252Cf plasma-desorption mass spectrometry of lipid A from Enterobacter agglomerans.

Endotoxins from gram-negative bacteria are believed to be causative agents of byssinosis, an occupational pulmonary disease associated with exposure to cotton dust in textile mills. Lipid A preparations from Enterobacter agglomerans, a gram-negative bacterium commonly found in cotton and cotton dust, have been analyzed using plasma-desorption mass spectrometry. Results indicate the existence of at least two lipid A types which differ only by the presence of an additional oxygen atom whose position has been localized to the acyloxyacyl ester-linked side-chain of the distal portion of the molecule. The lower molecular weight compound of the two structures has the same molecular weight and presumably the same empirical formula as a well-characterized lipid A from Salmonella minnesota. The mass spectra of lipid A compounds obtained from S. minnesota and E. agglomerans show strong similarities. Palmitoyl, hydroxymyristoyl, myristoyl, and lauroyl side-chains which are known to be present in the former are inferred from spectral evidence to be present in the latter.     

Plasma lipid analysis by hydrophilic interaction liquid chromatography coupled with electrospray ionization tandem mass spectrometry

A novel method for the analysis of endogenous lipids and related compounds was developed employing hydrophilic interaction liquid chromatography with electrospray ionization tandem mass spectrometry. A hydrophilic interaction liquid chromatography with carbamoyl stationary phase achieved clear separation of phosphatidylcholine, lysophosphatidylcholine, sphingomyelin, ceramide, and mono‐hexsosyl ceramide groups with good peak area repeatability (RSD% < 10) and linearity (R² > 0.99). The established method was applied to human plasma assays and a total of 117 endogenous lipids were successfully detected and reproducibly identified. In addition, we investigated the simultaneous detection of small polar metabolites such as amino and organic acids co‐existing in the same biological samples processed in a single analytical run with lipids. Our results show that hydrophilic interaction liquid chromatography is a useful tool for human plasma lipidome analysis and offers more comprehensive metabolome coverage.     

Differentiation of diiodothyronines using electrospray ionization tandem mass spectrometry

Diiodothyronines 3,5-diiodothyronine (3,5-T2), 3',5'-diiodothyronine (3',5'-T2), and 3,3'-diiodothyronine (3,3'-T2) are important metabolites of 3,5,3'-triiodothyronine (T3) and 3,3',5'-triiodothyronine (rT3; reverse T3). In this paper, a novel and rapid method for identifying and quantifying 3,5-T2, 3',5'-T2 and 3,3'-T2 has been introduced using electrospray ionization tandem mass spectrometry (ESI-MS/MS). Fragmentation patterns were proposed on the basis of our data obtained by ESI-MS/MS. MS2 spectra in either negative ionization mode or positive ionization mode can be used to differentiate 3,5-T2, 3',5'-T2 and 3,3'-T2. On the basis of the relative abundance of fragment ions in MS2 spectra under the positive ionization mode, quantification of the 3,5-T2, 3',5'-T2 and 3,3'-T2 isomers in mixtures is also achieved without prior separation.     

Differentiation of monoiodothyronines using electrospray ionization tandem mass spectrometry

In this work two monoiodothyronines, 3-T1 and 3'-T1, have been analyzed using electrospray ionization tandem mass spectrometry (ESI-MS/MS). Fragmentation patterns were proposed based on our data obtained by ESI-MS/MS. MS2 spectra in either negative or positive ion mode can be used to differentiate 3-T1 and 3'-T1. Based on the relative abundance of fragment ions in MS2 spectra in the negative ion mode, quantification of the 3-T1 and 3'-T1 isomers in mixtures is achieved without prior separation. Solid-phase extraction in combination with ESI-MS/MS provides a practicable procedure that can be used to determine the molar ratio of 3-T1 and 3'-T1 in human serum with an error less than 3%. The detection limits for 3-T1 and 3'-T1 were 0.5 and 0.7 pg/microL, respectively.     

Structure of Lipid A from Pseudomonas corrugata by electrospray ionization quadrupole time-of-flight tandem mass spectrometry

The use of the electrospray ionization quadrupole time-of-flight tandem mass spectrometry (ESI-QTOFMS) technique for the structural determination of Lipid A from Pseudomonas corrugata is described. This technique appears to be more sensitive with respect to other commonly used tandem mass spectrometric approaches, and was very valuable in the structural determination of the highly heterogeneous Lipid A fractions. The Lipid A fraction consists mainly of a pentaacyl component in which 3-hydroxydecanoyl [10:0(3-OH)] and 3-hydroxydodecanoyl [12:0(3-OH)] are linked as primary acyl substituents to the classical bisphosphorylated beta-(1' --> 6)-linked D-glucosamine disaccharide. Secondary substitution of N-acyl fatty acids with dodecanoyl residues [12:0] and/or its 2-OH derivatives was also observed.     

Structural determination of sphingomyelin by tandem mass spectrometry with electrospray ionization

Alkaline metal adduct ions of sphingomyelin were formed by electrospray ionization in positive ion mode. Under low energy collisionally activated dissociation (CAD), the product ion spectra yield abundant fragment ions representative of both long chain base and fatty acid which permit unequivocal determination of the structure. Tandem spectra obtained by constant neutral loss scanning permit identification of sphingomyelin class and specific long chain base subclass in the mixture. The fragmentation pathways under CAD were proposed, and were further confirmed by source CAD tandem mass spectrometry. The total analysis of sphingomyelin mixtures from bovine brain, bovine erythrocytes, and chicken egg yolk is also presented.     

Discrimination of cyclic peptide diastereomers by electrospray ionization tandem mass spectrometry

In this research, the characteristic ions' abundance ratio between two isomers A and B in MS/MS mass spectra was defined as a parameter for discriminating diastereomers. Through this ratio, the discrimination of four pairs of cyclic peptide (CP) diastereomers was successfully achieved. Furthermore, in the analysis of diastereomers' mixtures, both calibration curve and calculational methods were substantiated to have high precision and accuracy. The average absolute errors of the two methods were 2.0 and 2.5% in the 48 measurements of 16 samples, respectively. This research provided a promising approach for the analysis of the CP diastereomers in the fields of asymmetrical synthesis, chiral natural products and structural biology by ESI‐MS/MS. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterization of the rutin-metal complex by electrospray ionization tandem mass spectrometry.

According to the strong application background of bioflavonoid and metal-flavonoid complexes, novel electrospray ionization tandem mass spectrometry (ESI-MSn) was applied to investigate the structure and fragmentation mechanism of transition metal-rutin complexes. In the full-scan mass spectra, different stoichiometric ratios of rutin-metal complexes were found. In the reaction between rutin and Cu, four kinds of complexes with four different stoichiometric ratios were produced. In the reaction between rutin and Zn, Mn(II), and Fe(II), only two kind of complexes with stoichiometric ratios of 1:1 and 1:2 occured. In further tandem mass spectrometric experiments of different rutin-metal complexes, product fragments came from the neutral loss of the external rhamnose and the internal glucose unit, oligosaccharide chain, aglycone, and small organic molecules. According to the MSn data, we proposed a mechanism for all fragments of the rutin-Cu complex A and the structure of two rutin-Cu complexes, C and D.     

Characterization of a novel microperoxidase from Marinobacter hydrocarbonoclasticus by electrospray ionization tandem mass spectrometry

Microperoxidases are small heme-peptides obtained by proteolytic digestion of cytochrome c, exhibiting peroxidase activity. They consist of a short- or medium-length polypeptide chain, covalently linked to an iron protoporphyrin IX moiety via two thioether bonds involving Cys residues at the c-porphyrin A and B pyrrole rings. These small molecules are interesting for a wide range of possible applications. We have structurally characterized, by means of electrospray ionization (ESI) mass and tandem mass spectrometric experiments, a novel microperoxidase called MMP-5 (Marinobacter MicroPeroxidase-5), obtained by proteolytic digestion of cytochrome c552, a monoheminic electron-transfer protein isolated from Marinobacter hydrocarbonoclasticus. This microperoxidase, which still maintains the functional peptide moieties for peroxidase activity, is devoid of the two amino acids intercalating the Cys residues linked to the c-porphyrin, thus increasing its water solubility. Once submitted to the ESI source potential, MMP-5 showed an interesting tendency for the reduction of the iron protoporphyrin substructure. This behaviour was clearly evidenced by the mass shift exhibited by the reduced form.     

Fragmentation of plumeran indole alkaloids from Aspidosperma spruceanum by electrospray ionization tandem mass spectrometry

The fragmentation of six plumeran indole alkaloids (PIAs) previously isolated from Aspidosperma spruceanum has been investigated by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) in the positive ion mode. The fragmentation pathways have been established on the basis of MS/MS experiments using fragment ions generated in‐source and deuterium‐labeled alkaloids as precursor ions and on the basis of accurate mass measurements. Our results demonstrated that the fragmentation routes observed for the protonated PIAs are essentially derived from a pericyclic reaction and from the opening of rings D and E, followed by 1,4‐hydrogen rearrangements. Product ions resulting from radical eliminations were also observed, contrary to the ‘even‐electron rule’. Our data reveals that some product ions from protonated PIAs provide crucial information for the characterization of the acyl substituent at N‐1, the methoxyl and hydroxyl groups at the aromatic moiety, and give evidence of an ether bridge between C‐18 and C‐21. The data reported here were used for the dereplication of these compounds in a stem bark methanolic extract of Aspidosperma spruceanum. Copyright © 2010 John Wiley & Sons, Ltd.     

Direct analysis by electrospray ionization tandem mass spectrometry of mixtures of phosphatidyldiacylglycerols from Lactobacillus

Electrospray ionization followed by collision-induced dissociation in a quadrupole ion trap mass spectrometer of mixtures of deprotonated phosphatidyldiacylglycerols afforded a group of three diagnostic ions of convenient abundance for each phosphatidyldiacylglycerol (PG) present in the mixture. Thus, it was possible to determine unmistakably the identity and substitution positions (sn-1 or sn-2) for both acyl groups of each PG present in the mixture. The method also allows the study of isomeric mixtures of PG and mixtures containing minor amounts of some PG from crude extracts of Lactobacillus acidophillus. The present results improve those of previous studies using fast atom bombardment and electrospray ionization tanden mass spectrometry, in which it was reported that it was possible to differentiate the identity and position of the sn-2 acyl substituent only by the presence of one ion, with variable abundance.     

Study of electrospray ionization tandem mass spectrometry of the benzofuranone compounds

A detailed analysis of benzofuranone compounds under multiple tandem mass spectrometry （ESI-MS^n） conditions is reported. Element composition data of the fragment ions were obtained with the aid of comparison of the multiple tandem mass spectra of four compounds, and the structures of which are identical except for some substituted groups or epimers or cis-trans-isomers. Attempts have been made to provide rational pathways for the formation of the fragment ions from these protonated compounds. And the structure-fragmentation relationships will facilitate the characterization of the structures of other analogs.     

Study of the electrospray ionization tandem mass spectrometry of sildenafil derivatives

A detailed analysis of the product ion spectrum generated from the protonated molecule of sildenafil (Viagra(R)) under multiple tandem mass spectrometry (ESI-MS(n)) conditions using an ion-trap mass spectrometer is reported. Molecular composition data of the fragment ions were obtained with the aid of comparisons of the multiple tandem mass spectra of eight sildenafil derivatives in two series, the structures of which are identical except for some substituted alkyl groups. Attempts have been made to provide rational pathways for the formation of the fragment ions from these protonated sildenafil derivatives. The structure-fragmentation relationships will facilitate the characterization of the structures of other sildenafil analogs.     

Characterization of isomeric 1,2,4-oxadiazolyl-N-methylpyridinium salts by electrospray ionization tandem mass spectrometry

The mass spectrometry behavior of 1,2,4-oxadiazolyl-N-methylpyridinium salts has been investigated. These substances are of current interest as perspective ionic liquids, compounds used as green solvents for synthesis, and for their catalytic properties. The studies have been developed through ESI-MS/MS experiments. The obtained results demonstrate that a readily distinction between the two isomeric classes, 3- N-methylpyridinium- and 5-N-methylpyridinium-1,2,4-oxadiazoles, is possible through ESI-MS/MS experiments. A deeper investigation on the principal fragmentation pathways of characteristic ions has been also developed.     

Structural characterization of isoprenylated flavonoids from Kushen by electrospray ionization multistage tandem mass spectrometry

Eighteen isoprenylated flavonoids (8 flavanones, 3 flavanols, and 7 chalcones) isolated from Kushen or synthesized were studied by positive and negative ion electrospray ionization multistage tandem mass spectrometry (ESI-MS(n)). Plausible fragmentation patterns were obtained by comparing their MS(n) spectra with each other, which were further supported by high-resolution MS data and two model compounds. It was shown that the 2'-OH group would make the C-ring of flavonoids studied more labile through a six-membered mechanism, resulting in base peaks of (1,3)A+ (positive mode) and (1,4)A(-) (negative mode). In addition, the 2'-OH is also responsible for the neutral loss of water in (+)ESI/MS(2) of flavanones. The neutral loss of water (or methanol) in (-)ESI/MS(2) of flavanols was elucidated by a E2 elimination mechanism. Different relative abundances (RA) of (1,3)A(+) and S(+) in (+)ESI/MS(2) spectra were used to discriminate flavanones with their open-ring products, chalcones, since the equilibrium for flavanone<-->chalcone isomerization in ESI ion source could not be obtained in positive mode.     

Collision-induced dissociation pathways of anabolic steroids by electrospray ionization tandem mass spectrometry

Anabolic steroids are structurally similar compounds, and their product-ion spectra obtained by tandem mass spectrometry under electrospray ionization conditions are quite difficult to interpret because of poly-ring structures and lack of a charge-retaining center in their chemical structures. In the present study, the fragmentation of nine anabolic steroids of interest to the racing industry was investigated by using triple quadrupole mass spectrometer, Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer, and a linear ion trap instrument. With the aid of an expert system software (Mass Frontier version 3.0), accurate mass measurements, and multiple stage tandem mass spectrometric (MS(n)) experiments, fragmentation pathways were elucidated for boldenone, methandrostenolone, tetrahydrogestrinone (THG), trenbolone, normethandrolone and mibolerone. Small differences in the chemical structures of the steroids, such as an additional double-bond or a methyl group, result in significantly different fragmentation pathways. The fragmentation pathways proposed in this paper allow interpretation of major product ions of other anabolic steroids reported by other researchers in a recent publication. The proposed fragmentation pathways are helpful for characterization of new steroids. The approach used in this study for elucidation of the fragmentation pathways is helpful in interpretation of complicated product-ion spectra of other compounds, drugs and their metabolites.