EJMS RSS Feed

Letter: Mass spectrometric approach of high pH- and copper-induced glutathione oxidation

The interaction between copper ions and γL-glutamyl-L-cysteinyl-glycine (glutathione, GSH) molecules may lead to the formation of the physiologically occurring Cu(I)–[GSH]₂ and Cu(II)-GSSG complexes. Since glutathione depletion in neurons and aberrant copper metabolism have been implicated in several neurodegenerative disorders, we studied here the interaction of GSH with copper ions (Cu²⁺) by electrospray ionization ion trap mass spectrometry (ESI-MS). Besides, we extended this approach to pH in excess of 10 by adding ethanolamine to the solution being investigated. As a result, the ESI-MS spectra revealed novel aspects regarding the speciation of copper-glutathione complex.

A template approach for the characterization of linear polyamines and derivatives in spider venom

A combination of high-performance liquid chromatography (HPLC) and atmospheric-pressure chemical ionization mass spectrometry (APCI-MS and APCI-MS/MS) was used to detect and characterize linear polyamine derivatives in the venom of the spiders Agelenopsis aperta, Hololena curta and Paracoelotes birulai. The compounds were identified with a template approach, by which the collision-induced dissociation (CID) spectra of known compounds are directly compared and correlated with those of the analytes. To facilitate the perception of the spectra and the recognition of the structural features of the analytes, an ion nomenclature closely leaned on the accepted nomenclature for fragment ions of peptides or nucleic acids is introduced. The structure identification of polyamine derivatives by direct correlation of MS spectra is possible because such compounds show very distinctive fragmentation behavior. Of particular relevance is the fact that the signal patterns that are observed with analytes possessing different polyamine backbones are not only distinct with regards to mass distributions but also with regards to relative signal intensities, resulting in fingerprint-like signal patterns. The direct correlation of these patterns—more than the correlation of the ion distributions—was found to be of key significance. With this, the new approach is fundamentally different from the sequencing of peptides or nucleic acids, which largely base on mass distributions. The method is more efficient and more reliable than the de novo interpretation of the MS data, and it even allows the identification of polyamine portions in compounds that are analyzed within mixtures.

Supplementary Material

Fragmentation characterization and differentiation of isomeric diglycosyl flavonoids using ...

Flavonoids exhibit a wide range of biological activities, and the fragmentation characterization and differentiation of isomeric diglycosyl flavonoids is an important area of research. In this study,ultra-high-performance liquid chromatography/electrospray ionization quadrupole time-of-flight tandem mass spectrometry was used to identify two pairs of isomeric diglycosyl flavonoids: naringin/narirutin and neohesperidin/hesperidin. The two pairs of flavonoids were identified by product ions mass spectra (MS/MS) of the precursor ions [M–H]^–. The results showed that characteristic product ions distinguishing flavonoids glycosylated with rhamnosyl-(α1→2)-glucosyl from isomeric flavonoids glycosylated with rhamnosyl-(α1→6)-glucosyl were the precursor ion [M–H]^– and its characteristic product ions Y₀^– and [^0,2X₀–H]^–.

Matrix-assisted laser desorption/ionization matrices for negative-mode metabolomics

Matrix-assisted laser desorption/ionization (MALDI) has been shown to be highly sensitive for analyzing low-mass compounds such as metabolites if the right matrix is used. 9-aminoacridine (9AA) is the most commonly employed matrix for negative mode MALDI-MS in metabolomics. However, matrix interferences and the strongly varying sensitivity for different metabolites make a search for alternative matrices desirable, in order to identify compounds with a different chemical noise pattern and/or favoring a different range of analytes. We tested the performance of a series of potential negative mode MALDI matrices with a mix of 29 metabolites containing amino acids, nucleotide phosphates and Krebs cycle intermediates. While ethacridine lactate was found to provide limits of detection (LODs) in the low femtomole range for nucleotide phosphates, amino acids and Krebs cycle intermediates in the low picomole range, 4-amino-2-methylquinoline showed LODs in the picomole range for most metabolites, but is capable of ionizing a broader range of analytes than both 9-AA and ethacridine.

Supplementary Material

A thiophene-containing compound as a matrix for matrix-assisted laser desorption/ionization ...

The electrical conductivity of the matrix crystal might be a new factor to enhance matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) sensitivity. In MALDI-MS, several compounds are used as a standard matrix. Utilization of such compounds is based on an a posteriori approach, but there is no theoretical guidance for selecting a matrix. In an attempt to further understand performance in MALDI-MS, we utilized peptide detection for random screening of a chemical library (12,383 compounds) for compounds with matrix functions in MALDI-MS. A lot of thiophene compounds were found to be a matrix, in which 2-[5-(2,4-dichlorobenzoyl)-2-thienyl]acetic acid (DCBTA) provided an important clue to measure the electrical conductivity of the matrix crystal, because the structure of DCBTA is analogous to conductive polymers and organic solar cells. Most of the crystals of standard matrices, such as a-cyano-4-hydroxycinnamic acid (CHCA), 3,5-dimethoxy-4-hydroxycinnamic acid [sinapinic acid, (SA)], and DCBTA showed electrical conductivity, whereas the conductivity of crystal was not observed in 2,5-dihydroxybenzoic acid (2,5-DHB). On the other hand, super-DHB using 2-hydroxy-5-methoxybenzoic acid [5-methoxysalicylic acid, (MSA)] as an additive to 2,5-DHB, improved the electrical conductivity of the crystal, that followed the enhancement of peak intensity in MS spectrum. These observations might indicate that the electrical conductivity of matrix crystals is a key consideration in obtaining efficient MALDI performance.

Supplementary Material

Detection of the epidermal growth factor receptor, amphiregulin and epiregulin in ...

The study of the expression and the tissue distribution of the tyrosine kinase drug-target EGFR is of interest in oncology as a marker of potential efficacy of treatment. It has been reported, however, that the response rates to anti-EGFR drugs are poorly linked to its expression. Clinical studies have also revealed a patient response correlation with the expression levels of two EGFR ligands; amphiregulin and epiregulin. Here we report the development of a matrix assisted laser desorption ionisation mass spectrometry imaging methodology for the study of EGFR, epiregulin and amphiregulin distribution in formalin fixed paraffin embedded Human placental tissue and a comparison to expression patterns obtained by immunohiostochemistry. Using on-tissue digests and imaging of specific peptides, the tissue distribution of these proteins has been obtained down to 30µm spatial resolution.

Qualitative characterization of Desmodium adscendens constituents by high-performance liquid ...

The many effects of the African medicinal herb Desmodium adscendens were studied in the 1980s and 1990s. In spite of this, a comprehensive analytical protocol for the quality control of its constituents (soyasaponins, alkaloids and flavonoids) has not yet been formulated and reported. This study deals with the optimization of extraction conditions from the plant and qualitative identification of the constituents by HPLC- diode array UV and multistage mass spectrometry. Plant constituents were extracted from leaves by liquid–liquid and solid matrix dispersion extraction. Separation was achieved via RP-C18 liquid chromatography with UV and MSⁿ detection and mass spectrometry analysis was conducted by electrospray ionization ion trap or orbitrap mass spectrometry. High resolution mass spectrometry (HRMS) was used for structural identification of active molecules relating to soyasaponins and alkaloids. The flavonoid fragmentations were preliminarily studied by HRMS in order to accurately characterize the more common neutral losses. However, the high number of isomeric species induced us to make recourse to a more extended chromatographic separation in order to enable useful tandem mass spectrometry and ultraviolet spectral interpretation to propose a reasonable chemical classification of these polyphenols. 35 compounds of this class were identified herein with respect to the five reported in literature. In this way we made up a comprehensive protocol for the qualitative analysis of the high complexity content of this plant. This result paves the way for both reliable quality control of potential phytochemical medicaments and possible future systematic clinical studies.