+ions by two‐bond ring cleavage processes gives rise to fragment ions which allow differentiation of 1 → 2 and 1 → 4 linkages. The influence of the structure of the constituent monosaccharides on the dissociation of the [M + H]+and [M + Na]+ions is discussed. An unusual type of fragmentation, which we suggest involves the elimination of internal monosaccharides residues, has not only been observed in the FAB mass spectra but also in the unimolecular decomposition and CID spectra of both [M + H]+ions and oxonium ions from several oligosaccharides containing monosaccharide residues wi

ISSN:1076-5174    

DOI:10.1002/jms.1190300704

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractGas chromatographic (GC) studies with halogen‐selective electrolytic conductivity detection (ELCD) showed that chlorinated carboxylic acids are major organochlorine compounds in lipids of eel (Anguilla anguilla) from the receiving waters of a chlorine bleaching sulphite pulp mill. To facilitate the recording of full mass spectra, chlorinated carboxylic acid methyl esters were cold‐trapped after capillary GC separation monitored with ELCD. Methyl dichlorooctadecanoate was identified using GC/mass spectrometry (GC/MS) with both electron impact (EI) and ammonia positive‐ion chemical ionization (PICI). Methyl tetrachlorooctadecanoate was indicated by GC/EIMS. Each chlorinated fatty acid was observed at two retention times, suggesting the presence of isomers. The original fatty acid methyl esters derived from the eel lipids were subjected to GC/MS in the selected‐ion monitoring mode; methyl dichlorooctadecanoate was detected using PICI and methyl tetrachlorooctadecanoate was detected using EI ion

ISSN:1076-5174    

DOI:10.1002/jms.1190300705

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractProton‐transfer reactions that proceed within methanol cluster ions were studied using an electron impact time‐of‐flight mass spectrometer. When CH3OH seeded in helium is expanded and ionized by electron impact, the protonated species, (CH3OH)nH+, are the predominant cluster ions in the low‐mass region. In CH3OD clusters, both (CH3OD)nH+and (CH3OD)nD+ions are observed. The ion abundance ratios, (CH3OD)nH+/(CH3OD)nD+, show a tendency to decrease as the methanol concentration increases, which is apparently related to the cluster structure and reaction energetics. The results suggest that the effective formation of (CH3OD)nH+ions at low concentration of CH3OD in the expansion is the result of the relatively facile rotation of methanol molecules within the smaller clusters that tend to form at low CH3OD concentration.Ab initiomolecular orbital calculations were carried out to investigate the rearrangement and dissociative pathways of ionized methanol dimer. Ion‐neutral complexes, [CH3OH2+…O(H)CH2] and [CH3OH2+…OCH3], are found to play an important role in the low‐energy pathways for production of CH3OH2++ CH2OH (and OCH3) from ionized

ISSN:1076-5174    

DOI:10.1002/jms.1190300706

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractFunctional group interactions and substituent effects ofo‐,m‐ andp‐aminobenzoic acids were examined in a quadrupole ion trap by evaluation of proton‐transfer and methylene substitution reactions. An electron‐withdrawing carboxylic acid group can enhance or reduce the gas‐phase basicity of aniline depending on its location and ability to participate directly in proton bridging. In fact, the gas‐phase basicity ofo‐aminobenzoic acid is enhanced by ∼ 7 kcal mol−1relative to themetaandparaisomers in which the substituents do not have cooperative functional group interactions. Collisionally activated dissociation studies of deuterium‐labeled ions provide evidence of proton migration from the amino group to the carboxylic acid group prior to fragmentation. Results of semi‐empirical molecular orbital calculations provided structures for the various protonated aminobenzoic acids. Foro‐aminobenzoic acid, the proton bridges between

ISSN:1076-5174    

DOI:10.1002/jms.1190300707

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe fast atom bombardment (FAB), frit‐FAB and electrospray ionization mass spectra of bis‐ammonium salts, C2+2X−, were compared. The most informative spectra were the FAB mass spectra withm‐nitrobenzyl alcohol as matrix and the Frit‐FAB mass spectra. The nucleophilic character of the iodine anion was es

ISSN:1076-5174    

DOI:10.1002/jms.1190300708

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractElectrospray coupled with tandem mass spectrometry is shown to have utility in determining the molecular mass and the sequence of short modified oligonucleotides. The product ion spectrum of a triply deprotonated molecule precursor is dominated by ions formed via two fragmentation pathways: first, fragmentation across the 5′PO phosphate bond, and second, loss of a non‐terminal base with concomitant cleavage of the ribose 3′CO bond. If either of these two pathways is complete with fragmentation occurring at each equivalent position along the phosphodiester backbone, then the oligomer may be sequenced. Alternatively, if both these pathways are only partially complete, their complementarity may be used for more extensive sequencing. The inductive effect of the modification on the nucleobase is shown to influence the latter fragmentation process. The greater the electron affinity of the base modification, the more facile is the loss of that base when the molecule is collisionally activated. In fact, this latter fragmentation dominates the product ion spectrum when a nucleobase contains a substituent that is highly inductively withdrawing. This domination can be such that few other first‐generation fragment ions are present in the product ion spectrum. Sequence information may then require utilization of second‐generation

ISSN:1076-5174    

DOI:10.1002/jms.1190300709

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

Abstract[5‐3H,13C6] Indole‐3‐acetic acid was fed to immature pericarp segments from fruits of tomato (Lycopersicon esculentumMill., cv. Moneymaker), resulting, after 24 h of incubation, in five radiolabelled peaks when analysed by reversed‐phase high‐performance liquid chromatography with radiocounting. The fractions were numbered in order of decreasing polarity. Fractions 4 and 5 had earlier been shown to contain indole‐3‐acetyl‐N‐aspartic acid and indole‐3‐acetyl‐O‐glucose. Based on results from strong alkaline hydrolysis, it had been concluded that fractions 1 and 3 contain an amide conjugate with a modified indole ring. This paper presents data supporting the structure of the labelled compounds in fractions 1 and 3 to be diastereomers of glucopyranosyl‐β‐1,4‐glucopyranosyl‐β‐1‐N‐oxindole‐3‐acetyl‐N‐aspartic acid. The identification of glucopyranosyl‐β‐1‐N‐oxindole‐3‐acetyl‐N‐aspartic acid in fraction 2 is also reported. These structures were elucidated by liquid

ISSN:1076-5174    

DOI:10.1002/jms.1190300710

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractRelative response factors (molar sensitivities relative to dibutyl phthalate) for homologous series ofn‐alkanes (C12C26), trimethylsilyl esters of C10C20fatty acids (FAs) and bistrimethylsilyl derivatives of C8C16ω‐hydroxy fatty acids (HOF As) were determined by integration of total ion chromatograms obtained using a conventional gas chromatograph‐mass spectrometer in the electron impact ionization mode. For the alkanes up to C22and for the FA‐TMS derivatives up to C18(C21including the TMS carbons), response factors increased linearly with total number of carbons (r2>0.99). The slope of this correlation (response factor = 0.0775n− 0.338, wherenis the total number of carbon atoms in each analyte) is essentially identical with those determined in earlier studies for smaller molecules not containing silicon. For the HOFA derivatives up to C14(C20including TMS carbons), the molar response factors also increased linearly with total number of carbons, but for reasons not yet apparent the regression line for these homologs was different (response factor = 0.0330n+ 0.456;r2>0.99). Response factors for higher homologs in all three series fell below the regression line for the lower homologs, the deviation increasing with increasing molecular mass and increasing GC retention time. In all three series the upper limit to the linear portion of the correlation corresponded to the homolog whose GC retention time wasca15 min under the conditions used; a high injection port temperature was found to be the most critical factor in extending the linear range of

ISSN:1076-5174    

DOI:10.1002/jms.1190300711

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY