Supramolecular self-assembling properties of membrane-spanning archaeal tetraether glycolipid analogues

The self-assembling properties of a new series of archaeal tetraether glycolipid analogues 1-6 that are characterized by a bipolar architecture with two similar or different glycosidic and/or phosphate polar heads and a lipid core possessing a cyclopentane unit and/or branched chains were studied by means of differential scanning calorimetry, optical microscopy, X-ray scattering, freeze-fracture electron microscopy and dynamic light scattering. Unsymmetrical phosphate derivatives 1 and 2 spontaneously formed thermostable multilamellar and unilamellar vesicles in which most of the bipolar lipids adopted a trans-membrane conformation, as revealed by freeze-fracture electron microscopy. Supramolecular aggregates of neutral glycolipids 3-6 were found to depend on both the saccharidic polar heads and the chain composition. The presence of one glycosidic residue with rather marked hydrophilic properties, such as the lactosyl moiety, was required to allow the formation of multilamellar vesicles. Surprisingly, the introduction of a cyclopentane unit in the bridging chain was able to induce an apparent two-by-two membrane association: this unusual behaviour might be the result of unsymmetrical interfacial properties of the lipid layer caused by the presence of the cyclopentane unit.     

Rapid discrimination of archaeal tetraether lipid cores by liquid chromatography-tandem mass spectrometry

Atmospheric pressure chemical ionization liquid chromatography-tandem mass spectrometry (APCI LC-MS/MS) of tetraether lipid cores of archaeal origin reveals distinct dissociation pathways for three classes of core lipid extracted from Methanobacter thermautotrophicus. Within these classes, two isobaric tetraether lipids, one a scarcely reported lipid constituent of M. thermautotrophicus and the other an artefact formed during extraction from cultured cells, were identified and distinguished via their MS(2) spectra. APCI LC-MS/MS discriminates different tetraether core lipid types and isobaric species and reveals the mass of the constituent biphytanyl chains within the tetraether cores, albeit without full elucidation of their structures. Furthermore, the method allows direct estimation of the relative proportions of tetraether core lipids from chromatographic peak area measurement, allowing rapid profiling of these compounds in microbiological and environmental extracts.     

Capillary supercritical fluid chromatography of archaebacterial glycerol tetraether lipids

The analysis of bacterial glycerol tetraethers by capillary supercritical fluid chromatography is described. Complete separation of ethers, differing only by the number of cyclopentane rings present in the isopranyl side chains could be achieved. On a 50% methylphenylpolysiloxane coated capillary, the ethers eluted in the order of increasing cyclopentane content. The analysis revealed the presence of two previously unreported structural isomers of glycerol tetraethers. The method can be used qualitatively and quantitatively as a fast and sensitive screening test for such compounds in living organisms and sedimentary organic matter.     

Analysis of intact tetraether lipids in archaeal cell material and sediments by high performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

A method combining normal phase high performance liquid chromatography (HPLC) with positive ion atmospheric pressure chemical ionization mass spectrometry (APCI-MS) was developed for the analysis of intact glycerol dialkyl glycerol tetraethers (GDGTs) in archaeal cell material and sediments. All GDGTs previously reported to occur in the thermophilic archaeon Sulfolobus solfataricus could be identified based on their mass spectra and retention time. Positive ion mass spectra consisted of abundant protonated molecules and fragment ions corresponding to loss of water and the glycerol moiety. In addition, two novel GDGTs representing alternative combinations of biphytanyl moieties were observed. Using this method, the tetraethers present in the thermophilic archaeon Metallosphaera sedula and two sediment samples were characterized. This rapid method will greatly contribute to the establishment of the sedimentary record of these compounds and increase our understanding of archaea and their occurrence in widely different environments.     

Preparation of carbon dioxide from magnesite for isotopic analysis

Summary Since the application of the isotope geochemical method to obtain information on the formation mechanism of magnesite deposits was considered promising, we have developed a method to prepare carbon dioxide from magnesite samples for oxygen and carbon isotope analyses, using phosphoric acid reaction at an elevated temperature of 95° C. Data showing the reproducibility of the method (better than ±0.2 for both carbon and oxygen) are presented. The oxygen isotope fractionation factor between the evolved CO₂ and magnesite at 95° C is 1.0080.

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Freisetzung von Kohlendioxid aus Magnesit zur Isotopenanalyse

Zusammenfassung Mit dem Ziel, durch isotopen-geochemische Untersuchungen den Bildungsmechanismus von Magnesitablagerungen aufzuklären, wurde ein Verfahren zur Freisetzung von Kohlendioxid aus den Magnesitproben zur O- und C-Isotopenanalyse ausgearbeitet. Dazu dient die Reaktion mit Phosphorsäure bei 95° C. Die Reproduzierbarkeit ist besser als ±0,2 für beide Elemente. Der Fraktionierungsfaktor für das Sauerstoffisotop zwischen CO₂ und Magnesit bei 95° C beträgt 1,0080.

     

Stable carbon and oxygen isotopic analysis of carbon monoxide in natural waters

Techniques have been developed to allow on-line simultaneous analysis of concentration and stable isotopic compositions ((13)C and (18)O) of dissolved carbon monoxide (CO) in natural water, using continuous-flow isotope ratio mass spectrometry (CF-IRMS). The analytical system consisted sequentially of a He-sparging bottle of water, a gas dryer, CO(2)-trapping stage using both Ascarite trap and silica-gel packed gas chromatography (GC), on-line oxidation to CO(2) using the Schütze reagent, cryofocusing, GC purification using a capillary column and measurement by CF-IRMS. Each sample analysis takes about 40 minutes. The detection limit with delta(13)C standard deviation of 0.5 per thousand is 300 pmol and that with delta(18)O deviation of 1.0 per thousand is 750 pmol. Analytical blanks associated with these methods are 21+/-9 pmol. The procedures are evaluated through analyses of temporally varying concentration and isotopic compositions of CO in an artificial lake on the university campus. The delta(13)C and delta(18)O values of CO showed wide variation in accordance with diurnal variation of CO concentration, probably due to significant isotopic effects during photochemical production and microbial oxidation of CO in the aquatic environment. The delta(13)C and delta(18)O values of CO should be a useful tool in studies of the mechanism and pathways of CO production and consumption in natural waters.     

Study and validity of 13C stable carbon isotopic ratio analysis by mass spectrometry and 2H site-specific natural isotopic fractionation by nuclear magnetic resonance isotopic measurements to characterize and control the authenticity of honey

Honey samples were analyzed by stable carbon isotopic ratio analysis by mass spectrometry (SCIRA-MS) and site-specific natural isotopic fractionation measured by nuclear magnetic resonance (SNIF-NMR) to first determine their potentials for characterizing the substance and then to combat adulteration. Honey samples from several geographic and botanical origins were analyzed. The δ¹³C parameter was not significant for characterizing an origin, while the (D/H)_I ratio could be used to differentiate certain single-flower varieties. Application of the official control method of adding a C₄ syrup (AOAC official method 998.12) to our authentic samples revealed anomalies resulting from SCIRA indices that were more negative than −1‰ (permil). A filtration step was added to the experimental procedure and provided results that were compliant with the natural origin of our honey samples. In addition, spiking with a C₄ syrup could be detected starting at 9-10%. The use of SNIF-NMR is limited by the detection of a syrup spike starting only at 20%, which is far from satisfying.     

Preparation,X-ray structure and reactivity of a stable glycosyl iodide

Highly selective reaction of methyl tetra-O-pivaloyl-beta-D-glucopyranuronate 2 with iodotrimethylsilane or (Me3Si)2 and I2 affords, in excellent yield, the 'disarmed' glycosyl iodide 1 which has good stability at 20 degrees C and excellent stability at 0 degrees C; the X-ray crystal structure of 1 is described, along with a comparison of its utility as a glycosyl donor to that of the corresponding bromide.     

2-Allyloxyphenyl glycoside as a new and stable type of glycosyl donors

A high-yielding coupling of a new and stable type of glycosyl donors, namely 2-allyloxyphenyl glycoside, with a variety of alcohols via NIS/TfOH reagent combination as effective activators at room temperature is described here.     

Microdetermination of ether lipids by the isotopic derivative technique

Summary Complex mixtures of ether lipids and ester lipids are subjected to reduction with lithium aluminiumhydride to yield 1-alkylglycerols, 1-alk-1'-enylglycerols, and alcohols. Acetylation of these reduction products with radioactively labelled acetic anhydride leads to mixtures of alkyldiacetylglycerols, alk-1-enyldiacetylglycerols, and alkyl acetates. These derivatives are resolved by thin-layer chromatography and then estimated by scanning of the chromatogram or by liquid-scintillation counting of the eluted fractions.

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Mikroanalyse von Ätherlipiden mit Hilfe der Radioreagens-Methode

Zusammenfassung Komplexe Gemische von Ether- und Esterlipiden werden mit Lithiumaluminiumhydrid zu 1-Alkylglycerolen, 1-Alk-1'-enylglycerolen und Alkoholen umgesetzt. Diese Reaktionsprodukte werden mit radioaktivem Essigsäureanhydrid acetyliert. Die markierten Derivate, Alkyldiacetylglycerole, Alk-1-enyldiacetylglycerole and Alkylacetate, werden dünnschichtchromatographisch getrennt. Das Verhältnis dieser drei Fraktionen wird durch Scanning der Chromatogramme oder durch Flüssigkeitszintillationszählen der eluierten Fraktionen bestimmt.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Intramolecular isotopic effect in the pyrolysis of ethyl-2d1 chloride

The thermal decomposition of deuterated ethyl chloride CH₂DCH₂Cl was studied in a static system in the pressure range of 0.1–26 torr, and the Arrhenius expression for the overall decomposition at the high-pressure limit and in the temperature range of 670–1100 K was found to be The intramolecular isotopic effects were first examined in the pressure range of 0.1–26 torr at 837 K, and the branching ratio k_H/k_D was found to decrease with increasing pressure. The RRKM-theory calculations describe the experimental data well. The intramolecular isotopic effect was also examined in the temperature range of 728–926 K, and the branching ratio at the high pressure limit was given by the expression when k_H and k_D are the rate constants for the HCl and DCl channels of elimination. The Arrhenius A factors obtained at the high-pressure limit together with the temperature-dependent expression of the branching ratio provided additional experimental data for an assignment (fine-tuned) of the vibrational frequencies of both activated complexes involved in the thermal decomposition of CH₂DCH₂Cl. The evaluated vibrational frequencies were then used in the RRKM calculations describing the pressure dependence of the intramolecular isotopic effect. The RRKM calculations and the experimental data were in good agreement, supporting the choice of vibrational frequencies for both the activated complexes as well as the transition-state model.     

Application of simultaneous thermal analysis mass spectrometry and stable carbon isotope analysis in a carbon sequestration study

The simultaneous analysis of evolved gases and the determination of stable isotope composition (delta13C) as part of a thermal analysis experiment have been used to (a) distinguish bulk chemical hosts for carbon (C) and nitrogen (N) within a soil and (b) track labelled C within a soil sequestration experiment. C3 and C4 dung was applied to a pasture soil, and soil samples taken for analysis. The results of thermogravimetry-differential scanning calorimetry-quadrupole mass spectrometry-isotope ratio mass spectrometry (TG-DSC-QMS-IRMS) show that the proportion of more refractory C (lignin-like) is greater for the dungs than for the soil organic matter (SOM), and that this increases with time within the soil. Analysis of evolved gases shows that nitrogen is associated with the decomposition of more refractory C, and is not so strongly associated with the labile C component. IRMS analysis distinguished C3 and C4 dung, and allowed the amount of C from these sources to be estimated for the soil samples. Most dung C enters the refractory SOM fraction. This paper demonstrates the potential of TG-DSC-QMS-IRMS in the investigation of SOM.     

Intramolecular 1,3-dipolar cycloaddition of N-alkenyl nitrones en route to glycosyl piperidines

Stereoselective intramolecular 1,3-dipolar cycloaddition of homochiral N-(alkenylglycosyl)nitrones, prepared by allylation of C-(glycosyl)nitrones and subsequent oxidation, is described. The previously described 2-aza-Cope rearrangement was not observed for these substrates, but evidences of E/Z isomerism during the cycloaddition were obtained. The obtained cycloadducts can serve as key precursors of imino disaccharide analogues. This is exemplified by a short route to a protected 2-furanosyl-4-hydroxy-6-phenyl piperidine.     

Thermotropic phase behaviour of mixed liposomes of archaeal diether and conventional diester lipids

During preformulation studies of pharmaceutical solid dosage forms, thermal analysis techniques are very useful to detect physical or chemical incompatibilities between the drug and adjuvants of interest that might interfere with efficacy and safety of the final drug product. Differential scanning calorimetry (DSC) and thermogravimetry (TG) are useful tools for this purpose. The aim of this study was to investigate the thermoanalytical behavior of olanzapine (OLZ) when mixed with several excipients commonly used in solid dosage forms such as microcrystalline cellulose, croscarmellose, dicalcium phosphate dihydrate (DCPD), lactose, magnesium stearate, and povidone. Following DSC and TG analyses, powder X-ray diffraction tests were carried out. Thermoanalytical methods showed evidence of interaction between OLZ and magnesium stearate, lactose, and povidone. These results can be useful during the selection of excipients for pharmaceutical formulation development.