Lipophilicity determination of some new crown ethers by reversed-phase thin-layer chromatography

Summary The lipophilicity of 28 modified crown ether derivatives was determined by reversed-phase thin-layer chromatography (RPTLC) using various organic phases and supports. The lipophilicity values determined in different RPTLC systems showed good correlations, however the quality of the organic phase (methanol, acetone, acetonitrile) and the support characteristics influenced to a small extent the determination.     

Strukturanalyse organischer Sulfide mit Hilfe der Gras-Chromatographie

Zusammenfassung Eine Methode der Identifizierung von Alkyl- und Arylgruppen organischer Sulfide wurde ausgearbeitet, die die Spaltung dieser Stoffe mit Raney-Nickel zur gaschromatographischen Bestimmung der dabei entstandenen Kohlenwasserstoffe ausnützt.

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Summary A method was developed for identifying alkyl- and aryl groups of organic sulfides. The method employs the cleavage of these materials with Raney nickel for the gas chromatographic determination of the resulting hydrocarbons.

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Résumé On a mis au point une méthode d'identification des groupes alkylés et arylés des sulfures organiques exploitant la dissociation de ceux-ci par le nickel Raney pour le dosage par chromatographic en phase gazeuse des carbures d'hydrogène qui se forment.

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Die Autoren danken den Kollegen Dr.M. Veea, Ing.J. Petránek und Ing.J. Gaspari für die Überlassung von Proben organischer Sulfide.     

Estudios sobre ácidos hidroxámicos

Résumé On propose un procédé de microdosage des groupements méthoxyles dans les pectines, qui repose sur la libération de ces groupements par saponification de l'hydroxylamine alcoolique dans un appareil, sur leur transformation en formiates de méthyle et sur leur distillation. Le formiate de méthyle forme ainsi l'acide formhydroxamique que l'on dose par colorimétrie à l'état de chélate avec le fer-III.On réalise l'hydrolyse de la pectine à 100° C en tube scellé. On fait réagir avec l'acide formique en excès, une partie aliquote de l'hydrolysat dans le micro-appareil de distillation déjà décrit. Le procédé convient pour 1 à 3 mg de pectine et la durée des opérations est de deux heures et demies. Sa spécificité est satisfaisante bien que le groupe éthoxyle puisse gêner. Son action est d'ailleurs peu vraisemblable, puisqu'il ne fait pas partie de la molécule de pectine. Les résultats du procédé sont en générale un peu plus bas que ceux des méthodes volumétriques servant à ce dosage. On a étudié la reproductibilité pour les esters méthyliques et l'on a mis en évidence une erreur par défaut de 2 à 4%. Les plus petites quantités de groupes méthoxyles que l'on puisse doser sont de 20g. Le procédé recommandé est une application particulière de méthodes applicables de façon générale au dosage des esters méthyliques dans les substances organiques. Ce sera l'objet d'une autre communication de cette série.

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Summary A micromethod is given for determining methoxyl groups in pectins. It is based of the liberation of these groups by saponification, conversion into methyl formate, and distillation of the latter into a receiver containing alcoholic hydroxylamine. The methyl formate reacts to give formhydroxamic acid, which is determined colorimetrically as iron(III) chelate.The hydrolysis of the pectin is conducted at 100° C in a sealed tube. An aliquot part of the hydrolysate is brought into reaction with excess formic acid in a microdistillation apparatus that was described previously. The procedure is suitable for 1 to 3 mg pectin and requires 21/2 hours for all partial operations. The specificity is satisfactory, even though ethoxyl may interfere. However, this latter is not likely to be encountered since ethoxyl has not been shown to be a constituent of the pectin molecule. The results given by the procedure are in general inferior to those of volumetric methods. The reproducibility was tested on methyl esters and showed a minus error of 2 to 4%. The smallest amount of methoxyl which can be determined in this way is 20g. The method proposed here is a special application of a method which can be applied in general to the determination of methyl esters in organic substances, which will be the subject of a later paper in this series.

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Zusammenfassung Es wird ein Mikroverfahren zur Bestimmung der Methoxylgruppen in Pektinen angegeben, das auf der Freisetzung dieser Gruppen durch Verseifung, deren Umwandlung in Methylformiat und dessen Destillation in eine Vorlage von alkoholischem Hydroxylamin beruht. Das Methylformiat bildet damit Formhydroxamsäure, die als Eisen(III)-chelat kolorimetrisch bestimmt wird.Die Hydrolyse des Pektins wird bei 100° C in einem verschlossenen Rohr ausgeführt. Einen aliquoten Teil des Hydrolysates läßt man in einem schon früher beschriebenen Mikrodestillationsapparat mit überschüssiger Ameisensäure reagieren. Das Verfahren eignet sich für 1 bis 3 mg Pektin und erfordert für alle Teiloperationen 2^1/2 Stunden. Seine Spezifität ist befriedigend, obwohl Äthoxyl stören kann. Dessen Einwirkung ist jedoch wenig wahrscheinlich, da es nicht als Bestandteil des Pektinmoleküls nachgewiesen ist. Die Ergebnisse des Verfahrens sind im allgemeinen niedriger als die Resultate volumetrischer Methoden. Die Reproduzierbarkeit wurde an Methylestern überprüftund zeigte einen Minusfehler von 2 bis 4%. Die Mindestmenge bestimmbares Methoxyl beträgt 20g. Das vorgeschlagene Verfahren ist eine spezielle Anwendung einer allgemein für die Bestimmung von Methylestern in organischen Substanzen anwendbaren Methode, die Gegenstand einer weiteren Mitteilung dieser Serie sein wird.

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Resumen Se indica una microtécnica de valoración de metoxilos en pectinas, basada en la liberación del radical metilo éster por saponificación; en su conversion en formiato de metilo y en su simultanea destilación y recepción en hidroxilamina alcalinizada. El formiato de metilo se transforma así en ácido formohidroxámico, cuya determinación fotocolorimétrica se realiza como quelato férrico.Estas operaciones requieren efectuar la hidrólisis de la pectina en tubo cerrado y a 100° C, y en tomar una alícuota del hidrolizado, que se pasa con un exceso de ácido fórmico al aparato de microdestilación, detallado en comunicaciones anteriores. El método permite operar con 1 a 3 mg de pectina y todas las operaciones insumen unas dos y media horas. La técnica presenta condiciones satisfactorias de especificidad, pudiendo interferir los radicales etoxilos, cosa poco probable, pues no son reconocidos como componente de la molécula de pectina. Los resultados obtenidos, comparados con los del método titrimétrico, son por lo general inferiores a éste y su reproducibilidad, verificada con ésteres metílicos, tiene errores por defecto de un 2 a 4%. La cantidad mínima de metoxilo valorado alcanza a 20g. La técnica que se indica, es una aplicacion particular de otra de carácter general, aplicable a la valoración de ésteres metílicos en sustancias orgánicas, que será motivo de otra futura comunicación de esta serie.

     

Determination of molybdenum, chromium and aluminium in human urine by electrothermal atomic absorption spectrometry using fast-programme methodology

Rapid and direct procedures for the determination of molybdenum, chromium and aluminium in human urine samples are developed. Fast-programme methodology is used to simplify the heating cycles. Hydrogen peroxide, nitric acid and Triton X-100 are added to the urine samples which are directly introduced into the furnace. For molybdenum, two successive injection steps are required due to the low level of this element in the samples analyzed. Calibration is carried out using aqueous standards for aluminium and the standard additions method for both molybdenum and chromium. The reliability of the procedures is checked by analyzing two certified reference materials.     

Determination of aristolochic acid by capillary zone electrophoresis

A simple and rapid capillary zone electrophoresis (CZE) method for the determination of aristolochic acid (AA) in dietary supplements and selected herbs is described. A clear separation of AA from other sample constituents was achieved within 5 minutes without any sample clean up. A mixture of 20 mM-morpholinethanesulphonic acid+10 mM-BisTrisPropane+0.2% hydroxyethylcelullose in 10% methanol serves as a background electrolyte. The linearity, accuracy, intra-assay and detection limit of the developed method are 200–6000 ng/mL, 95–103%, 3.5%, and 50 ng/ml, respectively. Ease of use, sufficient sensitivity and low running cost are the most important attributes of the CZE method. The proposed CZE method was compared with HPLC.     

An experimental and theoretical study of the Cp2VO2CO: use of 13CO3(2-) for structure investigation of d1-metallocene complexes

EPR study has shown that the anticancer agent vanadocene dichloride (Cp2VCl2) interacts with carbonate contained in physiological solutions. Chelate complex Cp2VO2CO (|A(iso)(51V)| = 175.1 MHz, g(iso) = 1.9861) is the only paramagnetic species formed in the range about the physiological pH (5.5-11.0). The super-hyperfine coupling (|a(iso)(13C)| = 24.1 MHz) was evidenced at measurements using 13C labelled carbonate. The structure of carbonate complex was validated by comparison of observed and theoretical calculated HFC tensors (at the density functional level of theory).     

15N,(1)H Heteronuclear correlation NMR of gramicidin A in DMPC-d(67)

We have studied gramicidin A, an environmentally sensitive polymorphic pentadecapeptide, fully 15N-labelled and dispersed in a highly deuterated phospholipid bilayer system. By submitting the sample to fast magic angle spinning, we were able to reduce the polypeptide amide hydrogen linewidths to 160 Hz, and hence to partially resolve them. By correlating these resonances with the 40 Hz wide dipolar coupled 15N in a 2D-CROPSY (cross-polarization spectroscopy) experiment, it was possible to observe the 20 partially overlapping 1H-15N signal pairs from the polypeptide backbone and sidechains. Both chemical shift distributions closely match those of the same peptide in SDS micelles, but only poorly match those of conformationally different gramicidin A in trifluoroethanol, dimethylsulfoxide, or methanol/chloroform mixture. Our results are indicative of the N-to-N right-handed beta6.3-helix conformation of gramicidin A and offer sufficient resolution to encourage development of experiments to measure orientational or distance restraints using through-space dipolar couplings.     

Determination of pesticides in waters by capillary gas chromatography with atomic emission detection

Capillary gas chromatography with atomic emission detection (GC-AED) was successfully used to separate and quantify 14 pesticides (organochlorines, organophosphorus compounds and pyrethrins) in water samples after liquid-liquid extraction with ethyl acetate. Monitoring the emission lines for elements such as chlorine, bromine and sulfur ensures nearly specific chromatograms for these elements, and markedly increases selectivity. Calibration curves were obtained by plotting peak area versus concentration and the correlation coefficients relating to linearity were at least 0.999. Each chromatographic separation takes 21 min and, since two injections are necessary, it requires approximately 1 h to analyze one sample. The method shows a precision of 4.3-8.2% (RSD), depending on the compound. The application of liquid-liquid extraction with ethyl acetate led to recoveries from spiked samples ranging from 76 to 113%. The sensitivity and linearity for the elements chlorine, sulfur, nitrogen and phosphorus were checked under the optimized conditions at their customary emission wavelength. The sensitivity and linearity for these compounds decreased in the order (atom and emission wavelength) Cl (479 nm)>S (181 nm)>P (178 nm)>N (174 nm). A study of the GC-AED system's response to chlorine concentration in eight pesticide molecules was performed and a linear relationship was found with a correlation coefficient of 0.987.     

Diorganotin(IV) derivatives of substituted benzohydroxamic acids with high antitumor activity

A series of diorganotin(IV) and dichlorotin(IV) derivatives of 4-X-benzohydroxamic acids, [HL(1) (X = Cl) or HL(2) (X = OCH(3))] formulated as [R(2)SnL(2)] (R = Me, Et, nBu, Ph or Cl; L = L(1) or L(2)), along with their corresponding mixed-ligand complexes [R(2)Sn(L(1))(L(2))] have been prepared and characterized by FT-IR, (1)H, (13)C, and (119)Sn NMR spectroscopy, mass spectrometry, elemental analysis, and melting points. In addition, single-crystal X-ray diffraction analyses were carried out for [Me(2)SnL(2)] (L = L(1) or L(2)), which show coordination structures intermediate between distorted octahedra and bicapped tetrahedra. The hydroxamate ligands are asymmetrically coordinated by the oxygen atoms, the carbonyl oxygen atom is further away from the metal center than the other oxygen atom. The complexes are stable monomeric species; most of them are soluble not only in chlorohydrocarbon solvents, but also in alcohols and hydroalcoholic solutions. In polar solvents, the mixed-ligand complexes gradually decompose into the corresponding single-ligand complex couples. The complexes exhibit in vitro antitumor activities (against a series of human tumor cell lines) which, in some cases, are identical to, or even higher than, that of cisplatin. For the dialkyltin complexes, the activity increases with the length of the carbon chain of the alkyl ligand and is higher in the case of the chloro-substituted benzohydroxamato ligand. The [nBu(2)Sn(L(1))(2)] complex displays a high in vivo activity against H22 liver and BGC-823 gastric tumors, and has a relatively low toxicity.