Intercalation of 1,2-Alkanediols into α-Zirconium Hydrogenphosphate

Intercalation compounds of α-Zr(HPO₄)₂ · H₂O with 1,2-alkanediols (from C3 to C16) have been prepared by replacing 1-propanol in α-Zr(HPO₄)₂ · 2C₃H₇OH with the desired 1,2-alkanediols by a treatment in a microwave field. It was found that the intercalates contain 1.5 molecules of diol per formula unit. The diol molecules are placed between the host layers in a bimolecular way with their aliphatic chains tilted at an angle of 51°. The diol molecules are anchored in the interlayer space by H-bonds. A mixed intercalate, containing 1,2-butanediol and 1,2-decanediol in a roughly equimolar ratio, is formed when the α-Zr(HPO₄)₂ · 2C₃H₇OH intercalate, suspended in a mixture of 1,2-butanediol and 1,2-decanediol, is exposed to microwave radiation. No new phase containing both types of the guest molecules was observed when the 1-propanol intercalate, suspended in a mixture of 1-propanol and 1,2-octanediol, is exposed to microwave radiation.     

Sampling and sample preparation

Summary Problems, techniques and means of water sampling are reviewed. Applicability and performance are discussed with regard to individual and composite samples, and also to automatic sampling. Storage and preservation of samples are dealt with.

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Probenahme und Behandlung von ProbenWasser

Zusammenfassung Probleme, Verfahren und Hilfsmittel bei der Probenahme von Wasser werden behandelt. Ausführung und Anwendbarkeit von Einzel und Mischproben sowie der automatischen Probenahme werden diskutiert, ebenso die Aufbewahrung und Konservierung von Proben.

Start of discussion held at the 6th Annual Symposium on Recent Advances in the Analytical Chemistry of Pollutants, April 21–23, 1976; Vienna, Austria.     

Über die Wahl der Lösungsmittelsysteme bei der papierchromatographischen Trennung organischer Verbindungen

Zusammenfassung An praktischen Beispielen wurde gezeigt, in welcher Weise die Trennung organischer Verbindungen mittels Papierchromatographie erzielt werden kann. Man ist nicht auf einige bewährte Lösungsmittel systeme allein angewiesen, sondern kann von Fall zu Fall systematisch neue und geeignete Systeme benützen. Es hat sich bewährt, sich nach den elementaren Löslichkeitsregeln für organische Stoffe zu richten, unter der Voraussetzung, daß die zu chromatographierende Verbindung in der stationären Phase gut, in der mobilen Phase dagegen weniger löslich ist. Durch Änderung der stationären Phase (Wasser, nicht wäßriges, polares Lösungsmittel, nicht polares Lösungsmittel) oder der Polarität und Zusammensetzung der mobilen Phase kann man das Wandern der Flecke am Chromatogramm beeinflussen, beliebige R_fWerte erhalten und in vielen Fällen auch eine beliebige Reihenfolge der Verbindungen am Chromatogramm erzielen.Da die Löslichkeit organischer Verbindungen von intermolekularen Kräften abhängig ist, erscheint das Problem im Zusammenhang mit strukturellen Einflüssen sehr kompliziert und muß für jeden Fall auf eigene Weise gelöst werden. Die Löslichkeitseigenschaften können weiter durch Benutzung reaktiver Lösungsmittel beeinflußt werden, die z. B. die Verbindungen in wasserlösliche Salze überführen können. Dabei ist an die möglichen Komplikationen, die bei ionisierbaren Verbindungen durch Dissoziation und Hydrolyse entstehen können, zu achten.Von den Hauptfaktoren, die eine Trennung ermöglichen können, seien die folgenden erwähnt: funktionelle Gruppen, ihre Anzahl, Polarität, gegenseitige Stellung, bzw. ihre Basizität oder Azidität, C-Atomanzahl in homologen Verbindungen, inter- und intramolekulare Wasserstoffbindungen, sterische Faktoren u. a. Es ist dann von der Art des gewählten Lösungsmittelsystems abhängig, welche der genannten Faktoren im Vordergrund stehen und welche beseitigt werden.Wenn die Löslichkeitsunterschiede der zu trennenden Stoffe zu gering sind, um gute Trennungen zu ermöglichen, ist es zweckmäßig, die Verbindungen in solche Derivate zu überführen, deren Strukturunterschiede größer sind.

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Summary Practical examples are given to show how organic compounds can be separated by means of paper chromatography. The operator is not limited to tested solvent systems, but can use new suitable systems as the occasion demands. It has been found best to abide by the elementary rules of solubility of organic compounds, provided the compound to be chromatographed is quite soluble in the stationary phase but less soluble in the mobile phase. By altering the stationary phase (water, nonaqueous, polar solvent, non-polar solvent) or the polarity and composition of the mobile phase, the migration of the stains in the chromatogram can be influenced, selectedR _f -values can be obtained, and in many cases it is also possible to secure a desired succession of the compounds on the chromatogram.Since the solubility of organic compounds depends on intermolecular forces, the problem in connection with structural influences appears very complicated and must be solved individually for each case. Moreover, the solubility characteristics can be affected by using reactive solvents; for instance, the compounds can be converted into water soluble salts. Under such circumstances, sight must not be lost of the complications which may arise because of the dissociation and hydrolysis of ionizable compounds. The following are among the chief factors, which may make a separation possible: functional groups, their number, polarity, relative position, their basicity or acidity, C-atom number in homologous compounds, inter- and intramolecular hydrogen bonds, steric factors, etc. It then depends on the type of solvent system selected, which of these factors are predominant and which can be neglected or eliminated.If the solubility differences are too slight to permit good separations, the compounds to be separated should, if possible, be converted into derivatives whose structural differences are more pronounced.

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Résumé Des exemples pratiques montrent comment il est possible d'effectuer la séparation de combinaisons organiques par Chromatographie sur papier. Il n'est pas uniquement fait appel à des systèmes de solvants éprouvés mais, dans certains cas, de nouveaux systèmes appropriés sont systématiquement utilisés.Il s'est avéré satisfaisant de faire appel aux règles élémentaires de solubilité des substances organiques sous réserve que la combinaison à chromatographier soit suffisamment soluble dans la phase stationnaire et moins soluble dans la phase mobile. En faisant varier la phase stationnaire (eau, solvant non aqueux, solvant polaire, solvant non polaire) ou la polarité et la composition de la phase mobile, il est possible d'influencer la migration des taches du chromatogramme, d'obtenir des valeurs deR _f désirées et, dans de nombreux cas, d'obtenir les combinaisons dans un ordre déterminé sur le chromatogramme.La solubilité des combinaisons organiques étant fonction des forces intermoléculaires il en résulte que le problème se complique considérablement dans la mesure où l'on considère les influences structurelles et que chaque cas particulier doit recevoir une solution qui lui est propre. Les propriétés de solubilité peuvent en outre être influencées par l'emploi de solvants réactifs qui peuvent transformer, par exemple les combinaisons en sels solubles dans l'eau. Il faut alors tenir compte des possibilités de complications qui peuvent apparaître par dissociation et hydrolyse des combinaisons ionisables.Parmi les principaux facteurs qui permettent une séparation, il convient de mentionner les suivants: les groupes fonctionnels, leur nombre, leur polarité, leur position relative, ou encore leur acidité ou leur basicité, le nombre d'atomes de carbone de combinaisons homologues, les liaisons hydrogène inter- et intramoléculaires, les facteurs stériques, etc. Suivant la nature du système solvant choisi pourront alors varier les facteurs dont l'effet est prépondérant et ceux dont l'effet est nul. Lorsque les différences de solubilité des substances à séparer sont trop faibles pour permettre des séparations satisfaisantes, il est commode de transformer les combinaisons en dérivés dont les différences de structure soient plus importantes.

     

Germacrene A is a product of the aristolochene synthase-mediated conversion of farnesylpyrophosphate to aristolochene

The biosynthesis of several sesquiterpenes has been proposed to proceed via germacrene A. However, to date, the production of germacrene A has not been proven directly for any of the sesquiterpene synthases for which it was postulated as an intermediate. We demonstrate here for the first time that significant amounts of germacrene A (7.5% of the total amount of products) are indeed released from wild-type aristolochene synthase (AS) from Penicillium roqueforti. Germacrene A was identified through direct GC-MS comparison to an authentic sample and through production of beta-elemene in a thermal Cope rearrangement. AS also produced a small amount of valencene through deprotonation of C6 rather than C8 in the final step of the reaction. On the basis of the X-ray structure of AS, Tyr 92 was postulated to be the active-site acid responsible for protonation of germacrene A (Caruthers, J. M.; Kang, I.; Rynkiewicz, M. J.; Cane, D. E.; Christianson, D. W. J. Biol. Chem. 2000, 275, 25533-25539). The CD spectra of a mutant protein, ASY92F, in which Tyr 92 was replaced by Phe, and of AS were very similar. ASY92F was approximately 0.1% as active as nonmutated recombinant AS. The steady-state kinetic parameters were measured as 0.138 min(-1) and 0.189 mM for k(cat) and K(M), respectively. Similar to a mutant protein of 5-epi-aristolochene (Rising, K. A.; Starks, C. M.; Noel, J. P.; Chappell, J. J. Am. Chem. Soc. 2000, 122, 1861-1866), the mutant released significant amounts of germacrene A (approximately 29%). ASY92F also produced various amounts of a further five hydrocarbons of molecular weight 204, valencene, beta-(E)-farnesene, alpha- and beta-selinene, and selina-4,11-diene.     

Quantitative validation of different protein precipitation methods in proteome analysis of blood platelets

For the preparation of proteins for proteome analysis, precipitation is frequently used to concentrate proteins and to remove interfering compounds. Various methods for protein precipitation are applied, which rely on different chemical principles. This study compares the changes in the protein composition of human blood platelet extracts after precipitation with ethanol (EtOH) or trichloroacetic acid (TCA). Both methods yielded the same amount of proteins from the platelet preparations. However, the EtOH-precipitated samples had to be dialyzed because of the considerable salt content. To characterize single platelet proteins, samples were analyzed by two-dimensional fluorescence differential gel electrophoresis. More than 90% of all the spots were equally present in the EtOH- and TCA-precipitated samples. However, both precipitation methods showed a smaller correlation with nonprecipitated samples (EtOH 74.9%, TCA 79.2%). Several proteins were either reduced or relatively enriched in the precipitated samples. The proteins varied randomly in molecular weight and isoelectric point. This study shows that protein precipitation leads to specific changes in the protein composition of proteomics samples. This depends more on the specific structure of the protein than on the precipitating agent used in the experiment.     

Electrochemical detector with a 20 nl volume for micro-columns liquid chromatography

Summary A flow-through two electrode wall-jet cell with a platinum measuring electrode and a cell volume of 20 nl has been designed and evaluated. It has been used to detect phenols by reversed phase liquid chromatography using short micro bore columns. The linear dynamic range between the measured current and the concentration is greater than 10³ (1.5×10^–7–5×10^–4 mol/l) and the minimum analyzable amount was found to be 10 pg for pyrocatechol. A negligible broadening in the detector permits the use of micro columns down to 0.5 mm internal diameter, packed with 5 m particles, without any substantial distortion of eluted zones.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Application of solid phase microextraction in the determination of paralytic shellfish poisoning toxins

A SPME-HPLC-post-column fluorescent derivatization method for the direct determination of saxitoxin (STX), the most potent paralytic shellfish poisoning (PSP) toxin, in water has been developed. Commercially available SPME devices with 50 microm Carbowax templated resin (CW/TPR) coating was found to be able to pre-concentrate STX from aqueous media. A special pre-conditioning treatment of soaking the SPME coating in 0.1 M NaOH solution significantly improved the extraction efficiency. The optimal pH for the SPME process is 8.1 and the equilibration time is 40 min. The partition coefficient, K, of the distribution of STX between the SPME coating and the aqueous media was measured to be 2.99 +/- 0.04 x 10(3). Extracted toxin on the SPME stationary phase was difficult to be desorbed by the HPLC mobile phase under dynamic desorption mode. A static ion-pairing desorption technique using a desorption solvent mixture of 20 mM sodium 1-heptanesulfonate in 30% aqueous acetonitrile acidified with 50 mM sulfuric acid was developed to overcome this problem. The method detection limit and repeatability achieved by this SPME-HPLC method were 0.11 ng ml(-1) and 3.7%, respectively, with a sample volume of just 5 ml of water. This analytical method is adequate for the monitoring of the PSP toxin in fresh/drinking waters. However, serious interference was observed when this technique was applied to saline water samples. This is probably due to competition of sodium ions with the cationic STX for absorption into the SPME stationary phase.     

Critical parameters and optimization of a magnesium-selective liquid membrane electrode for application to human blood serum

Summary The selectivity of a new magnesium ionophore (ETH 7025) induced in membranes of different compositions is experimentally studied in view of the ion activities in human serum. The required selectivity coefficient against calcium for the application of an ion-selective magnesium electrode to human serum is calculated for the worst case. Other critical parameters for the application of a liquid PVC-based ion-selective membrane to undiluted human serum discussed are: the sensor lifetime which is related to the lipophilicity of the carrier as well as the ruggedness of the membrane against interactions with components of the relatively lipophilic sample.     

Reactions of Electron-Rich Olefins with Proton-Active Compounds

Proton-active substances react with certain electron-rich olefins with cleavage of the central C?C double bond to give compounds that can be formally regarded as insertion products of nucleophilic carbenes. If they satisfy certain structural conditions, they isomerize with β elimination to give open-chain compounds. Both CH-acidic compounds and compounds containing NH or OH groups can undergo this reaction. The mechanisms are discussed, and the importance of the intermediate products to biochemistry (thiamine, tetrahydrofolic acid) is indicated.