Liquid Secondary Ion Mass Spectrometry Research Articles

High sensitivity mass spectral characterization of glycosphingolipids from bovine erythrocytes, mouse kidney and fetal calf brain

Stage-specific embryonic antigen (SSEA) glycosphingolipids (GSLs) found in the central nervous system are implicated in regulating cell-cell recognition, targeting and migration of cells during development. Through the action of fucosyltransferase enzymes, SSEA-1 (Lewis x) glycolipids are biosynthesized in the brain by fucosylation of lipid substrates with the neolacto series glycolipid core structure [Galβ1 → 4GlcNAcβ1 → 3Galβ1 → 4Glcβ1 → 1'Cer] (originally termed paragloboside) or its higher analogs. In order to optimize methodology for high sensitivity structural determinations of SSEA-1 type glycolipids from fetal calf brain, potential precursors and SSEA-1 glycolipids of previously established structure were first isolated from bovine erythrocytes and beige mutant mouse kidney, purified by column chromatography and characterized by matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) MS, liquid secondary ionization mass spectrometry (LSIMS), and tandem mass spectrometry (MS/MS), among other techniques. Peracetylated derivatives were detected at the low femtomole level by MALDI-TOF MS and the subnanomole level by LSIMS. MALDI-TOF MS produced mainly [M + Na] + and [M + K] + species. On the basis of the direct and tandem mass spectral analyses of peracetylated and permethylated derivatives, the carbohydrate sequences in the selected bovine erythrocyte and mouse kidney GSL fractions were found to be consistent with those of glycolipids previously-reported from larger-scale studies of these sources. Their heterogeneous ceramide moieties were characterized by collision induced decomposition (CID) MS/MS of abundant Z 0-type ions in the LSI mass spectra of the permethylated GSLs. MALDI-PSD-TOF mass spectral analyses of low and subpicomole amounts of derivatized GSL fractions from fetal calf brain provided carbohydrate sequence information that indicates the presence of mono- and difucosylated SSEA-1 neolacto series glycolipids and their nonfucosylated analogs.

Liquid secondary ionization mass spectrometry and collision‐induced dissociation study of 2-chloro-N10-substituted phenoxazines

Liquid secondary ionization mass spectrometry and collision‐induced dissociation study of 2-chloro-N10-substituted phenoxazines

Liquid secondary ionization mass spectrometry and collision-induced dissociation study of 2-chloro-N10-substituted phenoxazines.

Positive-ion liquid secondary ionization mass spectrometry in combination with 3-nitrobenzyl alcohol as the liquid matrix was used to investigate the mass spectral features of a set of 21 N10-substituted derivatives of 2-chlorophenoxazine. The N-10 substitution included propyl, butyl and acetyl groups containing various secondary amines (N,N-diethylamine, N,N-diethanolamine, morpholine, piperidine, pyrrolidone or beta-hydroxyethylpiperazine) or a chloro group. These compounds are potent multi-drug resistance modulators. The molecular ions are observed as M+ and [M + H]+ ions. In general, the fragmentation pathways of these molecules are similar and very straightforward. The phenoxazine ring system remains stable under the Cs+ ion beam bombardment conditions, while fragmentations are observed along the length of the alkyl and acetyl side-chains. The fragmentation reactions were corroborated by acquiring product ion and constant neutral loss tandem mass spectrometric scans of the pertinent ions.

Liquid secondary ionization mass spectrometry and collision-induced dissociation study of 2-chloro-N10-substituted phenoxazines

Liquid secondary ionization mass spectrometry and collision-induced dissociation study of 2-chloro-N10-substituted phenoxazines

Molecular Meccano, 27. A Template‐directed Synthesis of a Molecular Trefoil Knot

AbstractA design logic for the self‐assembly of a molecular trefoil knot and of its isomeric trivial knot is described. The approach relies on the formation of a double‐stranded supramolecular complex between an acyclic π‐electron rich 1,5‐di‐oxynaphthalene‐based polyether and an acyclic π‐electron deficient bipyridinium‐based tetracation. The reversible complexation of the two acyclic complementary components in solution is followed by the irreversible formation of covalent bonds connecting the termini of these two precursors within the supramolecular complex, affording both a trefoil knot and a trivial knot, though only in extremely low yields. The isomers were separated by preparative high‐performance liquid chromatography and characterized by liquid secondary ion mass spectrometry which revealed the binding of up to two ammonium ions in the case of only one of the two isomers – namely, the trivial knot. In addition, we have performed binding studies between some model acyclic and macrocyclic 1,5‐dioxynaphthalene‐based polyethers and the bipyridinium based precursor of the knots. One of the complexes was also characterized in the solid state by X‐ray crystallography which revealed the formation of a [2]pseudorotaxane in the solid state.

Mass spectrometric study of the amipurimycin hexopyranosidic sugar moiety

Amipurimycin is a natural nucleoside that displays a remarkable activity in vitro and in vivo against Pyricularia oryzae, which is responsible for the rice blast disease. Six important precursors for the synthesis of the Amipurimycin sugar moiety were prepared. In order to obtain structural information a mass spectrometric study of these compounds was performed using liquid secondary ion mass spectrometry (LSIMS) with high-energy collision-induced dissociation (CID) experiments on a four-sector instrument. Elimination of methanol is the preferential fragmentation path for five of the six protonated molecules, indicating that protonation plays an important role in the process, whilst for the other protonated molecule loss of water is the main fragmentation. Examination of the [M + Li] + precursor ion spectra shows that loss of methanol does not occur in three of them, but in the other three gives rise to fairly abundant ions, indicating that in this case methanol elimination implies intramolecular hydrogen transfer, the resulting ion having a very stable structure.

Sialyl-LewisxSequence 6-O-Sulfated atN-Acetylglucosamine Rather Than at Galactose Is the Preferred Ligand forl-Selectin and De-N-acetylation of the Sialic Acid Enhances the Binding Strength

Oligosaccharide sequences based on sialyl-Lewisxwith 6-O-sulfation at galactose (6′-sulfo) or atN-acetylglucosamine (6-sulfo) and expressed on high endothelial venules are considered likely endogenous ligands for the leukocyte adhesion molecule, L-selectin. In the course of high performance TLC of three hexaglycosylceramides 6′-sulfo sialyl Lewisx, 6-sulfo sialyl Lewisx, and 6′,6-bis-sulfo sialyl Lewisx, synthesized chemically for selectin recognition studies, two minor by-products were detected and isolated from each parent compound. By liquid secondary ion mass spectrometry these were identified as isomers containing a de-N-acetylated sialic acid or having a modified carboxyl group. Binding experiments with the parent compounds and the non-sulfated sialyl Lewisxglycolipid show that 6-sulfation potentiates, whereas 6′-sulfation virtually abolishes L-selectin binding. Thus the hierarchy of binding strengths were 6-sulfo sialyl > sialyl = 6′,6-bis-sulfo sialyl ⪢ 6′-sulfo sialyl Lewisx. Whereas modification of the sialic acid carboxyl group markedly impaired L-selectin binding, de-N-acetylation resulted in enhanced binding. The natural occurrence on high endothelial venules of this ‘super-active’ de-N-acetylated form of 6-sulfo sialyl Lewisx, and related structures, now deserves investigation.

Ferrichrome: Surprising stability of a cyclic peptide-Fe III complex revealed by mass spectrometry

Ferrichrome, a fungal siderophore that is also utilized by some bacterial species, was studied with liquid secondary ion mass spectrometry (LSIMS) and matrix-assisted laser desorption ionixation (MALDI) mass spectrometry. A strong ionic signal corresponding to a FeIII complex was observed with LSIMS in the positive ion mode. Switching the polarity of the mass spectrometer did not necessarily result in reduction of ferric ion, although certain conditions led to appearance of a FeII complex signal as well. The results of the structural studies of the metal ion-cyclic peptide complex with collisionally induced dissociation allowed unambiguous identification of the chelation sites. The action of the siderophore on FeIII was studied by in vitro chelation of ferric ion (from ferric citrate) by the iron-free ferrichrome. Effective chelation of ferric ion was compared to actions of the iron-free ferrichrome on other metal ions. Unlike LSIMS, desorption with MALDI did not form selectively molecular ions of intact ferrichrome: the spectra contained abundant peaks corresponding to the cyclic peptide itself and its nonspecific association with alkali metal ions.

Étude des acylcarnitines plasmatiques par spectrométrie de masse en tandem. Application au diagnostic des maladies héréditaires du métabolisme

L-carnitine is known to transport long chain fatty acids through the mitochondrial membrane but also to export accumulated acyl-CoA's as acylcarnitine esters. Acylcarnitine identification in body fluids allows the diagnosis of mitochondrial inborn errors especially fatty oxidation defects. Tandem mass spectrometry represents a new method for isolation and identification of acylcarnitines in plasma or in blood spotted onto filter paper (Guthrie cards). In order to validate our method, we studied 30 plasmas from children affected with 15 different inborn errors of metabolism and five amniotic fluids from fetuses affected with several organic acidurias. Fourty-six samples from children at risk for mitochondrial fatty oxidation disorders have been analyzed. We developed a method of tandem mass spectrometry with liquid secondary ion mass spectrometry using deuterated acylcarnitines as internal standards. This method is very sensitive (detection limit = 2 microM). In all affected patients specific acylcarnitine signals corresponding to the metabolic block were constantly found. This confirms the diagnosis and validates the method. Among the 46 at risk children, four defects of long chain fatty acid oxidation were identified. This new method is of great interest especially for the long chain fatty acid oxidation defects. These defects are very difficult to diagnose with classical methods as urinary organic acid profiling. A small amount of plasma (100 microL) or blood spotted onto paper is required. The acylcarnitine profile allows a rapid diagnosis if a dedicated apparatus is available.

Nod Factors from Sinorhizobium saheli and S. teranga bv. sesbaniae Are Both Arabinosylated and Fucosylated, a Structural Feature Specific to Sesbania rostrata Symbionts

Sesbania spp. can establish symbiotic interactions with rhizobia from diverse taxonomical origins, including the newly described Sinorhizobium saheli and S. teranga bv. sesbaniae, in addition to the Sesbania rostrata-specific symbiont Azorhizobium caulinodans. These different rhizobia exhibit a narrow host range, which is limited mainly to Sesbania spp. Nod factors from overproducing strains of S. saheli ORS611 were purified and their structures determined. Remarkably, the terminal reducing glucosamine of most compounds was found to bear both an arabinosyl group on C-3 and a fucosyl substitution on C-6. Other structural features are as follows: Nod factors are mainly chitopentameric compounds, N-methylated, O-carbamoylated and N-substituted either by a C18:1 or a C16:0 acyl chain at their nonreducing end. Nod factors from an overproducing strain of S. teranga bv. sesbaniae ORS604 were found to be identical to those of S. saheli on the basis of high-pressure liquid chromatography separation and liquid secondary ion mass spectrometry analysis. The Nod factor double glycosylation, i.e., arabinosylation and fucosylation, which appears to be unique to Sesbania symbionts, probably reflects a high selection pressure from Sesbania host plants.

Characterization of stereoisomeric furanosidic derivatives by direct chemical ionization mass spectrometry and liquid secondary ion mass spectrometry with tandem mass spectrometry. (Part II)

Characterization of stereoisomeric furanosidic derivatives by direct chemical ionization mass spectrometry and liquid secondary ion mass spectrometry with tandem mass spectrometry. (Part II)

Characterization of supported and unsupported transition metal compounds by liquid secondary ion mass spectrometry

The positive ion liquid secondary ion mass spectra (LSIMS) of metal acetylacetonates (acacs) contain cluster ions that involve multiple metal centers. Several metal acacs form adduct ions with m-nitrobenzyl ( m-NBA) alcohol used as the LSIMS support matrix. In these adduct ions, deprotonated m-NBA molecules act as bridges between metal centers. The LSIMS of a series of dirhodium carboxylates show that the electron-withdrawing strength of the carboxylate group controls whether the base peak in the mass spectrum is the molecular ion or an adduct ion formed between the molecule and a matrix molecule of sulfolane. However, no cluster ions are formed for these dirhodium compounds. Similarly, highly charged cationic compounds do not form cluster ions, nor do they form adduct ions with the LSIMS solvent. Instead, the counter ion is retained to maintain a single positive charge in the ion. LSIMS spectra of neutral and charged metallocene compounds are compared. Contrary to the assertions that these compounds cluster extensively in the gas phase, the LSIMS provide no evidence for this process. To support studies of surfaces prepared for catalytic studies, silica- and clay-supported transition metal acacs were characterized by LSIMS. Release of the supported transition metal compounds from the surface occurs during ion exchange.

Characterization of stereoisomeric furanosidic derivatives by direct chemical ionization mass spectrometry and liquid secondary ion mass spectrometry with tandem mass spectrometry. (Part II)

Characterization of stereoisomeric furanosidic derivatives by direct chemical ionization mass spectrometry and liquid secondary ion mass spectrometry with tandem mass spectrometry. (Part II)

Characterization of Phospholipids by Electron Impact, Field Desorption and Liquid Secondary Ion Mass Spectrometry

Dimyristoylphosphatidylglycerol (DMPG), dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) were characterized by electron impact (EIMS), field desorption (FDMS) and liquid secondary ion (LSIMS) mass spectrometry. The results showed that the fragmentation processes of the three phospholipids are very similar. In the EI mass spectra, no molecule-ion peaks were found, the peaks of the fatty acid chains being dominant. The results of FDMS and LSIMS showed that both techniques worked particularly well with all three kinds of phospholipids. The FD mass spectra of all three phospholipid gave strong MH+ peaks, and no fragmental peaks were found except that of DMPC. With LSIMS, the fragmentations of all the phospholipids were extensive and clear, and gave dominant peaks of MH+. The cleavages around phosphate groups were the most abundant. An interesting phenomenon was found in the LSIMS measurements that all three kinds of phospholipids formed intense peaks of molecule-ion clusters, [2M+H]+, [3M+H]+ and [4M+H]+, etc. It was found that the formation of the molecule-ion clusters was related to several factors: concentration, ionic strength, pH, etc., among which concentration is the most important. The degree of cluster formation increased with increase in concentration of phospholipid. The results also showed that the nature of the matrix is critical to a successful LSIMS analysis of phospholipids, and (S)-glycerol was confirmed as a very satisfactory matrix for these phospholipids. © 1997 John Wiley & Sons, Ltd.

Characterization of Phospholipids by Electron Impact, Field Desorption and Liquid Secondary Ion Mass Spectrometry

Dimyristoylphosphatidylglycerol (DMPG), dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) were characterized by electron impact (EIMS), field desorption (FDMS) and liquid secondary ion (LSIMS) mass spectrometry. The results showed that the fragmentation processes of the three phospholipids are very similar. In the EI mass spectra, no molecule-ion peaks were found, the peaks of the fatty acid chains being dominant. The results of FDMS and LSIMS showed that both techniques worked particularly well with all three kinds of phospholipids. The FD mass spectra of all three phospholipid gave strong MH+ peaks, and no fragmental peaks were found except that of DMPC. With LSIMS, the fragmentations of all the phospholipids were extensive and clear, and gave dominant peaks of MH+. The cleavages around phosphate groups were the most abundant. An interesting phenomenon was found in the LSIMS measurements that all three kinds of phospholipids formed intense peaks of molecule-ion clusters, [2M+H]+, [3M+H]+ and [4M+H]+, etc. It was found that the formation of the molecule-ion clusters was related to several factors: concentration, ionic strength, pH, etc., among which concentration is the most important. The degree of cluster formation increased with increase in concentration of phospholipid. The results also showed that the nature of the matrix is critical to a successful LSIMS analysis of phospholipids, and (S)-glycerol was confirmed as a very satisfactory matrix for these phospholipids. © 1997 John Wiley & Sons, Ltd.

Gangliosides of dogfish ( Squalus acanthias) brain

Eighteen gangliosides were isolated from dogfish ( Squalus acanthias) brain, and their structures and compositions were determined by methylation analysis, enzymatic hydrolysis and partial hydrolysis with mild acid. Tetra- and pentasialogangliosides were also analysed by liquid secondary ion mass spectrometry. The dogfish brain gangliosides were characterized by a variety of molecular species. The most abundant ganglioside was GM2 (22.8% of the total sialic acid content), followed by GQ1c (16.0%), GP1c (13.4%), and GD2 (12.5%). The abundance of gangliosides containing a gangliotriaose core (GM2 and GD2), and c-series polysialogangliosides (GQ1c and GP1c) was a prominent feature of dogfish brain, differing from the brain gangliosides of teleosts and other vertebrates. A battery of trisialogangliosides was also found. A ganglioside which had an a- and α-series hybrid-structure (IV 3NeuAc,III 6NeuAc,II 3NeuAc-Gg 4Cer) comprised 1.4% of the total. The major fatty acids comprised 16:0, 18:0, 18:1, 22:1 and 24:1. The gangliosides with a gangliotriaose core predominantly contained 22:1. Sphinganine and 4-sphingenine comprised the long-chain bases.

Brain Contains HNK-1 Immunoreactive O-Glycans of the Sulfoglucuronyl Lactosamine Series that Terminate in 2-Linked or 2,6-Linked Hexose (Mannose)

The monoclonal antibody HNK-1 originally raised to an antigenic marker of natural killer cells also binds to selected regions in nervous tissue. The antigen is a carbohydrate that has attracted much interest as its expression is developmentally regulated in nervous tissue, and it is found, and proposed to be a ligand, on several of the adhesive glycoproteins of the nervous system. It is also expressed on glycolipids and proteoglycans, and is the target of monoclonal auto-antibodies that give rise to a demyelinating disease. The epitope, as characterized on glycolipids isolated from the nervous system, is expressed on 3-sulfated glucuronic acid joined by beta1-3-linkage to a neolacto backbone. Here we exploit the neoglycolipid technology, in conjunction with immunodetection and in situ liquid secondary ion mass spectrometry, to characterize HNK-1-positive oligosaccharide chains derived by reductive alkaline release from total brain glycopeptides. The immunoreactive oligosaccharides detected are tetra- to octasaccharides that are very minor components among a heterogeneous population, each representing less than 0.1% of the starting material. Their peripheral and backbone sequences resemble those of the HNK-1-positive glycolipids. An unexpected finding is that they terminate not with N-acetylgalactosaminitol but with hexitol (2-substituted and 2,6-disubstituted). In a tetrasaccharide investigated in the greatest detail, the hexitol is identified as 2-substituted mannitol.

Structure of the Monophosphoryl Lipid A Moiety Obtained from the Lipopolysaccharide of Chlamydia trachomatis

Monophosphoryl lipid A was prepared from the lipopolysaccharide of Chlamydia trachomatis, converted to the methyl ester, and fractionated by reverse-phase high-performance liquid chromatography. The peak fractions were collected and analyzed by mass spectrometry. Matrix-assisted laser desorption/ionization and liquid secondary ion mass spectrometry of the first of two major high-performance liquid chromatographic fractions showed multiple quasi-molecular ions of MNa+ at m/z 1780, 1794, 1808, 1822, and 1836. The positive-ion liquid secondary ion mass spectrometry spectrum also showed a minor series of peaks at m/z 1916, 1930, 1944, 1958, and 1971, consistent with the formation of matrix adducts with 3-nitrobenzyl alcohol. Oxonium ions representing the distal subunit were observed at m/z 1057, 1071, 1085, 1099, and 1113. The second fraction was similarly analyzed and found to contain structural homologs of the first fraction. Based on this study, the major lipid A component of chlamydial lipopolysaccharide is a glucosamine disaccharide that contains five fatty acids and a phosphate in the distal segment. Three fatty acyl groups are in the distal segment, and two are in the reducing end segment. The acyloxyacyl group is located in the distal segment in amide linkage. Two structural series, differing by 14 atomic mass units in the reducing subunit, were observed. Chlamydial lipid A is complex and consists of at least 20 homologous structural components. The relatively low potency of Chlamydia trachomatis lipopolysaccharide in activating lipopolysaccharide-responsive cells might be related to the unusual fatty acid composition of the lipid A moiety.

Reaction of C60 with Oxygen Initiated by Radicals from Azo(Bisisobutyronitrile)

In an o-dichlorobenzene solution exposed to an atmosphere of air or pure oxygen, C60 reacts with radicals generated by thermal decomposition of azo(bisisobutyronitrile) and with oxygen to form mixtures of highly substituted and oxygenated monomelic, dimeric, and trimeric derivatives. LSIMS, LDMS, and SIMS (Liquid Secondary Ion, Laser Desorption, and Secondary Ion Mass Spectrometry) of these mixtures give clusters of peaks for C2n from C40 to greater than C200. Elemental analyses show large H, N, and 0 contents that increase with the amount of AIBN and the partial pressure of oxygen during the reaction. 1H and 13C NMR spectra consist of broad bands assigned to complex mixtures of substituted fullerenes containing many 2-cyano-2-propyl groups derived from AIBN. Diffuse reflectance infrared spectra show hydroxyl and carbonyl functional groups. Thermal gravimetric analysis (TGA) of the mixture prepared under oxygen retained 40% of the initial weight at 640 °C, while <19 % of the initial weight remained from the mixture prepared under argon.

POSITIVE ION LIQUID SECONDARY ION MASS SPECTRA OF AROMATIC SULFONIUM SALTS

Organic sulfonium salts exist as pit-charged species in the matrices normally used for liquid secondary ionization mass spectrometry. Positive ion LSIMS mass spectra of the sulfonium salts therefore exhibit the intact cation (C+) as the dominant ion species. Generally, the fragment ions are of 30–40% relative intensity and are formed through simple cleavages and rearrangements. Cluster ions such as CAC+ and C3A2 + are also present in the mass spectra (A is the counter ion of the salt). These cluster ions provided confirmation of the molecular weight. Adduct ions are formed between organic sulfonium salts and matrices used in LSIMS such as diethanolamine and triethanolamine. Beam-induced reactions are identified by comparison of mass spectra obtained with electrospray ionization, and by changes in ion products with changes in solvent matrix.