Desorption Chemical Ionization Mass Spectrometry Research Articles

Further studies on the thermal decomposition processes in polycarbonates

The thermal decomposition mechanisms of poly(trimethylene carbonate), poly(neopentylene carbonate), poly(2-phenyltrimethylene carbonate) and poly(p-xylylene carbonate) have been investigated by EI/CI direct pyrolysis mass spectrometry and by desorption chemical ionization (DCI) mass spectrometry. The results indicate that all four polycarbonates decompose by an intramolecular exchange, an ionic process that produces cyclic carbonates as pyrolysis products. Other thermal processes (Reactions 1c-li, Scheme 1) also occur during the pyrolysis, and are all explained on the basis of well-established ionic reactions (Scheme 1).

A facile method for the localization of a double bond in aliphatic compounds

AbstractOlefinic aliphatic compounds can be transformed on a microscale into the corresponding epoxides by reaction with m‐chloroperbenzoic acid. The crude reaction mixture can be analysed without further work‐up, by gas chromatography followed by chemical ionization mass spectrometry or desorption chemical ionization mass spectrometry with nitric oxide as the chemical ionization gas.

Applications of thin layer chromatography, high performance liquid chromatography and mass spectrometry in the fermentation and isolation of the antibiotic nybomycin.

Thin layer chromatography (TLC), high performance liquid chromatography (HPLC) and mass spectrometry (MS) methods have been developed for the analysis of the antibiotic nybomycin, its derivatives deoxynybomycin and nybomycin acetate, during the fermentation and isolation of nybomycin. Using a quantitative HPLC based assay, the time course of nybomycin production (nybomycin titers) in 1000 liter fermentations was determined. Desorption chemical ionization mass spectrometry (DCI/MS) of standard nybomycin samples, fermentation broth samples and purified fractions suggested the co-production of deoxynybomycin which was not reported previously from this organism. TLC and HPLC were used to confirm the presence of deoxynybomycin in the crude extracts of fermentation broths.

Characterization ofin vitro metabolites of the antipsychotic drug tiospirone by mass spectrometry

Metabolism of the antipsychotic drug tiospirone was studied in vitro with phenobarbital-induced rat liver microsomes. Metabolites were isolated and purified to homogeneity by high-performance liquid chromatography. It was possible to characterize the metabolites as trimethylsilyl (TMS) derivatives by gas chromatography/electron impact mass specrometry (GC/EIMS) so long as the sulfur was present in the reduced form. However, sulfoxide and sulfone analogs of tiospirone underwent reductive decomposition on the GC column. In addition, no molecular ions were observed in the EI spectra of these analogs. Desorption chemical ionization/mass spectrometry (DCI/MS) in the positive ion mode with methane as reagent gas successfully distinguished sulfoxides and sulfones from their parent sulfides. Protonated molecular ions were observed together with structurally significant fragment ions. Five microsomal metabolites of tiospirone were characterized by a combination of GC/EIMS and DCI/MS. From the structures of the metabolites three major pathways of metabolism were identified: N-dealkylation of the butyl side chain at the piperazinyl nitrogen, hydroxylation alpha to the glutarimidyl carbonyl at C-6 on the azaspirodecanedione ring, and sulfoxide formation on the benzisothiazole moiety.

Photodegradation of CI Acid Orange 60 and CI Acid Green 25 in an Amide Environment

Photodegradation, in solution and in nylon 66 fiber, of two automotive acid dyes (CI acid orange 60 and CI acid green 25) for nylon carpet has been investigated. Photofading in solution was done in dimethylformamide (DMF) with the aid of a 254-nm light source, and the work in nylon fiber used the xenon arc light of an Atlas CI 65 weatherometer. The results show that these dyes fade via a photoreduction process under both sets of conditions, and they suggest that DMF is a suitable model for nylon in characterizing the photodegradation of acid dyes. The structures of the degradation products of the two dyes were determined with the aid of fast atom bom bardment and desorption chemical ionization mass spectrometry and by HPLC and TLC comparisons with authentic samples.

Desorption chemical ionization and field desorption mass spectrometric analysis of antitumor Catharanthus (Vinca) alkaloids

Antitumor Catharanthus (Vinca) alkaloids, vinblastine and vincristine, and their chemically modified derivatives N-deformylvincristine, N-deformyl-4-deacetylvincristine, vindesine, 4-deacetylvinblastine, and 4-deacetylvincristine, after purification by high-pressure liquid chromatography were analyzed using the soft ionization technique of desorption chemical ionization mass spectrometry or field desorption mass spectrometry. The dominant signal from the free bases by these techniques was their respective protonated molecular ion. These studies suggest that these techniques can be conveniently applied for characterization of the metabolites and/or in vitro degradation products of the antitumor alkaloids.

Chemical ionization mass spectral characteristics of analogs of steviol, the aglycone of the plant-derived sweetening agent, stevioside

The use the naturally occurring ent-kaurene diterpene glycoside, stevioside, as a sucrose substitute in several countries has resulted in the need for improved methods to analyze its potential metabolites. Altogether 21 diterpenes related in structure to steviol, the aglycone of stevioside, have been subjected to desorption chemical ionization mass spectrometry using methane, ammonia and dimethyl ether as reagent gases. Both methane and ammonia provided the molecular weights of these derivatives, but failed to produce any adduct ions of particular diagnositc value for differentiating compounds in the steviol series. On the other hand, dimethyl ether produced positive ion chemical ionization spectra that differed according to the nature of the functional groups represented among the steviol derivatives examined. Prominent adduct ions observed using dimethyl ether were [M + 1 − 18]+, [M + 1]+, [M + 45 − 32]+, [M + 45]+ and [M + 47]+. Mechanisms have been proposed for the formation of these adducts.

Host-guest complexation in the gas phase by desorption chemical ionization mass spectrometry

Host-guest complexation in the gas phase by desorption chemical ionization mass spectrometry

The synthesis of disperse and cationic dyes from acid dye structures

This paper is concerned with the conversion of some mono- and di-sulfonated naphthol azo dyes to disperse dyes suitable for poly(ethyleneterephthalate) fibers, and cationic dyes for cationic dyeable polyester and acrylic fibers. The chemical structure of these new dyes has been confirmed by 1H-NMR, FAB or DCI mass spectrometry, and in some cases by elemental analysis. Some fastness properties and absorption spectral data of both types of dyes are also reported, as well as an interesting limitation in the naphthalene-based acid dyes suitable for the described conversion.

Adduct formation identification between phenyl glycidyl ether and 2′-deoxyadenosine and thymidine by chromatography, mass spectrometry and nuclear magnetic resonance spectroscopy

Thymidine 2′-deoxyadenosine were reacted with phenyl glycidyl ether in order to study the formation of the corresponding 2′-deoxynucleoside adducts. Separation methods were elaborated using either reversed-phase high-performance liquid chromatography with photodiode-array detection, or centrifugal circular thin-layer chromatography. The adducts were isolated on a preparative scale and were fully characterized by UV spectroscopy, desorption chemical ionization and fast atom bombardment mass spectrometry and 270- and 360-MHz 1H NMR spectrometry. For thymidine the main adduct was characterized as N-3-(2-hydroxy-3-phenoxypropyl)thymidine. With 2′-deoxyadenosine, predominantly N-l-(2-hydroxy-3-phenoxypropyl)-2′-deoxyadenosine was formed. With longer reaction times, the formation of a minor amount of dialkylated 2′-deoxyadenosine was observed. These nucleoside adducts will be used as marker compounds for studies of DNA adduct formation.

Molecular paleobotany ofNyssaendocarps

SUMMARY Fruit endocarps of three recent Nyssa species from southern Georgia and endocarps of three Nyssa species from the late-Oligocene Brandon lignite, VT. are characterized and compared using pyrolysis gas chromatography–mass spectrometry (PYGCMS), pyrolysis-mass spectrometry (PYMS and desorption chemical ionization mass spectrometry DCIMS), and microscopic techniques. PYGCMS and PYMS demonstrated that during the lignitization process almost all of the carbohydrate material is removed from the endocarp fibre walls. Some hexose oligomer residues do survive lignitization as levoglucosan was observed in the PYGCMS trace of the lignitic endocarp N. fissilis and mass peaks indicative for anhydrohexose oligomers were observed in DCIMS spectra of N. fissilis and N. brandoniana. The PYGCMS data on the mixed guaiacyl–syringyl lignin in the recent and fossil endocarp wall have very similar pyrolysis product distributions. The abundance of phenolic pyrolysis products with aliphatic side chains suggest a different less oxygenated lignin in the endocarps compared to the Nyssa xylem cell walls. In spite of the significant chemical changes which occur during the early coalification process considerable microscopic detail can be preserved. Some fibre cell walls even retained an anisotropic character which may be caused by preserved crystalline cellulose. The effect of storage conditions on the chemistry of the paleobotanical samples was investigated by PYMS and multivariate analysis. Fossil endocarps stored in glycerin/ethanol experienced some extraction of a soluble lignin-derived fraction whereas water-stored endocarps did not. The residues of water glycerol/ethanol stored samples have similar polyphenolic polymers.

Mass spectrometric analysis of anatoxin-a.

Secondary ion mass spectrometry (SIMS), gas chromatography/mass spectrometry (GC/MS), desorption chemical ionization/mass spectrometry (DCI/MS), and thermospray/mass spectrometry (TSP/MS) were evaluated for the detection of a low-molecular weight biological toxin, anatoxin-a. The lowest detection limit was obtained using isobutane or ammonia DCI/MS. Tandem mass spectrometry (MS/MS) was used to enhance the selectivity and sensitivity of the analysis. The detection limit for the pure material is 10 pg, and 100 pg of the toxin can be analyzed directly from urine using DCI/MS/MS.

Aspergillus parasiticus Accumulates Averufin and Versicolorin A in the Presence of Bicarbonate

Sodium bicarbonate has previously been shown to inhibit aflatoxin production by Aspergillus parasiticus. The abnormal pigmentation of colonies grown in the presence of bicarbonate suggested that intermediates of the aflatoxin biosynthetic pathway were accumulating. Aspergillus parasiticus NRRL 2999 cultures grown in the presence of sodium bicarbonate were extracted with acetone and chloroform. Thin layer chromatograms of these extracts were compared to the thin layer chromatograms of extracts from mutant strains which accumulate norsolorinic acid, averufin, and versicolorin A. Development by four separate solvent systems suggested that averufin and versicolorin A accumulated in the bicarbonate-grown wild type cultures. The identity of these intermediates was confirmed by desorption chemical ionization mass spectrometry which showed M+1 peaks of 369 and 339 where M is the molecular weight of averufin and versicolorin, respectively.

New-found phenolic glycolipids in Mycobacterium bovis BCG: Presence of a diglycosylated glycolipid

Abstract A crude phenolic glycolipid extract from Mycobacterium bovis bacille Calmette-Guerin (BCG) was fractionated until homogeneity at the intact level into four phenolic glycolipids called B, B-1, B-2, and B-3 according to their polarity. The apolar one, which is the most abundant was assigned to the well-known mycoside B. The B-2 and B-3 phenolic glycolipids were purified by direct-phase high performance liquid chromatography using a 5 micron Spherisorb column but were only recovered in small amounts (3 mg). A linear gradient of 0-20% methanol in chloroform was used. The B-1, B-2, and B-3 glycolipids were subjected to suitable modern analytical techniques selected for their potential to elucidate the structure at the intact level. Desorption chemical ionization-mass spectrometry allowed the molecular mass of B-3 to be determined as 1652 Da for the major homolog establishing the molecular formula as C103H192O14. Thus, the B-3 polar phenolic glycolipid contained two deoxyhexoses, one molecule of phenolphthiocerol esterified by two molecules of mycocerosic acid. Using two-dimensional 1H NMR (correlated chemical shift and nuclear Overhauser effect spectroscopy) at the intact level the B-3 oligosaccharide structure was determined as an alpha-L-Rhap-(1----3)-2-O-Me-alpha-L-Rhap. This is the first report of a diglycosylated phenolic glycolipid in a nonpathogenic mycobacteria. The disaccharide unit, the antigenic determinant, appears to be characteristic of M. bovis BCG. This polar glycolipid B-3 and the apolar ones, B-1 and B-2, were reactive in enzyme-linked immunosorbent assay against serum from rabbit hyperimmunized with M. bovis BCG.

Characterization of high molecular weight macrocycles by desorption chemical ionization mass spectrometry

AbstractA series of multi‐armed macrocycles with molecular weights up to 4400 Da was studied by desorption chemical ionization. Both negative‐ and positive‐ion spectra exhibited excellent signal‐to‐noise ratio, despite the limited amount of material sampled (0.1–1 pmol). The molecular ions generally represent the base peaks of the spectra, but the extent of fragmentation increases as the source temperature is raised.

Evidence for oligomers in pyrolysates of microcrystalline cellulose

Microcrystalline cellulose was analysed by platinum filament pyrolysis desorption chemical ionisation mass spectrometry (DCI-MS) under ammonia chemical ionisation conditions. This polysaccharide was also pyrolysed on a preparative scale as well as by off-line Curie-point pyrolysis and subsequently analysed by ammonia DCI-MS. The DCI-MS data of the native polysaccharide show ion series corresponding to ammonium adduct ions of anhydrocello-oligosaccharides up to anhydrocello-hexaose. In the preparative-scale and the off-line Curie-point pyrolysates up to the pentamer could be detected. Related ion series corresponding to the ammonia adducts of ring fragments left on the saccharide chain were also seen. It is uncertain whether these compounds are formed during pyrolysis directly from the native polymer or arise from the corresponding anhydro-oligosaccharides during the ionisation process. The three pyrolysis methods tested yield comparable results with respect to the pyrolysis products formed, which indicates that the mechanism of formation of anhydrocello-oligosaccharides from cellulose is a generally significant process. Curie-point pyrolysis-gas chromatography data should be interpreted with caution since the oligomeric part of the pyrolysate is not monitored by this method.

Scope and limitations of several pyrolysis methods in the structural elucidation of a macromolecular plant constituent in the leaf cuticle of Agave americana L.

Cuticles of Agave americana contain a substantial amount of an insoluble, non-hydrolyzable macromolecular substance of a highly aliphatic nature. Based on Fourier transform infrared (FTIR) and 13C cross-polarization magic angle spinning NMR spectroscopy it was established that the isolated macromolecular substance consists of a polysaccharide and polymethylene moiety in an estimated ratio of 60:40 by weight. After treatment with acid this ratio changed to 37: 63. The isolates obtained before and after the acid treatment were subjected to Curie-point pyrolysis-gas chromatography with flame ionization detection, Curie-point pyrolysis-gas chromatography/mass spectrometry, Off-line pyrolysis in combination with gas chromatography and gas chromatography/mass spectrometry, desorption chemical ionisation mass spectrometry, time/temperature-resolved pyrolysis-field ionization mass spectrometry and heating experiments in a closed system in order to elucidate the molecular structure. Each of the methods applied has its own specifications with respect to pyrolysis conditions and response factors of different classes of pyrolysis products. The data obtained are highly complementary and, in combination with FTIR and 13C NMR, several new features of the insoluble, non-hydrolyzable aliphatic biopolymer were revealed.

Comparison of electron impact, desorption chemical ionization, field desorption, and fast atom bombardment mass spectra of nine monosubstituted Group VI metal carbonyls

Nine monosubstituted group VI metal pentacarbonyls of the type M(CO)/sub 5/L (where M = Cr, Mo, or W; and L = P(C/sub 6/H/sub 5/)/sub 3/, As(C/sub 6/H/sub 5/)/sub 3/, or Sb(C/sub 6/H/sub 5/)/sub 3/) were synthesized and purified by recrystallization so that they contained no unbound ligands, excess reagents, or other contaminants as measured by high-performance liquid chromatography. Positive ion mass spectra were obtained by electron impact (EI), desorption chemical ionization (DCI), field desorption (FD), and fast atom bombardment (FAB) mass spectrometry. B/E linked scanning was used to confirm the fragmentation pathway in FAB mass spectra. While all four ionization methods formed molecular ions, M/sup +/, the desorption ionization methods tended to produce more abundant molecular ions than EI. FD, for instance, formed molecular ions without any fragmentation. The most abundant fragment ions of the ligand (L) were observed with DCI. FAB spectra contained abundant molecular ions and extensive structural information in ion fragments.

Characterization of a lipid-rich fraction synthesized by streptomyces avermitilis

Isolation of the macrocyclic lactone parasiticide avermectin and other closely related natural products produced by Streptomyces avermitilis also yields a lipid-rich fraction. The latter has been characterized by techniques based on gas-liquid chromatography ( GLC) and mass spectrometry ( MS). Initial examination of the lipid-rich fraction by direct probe electron-impact ( El) MS and packed-column GLC showed that it consists primarily of a mixture of triglycerides possessing C 14-C 17 acyl groups. Further examination of this fraction by capillary column GLC- MS demonstrated that it contains low levels of C 15-C 17 free fatty acids, squalene and diglycerides and, as the major components, at least ten mixed acyl triglycerides (total number of acyl carbon atoms ranging from 43 to 50). Prominent among the triglycerides were a C 15-C 15-C 16 species, a C 15-C 16-C 16 species and a C 15-C 16-C 17 species. Capillary-column GLC and GLC- MS of the fatty acid methyl esters resulting from transesterification demonstrated that the major triglyceride acyl groups are anteiso-C 15(12-methyltetradecanoyl), iso-C 16 (14-methylpentadecanoyl), n-C 16 (hexadecanoyl) and anteiso-C 17(14-methylhexadecanoyl). Lower levels of the methyl esters of the following fatty acids were observed: iso-C 14(12-methyltridecanoic), n-C 14(tetradecanoic), iso-C 15(13-methyltetradecanoic), n-C 15(pentadecanoic), iso-C 17 (15-methylhexadecanoic) and n-C 17 (heptadecanoic). Little evidence was seen for either unsaturated acyl groups or acyl groups of less than 13 or more than 18 carbon atoms. Desorption chemical ionization MS (ammonia reagent gas) analysis confirmed the nature of the lipid-rich fraction, and is an attractive one-step approach for determining the molecular weights and distribution of triglycerides in a mixture.

Bacteriophage endoglycanases and desorption chemical ionization mass spectrometry (DCI-MS) to sequence bacterial antigens.

Bacteriophage endoglycanases and desorption chemical ionization mass spectrometry (DCI-MS) to sequence bacterial antigens.