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Letter: Identification of polyborate ions in aqueous solution by electrospray ionisation ...

Ultra-high-resolution mass spectrometry was used to investigate polyborate species in aqueous solution. The mass spectrum of boric acid revealed clusters of polyborate ions. Constituents with up to 19 B atoms were assigned and 15 species and their relationship were investigated in depth with collision-induced fragmentation. Based on the observed fragments, we proposed herein a potential fragmentation pathway for the observed polyborate molecules.

Identification and relative quantification of proteins in Escherichia coli proteome by ...

A method for identifying and quantifying proteins with relatively low-cost orthogonal acceleration time-of-flight mass spectrometry (oa-ToF-MS) was tested. Escherichia coli (E. coli) K12 MG1655 cell lysate was separated by 1D gel-electrophoresis; fractions were digested and separated fast and reproducibly by ultra-performance liquid chromatography (UPLC). Peptides were identified using oa-ToF-MS to measure exact masses of parent ions and the fragment ions generated by up-front collision-induced dissociation. Fragmentation of all compounds was achieved by rapidly cycling between high- and low values of energy applied to ions. More than 100 proteins from E. coli K12 proteome were identified and relatively quantified. Results were found to correlate with transcriptome data determined by DNA microarrays.

Supplementary Material

Discovery of rifampicin as a new anti-glycating compound by matrix- assisted laser ...

An in vitro insulin glycation assay was developed for screening glycation inhibitors. The assay involves the use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for monitoring the formation of glycated insulin. The assay is simple, rapid and amenable for high throughput screening. Using this assay we have discovered a strong anti-glycation activity for the anti-tuberculosis drug rifampicin. These results were compared with bovine serum albumin glucose fluorescence assay. In addition, the IC₅₀ of rifampicin was lower than that of aminoguanidine, a known anti-glycating agent, suggesting that rifampicin is a more potent glycation inhibitor.

Differentiation of four pairs of furocoumarin isomers by electrospray ionization tandem mass ...

A mass spectrometric method based on the combined use of electrospray ionization, collision-induced dissociation (CID) and ion-trap time-of-flight (IT-ToF) tandem mass spectrometry was used to identify four pairs of furocoumarin isomers. Our results show some characteristic mass spectrometric differences in isomeric furocoumarins. In the MS² spectra, the relative abundance ratios of m/z 131 [M + H – 2CO]⁺ to m/z 143 [M + H – CO₂]⁺ and m/z 115 [M + H – CO–CO₂]⁺ of psoralen are less than one, but both ratios are greater than one in the case of isopsoralen. The relative abundance of m/z 159 [M + H – CO₂]⁺ is much higher than that of m/z 175 [M + H – CO]⁺ in the case of bergaptol, but this trend is reversed in xanthotoxol. Moreover, three diagnostic ions of m/z 189 [M + H – CO]⁺, m/z 185 [M + H – CH4O]⁺ and m/z 161 [M + H – 2CO]⁺ are observed in the MS² spectrum of xanthotoxin but not in that of bergapten. Further, two diagnostic ions of m/z 226 [M – H – CH₃ – CO]^– and m/z 210 [M – H – CH₃ – CO₂]^– are observed in the MS² spectrum of isoimperatorin but not in that of imperatorin. The relative abundance of product ions associated with some diagnostic ions can be used to characterize furocoumarin isomers.

Behaviour of 4-(-2-hydroxyethyl)-1-piperazineethanesulfonic acid under electrospray ionization ...

Our previous experiments on ESI-MS analysis of reaction mixture solutions containing HEPES (4-(-2-hydroxyethyl)-1-piperazineethanesulfonic acid), a commonly used buffer, indicated that HEPES species did not significantly suppress analyte species, even in reaction mixture solutions with significant amounts of HEPES. With the purpose of investigating the behaviour of HEPES under ESI-MS conditions, HEPES aqueous solutions and HEPES aqueous solutions containing analyte with high and low polarity and with different acid/base chemistry, were therefore investigated. For electrosprayed aqueous solutions of HEPES with concentrations above 10^–5 M, an enhanced formation of HEPES multimer ions, regarding HEPES monomer ions formation, was observed. This enhanced formation of HEPES multimer ions is much higher than the one observed for other polar compounds, such as acetyl–arginine, acetyl–lysine and histidine. Information from solution behaviour such as, HEPES concentration, solution pH, and instrumental factors, namely the capillary temperature, was related with information from mass spectra. The results obtained led us to conclude that the formation of HEPES ions is related with the initial solution composition. The influence of analyte species on HEPES species formation, for electrosprayed HEPES solutions with analyte, was also investigated. The variations observed for HEPES monomer and multimer ions abundances, which were found to be consistent with those observed for analyte monomer ions abundances, were related with type of analyte, i.e. to their acid/base nature. Strikingly, the variations observed between HEPES monomer and multimer ions abundances, enable to discriminate among the different influence of analyte species on HEPES species formation. The results obtained also enabled to provide an explanation for the observation that HEPES species do not suppress significantly analyte species ion signals, when high concentrated HEPES solutions with analyte are electrosprayed. According to our results, the association behaviour between HEPES species seems to be preserved in the gas phase during electrospray ionization. This observation may provide some information that may be useful regarding the behaviours involved in the gas phase ion formation process from charged droplets during electrospray ionization or, at least, to differentiate among behaviours.

Electron ionization-induced mass spectral study of 5-methylenecarboxy ...

Electron ionization (EI) mass spectral fragmentation of 2-thio-5-methylenecarboxy (5-methylenecarbonylalkoxy)uracils and their derivatives, five new 2-alkoxycarbonylalkylthio-5-methylenecarboxy (5-methylenecarbonylalkoxy)uracils and three new 3-oxo�thiazolo-[3,2-a]-pyrimidine-6- methylenecarbonylalkoxy-5-ones are investigated. Fragmentation pathways whose elucidation is assisted by accurate mass measurements and metastable transitions are established. The correlations between the abundances of the selected fragment ions and the molecular ions of investigated compounds are discussed. The data obtained create the basis for differentiating structural isomers and can be used for distinction of the compounds investigated from the series of 2- (or 4-) alkoxycarbonylalkylthiouracils, 2- alkoxycarbonylalkylthio-6-carboxyuracils and 1-alkoxycarbonylalkyluracils from their isomers and metamers.

Characterization of free radical spin adducts of the DIPPMPO using mass spectrometry and 31P NMR

5- Diisopropyloxy-phosphoryl-5-methyl-1-pyrroline-N-oxide (DIPPMPO) was used to trap a variety of free radicals and the stable compounds generated by the natural decomposition of the initially formed spin adducts were characterized by ³¹P nuclear magnetic resonance (NMR) and mass spectrometry. Initially, the starting spin trap DIPPMPO was completely characterized using GC-MS and its fragmentation pathway was studied in detail. Then, DIPPMPO was used to trap an oxygen-centered free radical (the hydroxyl radical ^•OH) and two carbon-centered free radicals (methyl ^•CH₃ and 1-phenyl-ethanol-1-yl ^•CCH₃(OH)Ph radicals). The ³¹P NMR signals were thus assigned and the structures of adducts were studied and confirmed by mass spectrometry. Overall, the fragmentation pathways of the radical adducts proceed mainly via the loss of the diisopropyloxy(oxido)phosphoranyl radical. For the specific case of trapping ^•OH radicals, it is possible to visualize the rearrangement of the nitroxide radical adduct to its nitrone form as invoked in the literature. This spin trapping technique, coupled with ³¹P NMR and MS, provides a tool for the identification of short-lived and low molecular weight free radicals present in a variety of processes.

Molecular ions and protonated molecules observed in the atmospheric solids analysis probe ...

Atmospheric pressure chemical ionisation (APCI) has often been used to ionise steroids in mass spectrometry, usually when interfaced to high-performance liquid chromatography (HPLC). However, in positive ion mode, a dehydrated protonated molecule is often observed with a loss of structural information. The recently introduced technique of atmospheric solids analysis probe (ASAP) has the advantage that the sample can be analysed directly and does not need to be interfaced to HPLC. Existing ionisation sources such as direct analysis in real time (DART) and desorption electrospray ionisation (DESI) have shown the advantage of direct analysis techniques in a variety of applications. ASAP can be performed on commercial atmospheric pressure ionisation (API) mass spectrometers with only simple modifications to API sources. The samples are vaporised by hot nitrogen gas from the electrospray desolvation heater and ionised by a corona discharge. A range of commercially available steroids were analysed by ASAP to investigate the mechanism of ionisation. ASAP analysis of steroids generally results in the formation of the parent molecular ion as either the radical cation M^+• or the protonated molecule MH⁺. The formation of the protonated molecule is a result of proton transfer from ionised water clusters in the source. However, if the source is dry, then formation of the radical cation is the primary ionisation mechanism.