Electrospray[+] tandem quadrupole mass spectrometry in the elucidation of ergot alkaloids chromatographed by HPLC: screening of grass or forage samples for novel toxic compounds

Ergot alkaloids are mycotoxins generated by grass and grain pathogens such as Claviceps, for example. Ergot alkaloid-poisoning syndromes, such as tall fescue toxicosis from endophyte-infected tall fescue grass, are important veterinary problems for cattle, horses, sheep, pigs and chickens, with consequent impact on food, meat and dairy industries. Damage to livestock is of the order of a billion dollars a year in the United States alone. HPLC with UV and fluorescence detection are the predominant means of ergot alkaloid determination, with focus on quantitation of the marker compound ergovaline, although ELISA methods are undergoing investigation. These techniques are excellent for rapid detection, but of poor specificity in defining new or poorly characterized ergot alkaloids and related compounds. This paper demonstrates the facility of using electrospray(+) mass spectrometry with multiple reaction monitoring (MRM) detection during chromatographic examination of ergot alkaloid standards of lysergic acid, lysergol, ergonovine, ergovaline, ergotamine, ergocornine, ergocryptine and ergocrystine by HPLC. Ergoline-8 position epimers could be separated on the gradient HPLC system for ergocornine, ergocrystine and ergonovine and appeared as shoulders for ergotamine and ergovaline; epimers generally showed different patterns of relative intensity for specific MRM transitions. There was reasonable correspondence between retention of standards on the 2-mm ESI(+)MS phenyl-hexyl-based reverse phase column and those on the 4-mm C18-based column. Since up to 10% of clinical cases involving toxin exposure display unidentified chromatographic peaks, 11 samples of feed components associated with such cases were studied with developed MRM methods to attempt elucidation of crucial components if possible. Ergotamine appeared in all, ergovaline appeared in five and ergocornine appeared in six; ergonovine, ergocryptine, ergocrystine and lysergol also appeared in several. In addition, molecular weights of compounds newly revealed by mass spectrometry suggested ergosine, ergostine and ergoptine in four samples, for which standards were not available. Dehydrated products of ergotamine, ergocrystine and ergocornine were discovered, along with dihydrogenated ergocrystine and ergocryptine in seven of the samples, and the issue was raised as to whether dehydration was strictly an instrument-derived artifact. Finally, five of the samples, along with fescue seed standard, evidenced one or more of 14 new ergot alkaloids ranging in size from 381 to 611 molecular weight and with key mass spectral characteristics of ergot alkaloids, specifically the pair of peaks m/z 223 and 208, corresponding to the ergoline ring system and its demethylated variant, respectively. It is anticipated that findings such as these will provide impetus to future development of analytical methodology for these heretofore relatively rare ergot alkaloid species.     

Configuration and optimization of semiconductor gas sensors as gas chromatographic detectors

A tin oxide, gas-sensitive semiconductor sensor was configured as a gas chromatographic detector and its performance was optimized. Two sensor housings were compared but little difference was found in performance. The flow rate and temperature of the column and the internal heater voltage of the sensor affected both the sensitivity and peak shape. The temperature of the sensor surface was the most critical parameter. Optimal conditions for the gas chromatographic detection of a mixture of alkanes (C₁–C₅) and hydrogen were identified by using the simplex technique. The detection limit for hydrogen was improved by a factor of five to 20 ppb (v/v), illustrating the value of optimization and the excellent sensitivity of the detector. It is concluded that semiconductor gas sensors offer significant advantages as gas chromatographic detectors for the determination of reducing gases.     

On the Origin of the Heterogeneous Emission from Pyrene Sequestered Within Tetramethylorthosilicate-Based Xerogels: A Decay-Associated Spectra and O2 Quenching Study

Steady-state and time-resolved fluorescence spectroscopy are used to determine the local microheterogeneity surrounding pyrene molecules sequestered within tetramethylorthosilicate-derived xerogels. After compensation for the intrinsic background emission from the xerogel, we find that the pyrene intensity decay kinetics are best described by a two-term rate law. This is consistent with the pyrene molecules distributing primarily into two microenvironments. Under ambient conditions, the individual pyrene microenvironments exhibit excited-state fluorescence lifetimes that differ by 100 ns. However, the pyrene I₁ to I₃ band ratios that are associated with each microenvironment are statistically equivalent to one another. These results show that the local dipolarity surrounding these pyrene microenvironments are similar, but the decay rates associated with each microenvironment are very different. The longer-lived pyrene species (Environment #1) constitutes 1/2 of the total fluorescence and it exhibits an O₂ quenching sensitivity (K_sv1) of (5.19 ± 0.52 × 10^–3 %O₂ ^–1 and a bimolecular quenching constant (k_q1) of (2.30 ± 0.23) × 10⁴ %O₂ ^–1 s^–1. Environment #2, associated with the shorter-lived pyrene species, exhibits an O₂ quenching sensitivity (K_sv2) of (2.31 ± 0.16) × 10^–2 %O₂ ^–1 and a bimolecular quenching constant (k_q2) of (2.11 ± 0.23) × 10⁵ %O₂ ^–1 s^–1. These results are interpreted as follows: Environment #1 consists of pyrene molecules sequestered within a relatively rigid siloxane network wherein non-radiative decay pathways are lessened, but these pyrene molecules are not quenched readily by O₂. Environment #2 consists of pyrene molecules adsorbed onto surface silanols within the xerogel. These pyrene molecules are quenched by the silanols and they are simultaneously more accessible to O₂ compared to Environment #1.     

Crystal structure analysis of 3,4-dimethyl-2,5-dihydrothiophen-1,1-dioxide

The geometry of 3,4-dimethyl-2,5-dihydrothiophen-1,1-dioxide was determined by X-ray diffraction: cell dimensions are reported together with bond lengths and bond angles. While bond lengths are smaller than those for the homologue 3-methyl-2,5-dihydrothiophen-1,1-dioxide, bond angles are similar. TheMe-C₃-C₄-Me torsion angle is 5.1±0.5°. These results are consistent with its relatively slow rate of decomposition.

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Kristallstrukturanalyse von 3,4-Dimethyl-2,5-dihydrothiophen-1,1-dioxid

Zusammenfassung Die Geometrie von 3,4-Dimethyl-2,5-dihydrothiophen-1,1-dioxid wurde mittels Röntgendiffraktion bestimmt. Es werden die Dimensionen der Einheitszelle zusammen mit Bindungslängen und Bindungswinkeln berichtet. Die Bindungswinkel sind sehr ähnlich denen des homologen 3-Methyl-2,5-dihydrothiophen-1,1-dioxids, die Bindungslängen sind jedoch kürzer. DerMe-C 3-C 4-Me Torsionswinkel ist 5.1±0.5°. Diese Ergebnisse sind mit der relativ langsamen Zersetzungsgeschwindigkeit im Einklang.

     

A concise synthesis of the octalactins

The total synthesis of octalactins A and B has been achieved in 15 steps (longest linear sequence) and 10% overall yield from commercially available materials. Key steps include the Paterson-Aldol reaction for the rapid assembly of the carbonate 46, methylenation of 46 and subsequent Claisen rearrangement of the corresponding alkenyl-substituted cyclic ketene acetal to provide the core unsaturated medium-ring lactone 47, and the use of enzyme-mediated acetate deprotection in the presence of a medium-ring lactone.     

Synthesis and structures of the first bismuth-ester complexes using heterobifunctional thiolate anchored ligands and mass spectrometric identification of ligand-bridged derivatives

The first systematic series of bismuth complexes involving ester donors, Bi(SCH(2)C(O)OCH(2)CH(3))Cl(2), Bi(SCH(2)C(O)OCH(3))(2)Cl, and Bi(SCH(2)COOCH(3))(3), has been isolated and characterized by spectroscopic (IR, Raman) and X-ray crystallographic data. In addition, these and other species have been identified by electron-impact, electrospray, and atmospheric pressure chemical ionization mass spectometry. The generally applicable synthetic methodology involves the use of heterobifunctional ligands containing a thiolate moiety as an anchor to facilitate coordinate interactions between weak donors (carbonyls) and weak acids (bismuth). The bifunctional nature of the ligands is manifested in both chelating and bridging roles. Important comparisons can be made with the pharmaceutical agent "colloidal bismuth subcitrate" (CBS). The observations allow for a new appreciation of bioactive bismuth compounds, by providing an approach to study the interaction of biorelevant functional groups with bismuth.     

Determination of arsenic by inductively-coupled plasma atomic emission spectrometry enhanced by hydride generation from organized media

A method is described for the determination of arsenic, which combines a continuous flow hydride generation technique with an inductively coupled plasma atomic emission detection system. Some atomic absorption preliminary studies are described as well. Arsine is generated with NaBH(4) from a didodecyldimethylammonium bromide (DDBA) vesicular medium. The analytical performance of this vesicles-enhanced method is superior to the generation of the hydride from aqueous media: the detection limit (0.6 ppb) is improved by a factor of 2 and greater tolerance to interferences is observed for arsine generation from DDBA vesicles. Precision of As determinations is also improved. The proposed method has been validated for low As levels determinations in two Certified Reference Materials (CRM) sediments with satisfactory results. The potential of organized media to improve hydride generation is addressed.     

Mass spectral fragmentation pattern of 2,3-dimethyl- and 2-methyl-3-phenyl-4-arylazoisoxazol-5-ones

2,3-Dimethyl-4-arylazoisoxazol-5-ones and 2-methyl-3-phenyl-4-aryiazoisoxazol-5-ones undergo considerable fragmentation on electron impact. The base peaks in the mass spectra are at mass 56 and 118 respectively attributed to the N-methylacetonitrile cation and the N-methylbenzonitrile cation.     

Computer Assisted Structural Interpretation of Mass Spectral Data

An interactive system of programs has been developed to assist in structure elucidation based on mass spectral data. The program relies on algorithms for generating all the structural isomers that constitute alternative explanations of the observed data and it associates relative plausibility values with the different isomers. The structure assembly part of the program allows for the use of overlapping substructural components, such as substructures inferred from the appearance of particular ion patterns in the spectrum of an unknown compound. Mass spectrum interpretation procedures used with this structure assembly process could exploit any form of spectrum-substructure correlation scheme. In this work, the emphasis has been on the use of detailed and class specific spectrum-substructure correlations. Applications of the program are illustrated by means of an example analysis of the mass spectra of a variety of marine sterols.     

Formation of aminosilane-functionalized mica for atomic force microscopy imaging of DNA

Factors affecting the functionalization of mica with aminosilanes, in particular, aminopropyltriethoxysilane (APTES-mica), formed from the vapor phase have been systematically studied. The relative humidity (RH) during vapor deposition has been varied, and postdeposition treatment through baking has been used, as well as the comparison of mono and trifunctionality, to investigate how optimal surfaces for AFM imaging of DNA are formed. It is found that the stability of the APTES layers is a consequence of lateral polymerization and not covalent attachment to the mica substrate. At low RH (<25%), DNA adopts an open, well-resolved conformation, whereas at >25% RH, DNA surface-induced condensation occurs. Contact mode AFM scratching experiments show that two main structures of the silane layer exist at different humidity: a monolayer exists at RH < 25%, and a bilayer structure exists at RH > 25%. Finally, structural changes that these two layer types undergo after baking at 150 degrees C were investigated by AFM and X-ray photoelectron spectroscopy (XPS), and these now prevented DNA from binding to the APTES-mica, except in the presence of Mg(II) ions.