The separation of date (Phoenix dactylifera) sterols by liquid chromatography

Summary Isolation of a crystalline plant sterol mixture from the sarcocarp of the date was followed by successive extraction and column chromatography. The composition of the mixture was examined by gas chromatography. An additional gas chromatographic-mass spectroscopic identification of the sterol mixture was carried out after conversion of the sample into its trimethylsilyl derivates. Cholesterol, campesterol, stigmasterol,-sitosterol and isofucosterol were found from the identification of molecular ions, the assignment of fragment ions and the comparison of each spectral feature with that of the authentic compound. The sterol mixture was then examined by high-performance liquid chromatography employing a Zorbax ODS column and an acetonitrile-water-0.1M sodium acetate (90101) solvent system, and the peaks were detected with radiation at 210 nm. Six peaks were found on the chromatogram. The identification of each peak by means of gas chromatography and infrared spectroscopy was followed by the collection of each component. The peaks were an unknown (ghost) peak, isofucosterol, cholesterol, stigmasterol + campesterol, campesterol and-sitosterol, successively. The plant sterol mixture has only been analysed on reverse-phase column packings whereas the hormonal corticosteroids and male or female hormonal steroids have been separated on both normal and reverse-phase column packings.

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Zusammenfassung Nach Isolierung aus dem Fruchtfleisch der Dattel wurde ein Gemisch kristallisierter pflanzlicher Sterine der stufenweisen Extraktion und Säulenchromatographie unterworfen. Dessen Zusammensetzung wurde gaschromatographisch untersucht. Außerdem wurde dieses Steringemisch gaschromatographisch-massenspektrographisch nach Überführung in die entsprechenden Trimethylsilylderivate identifiziert. Cholesterin, Campesterin, Stigmasterin,-Sitosterin und Isofucosterin wurden durch Nachweis der Molekularionen, durch Zuordnung der Fragmentionen und durch Vergleich mit dem spektralen Verhalten der betreffenden authentischen Verbindung festgestellt. Das Steringemisch wurde dann im Wege der Hochleistungs-Flüssigchromatographie untersucht. Hierzu diente eine Zorbax ods-Säule und ein Lösungsmittelgemisch aus Acetonitril—Wasser—0,1M Natriumacetat (90 10 1). Die Peaks wurden durch Lichtstrahlen von 210 nm nachgewiesen. Sechs Peaks wurden gefunden. Nach Identifizierung durch Gaschromatographie und IR-Spektroskopie wurde jede einzelne Verbindung gesammelt. Neben einer unbekannten Zacke entsprachen die Peaks der Reihe nach dem Isofucosterin, dem Cholesterin, Stigmasterin+Campesterin, Campesterin und-Sitosterin. Das Gemisch der pflanzlichen Sterine wurde nur mit phasenverkehrten Säulen analysiert, während Corticosteroidhormone sowie männliche und weibliche Steroidhormone sowohl auf normalen wie auf phasenverkehrten Säulenpackungen getrennt wurden.

     

Nuclear spin driven quantum tunneling of magnetization in a new lanthanide single-molecule magnet: bis(phthalocyaninato)holmium anion

The first measurements of magnetization hysteresis loops on a diluted single crystal of [(Pc)2Ho]-.TBA+ (Pc = phthalocyaninato, TBA = tetrabutylammonium) in the subkelvin temperature range are reported. Characteristic staircase-like structure was observed, indicating the occurrence of the quantum tunneling of magnetization (QTM), which is a characteristic feature of SMMs. The quantum process in the new lanthanide SMMs is due to resonant quantum tunneling between entangled states of the electronic and nuclear spin systems, which is an essentially different mechanism from those of the known transition-metal-cluster SMMs. Evidence of the two-body quantum process was also observed for the first time in lanthanide complex systems.     

Mechanistic study of electrocatalytic oxidation of formic acid at platinum in acidic solution by time-resolved surface-enhanced infrared absorption spectroscopy

Surface-enhanced infrared absorption spectroscopy (SEIRAS) combined with cyclic voltammetry or chronoamperometry has been utilized to examine kinetic and mechanistic aspects of the electrocatalytic oxidation of formic acid on a polycrystalline Pt surface at the molecular scale. Formate is adsorbed on the electrode in a bridge configuration in parallel to the adsorption of linear and bridge CO produced by dehydration of formic acid. A solution-exchange experiment using isotope-labeled formic acids (H(12)COOH and H(13)COOH) reveals that formic acid is oxidized to CO(2) via adsorbed formate and the decomposition (oxidation) of formate to CO(2) is the rate-determining step of the reaction. The adsorption/oxidation of CO and the oxidation/reduction of the electrode surface strongly affect the formic acid oxidation by blocking active sites for formate adsorption and also by retarding the decomposition of adsorbed formate. The interplay of the involved processes also affects the kinetics and complicates the cyclic voltammograms of formic acid oxidation. The complex voltammetric behavior is comprehensively explained at the molecular scale by taking all these effects into account.     

Ru-catalyzed ring-opening and substitution reactions of heteroaromatic compounds using propargylic carboxylates as precursors of vinylcarbenoids

[reaction: see text] The reaction of heteroaromatic compounds with propargylic carboxylates in the presence of a catalytic amount of [RuCl(2)(CO)(3)](2) or PtCl(2) gives trienes in good yields. The key intermediate is an electrophilic (1-acetoxylvinyl)carbene complex generated from the activated propargylic acetates with transition metals.     

Global tuning of local molecular phenomena: an alternative approach to bionanoelectronics

We have applied simultaneous horizontal and vertical bias to a single molecule (2 nm(2)) in an ordered and disordered matrix to virtually isolate and tune its property without taking it out physically from its environment. Using a dedicated electrode system, we have locally tuned nanoscale properties vertically by STM, while stabilizing its environment by applying a global electric field horizontally. Using this technique, we report tuning of molecular conformations in room temperature, whose evolution of states has been statistically investigated. We have also shown control on switching of a few selected conformations by applying dual bias simultaneously. As we avoid any direct injection of charge into the system via electrode contact, this technique could be used as a generalized method to tune phenomena evolved in an environment of weak interaction from a large distance without destroying the property.